The reason for things

[Techknowman]

I'm working on a Peavey PV8.5C that of course the customer needs by Monday a week from next. We have all been there.

(crawl up on my soapbox)
Of course the unit was repaired by someone prior to me and they left me a mess!
The unit caught fire because the last guy used standard carbon resisters where the Service manual and schematics called out flame proof ones.
This is the result!

There is always a reason for certain requirements.
He also substituted 4 of the .33 ohm emitter resistors for .1 ohms on the NPN side of the amp only.
(getting down off my soapbox)
So my grocery list for this one is...
Q210, 70483180
Q214, 70473180
CR244, SAC187
C231, .22R100M
R250, 180 ohm flame proof
R254-257, .33 ohm 5Watt

I guess I got lucky most of the main outputs are still good.

Peavey-PV8.5C

I'll add photos of the finished repair when I get there

[Enzo]

I just tried to lead a guy through one of these, though not turned to charcoal like yours.

If you care to look, scroll down to power amps section, and in that the 8.5C should be near the top:
• Index page

The outputs seem OK. Once it is running, with proper value ballast resistors, check current through each - well, voltage across each - to check for any output not holding its weight or drawing excessive.


Geez, make sure to grind away all that carbonized pc board material.

[Techknowman]

Wow what a deal you got yourself into on that post!
Lol. you have a lot! of patients!
Yea I got the board cleaned up real nice. got new copper jumpers inplace of the burned and pealed up traces.
Just need to get the parts.
If you don't mind, if you have the schematic. Can you look at it with the following questions in mind.
As I wrote Q210 and Q214 Shorted, base to collector on both.
The other TO3's seem ok via checking.
Should I use a PV original part to just replace these or can I use the MJ-15024 and 25?
If not the sub, is it best to get them direct from peavey or a service shop like yourself?
I would like to not have to replace all of them just to do it if I don't have to, I guess it depends on cost and avalability

[Ronsonic]

Seems to me you only need one part. The one in the photo. I'd at least check with PV about replacing that board and getting done.

[Enzo]

That sub is PV recommended, and I stock those MJ series parts anyway. SO I freely use the generic. But nothing wrong with ordering direct from PV. COmpare their price with prices from Mouser or Allied.

DOn't you already have the schematic?

[bkahuna]

Of course the unit was repaired by someone prior to me and they left me a mess!
The unit caught fire because the last guy used standard carbon resisters where the Service manual and schematics called out flame proof ones.
This is the result!

My experience with these is that when they fail, they usually catch fire, or at least shoot out lots of sparks, regardless of whether someone else has repaired them or not. I've seen plenty of those pcbs looking just like that when no one else had been in them. I'm not saying your predecessor didn't help it along, but these amps don't really need much help to explode on their own!

I think part of the problem is the inclusion of a circuit breaker instead of a fuse...the user can just keep resetting the breaker when it blows, and continue powering it on over and over causing more damage each time, until sparks fly out and they finally get the idea that there's a problem!

[jrfrond]

That sub is PV recommended, and I stock those MJ series parts anyway. SO I freely use the generic. But nothing wrong with ordering direct from PV. COmpare their price with prices from Mouser or Allied.

It's true! I've heard from more than one Peavey servicer that they like it just for the parts prices. I don't usually order my power xistors from Peavey, but I wouldn't hesitate if I really needed them and no one else had stock.

[Enzo]

PV prices are reasonable. yes, you can find things cheaper elsewhere, but still reasonable. Their parts prices usually include shipping.

Kahuna, I have to say my experience on this PV series of PV amps has been the other way around. I have had to tear them down and replace a lot of parts, but I have not had a bunch of charcoal on them... so far. Little bursts of smoke on a small resistor for sure though.

[Techknowman]

MJ series parts anyway. SO I freely use the generic. Don't you already have the schematic?

The question is can I use the MJ series in Q210 and Q214 to drive the PV orignals that are still "good"?
Yes I have the schematic. I was asking you to reference it with the above question.
Thanks for your time Enzo and all!

[bkahuna]

Kahuna, I have to say my experience on this PV series of PV amps has been the other way around. I have had to tear them down and replace a lot of parts, but I have not had a bunch of charcoal on them... so far. Little bursts of smoke on a small resistor for sure though.

The end users where you're from must be smarter than mine. .
I've actually had these come in with the complaint "circuit breaker bad", and then I find out it really IS bad because when it started blowing they kept resetting it until it simply gave out and refused to be reset anymore. So yeah, the breaker is bad, and the outputs are shorted, and the pcb is cooked and on and on...

[Enzo]

Well, I don't know that I'd send my customers to NASA as engineers just yet...

The biggest pain in the ass on this series is extracting the power transistor board from the chassis.


MJ series - for the most part, the PV house numbered transistors ARE the Motorola MJ series. SO yes, you can mix them.

The only time mixing is an issue is when they are side by side working in parallel. SO if ther are three outputs per side, you don't want two Motorolas and an RCA. You want three of one or the other. But the driver is not in parallel with anything, it acts alone. SO you can use any part of reasonable spec as that driver. On the outputs, you can have three Motos on the push and three RCAs on the pull even. Because transistors on the opposing sides are not in parallel. The concern is that all the parallel outputs share current equally.

[Techknowman]

The biggest pain in the ass on this series is extracting the power transistor board from the chassis.
MJ series - for the most part, the PV house numbered transistors ARE the Motorola MJ series. SO yes, you can mix them.

Yes it is. Thanks. I ordered them from mouser today. should have this unit fixed up and ready to go soon.

I have 3 QSC units to finish up.
A 1400 blew all outputs in both channels and smoked the caps. Looks like it could have been lightning damage. This one could be a dumpster Gem!
The MX1500 has a shorted bridge rectifier for one of the channels. it also burned up the NTC, this one was one of those, customer reset the breakers until something smoked, units. Outputs seem good, Fingers and toes crossed.
The MX2000A looks like its going to be fun to dismantle to check it out. It could be a very $$$ unit.

[Techknowman]

Damn i just relised that this PV8.5C needs a volume pot.
Peavey # 71190335 (VR101). Anybody got one? salvage part?
If not I still have time to get it from peavey, just hope they have it in stock.

[Techknowman]

I think part of the problem is the inclusion of a circuit breaker instead of a fuse

I would have to agree.
Its a lot cheaper for the user to push the circuit breaker in 10 times. But few users will pay for 10 fuses and keep popping them, 1 or 2 usually drives the point home!

[Techknowman]

Got some of the work done
,