Peavey session 500 (400 B/Gmodule)

[Sandwich]

yes sir!!

i also emailed with peavey and i got also that to check out the condensors R19 and R20

[52 Bill]

...to check out the condensors R19 and R20

Those are resistors, thus the "R" designation.

They are large rectangular blocks of white ceramic. They are located at the top center of the board. You can test them with an ohm meter with the power off, or you can test them while they are functioning with your voltmeter. When they fail (it usually is only one that dies), they usually go open.

If you test the voltages on the board as Enzo suggested, you should find +52 volts on one end of R20 and +26 volts on the other end. On one end of R19 you should find the same +26 volts as on R20 and +1 volt on the other end.

[Sandwich]

Those are resistors, thus the "R" designation.

They are large rectangular blocks of white ceramic. They are located at the top center of the board. You can test them with an ohm meter with the power off, or you can test them while they are functioning with your voltmeter. When they fail (it usually is only one that dies), they usually go open.

If you test the voltages on the board as Enzo suggested, you should find +52 volts on one end of R20 and +26 volts on the other end. On one end of R19 you should find the same +26 volts as on R20 and +1 volt on the other end.

yes sorry for that. the head has ben bubbling trough out with this amp .
the volt meter said that the tops of R 19 and 20 are reading around 24 volts and the bottoms of R19 reads -00,6 V and the bottom of R20 is 56 V so it seems that R20 has died . am i correct? so R20 has to be changed ? or maybe both?

[52 Bill]

...the volt meter said that the tops of R 19 and 20 are reading around 24 volts and the bottoms of R19 reads -00,6 V and the bottom of R20 is 56 V so it seems that R20 has died . am i correct? so R20 has to be changed ? or maybe both?

No, those voltages are close to what should be there. R20 and R19 are basically a voltage divider. They are wired in series, so there is 56 volts on one end of R20. Then at the junction of R20 and R19 there is 24 volts, about half of the supply 56 volts. And finally at the other end of R19 you have 0.6 volts, which is a low compared to the posted voltage of 1.17 volts.

Unplug the amp and read the resistance value across each resistor.

Have you checked the other voltages around the board?

[Sandwich]

No, those voltages are close to what should be there. R20 and R19 are basically a voltage divider. They are wired in series, so there is 56 volts on one end of R20. Then at the junction of R20 and R19 there is 24 volts, about half of the supply 56 volts. And finally at the other end of R19 you have 0.6 volts, which is a low compared to the posted voltage of 1.17 volts.

Unplug the amp and read the resistance value across each resistor.

Have you checked the other voltages around the board?

I started checking around the board and i got stuck on U3. the fift leg give out 15 volts to leg 1, 2 and 3. and then i checked them but nothing comes outa them and then i also checked the resistors and nothing there either. it seems i will have to change possibly U3

[Sandwich]

Guy guys!!

I checked leg #8 on U3 then i heared something bruzzing and i started listening closer then it just came from the speaker !!! So it seems we are getting closer to a solution here.
but why there isnt cuming any 15 volts for legs 1 2 and 3 is a little mystery but ill se if there is something wrong with the soldering

[Sandwich]

i also checked the schematics and looked at TL074 which showed that leg #1 (which is a dot on the TL074)was going at first to CR4 and following the schematics the TL074 should be the other way placed so i soldered it of and placed it the other way like it say in the schematics (leg #1 goes to R9) then i soldered it and then placed the card and screws on and cables etc. and powered it up then leg #4 starts to fry. #4 leads to these marked as "J". I dont have any clue about this now.

[Enzo]

J means jumper wire. You are looking at the pictorial, not the schematic.

Pin 4 of the TL074 is the +15v power supply, and pin 11 is the -15v power supply. That is shown on the left side of the schematic where it says U1C, LED Driver.

When that IC was in backwards it was probably destroyed, so now with proper power applied it just burns up, because it was dead already.

The TL074 is a 14 pin IC, and you can install a 14-pin IC socket on the board and then just plug new ICs into it.

Put a good 074 in there.


15v on legs 1,2,3? Where do you expect to find 15v on pins 1,2,3? What IC? I don;t expect that.

[Sandwich]

ok now there comes sound when i touch the input pin. so now we have progress

[Sandwich]

ok and i assemlbled the amp chassis with the driveboard and main board and plugged in a guitar and there was sound. a dist sound very quiet. i had gain and post gain all the way so i could hear it. Now is the thing im wondering just is if its the potentiometers that are the next issue.

[52 Bill]

Before you move on to the pre-amp, you still need to finish checking the power amp.

You say that the power amp is passing signal now, when you touch the input pin. Is the buzz you hear from the speaker loud or quiet? If you inject a signal into the power amp at this point does the amp play loud and clear?

[Sandwich]

Before you move on to the pre-amp, you still need to finish checking the power amp.

You say that the power amp is passing signal now, when you touch the input pin. Is the buzz you hear from the speaker loud or quiet? If you inject a signal into the power amp at this point does the amp play loud and clear?

the buzz is quiet.
and after injecting a signal the sound isnt loud.

[Sandwich]

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[Sandwich]

ok now we are getting somewhere but now a 47 ohm resistor fries after turning power on and then i checked out the indicator (L1) wich i saw that has been replaced with a resistor from the former repairmen. and the indicator is a 100mh and i dont know how many ampheres it should be (the 100mh that ive found are 20 mA) and also what the resistance should be. the resistor wich is after the indicator through the transistor is like it reads in the schematic 47 ohm resistor (R61).

But one good thing is that i get more sound out of the amp now and it seems to be with this indicator and the resistor, wich followly will give power to the transistors to the output board.

[Enzo]

Wait, moving back a few posts. You were not trying to power up the board without the large power transistors connected, I hope. Were you? That might explain the 47 ohm resistors if so.

Otherwise those 47 ohm resistors are in series with the 5331/5332 pre-driver transistors.
And that often means they are damaged.

L1 is a small inductor, it will look like a resistor.

The rows of power transistors MUST be connected to the main power amp board.