Peavey session 500 (400 B/Gmodule)

[Sandwich]

Hi im new here.

Im working on a session 500 that is exact by month and year as old as i am.
Problem is that it powers up but it doesnt give any output. Then i started doing some research on this thang. And
i changed all capacitors on the main and the driveboard. I also changed the transistors on the output board. And... also some transistors and the voltageregulatorson the driveboard (400 B/G module). And tried power it up but no luck this time either. So have any of you guys any ideas what this could be?

[52 Bill]

Originally Posted by Sandwich

Problem is that it powers up but it doesnt give any output. Then i started doing some research on this thang. And
i changed all capacitors on the main and the driveboard. I also changed the transistors on the output board. And... also some transistors and the voltageregulatorson the driveboard (400 B/G module). And tried power it up but no luck this time either. So have any of you guys any ideas what this could be?

Welcome to the board.

By "powers up", do you mean that all of the power supply voltages are up where they should be or do you mean the pilot light goes on?

Try and isolate the problem. Do you have a schematic? A voltmeter? Swapping out transistors is fun for the experience, but is not a very smart approach to troubleshooting.

Check the power supply first. Then check the power amp and then the pre-amp sections.

[Sandwich]

well im pretty new in this electrics, but after some studying ive got the point.
amp goes on and the green led is on. and you hear the bruzze in the amp as when electric is on.
I have schematics for it and went trough every component and found some wrong components in wrong places so i replaced them with those that had to be there following schematics.
I have a voltmeter wich im not so familiar with cause there wasnt any good manuals with it, and im not sure where to start with the meter when for example measuring ohms if it has to be 200k or 2m or 20k etc etc. dont know where to start from. to isolate a problem is a thing also im not familiar with so information is welcome

[52 Bill]

Originally Posted by Sandwich

amp goes on and the green led is on. and you hear the bruzze in the amp as when electric is on.

OK, so maybe the power amp is working. Plug your guitar into the power amp in or the FX return jack. Do you hear any sound from the speaker?

Does the amp have reverb? If it does turn the reverb control up a little and shake the reverb tank. Do you hear the springs through the speaker?

If neither of these tests work, start by taking voltage readings on the dc power supply. Set your meter to the 200 vDC range, hook the black lead to the chassis of the amp and use the red lead to carefully read the voltages. Look for the two large filter caps in the power supply. Each one should have a fairly high voltage on it. One will be for the positive supply and one will be for the negative supply, maybe around 50 vDC.

The next section of the power supply will be for the ic's, so the + & - 50 volts will be reduced to + & - 16 volts. Follow the schematic and check for these voltages.

Let us know what you find.

[Enzo]

WARNING WARNING WARNING

I was immediately struck when I saw

I have schematics for it and went trough every component and found some wrong components in wrong places so i replaced them with those that had to be there following schematics.

That right there looks to me like the kiss of death. We have to assume this thing left the factory in working condition and that someone has been using it. Now it has failed. So either those wrong parts were always there and it worked anyway, or they have been added since the failure. I would be very suspicious you might have misinterpreted something here.

In any case, if no sound comes out:

Check the speakers and their wiring. Touch a 9v battery's terminals to the speaker terminals briefly. Disconnect them from the amp first. The speakers should pop with each touch.

COnnect different speakers to the amp for a listen.

Then follow Bill's advice too. Are power supplies present? All internal fuses intact?

[Sandwich]

Originally Posted by Enzo

WARNING WARNING WARNING

I was immediately struck when I saw


That right there looks to me like the kiss of death. We have to assume this thing left the factory in working condition and that someone has been using it. Now it has failed. So either those wrong parts were always there and it worked anyway, or they have been added since the failure. I would be very suspicious you might have misinterpreted something here.

In any case, if no sound comes out:

Check the speakers and their wiring. Touch a 9v battery's terminals to the speaker terminals briefly. Disconnect them from the amp first. The speakers should pop with each touch.

COnnect different speakers to the amp for a listen.

Then follow Bill's advice too. Are power supplies present? All internal fuses intact?

i hope death uses lipgloss .
The wrong components have been added there since the failure and those components have been added there cause the repairman didnt even try to get schematics, so he tried his own luck.

power supply is present and internal fuses are ok. The research continues...

[Sandwich]

ok little more research....
i measured the powersupply transformer that is connected to the driveboard wich gives 52 volts and 15 volts. The readings of the measurements werent stable numbers bumped up and down. So i started wondering if the transformer that is the issue?

[Enzo]

Oh well.

If your voltages were jumping around and that was what was wrong, the amp would still make sound. If both polarities of 15v and both of 50v are present, then the transformer is fine.

Isolate the problem. Plug the guitar or some signal into the POWER AMP IN jack on the amp. ANy sound out the speakers? If so the power amp works, if not, it doesn't. Then plug a guitar into the front inout jack, and connect a cord from PREAMP OUT to some other amp with speaker for a listen. Does sound come out the other amp? if so the preamp works, and if not the preamp is bad.

HAve you verified the power amp is indeed a 400BG? I added the schematic below for anyone following along.

If the power amp is bad, pull the Molex connector off the end of its circuit board farthest from the large capacitors.. That connector handles the cable from the preamp. Fire up the amp with speakers connected. See the four pins sticking up where that connector went? The one closest the corner is the inout. Touch it with your finger. There should be hum out the speaker when you do. If hum results, the amp works. If no hum, then look on the schematic. There are numerous DC voltages specified on there. Get out your meter and start checking the amp versus the drawing in that regard.

Also, if the ICs are in sockets (I think they were on that model) try this. On the power amp board, the small 8-leg IC closest to the input connector we removed should have a part number on it ending in 478. Like most ICs it will have either a notch at one end or a round dot in one corner. Note which way that feature is pointing, then gently remove the IC from its socket. Now fire up the amp- and see if it now makes sound.


If the preamp was bad, we must reconnect the input cable to the power amp. The preamp gets its power down that cable, the power supplies are on the power amp. We need to verify that both +/-15VDC supplies are making it to the preamp board. That four pin Molex connector uses two of its pins for those voltages, so you can probe down into that connector, then go to the other end of the cable and check there. Right in the center of the preamp board is one chip twice as long as the others. It is a type TL074. The center leg on each side is one of the 15v supplies. SO carefully check the voltage there on those two pins. if it gets that far, it should be throughout the preamp. Beyond that we need more specific information.

[Sandwich]

Originally Posted by Enzo

Oh well.

If your voltages were jumping around and that was what was wrong, the amp would still make sound. If both polarities of 15v and both of 50v are present, then the transformer is fine.

Isolate the problem. Plug the guitar or some signal into the POWER AMP IN jack on the amp. ANy sound out the speakers? If so the power amp works, if not, it doesn't. Then plug a guitar into the front inout jack, and connect a cord from PREAMP OUT to some other amp with speaker for a listen. Does sound come out the other amp? if so the preamp works, and if not the preamp is bad.

HAve you verified the power amp is indeed a 400BG? I added the schematic below for anyone following along.

If the power amp is bad, pull the Molex connector off the end of its circuit board farthest from the large capacitors.. That connector handles the cable from the preamp. Fire up the amp with speakers connected. See the four pins sticking up where that connector went? The one closest the corner is the inout. Touch it with your finger. There should be hum out the speaker when you do. If hum results, the amp works. If no hum, then look on the schematic. There are numerous DC voltages specified on there. Get out your meter and start checking the amp versus the drawing in that regard.

Also, if the ICs are in sockets (I think they were on that model) try this. On the power amp board, the small 8-leg IC closest to the input connector we removed should have a part number on it ending in 478. Like most ICs it will have either a notch at one end or a round dot in one corner. Note which way that feature is pointing, then gently remove the IC from its socket. Now fire up the amp- and see if it now makes sound.


If the preamp was bad, we must reconnect the input cable to the power amp. The preamp gets its power down that cable, the power supplies are on the power amp. We need to verify that both +/-15VDC supplies are making it to the preamp board. That four pin Molex connector uses two of its pins for those voltages, so you can probe down into that connector, then go to the other end of the cable and check there. Right in the center of the preamp board is one chip twice as long as the others. It is a type TL074. The center leg on each side is one of the 15v supplies. SO carefully check the voltage there on those two pins. if it gets that far, it should be throughout the preamp. Beyond that we need more specific information.

ok. i take it in steps. i tried out the 9v battery on the speaker and it worked so the speaker is ok

And im 100% sure that it is the 400 B/G module.

15 volts come out fine in the middle foot TL074

i genttly removed the ic 70487478 and powered it up
but no sound

And every little hint i keep learning from
so keep em coming

[Enzo]

How about disconnecting the Molex connector and touching the pin with your finger?

The point of doing this is the same as if you hear nothing from an amplifier and pull ther cord from the guitar and touch it just to see if the amp is on.

If the power amp stays silent, and it has reasonable DC voltages throughout, then try a new TL074 on the power amp. You can exchange the power amp TL074 for the one in the preamp.

[Sandwich]

you mean that put finger on these two in the picture

http://s714.photobucket.com/albums/w...rent=400bg.jpg

[52 Bill]

Originally Posted by Sandwich

you mean that put finger on these two in the picture

No, I think the one you circled is the reverb tank connector.

Edit:Sorry, it goes to the compressor led and switch not the reverb.

Look all the way to the left edge of the board. As Enzo noted, two of those pins will have the pre-amp power supply of + and - 15 volts. The other two pins are the input to the power amp and a ground.

Touch the pin that goes to the input to the power amp.

[Enzo]

Bill is right. All the way left upper left corner. The top pin is the input. That is the pin that has C16 going to it.

[Sandwich]

Originally Posted by Enzo

Bill is right. All the way left upper left corner. The top pin is the input. That is the pin that has C16 going to it.

ok now i get it . so i touch that pin and no sound

[Enzo]

If the amp is powered up and a speaker connected, then touching that post should make sound. If you get none, then the power amp is faulty. Now start through the circuit and check the various DC voltages that are on the schematic.

[Sandwich]

yes sir!!

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

[52 Bill]

Originally Posted by Sandwich

...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]

Originally Posted by 52 Bill

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]

Originally Posted by Sandwich

...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]

Originally Posted by 52 Bill

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]

Originally Posted by 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?

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

[Sandwich]

------

[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.

[Sandwich]

Originally Posted by 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.

they were powered up with the powertransistors everything was connected when i power up.

what is it that damages transistors when new have been replaced.

yes i know that small indicators look like resistors but where do you see the difference. i tried to get some pics outa tha komponent that was instead the indicator so you could get a closer look but like my luck is the camera runs outa batteries.

the only difference i see is the form of the thing
http://www.vekoy.com/product_info.php?products_id=8347

[Enzo]

The amp should function without it at least for testing.


When amps blow up, you can quickly find the bad output transistors. You then need to check the drivers. The drivers are the end transistor in each row of four on the power transistor strips. You need to verify that all those large cement power resistors are OK. Check them for open, they won;t be wrong, just OK or open. The predrivers - the ones on the small heatsinks are often stressed by output failures. Those 47 ohm resistors around the 5332/5331s MUST be checked for opens. Make sure R19,20 are not burnt open. MAke sure CR9,CR14 are not shorted or open. CR9 has a 33 ohm resistor in parallel, so that is what an ohm meter will read. You may have to unsolder it to test. CR14 is a dual diode and on diode test, it shows twice the normal diode reading. Again, check for not shorted or open.

When it keeps burning up parts, it is because the repair was not completely done.

Work without a speaker. Once the unit no longer blows fuses, and doesn;t draw excess current from the wall, look at the DC voltages on the schematic and verify them on your unit.

Q1, Q7 are limiting transistors, and CR10,15 arewhat connects them to the circuit. Check the transistors. Unsolder one end of each diode and lift it from the board, that eliminates those two circuits as trouble. We reconnect them later after testing.

Once all that stuff is OK, the amp output should be stable. Not blowing fuses. Hopefully no DC in the output. If that is the case, then we send a signal thro0ugh and see what happens.

[Sandwich]

Originally Posted by Enzo

The amp should function without it at least for testing.


When amps blow up, you can quickly find the bad output transistors. You then need to check the drivers. The drivers are the end transistor in each row of four on the power transistor strips. You need to verify that all those large cement power resistors are OK. Check them for open, they won;t be wrong, just OK or open. The predrivers - the ones on the small heatsinks are often stressed by output failures. Those 47 ohm resistors around the 5332/5331s MUST be checked for opens. Make sure R19,20 are not burnt open. MAke sure CR9,CR14 are not shorted or open. CR9 has a 33 ohm resistor in parallel, so that is what an ohm meter will read. You may have to unsolder it to test. CR14 is a dual diode and on diode test, it shows twice the normal diode reading. Again, check for not shorted or open.

When it keeps burning up parts, it is because the repair was not completely done.

Work without a speaker. Once the unit no longer blows fuses, and doesn;t draw excess current from the wall, look at the DC voltages on the schematic and verify them on your unit.

Q1, Q7 are limiting transistors, and CR10,15 arewhat connects them to the circuit. Check the transistors. Unsolder one end of each diode and lift it from the board, that eliminates those two circuits as trouble. We reconnect them later after testing.

Once all that stuff is OK, the amp output should be stable. Not blowing fuses. Hopefully no DC in the output. If that is the case, then we send a signal thro0ugh and see what happens.

one dumb question: does a open resistor mean that there comes out more ohms than its ment to be?

R 19 and 20 are OK. R19 was 1.9k ohm and R 20 also 1.9k ohm. so both were very close to 2k ohms.

where can i find a CR14 i dont find it anywhere?

[Enzo]

Electricity needs a complete path. For example from a battery current comes out one end, flows through wires and whatever and back in the other end. That makes a circuit - like a circle. If that path is broken, we have an open circuit.

Turn your meter to ohms, don;t connect the probes to anything. The reading you see is an open circuit. Now you connect a resistaor across the probes and the circuit is closed, and a resistance reading results.

If you read a resistor and the reading acts like there is no resistor there - like your probes were detached - that is open. if the part is soldered onto the boasrd, then other parts on the board offer paths for the current. SO sometimes you must remove the part to truly measure it.

1.9k is more than close enough to 2k.

CR14 is on the heat sink, probably sticking through a little hole.


And if a resistor shuol;d be 100 ohms but measures out at 500 ohms, it isn't open, but might as well be, it is certainly not right.

[phylomatic]

Hey man, check this thread. It could very well be the old peavey speaker if your still using the original Black Widow. My amp didn't work for years and I have a Session 500 and all that was the problem was this stupid issue with the speaker. Easy, easy, easy fix for me, but you may have some serious issues since you've been changing out parts. But definitely check this because the speaker is so easy to maintenance.

Bass amp crackling noise