Hafler DH-200 Power amp blowing main fuse - Transformer or Bridge Rectifier issue?

R

rocknroller

Active Member
Have this hafler blowing the 5A slo-blow F1 main AC fuse immediately on power on. Tool out the main left right channel fuses (F2/F3) still blows. Took the leads off C16/C17 still blows. The only things left is a wax potted rectifier and the transformer. How to test each?

hafler power supply.jpg
 
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Once bridged rectifier is disconnected from the transformer. The bridged rectifier is tested like 4 individual diodes.
 
If any of the diodes are shorted. It was probably due to lightning or severe power surge.
 
whoaru99 said:
Can't you detach the transformer leads from the rectifier bridge?
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Sure he can. Simply remove the 2 red wires from the bridge rectifier and tape them off. That's what the R means in the posted schematic. The challenge is that the bridge rectifier is on the bottom chassis between the 2 big filter caps - difficult without removing something else first.

I'll bet the fuse doesn't blow at that point, though.

Cheers,

David
 
whoaru99 said:
Can't you detach the transformer leads from the rectifier bridge?
Click to expand...

OK did that, Fuse till blows. That basically leaves the transformer. I can't see anything else in the circuit that could cause a dead short across the power. I measured the ohms between the two primaries on the transformer - basically shows a short (1 ohm or less) so I guess it's toast?
Manual shows part # 464002 but stamped on the side was A64002 and 8317923. Thoughts for a suitable replacement?
 
Could the wires on the power switch be in the wrong place, as its a lighted switch and if terminals 1 and 3 got reversed it would be a dead short. At work we have equipment that uses the same kind of switch and a coworker put it in wrong with the same type problem.
 
stillspin'n said:
Could the wires on the power switch be in the wrong place, as its a lighted switch and if terminals 1 and 3 got reversed it would be a dead short. At work we have equipment that uses the same kind of switch and a coworker put it in wrong with the same type problem.
Click to expand...

This seems probable - especially since when I got this the switch was inside the case. Not sure if the pins are marked in any way to tell which is 1 or 3 though. I'll check.
 
stillspin'n said:
Could the wires on the power switch be in the wrong place, as its a lighted switch and if terminals 1 and 3 got reversed it would be a dead short. At work we have equipment that uses the same kind of switch and a coworker put it in wrong with the same type problem.
Click to expand...

Bingo. Sometimes the simplest solutions are right in front of you. When I got it, I "assumed" the previous owner had the switch wired properly, even though it was pulled out. Thank you for pointing me to the solution!! Resoldering that bridge rectifier I had cut the transformer leads off earlier was a major PITA. Took forever to get the solder to take!!

Anyway all is in order now and functioning.

Fuse Question - This is outfitted with 2 amp (external) speaker fuses. the service manual says to put in 5 amp ones if you are load testing or driving high power to 4 ohms, yet the specification section mentions nothing about 4 ohms support or power rating at that level. Is is safe to run this unit at 4 ohms? Any idea on the RMS power at that load?
 
Specs are 100 watts per channel at 8 ohm at .012 thd, and 175 watts at 4 ohms, info from the web, as memory serves I remember a sales ad stating it could drive as little as a half ohm load. I know I have driven 2 pairs of Infinity's on one of these amps with no problems, of course I never drove it to a point blowing the fuses, but did push rather hard.
 
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