[TechAssist] Re: Harman Cardon stereo receiver model HK-570i- new outputs run hot
- From: "George" <grndmstrg@xxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Tue, 3 Jun 2003 17:54:06 -0700
Gary,
Get the originals, the drive level was designed to match them, and you
should not have a problem adjusting those trimpots within their adjustment
range. First short the inputs (no signal applied) and set any volume
controls to minimum then with no load on output for maximum sensitivity and
with the voltmeter connected from common ground to the junction of the two
.22 ohm limiter resistors. Adjust both pots alternately for minimum. Also do
the same on the other side. You should be ok. LOL
George
Afana Electronics
Moreno Valley, CA
----- Original Message -----
From: "Gary McCartney" <gary@xxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Tuesday, June 03, 2003 5:11 PM
Subject: [TechAssist] Harman Cardon stereo receiver model HK-570i- new
outputs run hot
> 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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