Peavey 2000 problem

[drewl]

I have a Peavey 2000 power amp, good news the power sections seem good, bad news the 15v supply is being loaded down.
I can unplug it's header to one of the channels and it comes up. Or if I unplug the input preamp board plug it comes up, so the problem is either on channel 2 or the preamp.
Anyone have a schematic so i can see where the supply goes to help me find where it's being loaded down?
Thanks.

[Enzo]

That schematic is page after page of 11x17s. Serious work to scan it. Send a nice email to parts@peavey.com and request the drawings.

ANy of the op amps getting hot? Or cracked? always a sign of a bad one.

The little low voltage supply board has a Vreg for +15 and a zener for -15. I assume the +15 does more jobs therefore. The three connectors in a row distrivute power to the boards. SHould be simple to see which board is the bad one.

If running the channels without the LV rails is a problem, remove the HV wires from each channel and tape them. Now the channels will only have what the LV supply sends them.

If it is a channel, look for two small glass diodes between the two 8 leg ICs. There are two ICs near one corner, and only one on the other corner. If those diodes short, it could load the rails.

If it is on an input card, then look for a bad IC.

And of course a shorted bypass cap could be there on any board.

[drewl]

Let's see, I requested a schem from peavey.
Now, of course the problem is with CH2 which is the one buried at the bottom of the unit.
I can pull the 15v header to ch2 off and ch1 will function, I think I checked the 3 opamps and the 2 diodes but I'll double check them again.
removing the input board header might be lifting a ground reference for ch2, I'll have to check, I only played with it for a short time and hope to get back to it later today.

[Enzo]

Doesn't the whole innards assembly pivot up for service? If I recall right, you unscrew the rear panel, or possibly remove it, and maybe a few screws on the bottom. Then there are two large screws, one on each side, and you lift the rear up. It is like opening a lap top computer or a lunch box or something. Now the bottom channel is staring you in the face.

Or am I thinking another model? Looking at the rear, is there a push button circuit breaker half way up the left edge? If so, it sometimes gets in teh way, push the wires back to clear it.

[drewl]

Yup...that's the model.
The top board is CH1, it works just fine. Ch2 the bottom board had the problem.
Peavey sent me the schem, so I started looking for the culprit, I decided to power it up and see if anything was getting hot....and BAM....found the problem...
seems a screw had worked it's way between the bottom of the board and the chassis.....it had moved and is no longer loading down the 15v supply....but it did kill something in the power amp section as now the collectors, or + and - HV are shorted.
So today the board, and half the chassis have to come out so I can fix what blowed up!

[Enzo]

I don't mind that chassis, I find the bottom board accessible when swung up and open like that.

One small benefit is those rider boards can be removed to see if they are part of your blowup.

[drewl]

What Power transistors you using for repairing these?
The Peavey ones are 4A 200V.
Just wondering what generic ones would fit the bill, I'm searching the usual distributors but any suggestions are welcome.
Thanks.

[Enzo]

Which factory numbers? I am too lazy to get the print back out at the moment.

Note that those are not 4 amp xstrs, they are power xstrs whose GAIN is specified at 4 amps current. For example the common MJ15003 is a 20 amp part, but its gain is characterized at 5 amps collector current. Your PV xstrs will cross to common Moto MJ series parts.

Email me for the PV cross ref document.

tmenzo at msn dot com

[drewl]

This things pissing me off now!
I rebuilt the bad channel 2, tested the preamp boards on the bench.
I had put ch1 which was good into the chassis in the ch2 slot and was going to test it before trying ch2 and now ch1 is bad!
Unless it was damaged from the beginning.
It blew the fuse in my variac, and the NPN transistors are hot!
now I have to pull that board out and fix it.

Edit: crowbar is blown on Ch1.
I assume it's okay to run the amp with both small boards of 4 xstrs off for testing, provided both are removed.

My brain's working better today, I figured out the flip up assembly for working on bottom board.



edit: Okay, Ch2 working fine with all 8xstrs sans SAC187......on to Ch1


edit#2: blown 15v zener on PNP side of Ch1, ch1 now functional sans SAC187.....

[saj888]

I have 2 in the shop. Got one working. The second one is driving me crazy. I repair an average of 15 power a week for over 20 years. All QSC, CROWN, CREST ETC. I also repaired quite a few of these troublesome Peavey 2000 amps. I got one channel in the second amp working. While power testing it. It suddendly drew a lot of current and stopped functioning. None of the outputs blew. I cant seem to find anything defective. Its a strange design. The output of the amp is connected to grounded. I will give more details when I have more time. Im too tired. My main tech who I trained from A to Z walked on me a few weeks ago. I'm back behind the work bench after some years. Im pretty rusty.

Take care.

[Enzo]

The "output" is not grounded, just the emitters. The speaker is in the return of the main filter caps. This is the same way most QSC amps are configured, so if you know them, you should be at home here.

If the power tansistors are not shorted and it is maxing current, verify the power supply is OK. Then explore the bias string in that channel. An open there would allow both sides to turn on hard and try to slam up against their rails. A cracked diode for example. Or a diode that somehow became shoprted to the heat sink.

And don't forget to check that SAC187 crowbar triac across the output. SImple enough to check, take an ohm meter to the speaker out terminal posts - are they shorted together?

[saj888]

The high current draw was just instantaneous. It crossed 10 amps on my 10 amp variac. After I switched off and turned back on the current draw is normal.Its passing dc close to the power supply voltage. Changed Ics. eliminated limiter ic and mosfet. ( it normally works without these) The voltage on ic u100a is 15 and 7. replaced zeners etc. still nothing.
checked all transistors, diodes, changed all small electrolytics except the n.p. caps which I dont have.
I am not big on theory. I am one of those practical hard core techs in the Caribbean. Got Fluke Dmm, Beckman scope, Leader audio generator, Sencore 46, two 2000watt 4 ohm dummy loads, BK component tester 10 amp variac with 3 100watt swithable bulbs that I installed, and a 4th bypass switch. etc. This is like one in every 100 amps that would drive us crazy.
I repair 10001 crest, 9001 crest, 5000crown, 3000 qsc, Mac Intosh etc. I sometimes build 120lb 4000watt monster amps. No problems at all.
And here we have a simple amp thats driving me crazy.

I dont know if the sudden stress is getting to me or if I'm allowing a minor problem seem complicated. Im considered to be the best in the country. have I lost the magic touch.
SAJ.

[Enzo]

Oh the best of us have dog repairs SAJ. I just figured out a Behringer Ep2500 that was driving me crazy until one moment I understood the layout and it fell into place.

OK, so NOW it is NOT drawing excess current, but it IS putting DC on the output terminals, is that right? In terms of their function, just which transistors had you found bad? SInce the parts all seem to check OK, I notice you checked all the semiconductors abd e-caps, but no mention of resistors. I would be concerned ther is an OPEN resistor somewhere. SOmewhere in the driver/predriver/voltage amp stages. If there was a snorted transistor, then it would be associated with that.