Help! Hartke LH 1000 channel problem

[rokkipoliisi]

Help needed! My Hartke LH 1000 started to turn my hair gray. When I turn on the amp, it warms up, the relay clicks and I have a sound on channel A but the B-side stays muted. It takes a while, sometimes 5 mins, and it clicks/pops again and I'll have both channels working fine.

I'm running the amp Dual Parallel one cab per channel - 2x10 300W/8ohm cab and a 1x15 300W/8ohm. Switched the cabs and wires, but every time I turn it on the b-side "wakes up" later and after that it keeps on going even for 3 hours! Effect send/return tested too and there's no problems.

Could it be a cold solder joint? I opened the hood and by a quick glance saw nothing. Gonna do more research tomorrow.

[diydidi]

Can You post a schematic perhaps. Would help to see if it has one or two relays?

[rokkipoliisi]

Looks like there's only one relay.

LH1000 v3.8.pdf

[Jazz P Bass]

You have to determine if there is an actual Vdc output fault or if it is the relay control ic circuit that is causing the delayed relay closure.
It may even be the relay itself.

I would suggest that you monitor the TA7317 side of R336 for dc voltage on the output, since this is the input pin that the TA7317 is looking at.
I think the trip voltage is anything over 900mv's.

If there is not any dc on the output you may want to consider changing out the electrolytic capacitors on the TA circuit.

[rokkipoliisi]

Thanks Jazz P Bass. I must check those out. I'm on the road now so I have a time to spend in internet and get more ideas what to search for when I get the amp on the table and open the hood.

[rokkipoliisi]

Ok, now I got the amp opened. The dc voltage after R336 was about 1,7Vdc. I tested the 2SC5200's and the 2SA1943's and they're ok. No burn traces on PCB and every clip seemed to be seateed tight. Checked the output jacks and their solder joints too - ok. Then I started to suspect the Bridge-switch. Wiggled it back and forth bridge-parallel couple of times - dunno if has anything to do with the problem.

I was in a hurry so that was about it for now. Gonna continue more tommorow. I think I have to remove PCB off the heat sink so I can check the soldering on PCB. Maybe it has healed over night :-).

[Jazz P Bass]

1.7 Vdc after R336 will trigger the protect circuit.

It would be interesting to know what that voltage point is when the relay finally clicks on.

[rokkipoliisi]

Yes, that came into my mind too and gonna check what the voltage reading is when it clicks on.

[Jazz P Bass]

With the Red DVM lead on R336 & the Black lead on chassis ground, what is the polarity of the '1.7Vdc'?
+ or -?

[rokkipoliisi]

It was negative.

[rokkipoliisi]

Metering .... Diode 309 dead.

[Jazz P Bass]

So it's repaired?

[rokkipoliisi]

I hope so. I didn't have a time to check the whole PCB today. I still have the voltages to check when the diode has been replaced.

I have my doubts still. I wonder if it's only the D309 that caused the whole problem? We'll see tomorow... I'll let you know what happens.

[52 Bill]

I hope so. I didn't have a time to check the whole PCB today. I still have the voltages to check when the diode has been replaced.

I have my doubts still. I wonder if it's only the D309 that caused the whole problem? We'll see tomorow... I'll let you know what happens.

Did you test it in or out of circuit? D309 is the power supply diode for the protection circuit, so I doubt that it could cause a voltage on the output line.

Have you tried adjusting the offset control SVR301?

Edit: Next time you check, read the dc voltage on the output line at the large choke R334. I don't know which side of R336 you are reading.

[rokkipoliisi]

Did you test it in or out of circuit? D309 is the power supply diode for the protection circuit, so I doubt that it could cause a voltage on the output line.

Have you tried adjusting the offset control SVR301?

Edit: Next time you check, read the dc voltage on the output line at the large choke R334. I don't know which side of R336 you are reading.

No, I haven't touched the trimmer yet. I have my doubts too that the main problem isn't D309.