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Author Topic: troubleshooting reverb on Princeton Chorus PR 82  (Read 283 times)

Deoxit Huffr

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troubleshooting reverb on Princeton Chorus PR 82
« on: March 18, 2017, 02:58:15 AM »

Greetings all...

I recently cleaned the pots on this amp, and all was working fine for a short while. Then the reverb just dropped out when I was playing.
I could hear the tank echoing then that stopped too.  I tried a different tank.. but still no luck.

I checked the RCA connectors and they look ok. Also took the amp apart and inspected the PCB and connections.
I don't see anything that looks disconnected or damaged. I don't know how to test the op amp itself.

Could I get some suggestions to isolate and possibly repair this problem??
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DrGonz78

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #1 on: March 18, 2017, 03:10:25 AM »

When you tap on the reverb tank does it make a crashing sound? If so then the recovery side of the reverb is working. Start at least there to see what we are working on. BTW here is the schematic. Might be helpful to test voltages the U2 chip and the U4 chip.
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A person who never made a mistake never tried anything new. -Albert Einstein

phatt

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #2 on: March 18, 2017, 12:06:10 PM »

Plus 1 what Dr Gonz said but I'll add that RCA plugs are notoriously prone to failure, especially after a reinstall or even a wiggle or twist. They are the most likely culprits.
Phil.
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Deoxit Huffr

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #3 on: March 18, 2017, 08:46:24 PM »

Thanks very much @DrGonz78 and @phatt

I am on my way to check these first... I do hope it's confined to those rather than the PCB.

Are there any good tuts or walkthroughs around for replacing the RCA plugs?  Do you need to remove
everything up to the board? Then I would need to do some soldering, which  I'm a beginner at that too.
« Last Edit: March 19, 2017, 12:24:42 AM by Deoxit Huffr »
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DrGonz78

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #4 on: March 19, 2017, 06:50:46 AM »

Are there any good tuts or walkthroughs around for replacing the RCA plugs?  Do you need to remove everything up to the board? Then I would need to do some soldering, which  I'm a beginner at that too.

Do you have an ohms meter to measure resistance? All you need to do is make sure the continuity from plug tip leads back through the wire to the solder joint on the board, and same measurement with ground portion of each RCA plug. It is possible for the wire to get compromised after all the wiggling around as Phat said. Prove this theory first and then move on to taking voltages on all the pins of the U2 and U4 chip. I think you ruled out a defective reverb tank by plugging in a brand new one.
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A person who never made a mistake never tried anything new. -Albert Einstein

DrGonz78

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #5 on: March 19, 2017, 07:18:58 AM »

Google and youtube can be your best friend in understanding this if you have never done it before.
https://www.youtube.com/watch?v=rrO9FrlSkOM

This gives you an idea how to do this but in your amp it has two wires soldered to the board instead of another plug on the end.
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A person who never made a mistake never tried anything new. -Albert Einstein

Deoxit Huffr

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #6 on: March 19, 2017, 10:10:56 AM »

Quote
Do you have an ohms meter to measure resistance?

 I am about to purchase a fluke 115 , should that cover me for any testing I need to do ?

 Yes I saw that on the PCB, clearly the RCA plug leads run right into the board. Wish it would be something as simple as plugging in a new part.
I did google for this part, and did not see one with the plugs and open ends to solder to the board.  I suppose that means I will have to strip
and split to make it solderable to the board.

 Seems like an "overboard" solution... I'd rather just find one for sale searching my friend google of course.
I do try to find what I'm looking for, but ignorance doesn't  help with choosing the search terms that get you where you need to go.

 Thanks for the suggestions,  I am hoping I'll learn something useful in the process.
« Last Edit: March 19, 2017, 10:20:32 AM by Deoxit Huffr »
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phatt

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #7 on: March 19, 2017, 11:15:37 AM »

Number one,, Go buy that DMM you will need it as this electronics game is very addictive.   8|
Then you can test the continuity of the RCA leads to establish IF it is in fact a dead RCA plug.
If so,, you can buy solder-able RCA plugs and cut the dead plug off and solder the new plug.
That will be the most likely culprit but you need the DMM to test FIRST otherwise you end up replacing parts for no reason and still may not fix the issue.
Phil.
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Deoxit Huffr

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #8 on: March 19, 2017, 05:24:53 PM »

right on phatt.... definitely don't wanna be cuttin' for nuttin' , thanks for the inputs input

might have to wait a day or two for amazon

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Deoxit Huffr

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Re: troubleshooting reverb on Princeton Chorus PR 82
« Reply #9 on: April 01, 2017, 07:47:40 AM »

So.. to update... much ado about nothing seemingly...

I left the amp disassembled for a while, then decided to just put it back together until I got a multimeter..
then put the new reverb tank back in, which did not work previously. I flipped on the power..and boom!  reverb again... go figure  :duh

I'm wondering if I could have caused some kind of charge build up that interfered with some circuits?  The RCA plugs were very clean
and did not show any wear or damage, and sure enough when I plugged them in this time.. bingo...


thanks again @DrGonz78 and @Phatt

I am including a little expanded schematic directly from Fender.
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