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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Dec Thu 31, 2015 9:32 pm 
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tbone8 wrote:
Mine is the newer above B030000

OK, the same advice applies except it's U2225 and U2255.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Dec Thu 31, 2015 9:35 pm 
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stevebyan wrote:
tbone8 wrote:
Mine is the newer above B030000

OK, the same advice applies except it's U2225 and U2255.


Will check voltages!


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Dec Thu 31, 2015 11:27 pm 
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tbone8 wrote:
stevebyan wrote:
tbone8 wrote:
Mine is the newer above B030000

OK, the same advice applies except it's U2225 and U2255.


Will check voltages!


I checked U2225, I think everything looks normal except the schematic say lead 14 and 16 should be 0V. 14 is channel 2 and 16 is channel 1 and those voltages range with turning the vertical position dial. Maybe they are zero when at midpoint in the dial? I accidentally found that resistors R2214 and R2218 each lead is connected to ground. No matter which side you touch, its grounded. Both test for proper resistance.

U2255 is really going to be a bear to get at to test, gulp, we need data from that one as well? Hope you guys have a great and safe new year. I will be home tinkering, maybe a glass of wine or two. I am too old to go out partying, be safe and thanks!

Attachment:
U2225 test voltages.png
U2225 test voltages.png [ 148.49 KiB | Viewed 1173 times ]


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Dec Thu 31, 2015 11:59 pm 
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tbone8 wrote:
I checked U2225, I think everything looks normal except the schematic say lead 14 and 16 should be 0V. 14 is channel 2 and 16 is channel 1 and those voltages range with turning the vertical position dial. Maybe they are zero when at midpoint in the dial

Somewhere in the manual it should say how the front panel controls should be set when taking your voltage measurements. I guess the vertical position control should be centered, but you'd have to check.

tbone8 wrote:
I accidentally found that resistors R2214 and R2218 each lead is connected to ground. No matter which side you touch, its grounded. Both test for proper resistance.

I'm confused by this statement. You'll need to clarify it. For instance, by "touching", do you mean you measured its voltage with respect to ground? Or that you measured a low resistance to ground?

I don't see how both ends of R2214 and R2218 could be connected to ground when you measure -0.3 volts on each.

tbone8 wrote:
U2255 is really going to be a bear to get at to test, gulp, we need data from that one as well?

The bias network voltages on U2225 are off; that's probably the place to start, after we clear up what's going on with R2214 and R2218. Let's ignore U2255 for now.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 12:32 am 
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+1 with Steve's questions. R2214 is connected directly to pin 14 and you measure -.3V there. Touching one of the sides of R2214 should give you -.3V.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 12:54 am 
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Also I could not find a complete schematics, the ones that I can find on the schematic pages only have the left side of the schematic.
Could you post a link to a good schematic.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 1:33 am 
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dan3460 wrote:
Also I could not find a complete schematics, the ones that I can find on the schematic pages only have the left side of the schematic.
Could you post a link to a good schematic.


I know what you mean, I did a lot of searching and found one that wasn't cut off.

http://www.download-service-manuals.com ... n=download


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 1:52 am 
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stevebyan wrote:
tbone8 wrote:
I checked U2225, I think everything looks normal except the schematic say lead 14 and 16 should be 0V. 14 is channel 2 and 16 is channel 1 and those voltages range with turning the vertical position dial. Maybe they are zero when at midpoint in the dial

Somewhere in the manual it should say how the front panel controls should be set when taking your voltage measurements. I guess the vertical position control should be centered, but you'd have to check.

tbone8 wrote:
I accidentally found that resistors R2214 and R2218 each lead is connected to ground. No matter which side you touch, its grounded. Both test for proper resistance.

I'm confused by this statement. You'll need to clarify it. For instance, by "touching", do you mean you measured its voltage with respect to ground? Or that you measured a low resistance to ground?

I don't see how both ends of R2214 and R2218 could be connected to ground when you measure -0.3 volts on each.

tbone8 wrote:
U2255 is really going to be a bear to get at to test, gulp, we need data from that one as well?

The bias network voltages on U2225 are off; that's probably the place to start, after we clear up what's going on with R2214 and R2218. Let's ignore U2255 for now.


I had one lead on the ground and another on R2214 and was rechecking voltages. I ran through the DMM settings and accidentally hit the continuity tester. Gives a beep when there is continuity. It beeped anywhere you touched those two resistors. Just now, I realized those resistors are only 49 ohms so when I checked it with the ohmmeter setting, it showed the correct resistance. My mistake on that. Any recommendations on what to check next? You don't think that micro chip is the culprit? I did recheck point 41 and 42 individually to ground instead of point to point like you told me to do. There is 34V on one and 34.88V on the other that don't change with turning the dial. Out of curiosity, why do you check those point to point instead of point to ground? Just curious. Hope you guys new years eve is going well. :D


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 3:23 am 
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I'm an old fart ready to go to bed, happy new year.

Voltage measurements are done against the chassis or the ground tests points in some of the boards. Let me study the schematics, maybe Steve have some ideas in the mean time.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 3:37 am 
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dan3460 wrote:
I'm an old fart ready to go to bed, happy new year.

Voltage measurements are done against the chassis or the ground tests points in some of the boards. Let me study the schematics, maybe Steve have some ideas in the mean time.


Ok man, glad I was at least able to find you a good copy of the manual for any future projects you have. See ya next year! :wink:


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 2:36 pm 
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Steve, I have a hunch that the problem is a little bit higher on the circuitry. I think we need to look at the vertical switching. I think we need to look at the voltages generated at each position of CH1,CH2, ADD, etc at the collectors of Q1636,Q1619,Q1719 and Q1617. There is very little difference in voltage applied to the diode switch for each channel. What do you think?
Tbone, please do this: apply a signal to either channel. Select trig/mode to auto. Select source to normal. Select coupling to AC. Is the trig light lit?

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 4:05 pm 
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I'm reading through here and I wish to stick my hand up to politely interrupt for just a second. It is advisable to never measure a live circuit with an Ohm meter or continuity tester. Just as you would never want to put an ammeter across battery terminals. A modern ohmmeter works by forcing a modest current (say, 1 mA) and measuring the resulting voltage drop on the component(s) under test. Testing on a live circuit may interfere with that measurement and also can make toast of your test equipment and or device that you're working on. The same goes for using a multimeter for checking diodes. Do not do it "hot."
8)

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 4:14 pm 
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+1, interruption well taken. Is good to have several set of eyes trying to help tbone.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 4:50 pm 
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tbone8 wrote:
Any recommendations on what to check next? You don't think that micro chip is the culprit?
I did recheck point 41 and 42 individually to ground instead of point to point like you told me to do. There is 34V on one and 34.88V on the other that don't change with turning the dial. Out of curiosity, why do you check those point to point instead of point to ground? Just curious.

It could be a fault in U2225 or it could be a fault in the surrounding circuitry. We have to do further checks.

The vertical channel of an oscilloscope is differential. That means it has two signal channels of opposite polarities. The actual signal is the difference between the two channels, not one or the other channel to ground. The electron beam in the cathode ray tube is deflected by the voltage difference between the top and bottom vertical deflection plates, hence the use of a differential amplifier.

You can check both points to ground and manually subtract them, but it was simpler and less prone to misinterpretation to just ask you to make the differential measurement.

dan3460 wrote:
Steve, I have a hunch that the problem is a little bit higher on the circuitry. I think we need to look at the vertical switching. I think we need to look at the voltages generated at each position of CH1,CH2, ADD, etc at the collectors of Q1636,Q1619,Q1719 and Q1617. There is very little difference in voltage applied to the diode switch for each channel. What do you think?

We've already verified that a signal (the voltage variation from the vertical positioning control) makes it to the input of the first stage of the vertical output amplifier. That means that the signal made it from the output of the vertical preamp through the vertical switching circuitry, the delay line driver, and the delay line itself. The signal doesn't make it any further, so the trouble is in the first stage of the vertical output amplifier or in it's load, the input to the second stage of the vertical output amplifier.

As for the manual, the scan at the tekwiki is good:
http://w140.com/465B_svc.pdf

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 4:55 pm 
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mescalero wrote:
I'm reading through here and I wish to stick my hand up to politely interrupt for just a second. It is advisable to never measure a live circuit with an Ohm meter or continuity tester. Just as you would never want to put an ammeter across battery terminals. A modern ohmmeter works by forcing a modest current (say, 1 mA) and measuring the resulting voltage drop on the component(s) under test. Testing on a live circuit may interfere with that measurement and also can make toast of your test equipment and or device that you're working on. The same goes for using a multimeter for checking diodes. Do not do it "hot."
8)

+1

And switching through the DMM functions would switch through the current ranges too, which would put pretty much a direct short across the circuit under test. Could be very damaging.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 5:55 pm 
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tbone8 wrote:
I checked U2225, I think everything looks normal except the schematic say lead 14 and 16 should be 0V. 14 is channel 2 and 16 is channel 1 and those voltages range with turning the vertical position dial. Maybe they are zero when at midpoint in the dial?

The manual says to use the following settings for checking the DC measurements on the vertical output amplifier:
vertical mode: CH1
vertical position: midrange
AC-GND-DC (both channels): GND

Would you please reverify pins 2, 3, 14, and 16 of U2225 with those settings?

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Fri 01, 2016 7:11 pm 
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Also check the DC voltages on the collectors of Q1426 and Q1428 at the output of the vertical switching logic (should be -1.2 volts), and the voltages at the vertical switching logic end of the delay lines (should be about 0 volts).

If pins 14 and 16 of U2225 are around -0.3 volts and and pin 2 is +0.17 and pin 3 is 0 volts, then the input transistors on U2225 are cut off. The negative voltage on pins 14 and 16 is suspect, as is the high and unbalanced voltage on pins 2 and 3.

Turn off the power and measure the resistance between pins 2 and 3, and use the diode-check function on your DMM to check the emitter-base junctions of the input transistors of U2225. That is, use the diode check function between pins 14 and 3, and then pins 16 and 2. Do the test twice on each transistor, reversing the leads between the two tests. One way should show about 0.6 volts diode drop, and the other way should show infinite resistance.

I'm going to have to read up on the trace separation circuitry. I don't know what it is supposed to do, and it's a bit complicated.

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 12:31 am 
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Happy 2016 to everyone!

Dan, I did what you asked and the trigger light does come on if I set the volts/div to to the right setting.

Steve, voltages are as follows with vert mode Ch1, vert pos midrange and GND both channels:

pin 2 .091-.130V, not steady, slowly drifts
pin 3 .114-.135V, not steady, slowly drifts
pin 14 .005V slow drift as well
pin 16 .011V slow drift as well
could not get a repeatable reading at either pin, don't know if it significant

Resistance between pins 2 and 3 were 29.6Ω

Diode function test
14(+) to 3 (-) .702V
14(-) to 3 (+) OL infinite resistance
16(+) to 2 (-) .722V
16(-) to 2 (+) OL infinite resistance

Collectors at Q1426 and Q1428 were -1.18V and -1.23V respectively. and end of delay lines were .007V.

I assume these readings are within normal limits? Hope everyone has a good 2016. I do use an isolation transformer and am careful to always switch the power off when changing settings.


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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 4:15 am 
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Looks good at the vertical switching end of the delay line and at the inputs to U2225. The emitter junctions of the input transistors on U2225 are good. The biasing voltages are off, so I suspect trouble in the trace separation bias circuit, but it could still be that U2225 is bad.

Let's focus on the bias network first. In studying it, I see that it's controlled by the horizontal time base mode. What is your horizontal time base mode setting?

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 Post subject: Re: Picked up a Tek 465B, need a little direction
PostPosted: Jan Sat 02, 2016 5:37 am 
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stevebyan wrote:
Looks good at the vertical switching end of the delay line and at the inputs to U2225. The emitter junctions of the input transistors on U2225 are good. The biasing voltages are off, so I suspect trouble in the trace separation bias circuit, but it could still be that U2225 is bad.

Let's focus on the bias network first. In studying it, I see that it's controlled by the horizontal time base mode. What is your horizontal time base mode setting?


It was set on 50μs.


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