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Old 02-27-2020, 06:07 AM   #1
Amapola
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Default Harman Kardon PM655 - strange values of voltage

Hi,

I doing a check in this amp (240v version and the switch is on the 240v ) and saw something strange...
After the schematics (power supply zone) ; instead to have on collector +35.6v for Q5 2SD669 and -35.6 v for Q6 2SB649 i have 40.7v and -40.7v ! For the rectifiers bridges i have 44.8v and -44.8v for both...
For info, all the +/- caps are new ; i even took caps with higher "operating voltage" (if it was given for 16v, i put 25v ...)

Any idea about this difference of 5v ?
Is there someone who spot it too ?

I even asked myself if there wasnt a mistake with the +35.6 and -35.6 v quotes in the schematics for q5 and q6 ^^?!!... Because we can find +44v and -44v in the power driver zone (track come from bridge rectifier) .

...i mean the 4 resistors of 33ohm in the schematics (r19 and r21 for q5 and r20 and r22 for q6) cant block 5v !

What do you think about it ?

Thanks for light about it

Thanks in advance
Cheers
Attached Files
File Type: pdf Harman-Kardon-PM-655-schematics.pdf (17.00 MB, 2 views)
File Type: pdf POWER SUPPLY ZONE PM655.pdf (167.0 KB, 3 views)
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Old 02-27-2020, 09:24 AM   #2
petehall347
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Default Re: Harman Kardon PM655 - strange values of voltage

35 volts is unregulated . mains power maybe slightly high
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Old 02-27-2020, 09:33 AM   #3
R_J
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Default Re: Harman Kardon PM655 - strange values of voltage

I agree, what is important is the regulated emitter voltage, +- 24v. Check the voltage across C6 and C7, it is listed as 44 volts, is it also slightly higher? if it is, it is just a slightly higher mains, 245vac?

Last edited by R_J; 02-27-2020 at 09:40 AM..
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Old 02-27-2020, 11:31 AM   #4
Amapola
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Default Re: Harman Kardon PM655 - strange values of voltage

I checked i have 237/238vac .

I have 44.4v for c6 and c8 and -44.4v for c7 and c9...

I checked and adjusted the dc balance and idling current too...it's ok for both channel.

...the heatsink of q5 and q6 are very hot for info , hot like this just while the amp was "on" during 15/30 mins for the dc balance and idling adjustment ; because i checked 1 time, i adjusted and leave 15mins again to recheck
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Old 02-27-2020, 11:42 AM   #5
R_J
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Default Re: Harman Kardon PM655 - strange values of voltage

Is the plus and minus 24 volts ok, and what about the plus and minus 15 volts, Did you replace C17 and C18? they could be bad, and that could cause Q5 and Q6 to run a bit hot. But I doubt there is any real problem
Q5 and Q6 are active filters for the tone control circuit voltages.
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Old 02-27-2020, 01:31 PM   #6
Amapola
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Default Re: Harman Kardon PM655 - strange values of voltage

between r23 et r49 i have +23.6v and between r24 et r50 i have -23.7v

c23 i have +14.9v and -15v for c24

24v for c21 and -23.4v for c22

the plus and minus for 25v and 15v should be ok

yes i changed c17 and c18 by 35v version instead of 25v ...in fact all the i changed all +/- caps

Last edited by Amapola; 02-27-2020 at 01:40 PM..
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