Peavey M7000 Power amp

[yba-1 user]

Anyone with a scematic?

[Jazz P Bass]

Got me on that one.
How about calling Peavey.(first thing in the morning is best. They are in Mississippi.)
877- 732-8391
You'll have it in about 10 minutes.
Post it here when you get it

[doctor]

Got me on that one.
How about calling Peavey.(first thing in the morning is best. They are in Mississippi.)
877- 732-8391
You'll have it in about 10 minutes.
Post it here when you get it

Here it is

[yba-1 user]

I appreciate it ! Thanks

[Lynx]

Sorry for the necro post, but could someone please upload the very same schematic that doctor posted above?
The download link seems to be broken or the attachment is not available or whatever.
Btw, hello forum

[Enzo]

We had a server crash, leaving the file names on empty files.

If they repost soon, great, but you can always get any Peavey schematic from customer service at Peavey.

[g1]

This one should work.

[Lynx]

You are awesome Sir, many thanks :-D
Btw, love your avatar.
Godspeed Lemmy, RIP.

[Lynx]

So, now things got real interesting.
Problem is that the DDT LED comes on for one of the channels, which leads to the channels corresponding relay not being energized.
A quick browse through the schematics indicates that Q25, a SBS14 Diac sensing the output voltages to the speakers, could be a candidate to the problem as, well, the DDT LED comes on even though there's actually no speakers attached to the output, if that makes any sense at all.
The way I understand it transistors Q29/Q30/Q31 triggers as a result of the Diac (false....?) triggering, leaving Q32 unbiased, which leaves Q28 unbiased which in turn leads to no voltage to the relay coil.
How far away am I in my thinking here?
The reason to why I checked that route in the first place was that I noticed that the other channel, which works like a charm, lights up it's power LED the very moment it's relay get's energized, hence the hint to check these transistors.

[Lynx]

Also noticed that TB2, a normally closed overheat protection switch, also could be responsible for shutting off the relay.
Got to measure those tomorrow, looks real interesting.
Amazing what a difference a schematic can make, it violently triggers my curiosity

[Jazz P Bass]

I don't see the DDT led 'turning off' the output relay.

There is a DDT Defeat Switch.
Does engaging that switch turn off the DDT led?
If not, then I would suspect U3 (TL072 ic)

If the relay will not energize, you may have Volts dc on the output.

[Lynx]

Aha, thanks for clarifying.
Ok, I'll check for DC voltages on the output.
As the difference between the channels is that the one working doesn't light up it's DDT LED, but OTOH it both lights up it's power LED and energizes it's relay, I, however erroneously, assumed that as the other channel, which only lights up it's DDT LED and doesn't either light up it's power LED nor energizes it's relay, had it's root cause in the DDT handling of it all.
Learning as I go, babysteps

[Enzo]

The thermal switch is not part of the relays system, and the SBS14 controls the crowbar triac on the output, not a relay.

The DDT compares the input and output, and stops clipping, it has no idea whether a speaker load is there or not. DDT is more likely a symptom than a cause.

Is the output of the bad channel skewed DC?

[Lynx]

For now the amp owner is going to check out proper function on it (or not) as I'm 'merely' troubleshooting it for him, then we'll see what gives.

The original problem was that the main fuse immediately blew when powered up, which led me to replacing 4 of the output transistors as the original transistors no longer is available and the replacement transistors shouldn't be mixed with the original ones all according to the recommendations made out by Peavey, hence the need to replace all 4 transistors in one of the output stages then.
I also replaced a triac which had blown, so now it powers up as planned, doesn't take unnecessary amounts of amperes when not in use, so what's left is the output relay which won't energize for one of the channels, we'll just have to see about that later on.

But anyway, all good tips and hints, many thanks gentlemen

[Lynx]

So the amp owner tested it and got no sound on the bad channel, as it's relay won't come on.
To top that then I measured the relay controlling transistors on the good (preamp) card and all the sudden it's relay also turned off, so no sound on either side now

Is the output of the bad channel skewed DC?

Oh yes, the bad channel shows 69VDC vs ground and the former good side 28VDC, so I reckon the relays indeed do their job in protecting the speakers.

I guess I have to go through some serious soldering now to find the faulty components.

Are there any general voltage charts for comparing/checking voltages?

As a very simple test, would it be possible to separate the power amp from the preamp and determine if the fault lies in the one or the other?
I'm thinking if I completely separate the power amp and feed it with 2 separate power supplies, which would give me between +30 to 0 to -30 Volts and then tie both the positive and negative rail controlling transistors to ground, if that would lead to getting zero Volts on both channel outputs, would I then be able to say that the power amp is OK?

Btw, I don't mean to hijack the thread, if my problems should be in a new thread altogether feel free to split/separate it or just say so and I'll do the honors myself.