Peavey Stereo Chorus 212 - No sound?

[Reding]

Good morning! I recently bought a Peavey Stereo Chorus 212 amp. It looks to be the original one, teal stripe around the faceplate and pretty simple looking internals for the amp (photos attached). The amp turns on just fine, and when adjusting the master volume it does make some scratching noises, as well as if I put my cellphone on top it makes interference noises, so I know there is power going to the speakers. I checked the fuses and those are fine as well. But when I plug in and instrument to either of the inputs and play it, or just insert a cable and place my thumb on and off the other end, there is no sound. Would anyone be able to suggest some troubleshooting tips to help determine where my problem is coming from with the no input audio issue? I certainly would love to get this amp going as I have heard it sounds pretty rad.

[Pixel]

Have you tried the preamp output or power amp input jacks on the back?

[Jazz P Bass]

First off.
There are 2 separate power amps in the SC 212.
To prove that they work:
The master volume control is a dual control. Rotating it affects both amps.
If you plug a signal into Pwr Amp In 1, the first power amp should provide a signal.
The same goes for Pwr Amp In 2. It will drive the second power amp.

If both amps function, then you have a preamp issue.
The Preamp Out 1 & 2 can be used to send a signal to another amplifer.

If nothing is there then you should start by checking the preamp voltages
+25, +15, -15 & -5 Vdc.

Note: there are 2 versions of this amp: 1989 & 1992.

[Reding]

Have you tried the preamp output or power amp input jacks on the back?

I did not have a second amp at my office to try that, but I will bring one tomorrow to try that.

[Reding]

First off.
There are 2 separate power amps in the SC 212.
To prove that they work:
The master volume control is a dual control. Rotating it affects both amps.
If you plug a signal into Pwr Amp In 1, the first power amp should provide a signal.
The same goes for Pwr Amp In 2. It will drive the second power amp.

If both amps function, then you have a preamp issue.
The Preamp Out 1 & 2 can be used to send a signal to another amplifer.

If nothing is there then you should start by checking the preamp voltages
+25, +15, -15 & -5 Vdc.

Note: there are 2 versions of this amp: 1989 & 1992.

To clarify (I am pretty new to the guitar amp world), when you say power amp input, I am assuming you mean on the back of the amp where there are two inputs. correct? But when it says "Power" does that mean the amp I am using needs to send wattage out that other amp into those inputs, or would I be able to use my Roland Cube Street's line-level output jack and plug a wire that into one of those PWR Amp inputs?

[Jazz P Bass]

Power Amp In means just that.
It allows access to the power amplifiers.
A line level signal in the jack will bypass the preamp and go directly into the Master control.

[g1]

would I be able to use my Roland Cube Street's line-level output jack and plug a wire that into one of those PWR Amp inputs?

Yes.

[glebert]

To clarify (I am pretty new to the guitar amp world), when you say power amp input, I am assuming you mean on the back of the amp where there are two inputs. correct? But when it says "Power" does that mean the amp I am using needs to send wattage out that other amp into those inputs, or would I be able to use my Roland Cube Street's line-level output jack and plug a wire that into one of those PWR Amp inputs?

You can also just plug a guitar directly into the PWR Amp inputs. The sound should come out clean and full sounding, though it won't be super loud (because you are feeding in a smaller signal to the power amps than the preamp normally would).

[Reding]

Power Amp In means just that.
It allows access to the power amplifiers.
A line level signal in the jack will bypass the preamp and go directly into the Master control.

Alrighty, so I ran the tests suggested, and I can confirm that when using the Power Amp in, both 1 and 2, I do get sound from the amp. Progress! But I am getting no output from the Pre 1 or Pre 2 output on the back. What would you suggest would be the next step of troubleshooting/diagnosing what's going on with the pre-amp section to be able to hopefully fix this amp?

[glebert]

See suggestion from JPB in post #3 on checking voltages.

[Reding]

First off.
There are 2 separate power amps in the SC 212.
To prove that they work:
The master volume control is a dual control. Rotating it affects both amps.
If you plug a signal into Pwr Amp In 1, the first power amp should provide a signal.
The same goes for Pwr Amp In 2. It will drive the second power amp.

If both amps function, then you have a preamp issue.
The Preamp Out 1 & 2 can be used to send a signal to another amplifer.

If nothing is there then you should start by checking the preamp voltages
+25, +15, -15 & -5 Vdc.

Note: there are 2 versions of this amp: 1989 & 1992.

My apologies, I looked at the schematics and am having difficulty discerning where the preamps are located on this board. Would you be able/willing to circle where it is that I am to be checking the voltages on this? Currently it looks like the forum isn't allowing me to upload this photo directly, but I have uploaded a photo of the full board to my Google Drive https://drive.google.com/file/d/1cNd...ew?usp=sharing

Thank you so much once again for your help!

[x-pro]

Schematic
https://www.audioservicemanuals.com/...-92-schematics
If you don't understand circuit diagrams, you'll break it when you repair it.

[g1]

That looks to be a mid '90s unit so I'm attaching the '92 schematics. Preamp components are generally near the front panel, power amp components in the yellow area around the heatsink.
You can verify the + and - 15VDC supplies at any IC's, 4558 IC's have supplies at pins 4 and 8.