Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Mon 11, 2019 10:53 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 82 posts ]  Go to page 1, 2, 3, 4, 5  Next
Author Message
 Post subject: TV-2/U repair
PostPosted: Sep Sat 15, 2018 9:09 pm 
Member

Joined: Mar Thu 29, 2018 3:41 am
Posts: 178
Location: Portland Oregon
I was given a TV-2/U. I brought the tester up slowly on a variac and tried to test a tube. The qualiymeter is way off. I couldn’t zero the meter either. I found some test sockets so I will measure the voltage being delivered tonight.

Does anyone have documentation or suggested reading on how to get this tester operating well- what point voltages should be, how to calibrate meters, etc?

I appreciate your help.

Dave


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Sat 15, 2018 9:59 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 5189
Location: Sunbury, Ohio 43074
http://bama.edebris.com/manuals/military/tv2u/
There's the manual. Schematic is a bit tough to read... there may be others out there. But you should read everything you can in there on how the tester works, and how to calibrate it. The sections on how the instrument works are quite instructive. Sometimes running through a calibration procedure is the best way to troubleshoot it anyway, and calibration might be all that's needed if you are fortunate.

The TV2 is quite a bit more complex than some so tread lightly in there till you get familiar with it.

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Sun 16, 2018 3:55 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 677
Location: Stafford, Texas USA
First the TV-2 was not designed by Hickok. It’s utilized modified Hickok circuits.

The TV-2 series, was produced in sixty’s and apparently designed by the Air King Company,
included four versions: TV-2/U, TV-2A/U, TV-2B/U, TV-2C/U.

The power supplies’ have Capacitors and resistors that must be replaced.
The TV-2 series has 4 Electrolytic Capacitors C1 2000 mfd 15 wv, C3 50 mfd 200 wv,
C4A 10 mfd 100 wv , C3B 10 mfd 300 wv, and about 15 paper capacitors.

Some good pictures here:
https://digilander.libero.it/pasqua49/C ... tester.htm

Better copies of manuals than Bama here:
http://www.militaryradio.com/manuals/TV ... 316-35.pdf
http://www.militaryradio.com/manuals/TV ... 316-12.pdf

Jimmie


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Mon 17, 2018 4:49 pm 
Member

Joined: Aug Mon 04, 2014 9:42 pm
Posts: 107
Getting the Gm centering control to work right is necessary to get a good reading. It's really a balance control, and when Hickok finally decided to add one in some of their later models, it was an internal adjustment. I found the simplified schematic portions of the circuit to be invaluable in understanding what was going on. Have fun!


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Mon 17, 2018 5:32 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 10957
Location: Latham NY 12110
Check the 83 tube if you have another tester. I just got another one of these and all I had to do was exercise all of the controls and switches, did each one at least 25 times. Don't go spraying contact cleaner all over. These were sealed in very good with a rubber gasket so they are usually very clean inside.


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Mon 17, 2018 6:22 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 4172
Location: Littleton, MA
TechyMechy wrote:
Does anyone have documentation or suggested reading on how to get this tester operating well- what point voltages should be, how to calibrate meters, etc?

The Field and Depot Maintenance manual lists trouble suspects for inability to balance the Gm Centering potentiometer in the troubleshooting chart at the bottom of page 21 and top of page 22. A defective type 83 tube could cause this trouble, too.

Since your TV-2/U seems to be basically functional except for the centering problem, you should run through the 5th Echelon Final Testing section in Chapter 4, except for the part where you compare transconductance measurements between the TV-2 and a laboratory vacuum tube bridge.

There isn't any way to calibrate the meters, or anything else about the TV-2. The precision resistors were expected to hold their value, and the meters were expected to remain accurate. Given that, the overall test result should be accurate. However, that was sixty years ago, and the service life certainly wasn't expected to extend to 2018.

So, you need to run through the 5th echelon tests, find out what meters are giving bogus numbers, go through the associated circuitry looking for drifted resistors, and then test the meter movement sensitivity to see if it matches spec. If the meter is good, then replacing the resistors should get the test back in spec, but if the meter sensitivity has changed, then you either need to fix the meter, re-design the circuit around the new meter sensitivity, or try to find a replacement meter (good luck finding an exact replacement that is also still good).

The parts list in TM11-6625-316-34P (available on BAMA) doesn't provide the meter specifications. Some are listed as "galvanometers", meaning they are current meters. For those, you need to reverse-engineer the circuit to determine what the designed sensitivity should be. You may be able to jigger the resistor values in the associated circuit to calibrate around a changed sensitivity of the meter.

The remaining meters are listed as "voltmeters". If one of those isn't reading correctly, the only fix would be to open up the sealed meter (probably requires a blowtorch to unsolder the case) and modify the internal range resistor to bring the voltmeter back into calibration.

By the way, the manual expects the measurements to be performed by an AN/URM-105 VOM or a ME-30A/U AC VTVM. The AN/URM-105 is a 20,000 ohms per volt multimeter, so a Triplett or Simpson VOM will be fine for that. If you only have a DMM, you should add a resistance in parallel with it to simulate the input resistance of the AN/URM-105. You need a different resistor for each range on the AN/URM-105; it has ranges of 1, 10, 100, and 1000 volts, so 20K, 200K, 2M, and 20M ohm resistors are needed.

The ME-30A/U is a Hewlett Packard HP-400D AC VTVM. The best modern replacement for that would be a DMM.

_________________
Steve Byan http://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Mon 17, 2018 9:19 pm 
Member

Joined: Mar Thu 29, 2018 3:41 am
Posts: 178
Location: Portland Oregon
Thanks so much for the information.

I am reading and making sure I understand the manual TM11-6625-316-35 (Field and Depot Maintenance Manual). I made it through Chapter 1 and am now starting to read the trouble shooting section.

It is a great idea to trouble shoot by doing the 5th Echelon tests first. Would a test socket work for easier measurement of voltages on the octal socket?

I wish I could find a clean BOM for the tester. I feel like I should blanket replace all of the electrolytic capacitors. I see that the capacitors have a military designation (which I don't fully understand). I found like C2 listed in this site:

C2: CE41C202E
http://www.surplussales.com/Capacitors/ ... 999uF.html

Should one buy the surplus capacitors or should I buy new standard capacitors and build fixtures to hold them? Would you folks purchase canned capacitors or use bare capacitors (when canned are available)? What temperature spec would you use (85 C or 105C)?

The same goes with the resistors. I have found the values but I haven't found the power rating or accuracy for all of the resistors. I found R27 on the web (RC20GF391K) which is a 1/2W carbon composite resistor. What is your opinion if I replace the out of spec resistors (by looking at the color code) which don't have the power specified with 1W, 1% metal film resistors. Luckily, the 2W resistors are specified.

The Field and Depot maintence manual seems pretty complete. I am hoping that I can get this tester to work as good as new.

Is there any information on how to make this tester "better?" Does anyone have information on the inherent issues with the tester or things I should do to make it better? I've read where the filament voltage will droop with high current tubes which could be fixed by using 18 gage wires (this seems like alot of work) or that the shunt pot may be non linear or that the grid DC is not very even (has a lot of harmonics in it that will interfere with the AC injection). Would you use a test socket to set the exact voltages at the socket and see if something is not quite right under test (say using a DMM and potentially an O scope)?

When you test a meter sensitivity, do you simply hook the meter up to a limiting resistor and DC power supply (maybe a current limiting power supply) and adjust for the meter full scale and potentially check linearity? How do you do that?

Thanks for your help.

Dave


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Mon 17, 2018 9:31 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 5189
Location: Sunbury, Ohio 43074
First of all, I would not even consider replacing any resistors just yet. To start that is probably going to put the tester on a quick path to the scrap bin. As for the electrolytics, while you could replace them with any modern equivalent, you might find that they don't need it, or at least they do not ALL need it. Before you start with any replacements, I'd go by the values and voltages on the PART and not necessarily on the bill of materials or schematic. While they probably will match, they won't in all cases. Plus in some places it's possible that a value was hand selected during testing and calibration, and will not match the schematic either.

This is commercial/military gear, and keep in mind that much higher quality and tolerance components were generally used than what you'd find in, say, a table radio. Even 60 year old electrolytics can be just fine, depending on how the unit was used and stored. I presume you did a slow powerup on a variac initially to at least let them reform a bit ??

If you want to test resistors, test them based on the VALUE ON THE RESISTOR, and not on what the schematic says it should be. If it meets this test within tolerance, which in some cases may be +/- 20%, leave it be until it proves it needs replacement. You will probably have to disconnect one end to get a valid resistor test. Did i mention I don't do this until testing proves it necessary? :-D but that's just me ...

I've said enough times.. I am not a fan of shotgun replacing components in a commercial, and especially a military commercial, piece of equipment. Electrolytics can be "rough tested" usually in circuit by just using an old fashioned VOM. If they are not shorted or leaky that way, I'd leave them be until further testing shows the need for new ones.

Others will probably shoot flaming arrows at me ... but oh well. I burn well :-D

Ok, all that said, once you know it's at least somewhat working correctly, THEN you might want to consider electrolytic replacements. You can do them one by one, and test the unit after each replacement. Sounds time consuming, but try shotgunning it and making even one mistake. .. and you will experience a new dimension in wasted time :)

Good luck !

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Tue 18, 2018 1:45 am 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 4172
Location: Littleton, MA
TechyMechy wrote:
I wish I could find a clean BOM for the tester. I feel like I should blanket replace all of the electrolytic capacitors. I see that the capacitors have a military designation (which I don't fully understand). I found like C2 listed in this site:

C2: CE41C202E
http://www.surplussales.com/Capacitors/ ... 999uF.html

Should one buy the surplus capacitors or should I buy new standard capacitors and build fixtures to hold them? Would you folks purchase canned capacitors or use bare capacitors (when canned are available)? What temperature spec would you use (85 C or 105C)?

The same goes with the resistors. I have found the values but I haven't found the power rating or accuracy for all of the resistors. I found R27 on the web (RC20GF391K) which is a 1/2W carbon composite resistor. What is your opinion if I replace the out of spec resistors (by looking at the color code) which don't have the power specified with 1W, 1% metal film resistors. Luckily, the 2W resistors are specified.

Yeah, unless you have access to the government database of federal stock numbers, you can't tell the specs for the parts :-(

Maybe there is someone here on ARF who has access to the NSN database and can tell us the specs for the TV-2 meters.

For the caps, just look at the component - the capacitance and working voltage will be marked. Or Jimmie Stewart gave you the values in his post earlier in this thread.

You want 105 degree C parts. I'd either restuff the existing cans with new electrolytics, or remove the cans and use new electrolytics, depending on the chassis layout. Often I find it easier to restuff the electrolytic without removing it from the chassis, so you don't have to disturb the wiring. It's not always possible, you can't always get a saw in to cut off the can while it's still in the chassis. Don't bother looking for NOS or new FP-style electrolytics, just use the modern styles.

I'd immediately replace the paper capacitors. Barry's probably right, you should probably wait to replace the electrolytics unless they are obviously bad, but I'd shotgun them in advance. On the other hand, I have no fear of troubleshooting it if I should accidentally miswire the replacements.

For the resistors, again look at the color code on the part to find value and tolerance. You'll have to guess the wattage from the size.

This post on ARF might be helpful on the resistors:
viewtopic.php?t=297480

You should do a search on ARF for TV-2. There have been many previous threads on it.

TechyMechy wrote:
Is there any information on how to make this tester "better?" Does anyone have information on the inherent issues with the tester or things I should do to make it better? I've read where the filament voltage will droop with high current tubes which could be fixed by using 18 gage wires (this seems like alot of work) or that the shunt pot may be non linear or that the grid DC is not very even (has a lot of harmonics in it that will interfere with the AC injection). Would you use a test socket to set the exact voltages at the socket and see if something is not quite right under test (say using a DMM and potentially an O scope)?

Alan Douglas commented that for all the meters on the TV-2, it doesn't have one of the most useful ones - a plate current meter. You could add a couple of pin jacks to the front panel where you can plug in a VOM or DMM to read the plate current.

Otherwise, no, don't change anything. The filament voltage drop is mostly nonsense - the manual has you re-adjust the filament voltage after you light up the tube, so that compensates for the voltage drop from the current draw.

The TV-2 isn't a laboratory quality vacuum tube bridge, don't obsess over exact voltages at the tube socket, or less than perfect filtering on the plate and screen voltages. It's just a tube tester.

TechyMechy wrote:
When you test a meter sensitivity, do you simply hook the meter up to a limiting resistor and DC power supply (maybe a current limiting power supply) and adjust for the meter full scale and potentially check linearity? How do you do that?

Yeah, that's the basic idea for a milliammeter. Put a DMM in series with it, then a series resistor to limit the max current to something safe, then a variable resistor, connect it to a low voltage power supply. Turn down the variable resistor until the meter reads full scale and see what your DMM reads - that's the full scale of the meter. Then turn up the resistance and check the linearity at the cardinal points on the scale.

For a voltmeter, omit the series resistances, put the DMM in parallel with the meter under test, and use a variable voltage power supply.


If you can read technical German, this would be useful:
http://www.amplifier.cd/Test_Equipment/ ... g_V2_8.pdf

_________________
Steve Byan http://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Tue 18, 2018 6:00 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 677
Location: Stafford, Texas USA
Buy new standard capacitors and build fixtures to hold them. Purchase bare capacitors 105C.
Resistors do not buy old carbon composite resistor. Replace the out of spec resistors by looking at the color code;
replace with 1W 1% metal film resistors.

The specs for the TV-2/u meters are cover in TM 11-6625-316-12 Chapter 1 introduction on page 6 and 7
Jimmie


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Tue 18, 2018 3:06 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 4172
Location: Littleton, MA
Jimmie Stewart wrote:
The specs for the TV-2/u meters are cover in TM 11-6625-316-12 Chapter 1 introduction on page 6 and 7

Thanks for pointing that out. The information there is very helpful.

_________________
Steve Byan http://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Sun 30, 2018 10:28 pm 
Member

Joined: Mar Thu 29, 2018 3:41 am
Posts: 178
Location: Portland Oregon
I'm finally getting to the TV2 repair.

I tried the 5th echelon testing and basically got a bunch of garbage. The good thing is that all of the meters moved, the bad thing is that all of the values were way off. I decided to drop the chassis and take a look and I started on the trouble shooting section. I've just opened up the chassis and was starting to do the transformer resistance testing, etc.

I recorded all of the information in an excel spread sheet. Some of the key things I found out is as follows:

C2 is definitely bad. My Fluke 83 measures a resistance of something like 1 Ohm and my DerEEDE5000 couldn't make an accurate capacitance measurement on it.
C1 is about 18000uF and has a 50 Ohm resistance across the contacts. The can says it should have a capacitance of 14000 uF and a working voltage of 15V
C2 and C3 are about the correct capacitance values but they both have about 10K Ohms resistance. Their working voltages are above 200V

I think that I will buy new capacitors and replace all of these.

I measured all of the resistances and voltages according to section 2. I had *a lot* of resistance values that were off, especially on the precision resistors, but I did not lift a leg on any of the resistors until I replaced the capacitors.

I set my variac for 120V ac when making all of the measurements. I was careful to make shunt resistors for all of the voltage ranges for the ME-30A/U and the AN/URM-105. I made the shunt resistors taking into account the 10MOhm input resistance of my Fluke 83.

I don't know how close the measurements need to be for section 2. For example:

V1 looked OK in my opinion as far as measured vs spec values. The only potential issue is that for Pins 1 and 4, I measured 107Vdc when it should have been 100Vdc. Is this an issue?

For V3, pins 1 and 6 only measured 34 Ohms and voltabe was 92Vac. The spec is that they should have measured 80 Ohms and the voltage should have been 80Vac. Pin7 had a resistance of 12.5K Ohms and a 110 Vdc, but it should have been 12K Ohms and 100 Vdc. Pins 3-4 had 6.7 Vac when it should have been 6.5 Vac.

For V2, I was getting variable resistance readings and voltage readings really close to the spec values, but pin 1 and 6 resistances were variable as were the voltages.

I didn't remove the resistors to test their resistance. A couple of resistors were obviously strange (example Resistor 64 should have been a 1%- 1500 Ohm but I read zero ohms). the voltages were off on it too, for it had 81.8V on both side of the resistor where the spec said it should have zero and 95V. I think that the specified voltage values are wrong or I have something going on that I haven't figured out yet.

I also noticed that there was a lot of white dust on the components and a brown varnish material on many solder joints. See attached pics.

Should I just blow the dust off with compressed air?

I'll try to piece together a story with my data that I have collected thus far. If you are interested, I can send you my excel spread sheet.

Please let me know what you think.


Attachments:
IMG-1649_small.jpg
IMG-1649_small.jpg [ 86.44 KiB | Viewed 1774 times ]
IMG-1652_small.jpg
IMG-1652_small.jpg [ 66.89 KiB | Viewed 1774 times ]
Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Sun 30, 2018 10:49 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 4172
Location: Littleton, MA
TechyMechy wrote:
\I also noticed that there was a lot of white dust on the components and a brown varnish material on many solder joints. See attached pics.

Should I just blow the dust off with compressed air?

No! The white dust is probably cadmium oxide, from the cadmium plating on the steel parts. It's quite poisonous if inhaled, ingested, or otherwise introduced in to your body. Work outdoors, wear a dust mask, and wipe off the dust with a soft cloth wet with isopropyl alcohol. Discard the cloth. Wash your hands when you are done.

The brown varnish is "MFP varnish" - Moisture and Fungus Proof. See this recent ARF thread:
viewtopic.php?f=8&t=346858

_________________
Steve Byan http://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Sun 30, 2018 11:02 pm 
Member

Joined: Mar Thu 29, 2018 3:41 am
Posts: 178
Location: Portland Oregon
Cadmium Oxide....

I was working late on the tool last night and may have introduced a little into my eye because I wiped my eye with my finger. I don’t have any swelling but my left eye feels s little different from my right.

Is this a go see a doc right now issue or is this more of an extended exposure issue?

Dave


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Sep Sun 30, 2018 11:16 pm 
Member

Joined: Mar Thu 29, 2018 3:41 am
Posts: 178
Location: Portland Oregon
I just did a search on Cadmium Oxide. It is toxic at high levels. I’m fine, but it is best practice to follow the guidance previously given. I would also add the use of gloves when cleaning and throughly washing the gloves or throwing away.


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Oct Mon 01, 2018 1:01 am 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 5189
Location: Sunbury, Ohio 43074
It bears repeating that in some mil spec gear (most in my experience) it is not necessary to shotgun replace electrolytics, particularly cans. They were of much higher quality than consumer, or most industrial, gear back then.

Resistance readings across a capacitor can easily be meaningless as well unless you disconnect one side of the cap under test. Ditto with your capacitance meter. So I'd recommend trying that first. Are any getting warm? I believe, since you used a variac initially, the unit actually powered on and didn't blow fuses or smoke anything, your low ohms readings are actually reading something across the capacitor, not the cap itself.

My TV2 has all the original can electrolytics, and works fine. I'd suggest that most of them do. Storage conditions, which can also affect these caps, is minimized due to the sealed case that the TV2 lives in.

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Oct Fri 05, 2018 9:56 pm 
Member

Joined: Mar Thu 29, 2018 3:41 am
Posts: 178
Location: Portland Oregon
I finally made it most of the testing in the Chapter 2 "trouble shooting" and Chapter 4 "5th echelon" testing. I didn't lift legs on resistors or unsolder the leads to the transformers.

There are numerous discrepancies between the voltages delivered to the socket and the meter values. Some stuff works well like the resistances and short testing. Other stuff not so much, like the plate voltage test settings R and S only providing 21Vac and 11Vac when they should have been 35Vac and 20Vac, etc. The shunt control test was measuring 3.6 mA to reach full scale on the percent quality meter (when it should have been 4.92mA) when the shunt was set to 10 and the quality meter reached full scale when it was at 82 (without any current externally - it should have been full scale at a setting of 90 and with a current of 0.605 mA).

I have a couple of procedural questions:

1. For the strange value, high precision resistors - what do you think about using multi turn cermet trimmers like these:

https://www.vishay.com/docs/57028/64.pdf

2. When people replace resistors, what do you think about cutting out the element but leaving the leads soldered to the board, then make a hook in the lead and attach the new resistor? I think it will be a real bugger to unwrap these heavy leads from the board and is at high risk for screwing something up.

I'll disconnect the capacitors tonight and try to test them with my limited test capabilities. I have a Der EE DE5000 that should give good results for the ESR and value, but won't be able to test leakage. I have a ZM-3/U that I will use to try to test the capacitors. It is far from perfect, but hopefully it will give me some idea of the leakage.

I think that some of the resistors will be easy to replace for they are directly readable. I was planning on using 1W, 1% metal film resistors. I have not been able to determine the power ratings on most of the resistors. The 2W resistors are clearly defined, but the others are not. Are they 1/2W? The new resistors are much smaller than the carbon resistors originally used in these testers.

I'll give another update later this weekend.

Thanks for your help in answering the above questions and for giving guidance.

Dave


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Oct Fri 05, 2018 10:14 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 5189
Location: Sunbury, Ohio 43074
Quote:
1. For the strange value, high precision resistors - what do you think about using multi turn cermet trimmers like these:

https://www.vishay.com/docs/57028/64.pdf

2. When people replace resistors, what do you think about cutting out the element but leaving the leads soldered to the board, then make a hook in the lead and attach the new resistor? I think it will be a real bugger to unwrap these heavy leads from the board and is at high risk for screwing something up.

I'll disconnect the capacitors tonight and try to test them with my limited test capabilities. I have a Der EE DE5000 that should give good results for the ESR and value, but won't be able to test leakage. I have a ZM-3/U that I will use to try to test the capacitors. It is far from perfect, but hopefully it will give me some idea of the leakage.

I think that some of the resistors will be easy to replace for they are directly readable. I was planning on using 1W, 1% metal film resistors. I have not been able to determine the power ratings on most of the resistors. The 2W resistors are clearly defined, but the others are not. Are they 1/2W? The new resistors are much smaller than the carbon resistors originally used in these testers.


To directly answer the above questions:
1. There should be no reason to replace wirewound precision resistors. They very seldom change value, if ever. Carbons, yes, but not wirewound or precision spool resistors (which are really also wirewounds). If you have to, one of the mentioned precision multiturn pots can work, but they are likely to be far more expensive than ordering the proper precision resistor. They can also drift mechanically or environmentally. I'd think they add an unnecessary level of complexity to your restoration.

2. Personally, I'd opt for removing the entire old resistsor from the board. You are going to be heating the remaining lead to solder in the new one, and that could easily introduce a cold, high resistance, or intermittent connection to the board. It shouldn't be too tough with the proper tools to get the old resistors out. The proper tools are a temperature controlled soldering iron, and a solder sucker, or wick wire to remove the old solder. If you want to get fancy (I do) add a q tip with a bit of flux solvent on it to clean up before you put in the new resistor. Alcohol works in the absence of flux remover, but not as well.

Your DE5000 is not going to tell you much about the big electrolytics. It may, with the papers, but I'd replace those anyway. Ditto with the smaller (non sealed can) electrolytics. You need to test the big ones for leakage, at their operating voltage, to know what's up with them.

I'm sure you will get 30 or 40 other opinions :) 8)

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Oct Sun 07, 2018 9:58 am 
Member

Joined: Mar Thu 29, 2018 3:41 am
Posts: 178
Location: Portland Oregon
I've printed out the schematics and am following the layout. My goodness this is a complicated schematic.

I compared resistance measurements with voltages and I think I have a path forward for correcting my filament and bias discrepancies.

Filament
Resistors.....Spec.....Measurement...% Error...Affecting Filament voltages
R64............1500.....1702...............13.5%.....1.1, 1.5, 2, 2.5 V
R5..............7000.....9090...............28.5%.....3, 4.2, 5, 6.3, 7.5V
R4..............20000...24530..............24.4%.....10, 12.6, 14, 20, 26.5 V
R3..............70000...71800..............8.8%.......35, 50, 70V
R65............50000....51400.............7.9%.......117V

0.625V is delivering .723V to the socket. Does anyone know how to correct this so it will decrease the voltage to the socket?

BIAS

Resistor......Spec......Measurement.....% Error....Affecting Bias voltage
R10...........50000....51200................2.4%......50V
R11...........9900......11170................12.8%....10V
R12...........4300......5240..................6.2%......5V

I am trying to figure out my plate voltage discrepancies. Plate voltages vs. selector location is as follows:

Selector....Meter.....Measurement....Transformer Voltage - tap
G.............250.......255.2...............282V - 3, 282V - 14
H.............250.......254.9...............282V - 3, 282V - 14
J..............250.......252.9...............282V - 3, 282V - 14
K.............125.......131.1...............235V - 4, 235V - 13
L..............125.......131.8.............. 235V - 4, 235V - 13
M.............125......131.4................235V - 4, 235V - 13
N...............90........95.9................119.6V - 5, 119.8V - 12
O...............60........63.2................119.6V- 5, 119.8V - 12
Q...............62.5......67.2.................69.4V - 6, 69.3 - 11
R...............35.........21.8..ac...........69.4V - 6, NA
S...............20.........11.1..ac............0V - 7, NA

The 250V settings are within spec but the rest are out of spec. How can I correct the meter on my plate voltages? I cannot find the resistors for the plate meter.

I don't have a high voltage capacitor tester, but I did measure the values with my DerEEDE5000. I think that C1 and C2 may be suspect. I tested these all at 1000 Hz.

Cap...........Spec Value.....Measured Value....Resistance(low voltage)....Dissipation
C1.............1400.............1800...................400K............................. .417
C2...............330..............680...................400K.............................. .720
C3.................50...............58.77...............4M................................. .07
C4.................10...............10.3.................5M.................................. .035
C4b................10..............11.5.................5M.................................. .035

My Signal voltages are not right either. I think these are controlled by Resistors R50, R49, and R47. My values are as follows:

Select....Spec....Measured
A...........0.25....0.208
B...........0.25....0.208
C...........0.25....0.207
D...........0.50....0.417
E...........2.5......2.1


Resistor
R...........Spec.....Measured.....Accuracy
R50........7.14......7.05............0.5%
R49........7.14......7.07............0.5%
R47.......57.15....52.15............0.5%

These resistance differences are not enough to account for the low signal voltages. These circuits get really intertwined and it's hard to figure out what is happening. Do you have any suggestions on what to do with the Signal voltages (I measured these using the Echelon 5 - step 31 on page 42 of TM11-6625-316-35.

My Screen voltages are off too. I followed step 30 in the manual on Pg 42. These are my results:

Plate Selector...Plate Meter......Screen Meter.....Measured at socket
G...................250.................225.................230.1
H...................250.................180.................185
J....................250..................135.................139.5
K....................125..................115.................118.9 - screen meter did not get to 180
L.....................125...................90...................94.7 - screen meter did not get to 135
M.....................125..................60...................63.5 - screen meter did not get to 90
N......................90...................90...................95.6
P.......................60...................30...................31.6 - screen meter did not get to 60

I didn't have time to look at why the screen values may be off. I'll study the schematic tomorrow and see if I can get some insight.

I appreciate any input on how to fix the signal, plate and screen voltages. I think I have a good path forward for the bias and filament. I appreciate any input on how to fix the 0.625V setting on the filament circuit. I also am leaning toward replacing capacitors C1 and C2.

Thanks for your input!

Dave


Top
 Profile  
 
 Post subject: Re: TV-2/U repair
PostPosted: Oct Sun 07, 2018 12:34 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 4172
Location: Littleton, MA
TechyMechy wrote:
0.625V is delivering .723V to the socket. Does anyone know how to correct this so it will decrease the voltage to the socket?

You can't bring it down with the filament fine voltage control? Do you have the TV-2 on a variac, with the input voltage set to 115 volts? The 0.625 V filament winding is only rated for 8 mA, so it may have a high internal resistance. Try loading it with a 1 KΩ resistor and see what voltage you get.

TechyMechy wrote:
I am trying to figure out my plate voltage discrepancies. Plate voltages vs. selector location is as follows:

Selector....Meter.....Measurement....Transformer Voltage - tap
G.............250.......255.2...............282V - 3, 282V - 14
H.............250.......254.9...............282V - 3, 282V - 14
J..............250.......252.9...............282V - 3, 282V - 14
K.............125.......131.1...............235V - 4, 235V - 13
L..............125.......131.8.............. 235V - 4, 235V - 13
M.............125......131.4................235V - 4, 235V - 13
N...............90........95.9................119.6V - 5, 119.8V - 12
O...............60........63.2................119.6V- 5, 119.8V - 12
Q...............62.5......67.2.................69.4V - 6, 69.3 - 11
R...............35.........21.8..ac...........69.4V - 6, NA
S...............20.........11.1..ac............0V - 7, NA

The 250V settings are within spec but the rest are out of spec. How can I correct the meter on my plate voltages? I cannot find the resistors for the plate meter.

R36 is the plate range resistor for the 250 volt scale, and R36 in parallel with R63 sets the range for the R and S positions. If G through J are correct, then R36 is good. If K through Q are out of spec, it's because the meter no longer meets its linearity spec. There's nothing you can do about that.

What are you using to measure the AC voltages? Is is a true-RMS reading meter? You must use an average reading meter for this measurement, with a 10 KΩ input impedance (e.g. 10K resistor in parallel with a 10 MΩ DMM). Check using the correct measurement technique. If it still reads low, suspect R63.

TechyMechy wrote:
My Screen voltages are off too. I followed step 30 in the manual on Pg 42. These are my results:

Plate Selector...Plate Meter......Screen Meter.....Measured at socket
G...................250.................225.................230.1
H...................250.................180.................185
J....................250..................135.................139.5
K....................125..................115.................118.9 - screen meter did not get to 180
L.....................125...................90...................94.7 - screen meter did not get to 135
M.....................125..................60...................63.5 - screen meter did not get to 90
N......................90...................90...................95.6
P.......................60...................30...................31.6 - screen meter did not get to 60

Given that for the screen selector switch decks, S3 sections 3 and 4 rear, position H and position K are connected together, I'd say that position 4 has a dirty, bent, or broken switch contact on one of the sections. You should be able to get the same screen voltage on both positions H and K. This could be a problem on the other positions, too, but I didn't chase down the schematic connections for those.

_________________
Steve Byan http://www.byan-roper.org/steve/steve-at-play/


Top
 Profile  
 
Post New Topic Post Reply  [ 82 posts ]  Go to page 1, 2, 3, 4, 5  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: DaveInNC, Google [Bot], mblack, Retired Radio Man and 5 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB