Tektronix 2213A diagnose and repair help

[Coll]

Hello I am a newbie to electronics and get my practice on repairing boards. I was trying to measure a board and didnt realize that what I was measuring had earth referenced AC on it. So when I attached my ground clip it shorted through my scope damaging it. This happened on channel 1. The issue at the moment is the channel measures but it has this awful noise on the trace that really makes it difficult to read out. This issue is only isolated on that specific channel. I tried a spare v/div board that I had hoping that might clear up the issue but it hasn't. I also did a visual inspection and for a 25 amp short I do not see anything physical on the board. Since I do not understand fully how these circuits work I am unclear where to go from here. I would like to be able to complete this repair as it is my first and only scope that I have.

[David Hess]

Check to make sure the BNC ground on that channel is still connected.  Also make sure the probe's ground is continuous.

[Coll]

Yup done both. BNC ground still fully connected to chasis and the input resistor is still good reading exactly the resistance it should. The probe itself works as well. Check with a resistance reading also swapped a test probe from channel 2 and still get the same issue.

[David Hess]

I am inclined to think that there a ground blown out somewhere.  The A2 vertical board has five ground connections between it and the A1 main board that it rests on or at least that is what the schematic shows.  I would check those and especially the two at the end where the vertical signal connects.

[Coll]

I was thinking that but couldnt find a blown trace. thought maybe a blown cap too but nothing. last place to check if the front board. It's such a pain to remove. Unless this specific trace is hidden cause I swear I looked everywhere even the high voltage area.

[David Hess]

When I had a problem with burst noise on one channel of a 2230 which is the same basic design, I tracked back and forth through the vertical signal chain until I located the point immediately before and immediately after the part where the noise originated.

Note that in this case, you can use channel 2 to probe the signals on channel 1 but beware of the ground lead on the probe.  Do not connect it to anything except ground or maybe even remove it to prevent it accidentally bumping into something and causing a short.

[Coll]

Hmm, that is a good idea. I didn't consider that. I'll give it a try. If I remove the ground lead is there some setting I need to switch?

[David Hess]

Hmm, that is a good idea. I didn't consider that. I'll give it a try. If I remove the ground lead is there some setting I need to switch?

No, there is nothing special which needs to be done.  The probe already shares ground with the other oscilloscope circuits which is why it is dangerous to have its ground lead waving around inside the oscilloscope.  Attaching the ground lead will produce a lower noise measurement but that is unlikely to be needed for what you are tracking down.

[Coll]

I took the whole think apart cleaned up the boards decently well and put every back together the issue seems to have been resolved. I believe that short might have stressed an old joint I did when I was less experienced and cracked it. So that's fixed. Thanks for the suggestions everyone. One more thing now is I am looking for some guy or upgrade kit for the 2213A. I hear the caps need to be replaced but not so lucky on the information about that. Does anyone know?

[David Hess]

I took the whole think apart cleaned up the boards decently well and put every back together the issue seems to have been resolved. I believe that short might have stressed an old joint I did when I was less experienced and cracked it. So that's fixed. Thanks for the suggestions everyone. One more thing now is I am looking for some guy or upgrade kit for the 2213A. I hear the caps need to be replaced but not so lucky on the information about that. Does anyone know?

Unlike the 2213, there is nothing which *must* be replaced on the 2213A.  The various service bulletins are available here.

Or were you looking for refurbishment instructions?

[Coll]

Not really sure tbh. I just want to make sure it works and works well. Would refurbishment help get it into good performance? Wanna do something like this before calibrating so I don't have to do it again. Maybe refurbishment instructions you may have a better idea than I do.

[David Hess]

Not really sure tbh. I just want to make sure it works and works well. Would refurbishment help get it into good performance? Wanna do something like this before calibrating so I don't have to do it again. Maybe refurbishment instructions you may have a better idea than I do.

I am just going to go off the top of my head here but refurbishment of a 2213A/2215A includes:

1. New aluminum electrolytic capacitors.
2. Replacing the carbon composition resistors in the focus resistor chain with high voltage film resistors.
3. Replacing the RIFA line filter capacitors.

Replacing the aluminum electrolytic capacitors is likely to make the most difference to performance due to decreased power supply noise.

The risk of doing any of the above is damaging an already operating oscilloscope.

[Coll]

So should I just leave it alone calibrate it as is a move on?

[David Hess]

So should I just leave it alone calibrate it as is a move on?

Oh, how do I answer that?

It depends on your skill level and risk versus reward.  High skill lowers the risk of damaging the instrument.  If you have alternative instrument like another similar or better oscilloscope, then the risk is also lower that you will be left without any oscilloscope.

Complicating this decision is that there may be some risk to allowing the aluminum electrolytic capacitors to wear out.  2235 series power supplies seem to have a failure mode which might be brought on by worn out aluminum electrolytic capacitors.  I suspect this but do not know and cannot prove it yet.

I would not mess with it unless you decide to change the aluminum electrolytic capacitors and if you do that, then I recommend changing the RIFA capacitors and the focus chain resistors.  The later two are not worth bothering with otherwise.

[Coll]

I have some skill but I am unclear the possibility of damage we are talking about. I couldn't find adequate replacements for a lot of these caps because I am sure they have some specific use in mind. But I can for sure de-solder and solder on components