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


It is currently Aug Mon 03, 2020 1:06 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 48 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Nov Sun 17, 2019 7:33 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 7481
Location: Sunbury, Ohio 43074
The black coating is most likely high voltage "corona dope". (old trade name) for what is basically a paint on high voltage insulation. It may still be available, or perhaps you can scrounge up an old bottle from a restorer of old TV's. Without actually looking at the circuit, I'd imagine the points that were so coated were at the higher high voltage potentials, and this would have prevented arcing even if the terminal strips got dusty/dirty or otherwise.

As far as replacing the caps, it might seem like a good idea, although if your other repairs fix the problem it might be best just to leave them alone. I'm in the "if it's working don't fix it" camp with these kinds of instruments. They appear to be 400V caps, so you could test them the usual way if you have a cap tester that provides these working voltages. The Sprague TO series, Heathkit IT-11 or 28, etc. all can test a capacitor under it's stated working DC volgage, up to I believe 600V.

If an oil cap is not actually leaking oil, it may be just fine. Not assured, however.

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


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Nov Sun 17, 2019 8:58 pm 
Member

Joined: Mar Thu 29, 2012 8:51 pm
Posts: 319
Location: upper midwest
I made some comments and added photos in this thread that maybe of use in working on the HV in your 545A.

viewtopic.php?f=8&t=339646&hilit=tektronix+531&start=0

Those HV rectifier tubes would not be expected to glow during the timed warmup as they get their filament power from 1 turn wrapped on the HV transformer core. Said transformer is in the 60khz (if I recall correctly) oscillator so it won't be oscillating until they relay clicks and the B+ supplies all come up.


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Dec Wed 25, 2019 11:04 pm 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
To follow up a bit with the HV Supply Board.

I have sourced a complete set of NOS rectifier tubes so will replace all five. I have also discovered the triple series set of resisters tucked below the second rectifier tube from the left is barely producing one third of the required resistance. I have a spare set running on correct specs so will replace this resister set when the five rectifier tubes are out.

I noticed a warm varnish smell from the small HV transformer when I last powered the scope up. I have an NOS replacement on hand, if needed, but my main concern now is the 6 heavy duty capacitors sitting at the bottom of the HV Supply board. Three are large beige axiel lead ceramic disc caps rated at .01 mF @ 2KV. Next to them is a similar style brown ceramic cap rated at .05 mF @ 4KV and finally, on the right side of the board, two chunky red caps with axiel leads that look like a couple of chunks of pepperoni sausage. These are rated at 500mmF @ 10 KV.

My gut tells me to replace them all while accessible, but I am not sure how easily suitable replacements can be found. Not much wiggle room to fit caps that prove too large dimensionally. I am thinking if the transformer is warming up there is a good chance one or more of these 6 capacitors are no longer performing properly and the challenge of replacing the transformer is something I would prefer to avoid if at all possible.

Anyone worked with these kinds of caps before?

David
VE4DTD


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Dec Wed 25, 2019 11:18 pm 
Member

Joined: Jul Mon 01, 2019 4:42 pm
Posts: 568
Location: St. Louis, MO
Ceramics don't go bad very often. You can always take one leg out of circuit and test them. Do you have any reason to suspect them? Are they cracked? Pieces flaking off?

Still, modern components at the same ratings are tiny compared to how big they used to be. Your biggest problem might be having to shove a radial in the spot that an axial used to go. That and adding lead extensions because the included leads on the new, tiny part are just too short.


Last edited by ZombieElvis on Dec Wed 25, 2019 11:25 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Dec Wed 25, 2019 11:22 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 7481
Location: Sunbury, Ohio 43074
I tend to agree.... the ceramics seldom fail, in my experience. More likely your resistor issue may be causing the transformer warming.

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


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Dec Fri 27, 2019 6:38 pm 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
Thanks for the input on the ceramic capacitors, they appear to be in very good condition so I am going to bite the bullet and leave them alone for now. I will replace the duff resistor set and the 5 rectifier tubes and then see how the HV Supply performs with those improvements.

While on the topic of the HV Supply, it amazes me sometimes how much of a 'Conehead' I can be.

I could not understand why the NOS HV Supply Transformer I purchase had 10 fewer leads coming from it than the one currently mounted in the 545 A. While looking at the one in my scope more closely/patiently this week, with a small flashlight, I finally realized the 10 leads with heavy white insulation (four on the left side of the transformer and six on the right side, had nothing to do at all with the transformer. They were nothing more than a pair of jumper cables on the left and a trio on the right coming from various ceramic terminal boards in front of the transformer, looping around the side frames of the transformer and back to other terminals on the ceramic boards. Each pairing was held in place with a clear plastic sleeve of various lengths. Sheeesh!

Who says you are ever too old to learn!

David


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Dec Fri 27, 2019 10:44 pm 
New Member

Joined: Sep Thu 29, 2016 8:16 pm
Posts: 2
I know nothing about this scope, but the white loop wires you describe appear to be the 1 turn filament windings for the HV tubes. Very important to reinstall if you do have to replace the transformer. Someone may have good hints how to accomplish that, if necessary.

I have enjoyed reading your experience with this repair. I'm sure it has been an education.

Gil


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Dec Sat 28, 2019 2:33 am 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
Thanks for taking the time to post your comment, Gil.The last post on Page 1 of this thread shows the five loops of wire quite clearly.

I just pulled the CRT schematic in the manual and had yet another look at it. Makes all the sense in the world now. Not sure if that falls into the 'Learning Something New' category right now, or, if it fits better in the 'I Have Not Used a Lot of This Knowledge For Close to 40 Years Now' file.

I guess I am like this scope in a way. The more synaptic gaps I can get refiring in my brain now, the better off the electron flow for both of us!

Cheers,

David


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Dec Sun 29, 2019 12:28 am 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
Well, Happiness is spending a couple of hours carefully removing old suspect rectifier tubes and resisters, installing new replacements, turning the scope back on and having a nice bright trace line that responds to both vertical and horizontal instructions! Not sure when that last happened with this scope, but it was nice to finally see! Oh...and no warm HV Transformer any more!

Still some fine tuning to do, both with the scope and the Type CA Plug In, but still delighted with the progress.

David
VE4DTD


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Mon 06, 2020 3:21 am 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
A little bit of an update.

I took a look at the Internal Calibrator and found it could not be adjusted any closer to its required voltage of 100 Volts than 105.3. Found the 12AU7 had died on one side and the 6AU6 had gone very weak. Replaced both and was able to get the voltage down to 102.1 Volts.

Next looked at the Low Voltage Supply. The -150 V circuit was sitting at -167.7 volts. Its 12AX7 was dead on one side so replaced it with a brand new one. Not a significant change which led me to the 5651 in the circuit. I had three others to swap it out with, all used. The third and final one paid off, bringing the -150 volt circuit down to -152.6 volts: just at the upper acceptable limit. The remaining 4 voltages were well inside the 2% variance range. At that point I adjusted the -150 Volt circuit to bring it down to -150.1 volts, at which all other four were almost spot on. Going back to the Internal Calibrator, it just needed a small tweak upwards at that point to hit the magic 100.

I am now going to have to look more closely at the Intensity Control. It is the only control at the moment for which I get absolutely no response from the trace. My immediate interest is the variable resister Intensity Control itself, but I will take a close look at the other four resisters in the circuit as well.

David


Last edited by David Dunlop on Jan Mon 06, 2020 4:25 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Mon 06, 2020 3:25 am 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
While I think of it.

Does anyone know if two versions of the graticule bezel exist for the Tek 54x Series of scopes? A friend sent me a green filter for in front of the graticule, but when installed, the bezel is not deep enough to completely cover the filter/graticule combination. My scope may have had a wrong sized bezel installed at some point. The accessories section in the manual covers the filter options but only one bezel is listed.

David


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Tue 21, 2020 12:51 am 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
It’s interesting, sometimes, how chance can play a part in restoration projects.

A week ago, I was struggling trying to sort out the Intensity Circuit in this scope. I finally had a trace on the screen, but it would not respond at all to the Intensity Control on the front panel. Starting at the control end of the circuit, I had slowly checked the circuit through the scope to the last couple of components in the High Voltage Supply. At that point I decided I needed a break and headed upstairs for a mug of tea, leaving the scope to idle in the shop.

When I came back down about 20 minutes later, I saw I had turned out the shop lights when I left, which was odd, but when I reached in to turn them back on, I noticed only four glows from the area of the HV Supply in the scope. Turning the lights back on, it was evident, the brand new rectifier tube installed in the V822 position...the Intensity Supply rectifier, was the one that had failed. Checking the cathode terminals revealed a resistance that should not have been there. Out came the duff rectifier and in went another NOS one. Fired the scope back up and finally had intensity control for the trace. Another box on the restoration list ticked off.

The current problem being worked on is the length of the trace. Currently, when on the centre line, it is deflecting way off screen, both left and right. No combination of Horizontal Control adjustment on the front panel, or changes in the Sweep Length resister inside will bring both ends of the trace to the outer graticule lines at the same time.

Gotta love Baby Steps.

David
VE4DTD


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Wed 29, 2020 11:10 pm 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
I am still sorting out the issue of excessive horizontal trace length. There is a 6AL5 tucked away in one of the circuits, which has quite a mismatch internally between the two diodes. Checked two spares I had available and all three had the same issue. Also, all three tested very low in the bottom third of the ‘Good’ range on my tube tester. Out of curiosity, I have ordered 3 NOS replacements and will see where on the meter they test out at once received.

In the meantime, I am now looking at the Horizontal Amp Circuit to see what is going on there, regarding the inability to get the horizontal trace centred within the outer edges of the graticule.

Interesting how tubes can test out just fine but once under a working load again can fail. Glad I have three scopes worth of spares to work with!

David
VE4DTD


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Wed 29, 2020 11:19 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 7481
Location: Sunbury, Ohio 43074
Is the trace way wider than the screen with and without any signal applied? That might be a clue. Do any of the centering adjustments work? Is the X2 sweep width on (if it has one) ?

I can't wrap my head around how it can be way off on the left side, barring the above, unless there is some kind of blanking issue. Perhaps it's just too long of a trace, and way off center to the left... another among many possibilities.

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


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Wed 29, 2020 11:45 pm 
Member
User avatar

Joined: Aug Tue 28, 2018 9:22 pm
Posts: 2243
Location: Sanford Fla 32771 (USA)
Daid,
Have you a replacement CRT for your 545 ? If not I have a CRT from a 545 with a clean phosphor face, no burn marks.
Shipping would worry me, but you can have it in exchange for your bad CRT EDIT:and cost of shipping to Canada. I only use it for display.
Paul

_________________
Paul of Florida ….I had my patience tested. I’m negative.
https://paulsironhorse.smugmug.com/


Last edited by pauls.ironhorse on Feb Sat 01, 2020 4:21 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Thu 30, 2020 1:32 am 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
Hello Paul.

At the moment, I am pretty, certain the CRT is OK, just the circuits need sorting out. But thanks for the kind offer.

Barry.

The trace currently runs fully side to side of the CRT. The position lamps will still indicate if the balance of the beam is left or right and when both lamps go out, the Horizontal control indicator is pretty much centred, the vernier dial not quite so.

This is based on the start up control settings in the manual. In this mode, and after 15 to 20 minutes warm up, if I try adjusting the SWEEP LENGTH variable resister, it has no visible effect, turned either full left or right. I have checked the resister and it is in good working order.

If I turn the Horizontal Control either direction, I can get either the left end, or right end, of the trace to line up with the side of the graticule, but cannot get the opposite side to pull in to match.

If I feed the internal calibrator into the scope, I get a square waveform very close to 1 cm high and wide, good clean bottoms, but a bit of wrinkle on the tops. Nice sharp angles top and bottom.

Working the vertical control on the trace, it drops off scope +/- 3 cm from the horizontal centreline, as it should. I am curious about the 6AL5 at the moment as it is defined in the schematics as the ‘On/Off Diodes’ for the horizontal trace. I would like to make sure this is OK before looking more closely at the Horizontal Amp.

Cheers for now,

David
VE4DTD


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Thu 30, 2020 5:14 am 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 7481
Location: Sunbury, Ohio 43074
Does the CAL signal also run off the CRT left and right? If memory serves, and often it doesn't ...... with no signal the sweep width may exceed the CRT sides. I don't remember exactly. But with the CAL signal, and the trigger set properly, the trace should START at the first graticule line on the left side when all else is set up properly.

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


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Jan Fri 31, 2020 9:17 am 
Member

Joined: Nov Wed 15, 2006 7:56 am
Posts: 1416
Location: germany
David Dunlop wrote:
Working the vertical control on the trace, it drops off scope +/- 3 cm from the horizontal centreline, as it should. I am curious about the 6AL5 at the moment as it is defined in the schematics as the ‘On/Off Diodes’ for the horizontal trace.


David you are sure to have a CRT for 545A there?
The 545(no-A) is a ±3 display.

Martin


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Feb Sat 01, 2020 4:13 am 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
Barry.

Whether it is a passive trace, or the output display from the internal calibrator, the trace runs edge to edge of the CRT. Sigh.

Martin.

Hello. Nice to hear from you. According to the specs, the 545A CRT has a usable viewing area of 4 x 10 cms, with a correspondingly marked graticule. CRT is a Type T543P2. Of the four Tek scopes I picked up, the only one with a complete bezel, graticule, washers, nuts and light shield assembly was a RM 503, all of which I switched to the 545 A I am restoring. Consequently, my graticule is set up in a 10 by 10 cms grid. Which is fine by me. The one thing about the setup I did discover, however, is that the bezel for the RM 503 is thin enough it cannot accept a combination filter and graticule without a 1mm gap showing up between the bezel and front panel of the scope. Just discovered last week a thicker Tek bezel exists (I suspected this) and have ordered one.

One other small wrinkle. Neither of the two graticules I have are drilled for the small nylon, graticule adjustment cam in the lower left corner. Nice option, but I can work without it, so removed the cam assembly and tucked it safely away in the scope spares bin.

David
VE4DTD


Top
 Profile  
 
 Post subject: Re: Tektronix Type 545 A Oscilloscope CRT Replacement
PostPosted: Feb Sat 01, 2020 2:51 pm 
Member

Joined: Jul Tue 22, 2008 6:12 pm
Posts: 144
Location: Winnipeg, Canada
OK! Sometimes my ability to be dumber than a sack of hammers reaches monumental levels.

I was reviewing a couple of books on oscilloscopes last evening and had the Tek 545 A idling for a while. While reading one of the books, I ran across a fundamental section talking about the trace and how one needs a stable image on the CRT to be useful. If the trace is out of sync, it will simply roll across the CRT screen.

I reconnected the internal calibrator on the scope at that point to take another, hopefully more informed look at it. It was indeed rolling happily across the screen and I could not find any controls that could produce a static/stable image of the square wave. I am now wondering if this rolling trace, and it’s excessive horizontal deflection are related in some way in one of the circuits.

David
VE4DTD


Top
 Profile  
 
Post New Topic Post Reply  [ 48 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 16 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB