Peavey XXL repair!

[Enzo]

What happens if you unplug the auto-transformer completely, set the amp to 4 ohms.  Still no sound?

There should be a yellow and a blue wire from the main board over to the output jack board.  That is the main output.  Follow the yellow wire back, I think it should go to the main board, then from there back to a thermal breaker on the heatsink.  Check that thermal breaker, it should measure continuity between its terminals.  It opens when it gets real hot.  If it is stuck open, you get no sound.

Can you get clip wires on those yellow and blue wires?   APply a test signal to the power amp, doesn;t need a lot, just enough to hear when it works.  Now clip some speaker on your bench to the yellow and blue wires where they come off the main board.  Got sound?

Right next to where those wires connect are two power resistors - 0.33 ohm 5w.  Make sure they are not open.  They should check like a short.

For testing, you can connect one side of a test speaker to ground, and with a clip wire on the remaining speaker terminal, probe the yellow wire, then either end of the thermal breaker, then back to J12 from the second terminal of the thermal.

[ohmy!!]

What happens if you unplug the auto-transformer completely, set the amp to 4 ohms.  Still no sound?

There should be a yellow and a blue wire from the main board over to the output jack board.  That is the main output.  Follow the yellow wire back, I think it should go to the main board, then from there back to a thermal breaker on the heatsink.  Check that thermal breaker, it should measure continuity between its terminals.  It opens when it gets real hot.  If it is stuck open, you get no sound.

Can you get clip wires on those yellow and blue wires?   APply a test signal to the power amp, doesn;t need a lot, just enough to hear when it works.  Now clip some speaker on your bench to the yellow and blue wires where they come off the main board.  Got sound?

Right next to where those wires connect are two power resistors - 0.33 ohm 5w.  Make sure they are not open.  They should check like a short.

For testing, you can connect one side of a test speaker to ground, and with a clip wire on the remaining speaker terminal, probe the yellow wire, then either end of the thermal breaker, then back to J12 from the second terminal of the thermal.

Yes, still no sound.  The other things you guys mentioned I'll go through and check after I get off work tomorrow.  I'll let you know what I find out.

Thanks  :tu:

[J M Fahey]

Well, I'm getting tired of this bugger 
Go get your chainsaw, start it, and ...  :trouble
No, I'm kidding, not yet ... although sometimes it looks like the only option left.
Let's strip it to its bare bones and start from there.
We'll test the bare power amp, no bells or whistles:
solder a wire to the union of R26/R49 and the other one to the union of R32/R41 ; these are your speaker wires, solder them to a jack or, if long enough, straight to the speaker, which should be "free", no other leads connected to it.
Now go to pin 6 of U2B.
One leg of Q10 goes there, lift it (as in solder suck the pad, carefully pull that leg from the hole and leave it "in the air"). You've just removed the mute.
Now turn the amp on, then off , the speaker should click or thump (normal awakening of most SS amps).
If so, lift the right side of C21 , turn amp on and brush the free end with your finger, you should hear hum on the speaker.
In case nothing happens, oil your chaisaw, fill up its tank, and leave it in plain sight of the amp, just to show it you are serious.
Good luck.

[ohmy!!]

Can you get clip wires on those yellow and blue wires?   APply a test signal to the power amp, doesn;t need a lot, just enough to hear when it works.  Now clip some speaker on your bench to the yellow and blue wires where they come off the main board.  Got sound?

Sorry I didn't get back to you guys sooner, I've been busy with some work and other projects. I'm testing the amp now, first thing I've done is connect clip wires to those yellow and blue wires and a speaker, sure enough it's playing through the speakers.  Also maybe the rep at Peavey didn't know what they were talking about with this amp because after I had asked about the missing parts of the schematic they said this amp had only one transformer and that was the power transformer. 

[Enzo]

OK, as expected then the amplifier works, just the signal is not making it through the output jack board.

You clipped to the yellow and blue wires and got sound.  Leave the blue wire clip in place. now remove the other clip from the yellow wire, we will be using the test speaker now as a signal tracer.  Follow the yellow wire over to the jack board.  See where it connects to the jaqck boad through a plug.  Touch the clip to the terminal that gets the yellow wire.  SOund?  Move teh clip wire to that 5.6 ohm 5w resistor next to the coil of wire.  Touch it to each end.  GOt sound at each end of the resistor?   

At this point the sound goes to the impedance switch for routing through the output transformer.  At 4 ohm setting the switch directs it to the jacks directly.  But it DOES still go through the switch.  A bad switch or a switch with bad solder can still interrupt things.

With the jack board sitting so you can access the solder side - dismount it from the chassis if you need to - look at the end connection of the coil of wire and follow the copper trqace to the end of the switch.  Also note the middle terminals of the switch have a trace to the jacks.  The switch must connect these two together for sound to happen.  So touch your clip to the end terminal of the switch, the one from the coil of wire.  Now touch to the center terminal of the switch, the one with the L shaped copper trace that feeds to the jacks.  Got sound there?

What we did was use the speaker with one end connected to the blue wire, and stepped point by point down the path to the output jacks.  Once we find the point that has sound on one side and not the other, we have discovered the break.   My money now rests on the switch.

[ohmy!!]

OK, as expected then the amplifier works, just the signal is not making it through the output jack board.

You clipped to the yellow and blue wires and got sound.  Leave the blue wire clip in place. now remove the other clip from the yellow wire, we will be using the test speaker now as a signal tracer.  Follow the yellow wire over to the jack board.  See where it connects to the jaqck boad through a plug.  Touch the clip to the terminal that gets the yellow wire.  SOund?  Move teh clip wire to that 5.6 ohm 5w resistor next to the coil of wire.  Touch it to each end.  GOt sound at each end of the resistor?   

At this point the sound goes to the impedance switch for routing through the output transformer.  At 4 ohm setting the switch directs it to the jacks directly.  But it DOES still go through the switch.  A bad switch or a switch with bad solder can still interrupt things.

With the jack board sitting so you can access the solder side - dismount it from the chassis if you need to - look at the end connection of the coil of wire and follow the copper trqace to the end of the switch.  Also note the middle terminals of the switch have a trace to the jacks.  The switch must connect these two together for sound to happen.  So touch your clip to the end terminal of the switch, the one from the coil of wire.  Now touch to the center terminal of the switch, the one with the L shaped copper trace that feeds to the jacks.  Got sound there?

What we did was use the speaker with one end connected to the blue wire, and stepped point by point down the path to the output jacks.  Once we find the point that has sound on one side and not the other, we have discovered the break.   My money now rests on the switch.

Yep, I have sound at all the places mentioned. 

[ohmy!!]

Wait I think I was looking at the wrong one, the L shape that connects to the outputs has no sound.


the ones marked there.
http://img705.imageshack.us/img705/1218/img0685rc.jpg

[ohmy!!]

if i put a clip between these two i get sound from the speaker outputs.

http://img716.imageshack.us/img716/9724/img0685s.jpg

[teemuk]

Seems like the impedance selector switch is broken then.

You most likely also get input when you directly short between that "L"-shaped trace and top left or bottom right pins of that switch. Those two would be the other impedance selections.

[ohmy!!]

Yes teemuk.  Peavey lists the switch as $9.41 so at least it's not an expensive fix.

[Enzo]

I thought I mentioned this earlier, but now that you know it is the switch, look CLOSELY at the switch.  The way the switches are usually constructed is the metal frame has little tabs sticking out the bottom, and those tabs are bent under the little piece of material that holds the contacts and terminals.   If something smacks the little knob, it can push out the back of the switch by bending those tabs.  Then the switch will no longer work.  Sometimes such a damaged switch can be saved by putting it back together and bending the tabs tight down with pliers.

At this point, what is there to lose?  The switch is coming out one way or another anyway.

And switch or no switch, if you want to play the amp while waiting for a new part, temporarily tack solder a little piece of wire between the switch terminals to complete the circuit.

Peavey is great about having parts for their products.

Whether or not it is the case for your switch, that same sort of pushing out the bottom damage happens to sliders on m,ixers all the time.  Most times they are easily repaired.

[ohmy!!]

Now that you say that, as I'm messing with it now it feels a little loose compared to the other switches so I'll take it apart. 

Looks like it had popped off before, it's missing a metal piece in the switch that bridges the prongs for selection.

[J M Fahey]

it's missing a metal piece in the switch that bridges the prongs for selection.

Well, you've found it !!!  :tu: :tu: :tu:

[bry melvin]

Great now you have an amp that you might be able to use at home...at night...without a court appearance.... :tu:

You might try running the thing that way into a nice small 10"' (or two)for good tone at low volume...

I do that with my Carvins (carvin only makes 100watt SS amps)

My personal favourite for this is an old Sound City 2X10 ported cab (especially for recording) with Alnico 10s.

but...

At house volumes the 10" Crate Gx20M 10" sounds almost as good.(and much cheaper)

[ohmy!!]

Definitely, even through the 2x12 eminence legends I have it sounds much better at low volumes.  Of course I can keep using these during the day when nobody's home and just blast it, which I've been doing the past 30 minutes or so.  I'll probably go for a 1x10 or 2x10 for lower volumes like you said. This thing really has a lot of different tones you can pull out of it between the watt selector and damping switch (and the 9 different channel selection).  When you switch the damping down to loose it sound a lot more tube-like. It's pretty cool!  :tu:

The 3 clean channel selection on it are basically all different sounds I could get out of my Heritage clean channel.  Honestly, they probably could have had all the cleans in one channel and added a parametric like on the heritage and still have the same sounds. The classic selection under the lead channel also sounds like the heritage's lead channel.  I'm debating whether to sell the heritage now or not, but I'll probably keep it.