Output Relay Hartke 3500

[DanJ]

Hello all,

I have a Hartke 3500 bass amp with no output. What I have found is there is a relay on the output that is not switching. Can anyone tell me what exactly the relay is for? When I jumpered the relay, I have output, but there is a nasty humming noise with no input and all controls turned down. So I believe the relay not closing is an effect of my problem and not the cause. The only other thing that I see is that the B+ is 55VDC and the B- is -85VDC. Which I guess would explain the noise problem. Any ideas on the B+/B- problem would also be greatly appreciated. Thanks for any inputs.

DanJ

[Mark Black]

The relay is probably there to open the output circuit in the event the amp has a problem and puts out DC voltage, which can kill speakers.

Sounds like yours has a problem and the relay is trying to do exactly what it is supposed to. You should not jumper the relay. Or at least if you do don't hook up a speaker or any other kind of load. See if the amp is putting out DC voltage.

Other than those observations I don't have any specific knowledge of that model amp - hopefully someone else here will...

[Enzo]

Exactly. Your amp is most likely blown and producing DC.

Check the voltage on the output on the AMP side of the relay. Is there substantial DC? If so, look for shorted output transistors on the power amp.

Look for a failed solder connection under one of the main filter caps. Specifically the B+ one. If a rail should be 85 volts, and the filter cap goes away, then the resulting unfiltered DC will read about 60 volts. Close enough to your results.

[DanJ]

Good advice as usual

Enzo,

Thank you, as usual, your advice was spot on.

When I turned on the amp, it powered up ok, but had no output. I took the send output to another amp and it worked fine, so I went right to the power amp section. After checking all the drivers and not finding anything shorted I started to think about the big ol' relay mounted on the power amp board, generally when you turn it on there is a short delay, and then then the big "click" of the relay. Since I did not hear the relay closing, I started to suspect it. But considereing I've never seen one go bad I figured it was probably an effect of the problem and not the cause. After jumpering the relay and hearing the garbage output that I had this comfirmed my belief that the relay was ok. This led to my post. There is also an IC that I guess drives the relay, it takes a sample of the output and maybe a sample of the B+/B-??? This led to my usual question "How does it know?"

Anyhow, after I read my own post I had an epiphany on the B+ and went back to my shop and sure enough the filter cap on the B+ was bad (about 28VAC on the line).

This should have been an easy fix, but since I broke one of the cardinal rules of troubleshooting and got ahead of myself, it caused me alot of grief.

So I must give a big thanks to this forum, just being able to use it as a sounding board helped me out big time. Like I said, reading my own post helped me to realize my own problem. Then of course, had I not, there are great people here that would offer helpful advice to find the problem.

I've now rambled on too long so once again, thank you.

DanJ