Vintage hardan karmon hk590 I buzz and no sound help!

Ponkrawker19

Active Member
Just picked up a sweet vintage hk receiver for 15 bucks! Testing it out, right channel sounds beautiful. Left channel makes a loud humming sound. Furthermore, when I connect speakers (even with the power off) the is an unusually powerful arc coming from the speaker terminals. I am somewhat new to this hobby, and need a starting point. I'd Really love to get this baby up and running.appreciate any help in advance
 
So still trying to figure this one out. I have been dusting it off and looking over the caps to see if any are bulging. Nope. There is quite the spark in the speaker terminals when I try to hook it up, followed by loud buzz. Really need some help, or at least a place to start.
 
I wouldn't fire it up again with speakers connected until the fault is determined. Is the arc/spark occurring on both channels when you connect the speakers or just the left side? If you have a meter I would start by checking the DC offset. There's a sticky in the forum with info on how to do it.
 
Thank you so much for your reply. I'm going to grab a multimeter today and gonna get cracking. I really appreciate the help, and understand that my rookie questions can be an annoyance. Could you suggest a meter for a beginner like me? I plan on making a serious hobby/job as I am a vintage restorer/seller, and have several other vintage receivers with issues.
 
Must be an amp with hum in one channel.

Yes it's actually a Humming Kardon in this case.

Back to the repair. If you only see the spark when connecting up on the left channel then it is possible that one of the output transistors is shorting a supply rail to the output on that side (it could also be other problems but this is the first thing I would check). You will need to track down the service manual to do much more testing anyway.

If your planning on seriously getting into it then buying a multimeter from say Fluke or Agilent is a good idea but comes at a cost. They are tools that will last and can be recalibrated if required. If you want to try your hand without that level of commitment but still want something that should last then take a look at brands like Amprobe. Otherwise brands like Tenma, UNI-T (aka uni-trend) or Protek are still decent for a lot less money.

I live in the UK (and Australia) so I don't know what else is available in other regions but I would advise against using "no-name" products when it come to test and measurement gear. You will eventually need other (and more expensive) tools like scopes and signal generators if you really get into it. They say that the miser pays twice and buying cheap trash that won't last is not a good idea. There are a few exceptions. Rigol's digital scopes for instance offer great value for money.
 
Well I'd be removing and checking the output transistors for that channel. If they test okay then the service manual will be required to get any further. If they don't test okay then they need to be replaced. In that case there could be other faults such as the pre drive transistors so carful testing is needed to ensure you don't blow the new outputs. I don't have a service manual for this amp to look over so I can't be much more specific.

There are a few posts on checking transistors with a multimeter on here. Use the search to find them.
 
31v indicates a shorted output transistor.

Disconnect and depower the unit for several hours.

Go on YouTube and look up transistor testing, there are plenty of tutorial videos to get you going.

I hope you bought a meter with a diode test function.........

Start with the transistors connected to the heat sinks.
 
Upon inspecting the transistors, there seems to be a glue like residue surrounding the legs. I have had issues with brown glue becoming conductive and blowing ceramic caps in a tv I repaired. Could this issue be similar?
 
While the glue could be the cause it's more likely that some bad wiring of the speaker connections caused a short that destroyed the outputs. You should clean up the glue as a precaution as it won't be helping matters. Any parts that have come in contact with the glue that show signs of corrosion should also be replaced ideally.
 
Ok, so I have used the multimeter's diode setting and tested the output transistors by touching the leads to the legs in every combination possible. I get the same consistent readings for all.would this rule them out? If so, what should be my next step?
 
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