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

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

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

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

Quote from: Enzo on August 09, 2010, 08:40:34 PM
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. 

Quote from: Enzo on August 07, 2010, 11:56:57 PM

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. 

Quote from: Enzo on August 07, 2010, 11:56:57 PM
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:

Quote from: teemuk on August 07, 2010, 03:45:52 AM
While you wait for rest of the schemas from Peavey...

Transformer's primary looks like to be wired in between J10 and J11. There's four secondary wires coming out of the transformer, most likely common and three impedance taps. The board houses a selector switch. The condition of that circuit should be rather easy to test.

Note that this power amp is a grounded emitter circuit. It actually grounds the power transistor's emitters, causing output devices modulate the supply rail voltage according to output signal. The output signal is then taken from the center tap of the mains transformer, instead of using that as the common point like in most amps. It's not any more complex setup than a conventional power amp with ordinary emitter output but you just got to understand that you will be measuring things sort of backwards and conventional techniques used with conventional amps (e.g. measuring rail voltage, measuring emitter to common rresistance for shorts etc.) may give "strange" readings that make you scratch your head for hours.

The other half of the output board houses the additional controls. I don't know what the "damping" does (likely it's just a feedback-magnitude control) but basically this is just the plain T-Dynamics power amp circuit discussed in my book (there's a link for free-to-download .pdf on this site). It's shown in a much simplified form in that too. The first versions of that circuit used potentiometers for "power" control. Since then Peavey simply replaced them with fixed resistor values selected with switch. So, the power control is a two-pole switch for alternative resistance values that control gain of amps U2A and U2B. Again something of which's overall condition should be pretty easy to verify, even without complete schematics available at the moment. They either work or they don't.

Read the section of my book that discusses Peavey's tube emulating circuits. It deals with these circuits and may be helpful.

Addtionally, this site hosts some schematics of the first gen. TransTube amps with T-Dynamics. It will likely fill most of the blanks missing from the XXL schematic. Not exactly but still in a manner that gives you the overall picture.
http://www.about-guitar-amps.com/free_guitar_amplifier_schematics.html
You need to register but it's quick and free and you won't receive any spam from them.

Thanks, I'll register and read up on it!

Quote from: Enzo on August 07, 2010, 05:37:15 AM

Inside the amp, check this:  there is a small board for the output jacks and impedance switch.  On the end of this board is a small 4-pin connector to the auto-transformer, and right next to the speaker jacks is a small 3-pin connector to the power amp.  The power from the amp comes through a coil with parallel resistor on its way.  The amp output is wired to the 4 ohm tap.  Select 4 ohms on the switch, and you could unplug the transformer and still get full output.   SO) look at that coil of wire and the 5.6 ohm 5w resistor next to it at the end of the little board.  Is the solder to them intact?  Tug up on the coil a little, is either end broken free?   Measure the 5.6 ohm resistor.  Since it has a coil of wire in parallel, it should measure shorted.  If it reads 5.6 ohms, then the coil is open.

The solder is intact, it's pretty tight in there also.  The resistor does measure shorted.

Quote from: Enzo on August 07, 2010, 05:37:15 AM
OK, if the output transformer sings, that means the amplifier is driving signal into it.  SO if nothing gets to the speakers, I'd be thinking the wiring and impedance switch.

Try this.  Powr off.  plug a cord into a speaker out jack.  Set the impedance switch to 16 ohms.  Now at the free end of the cord measure resistance from tip to sleeve.  You are measuring the resistance of the 16 ohm output auto-transformer winding.  If you get open indication, then the switch, wiring, or transformer is open.  If you get an ohm or two, then it might be OK.  If you get a dead short, it may be a problem, but the low resistance of a good winding is hard to differentiate from a short.

I don't know if this makes a difference but I'm using an analog meter.  Whether I have it set to 10x, 100x or 1Kx and I measure this the needle doesn't make a move so I guess something is open. 

Just got the schematic from Peavey, here they are.

https://docs.google.com/fileview?id=0B5zWkfJSuEm8ODViMTJkMGMtNzYxNC00MTMzLTg3NmQtMmZmYmEyMGUxYWM4&hl=en

for whatever it's worth here's a few photos of it now that it's out of the head cabinet:



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No, no sound comes out of the speaker output on the XXL at all ever.  I was saying that I can use the preamp on the XXL when I run the preamp output on the XXL into a different amp's poweramp input and sound comes out of the other amp's connected speakers (speakers connected to the other amp not the XXL).  During which, I had some effects pedals looped on the XXL's effects send/return and the effects played out fine.  The only way I've been able to get sound is running the preamp into a different amp's poweramp with the speakers connected to the different amp.    Like you said you can't see them both so it's difficult to explain.



If I'm talking straight about the XXL head itself with a set of known working speakers plugged into it I get no sound.  When I run cables into each of the effects loops (preamp out/poweramp or effects send/return)  I still have no sound from the speakers.  I have run cables into the send/return as well as the preamp out/ poweramp in at the same time and separately. I hope that clears things up   .  I'm going to call Peavey for the schematic now so I'll have that shortly.  The only sounds that are being made from this amp are coming from the output transformer, not the speakers.

Thanks for all the input and help so far.

Yeah, I tried plugging a wire between the effects send and return.  It doesn't do anything different.  I'm going to get a hold of Peavey later today to get a schematic from them. I know the effects loop was working properly because I can plug the preamp out on the XXL into the poweramp in on my VTX and play it and ran some effects in the effects loop on the XXL.  This amp has effects send/return jacks as well as preamp out/power amp in jacks. Sorry if I'm not being clear enough.  

Quote from: phatt on August 05, 2010, 03:10:03 AM
If no luck then Go with Enzo's thoughts,, You need to establish a Real connection to the power amp output.
if it's like the one I worked on then several switches/ connections happen between poweramp out and speaker.
Phil.

The effects loop is working fine. How would I go about establishing a real connection to the power amp output??

Quote from: phatt on August 05, 2010, 03:10:03 AM
Hi ohmy,
            Hazata guess try the efx loop trick.
i.e. Loop a lead from Efxout to return.
just fixed an early Peavey special last week (has the auto tranny like yours)
the loop switch contacts where shot.

If no luck then Go with Enzo's thoughts,, You need to establish a Real connection to the power amp output.
if it's like the one I worked on then several switches/ connections happen between poweramp out and speaker.
Phil.

Yeah there's a little board that has the output jacks as well as a few switches to change up the Watts, tightness, and ohm selection for the speakers.

Alright, so I should be able to disconnect the output transformer and still be able to get sound out of it?