Airline GIM-9131A knowledge/repair question

[btah]

I stand corrected on something. I think there is a problem with the RCA cable that was hooked up to the output side of the reverb tank. This is with it unplugged from the tank. I checked it again an it is NOT infinite resistance between the plug and the shoulder. In fact, there is very little resistance. On the end of the RCA cable that has the solder connections there are two wires coming out of the cable. If I put one probe on one of the wires coming out I show very little resistance when I have the other probe on the shoulder and also very little resistance if I put the probe on the RCA pin. Bad cable, right?

[btah]

I am done for the night. Thanks for your help this evening.

[The Dude]

OK. Try this first. It should be the input side that reads low (across T3) and not the output, so first try switching the input and output wires on the tank and see if the hum goes away. If not go to this:

I'm not sure I totally understand, but I think you are measuring across the reverb transformer in the amp (see schematic T3). There will be very little resistance. To try to clean this up, can you just stick the probes in the connectors on the tank and tell us what resistance you have there? Input + to- and output + to -.

[btah]

Switching the input and output connections into the reverb tank made no difference. I can plug/unplug and switch the connections while the amp is on and there is no change at all to the buzz.

For the your other suggestion about T3, I will need to read that a bunch of times and try to locate T3. I see it on the schematic but I don't really know how that translates to the actual wiring.

For your suggestion about checking the resistance on the tank. Do you mean the following:
unplug both the input and output RCA connectors
Stick the + probe in the input connection and the - to the reverb tank metal cover?
Stick the + probe in the output connection and the - to the reverb tank metal cover?
If that is what you meant, there is zero resistance (or very minimal) in both cases.

I will check back in a while and redo my probe tests if I have that wrong...

[The Dude]

......For your suggestion about checking the resistance on the tank. Do you mean the following:
unplug both the input and output RCA connectors
Stick the + probe in the input connection and the - to the reverb tank metal cover?
Stick the + probe in the output connection and the - to the reverb tank metal cover?
If that is what you meant, there is zero resistance (or very minimal) in both cases......

Yes, that is what I meant. Except use the ground/outside of the plug instead of the tank cover. The plug ground is not always grounded to the tank chassis. Do not yet worry about T3.

So if you did that and have low resistance at the tank, you should have the same thing at the other end of the wires with the tank plugged in (on the amp side). Do you?- or is one of them infinite?

[btah]

Thinking about that more, I can't be correct. I must have been touching the ground portion of the plug on the tank. I will redo that later. I will have to find a better way to get the probes into the tank. Part of the wood case is in the way so I must have been touching the shoulder. I will find some type of help to get this test done.

[The Dude]

Can you just remove the tank for testing? It will be easier to get to the jack contacts. It wouldn't hurt to inspect it anyway. There may be broken springs in there.

[btah]

I redid the test and I think was correct. very minimal resistance between putting the probe in the connection and the outside of the shoulder. I then went back to where the wires connect in the amp. One of the RCA cables has two wires soldered to two different connection in the amp. Both of those read zero resistance to the reverb tank. The other RCA cable only has one wire. That wasn't a typo, there really is only one wire. Not sure if that is normal or not, but that is what it is. Anyway, there is also zero resistance between that solder connection and the tank.

Now I have to step out for an hour or so.

[btah]

Aside from going further, I have a question. For channel 2, if I have a guitar hooked up and turn the volume up with the reverb depth off, I hardly get anything out of the speaker. I have to turn the reverb up. Does that make sense? I thought the reverb would "adjust" the sound but not be in control of the loudness of the sound. If so, what is the point of the volume control?

[g1]

You are correct, it is not working right. The signal is not getting through between the ch.2 volume pot wiper and the grid of V2B (through the tone stack). Just the reverb part is getting around it.

[btah]

So channel 2 should work properly, meaning volume like channel 1, without the reverb in the path, is that correct?

[The Dude]

This may help us figure out the buzz problem, too! So, you say using Channel 2 you get little volume unless you turn the reverb up. Do you actually hear reverb or is it just louder?

[btah]

I hear reverb. Not being a musician I have to admit I don't know exactly what it should sound like. However, to me, it sounds like it is doing exactly what it should be doing.

[btah]

g1, what exactly do you mean by "signal"? As best I can tell by using my DVM the path matches the schematic and the resistances seem correct (as far as I can tell) and the paths to ground seem correct (as far as I can tell). Now, I was just checking resistances with to omh meter. Is the "path" what you mean by "signal" or do you mean checking voltages?

[g1]

I meant the signal is not getting through the signal path. You have checked for proper resistance of components, but have you checked for connections between components? Any 2 things that show connection, you should be able to measure very low resistance between them.
Otherwise, where there are caps that the signal passes through, resistance checks will not tell you if they are allowing the signal through. You would have to inject a signal and measure the AC voltage at various points along the signal path.