[TechAssist] Harman Cardon stereo receiver model HK-570i- new outputs run hot
- From: Gary McCartney <gary@xxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Tue, 03 Jun 2003 20:11:08 -0400
I have just installed new output transistors in one channel of this
Harman Cardon stereo receiver model HK-570i.
I can feel the temperature of the heatsink is 50 deg. C. where the new
outputs are mounted, and the section of the heatsink where the originals
are mounted is 40 deg. C. I have checked the idle current of both
channels at the dual 0.22 Ohm resistor and found that on the channel I
replaced the outputs, the voltage across the dual resistor is 50 mV but
on the channel with original transistors, the reading is only 15 mV
across the dual resistor.(tested while inputting a test sine wave, 3Khz)
There are two trim pots in the suspect channel, VR404 and VR402. Both
these pots seem to have bearing on the voltages measurements mentioned
above, but I can only lower it to 24 mV and I don't feel comfortable
leaving it with the pot adjusted to max. because I'm not really sure
this is what the exact purpose of these pots are.
The original transistors were 2SC2706 and 2SA1146. I ordered these from
my supplier but when they came, I had suspicions they were possiblt
remarked so I don't want to use them. Instead, I tried 2SC3182 and
2SA1265. The sound was fine but the heat bothered me. I then got a set
of NTE36 and NTE37 and the results are the same. I have checked all
transistors , diodes, and caps in the amp section.
Does anyone have the instructions to properly adjust the idle current on
this model?
Thanks for any help.
--
Gary McCartney
McCartney Electronics
7134 Fife Rd, RR 7
Guelph Ontario Canada N1H 6J4
Fax: (519)821-1530
email: gary (at) number63.ca
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