Hartke 7000 issue

[Stevonator]

New here, been reading around here after eliminating the relatively easy stuff.

Here's where I am:
Amp works fine except when "cold".
In the first 15 minutes or so of operation, I intemittently lose the whole high side output.
I can get it back by playing a loud pop on the high string. Will crackle before it comes back.
As long as I continue to play high, it stays, if I stop, it'll quit working after about 10 seconds.
After about 15-20 minutes use....it seems to work fine, but seems to be degrading over the last few weeks since it started.

What I have done:
Changed cabinets/cables .... no change/ problem only from high freq. outputs
Bypass preamps.................no change
Moved all freq and cab splits...no change
Pulled and inspected high side power board no signs of distorted components or bad joints.
Wiggle check connectors/ tap test....no change
Inspected the front board for distorted components/ bad joints none found.

I am an diagnostic automotive technician and am good with electrical and most electronic components, but don't usually deal in board level diag. I paid $200 for this thing 10 years ago and would just write it off except for the fact that I LIKE IT. That and I hate to scrap stuff because of $3 board parts. I'm good with identifying board parts and such and am good with DVOM's and automotive scopes but I've never used a bench scope before (no real difference except for speed as far as I know, auto scopes are like 5mghz, bench are more like 15 from what I understand.)

Can anyone point me in the right direction with where to go next? (Please don't say "the repair shop" cause I could have done that already) I feel I have skillset close enough to take a look at this and I'd rather learn than punt. I also am not the slightest bit afraid to listen to experience either. I have a very good friend who's a EE but I don't want to bug him for a favor if I don't have to.

Intermittents suck. I've found I can fix anything.....if it'll stay broke long enough.

Thanks in advance!

[g1]

Do you still get the same problem from the same side amp if you are in mono mode rather than biamped?
Possible problems are the mono/biamp switch or the protection relay for that side amp
(I seem to recall they used protection relays but don't have schematic so I could be wrong). Also recall these amps being prone to bad solder connections but it seems you have poked around a bit with no changes.
If it does use the protection relays you could try tapping on the relay to see if it cuts in and out, or swapping for the relay from the good side amp.

[Stevonator]

I thought about actually swapping the signal feed from the high side to the low side power module to prove whether it was in the power module or the front board, but wasn't sure the two modules were identical....same card number but the heavy connector to the module is reversed (probably just for logistical reasons because of it being on the opposite side of the case so they both face UP.)

Great point about the Mono/Biamp switch. Not a function I normally use....I *think* I tried that with no difference. Right now I have the high side card off the heatsink so I could inspect the card.

Can anyone tell me if the High and Low modules are identical ? If they are I'll swap sides and see if the problem moves....if it does it's in the power module if it doesn't it's somewhere on the front card. So how bout it...can I do the old swap-a-roo? Or do I risk blowing the good one. My gut says no problem, but I'm not in my normal pond.

If it were a protection issue I would expect it to get WORSE with use....not better. Anything's possible. There is a protection relay on the power card, but I guess first things first I should isolate it to the high side power card.

[Steve Conner]

That really sounds like a dirty or loose contact somewhere. Those protection relays would be well worth checking out, but also try all the switches, and any jack sockets that have switch contacts.

[Stevonator]

My personal thought was a cold or cracked joint....especially since there is a little of a history there with these....was actually suprised I didn't find any. BTW the protection relays are soldered to the board so no easy swap.