Peavey Dual amp

[Valvehead]

This is called a DUEL two twelve .

I dont have a scem-but posted a request.


I made a stupid mistake. I was trying to find why the switching for the tremelo was intermittent.

I noticed some cracked joints where the fsw plugs in.

So i started to re-flow them. Forgot the amp was on , but in standby.

Had a small spark............Now i have no signal , and no front lights on the amp . Power is on--fuses ok.

I think i shorted one of the switching transistors ?

If anyone has a scem , let me know

[olddawg]

I can't help you with a schematic although Peavey can. Call them. It sounds like a power supply problem to me. Do you have a multimeter? I'm sure you can find your basic power supply lines. I would still guess you overlooked an open fuse or a fusister. Did you check the fuses with an ohm meter? Sometimes they look good but are open at the ends where you can't see.

[Valvehead]

yes-there is a main , and 4 fuses on the board-all ok.




another thing-

just trying to cross ref. a transistor

the markings are , top to bottom :

SSJ
174
V430AF

[Gtr_tech]

Look like this?:http://www.bgmicro.com/images/tto-92.jpg

If so it sounds like a J174 jfet. Easy to find and common in a *lot* of amps. Usually used for signal switching applications.

[Valvehead]

yes , thats it.
waiting om a scem today

[Valvehead]

Ok , looking for some help on this one. Enzo- can ya take a look?

To save shipping and time taking the board in and out, i just ordered all the transistors.They were super cheap.

At this point ALL the transistors in the amp have been replaced.
I still cant find the problem.

Again, amp has no sound, wont switch channels, and the 2 channel LED's dont light up. Fuses ok.

I have the scem, i will try to post it

[Enzo]

Did you remove the fuses and check each with a meter? Do not try to check them while still in their clips.

REplaced ALL the transistors? Wow. Seems excessive to me.

I am with olddawg here, sounds like power supply. No lights, doesn;t work.

Start with the low voltage, page 1 lower left. You SURE the two 1A fuses F3,F4 are OK? Fine. Set your meter to AC volts and look at the fuses. You SHOULD see about 18VAC at BOTH ends of each fuse. Do you?

If so, the power light should come on. is there 18VAC on one leg of the power LED?

Got all those 18VACs, then set for DC volts. Look at the schematic. That AC is rectified and fed to 2200uf caps C55, C63. Got about 25VDC across each of those caps? Now find 1000uf C56 and C64. Got about 23VDC across each of those? If not, are the 22 ohm resistors open, R87,88 or R95,96?

About the only thing at risk on the FS jack board is the 23v supplies.

There is only one place the signal path has any contact with the low voltage stuff. That is at Q14, center left, and the diodes just above it. FInd CR19,20 - is either shorted? or another way - is there a bunch of DC on pin 2 of V3?

You replaced Q14? OK, with the amp running, one leg of Q14 is ground, one leg has about +23vDC (assuming we have working power supply), and the remaining leg is the signal path. if it has a low resistance to ground, then try removing it completely and see if the amp starts making sound.

Yes, please turn it off before soldering parts...

My vote is you have lost your +23VDC supply.

[Valvehead]

Man , this amp wont give up the fight...

I found that R87/88 were both open (thanks enzo). replaced them and got all the functions / sound back./

Now.....i have a real loud low hum. This goes away with master on 0, or if i pull the PI tube and/ or V3 .

Hmm C55 , and C56 were right there connected to those 2 resistors

[Enzo]

You replaced parts, but did you check their function? Those resistors feed the +23v rail. Is it 23v? COmpare to the negative supply voltage. FLip the meter to AC volts, how much AC is on that 23vDC? If we blew up the +23 supply, we also have to check anything that is wired to the +23.

Does turning the reverb to zero reduce the hum? The reverb circuit runs off +23. And we still have that mute, is CR19 shorted? IS Q14 leaky? Remove Q14, any help? Unsolder one end and lift CR19,20. ANy help?

[Valvehead]

you replaced parts, but did you check their function? Those resistors feed the +23v rail. Is it 23v?

Yes 23v



compare to the negative supply voltage. Flip the meter to ac volts, how much ac is on that 23vdc?


Across r87 3.4vac
r87 to ground= 1 end has 56vac , other end has 52vac



if we blew up the +23 supply, we also have to check anything that is wired to the +23.


Does turning the reverb to zero reduce the hum? The reverb circuit runs off +23. And we still have that mute, is cr19 shorted? Is q14 leaky? Remove q14, any help? Unsolder one end and lift cr19,20. Any help?




rev. Pot doesnt work unless fsw is plugged in. With fsw in , and rev. Pot to 10 it kills the entire amp.

If the fsw is plugged in and you shut of the reverb , the nasty hum goes away and amp works fine !

Q14 is new - i did remove it = no change to hum , i left it out and lifted cr19/cr20 = no change . All of those parts test good .

Those 2 diodes are getting the 23v+ and 23v-

....

[Enzo]

Ah. Is there DC on top of the reverb control? If so, Q6 is probably busted. Try removing Q6. I bet that will stop the reverb control from killing the amp. Of course you get no reverb that way, but it answers the questions.

And around Q6 is the transistor circuit running off the 23v rails for the reverb recovery. Look there.

I would take Q6 to the grand jury.

[Valvehead]

I tried swapping Q6 again . It was new anyway, as are all the transistors.

the 23V around the area mentioned are all there.

No DC at the reverb pot.

i checked everything around that reverb circuit--all tests good.

I have not powered it up with Q6 removed yet.

[manuel]

Enzo, I have a important question for you. I know this is not the right post. But, I know you had back in 2008 the Yamaha EMX 5014 Schematics. Any chance you still have it? I really need it.

Thanks in advance.

[Enzo]

Yes, I saw you asked for that in the EMX5014 thread. When I get a chance to dig it out and upload it to a hosting site, I will post the address.

[Enzo]

The reverb pot symptom was unusual. Pulling Q6 will tell us if that direction is fruitful of not. JFETs have no standard pinout, so it was possible the perfectly good replacement you installed has its legs in the wrong holes. SO by just eliminating the part, we find out if that circuit is causing the problem or not.