Hafler DH500 low bias

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So I had finally managed to get a hold of a functioning pair of boards such that my DH500 could live again. Having set the bias successfully, I set about swapping back in my preferred capacitors.
This seemed to go smoothly, however, afterwards the bias on one channel had dropped to 100mv or so, with no response available from the pot. (The pot is good by the way.)
I have got some voltage readings off of a few of the transistors, starting with Q9, the bias transistor(.9/.2/1.08)for E B C. Then for the driver transistors, Q12,13 there was .47/1.0/92, .19/.85/92. Those numbers are referenced to ground, since I was trying to follow the DH220 manual to get a clue.
I'm wondering what to make of it now, and whether or not if I want to start a transistor replacement-musical-chairs type of activity with these old boards.
Has anyone played around with one of these enough to maybe have an idea of what's going on? Thanks...
 
So I had finally managed to get a hold of a functioning pair of boards such that my DH500 could live again. Having set the bias successfully, I set about swapping back in my preferred capacitors.
This seemed to go smoothly, however, afterwards the bias on one channel had dropped to 100mv or so, with no response available from the pot. (The pot is good by the way.)
I have got some voltage readings off of a few of the transistors, starting with Q9, the bias transistor(.9/.2/1.08)for E B C. Then for the driver transistors, Q12,13 there was .47/1.0/92, .19/.85/92. Those numbers are referenced to ground, since I was trying to follow the DH220 manual to get a clue.
I'm wondering what to make of it now, and whether or not if I want to start a transistor replacement-musical-chairs type of activity with these old boards.
Has anyone played around with one of these enough to maybe have an idea of what's going on? Thanks...

The ones that appear low are Q12 and Q13 which are showing a .53v turnon voltage which should be around .6v to .65v and as high as .7v.If you changed caps on the board,check polarity but also check to see that you didn't lift a trace when removing the old caps.I usually look under a magnifying glass and then verify with my ohm meter or continuity check.
 
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I did have the boards functioning with proper bias prior to any hacking around, so the cause/effect of my recent "work" is what's effected things.

Maybe to try and reflow everywhere, since I have seen an original lead that had come loose on it's own/corrosion. I will also check for partially shorted caps, since some are polystyrenes, and I have melted one of those before once.

Thanks for the tips, appreciate it.

I will poke around some more with the meter here a bit more and see what I can turn up.
 
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This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.