I have a Hafler DH-500 that is giving me trouble. It’s worked flawlessly until a couple weeks ago when I turned it on and got nothing. The red light is on and solid (not flashing) and I noticed that the relay didn’t click. Assuming that it was the relay I picked up a NOS relay on ebay and installed it. Nothing. I put jumpers across the relay terminals to couple the amp with the outputs. The left channel works and sounds fine, but I get just a very low/quiet hum from the right channel. Any ideas? I’m at a loss… Thanks!
I'd suspect a missing power supply rail, maybe just for the input circuit. There are two resistors filtering it, R31-32 in this manual:
http://www.hafler.com/techsupport/pdf/DH-500_amp_man.pdf
I'd check those.
http://www.hafler.com/techsupport/pdf/DH-500_amp_man.pdf
I'd check those.
megajocke said:
Thanks for the reply! I checked R31 and R32 on both the working and non working channels. They were all 51 ohms -/+ 2 ohms - the schematic calls for 47 ohms, so I assume that is okay.
Any other thoughts?
Thanks!
Aaron
Will have a closer look at the circcuit tomorrow, but this may help for now.
Looking at the circuit on page 16 of the pdf has the fuse f401 blown. If it has leave it as it is. Do not connect the speaker.
The 3 pairs of FET outputs. Do any of them get hotter than the others. Normally I would not suggest running a faulty amp up but this one doesn't seem to protest from what you say.
It's possible one or more of the FET's is faulty.
From ground measure the voltage on the two diodes D15 and D16 ( the left hand ends 😉 technical description ) should be near to the supply voltage ie 85 - 90 volts.
Check R33 that connects to Q12 and Q13. Not burnt ? Whats the voltage across it, that's tags 4 and 9 to the outputs ?
Edit- Make sure the outputs are not getting hot. I recommend using a 100 watt filament bulb in series with the mains when fault finding. Can save a lot of grief.
Looking at the circuit on page 16 of the pdf has the fuse f401 blown. If it has leave it as it is. Do not connect the speaker.
The 3 pairs of FET outputs. Do any of them get hotter than the others. Normally I would not suggest running a faulty amp up but this one doesn't seem to protest from what you say.
It's possible one or more of the FET's is faulty.
From ground measure the voltage on the two diodes D15 and D16 ( the left hand ends 😉 technical description ) should be near to the supply voltage ie 85 - 90 volts.
Check R33 that connects to Q12 and Q13. Not burnt ? Whats the voltage across it, that's tags 4 and 9 to the outputs ?
Edit- Make sure the outputs are not getting hot. I recommend using a 100 watt filament bulb in series with the mains when fault finding. Can save a lot of grief.
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