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|11th January 2011, 12:31 PM||#1|
Join Date: Aug 2006
Blog Entries: 2
Harman/Kardon AVR45: Display problem
I got a broken Harman/Kardon AVR45 from a repair shop, they said they couldn't fix it, and it had been taken to various repair shops in the past. The rule was to not leave equipment at the shop for over 30 days or it would disappear, and the amp was never reclaimed.
I was also given another amp the same way, a Denon AVR-588. The problem was the -15V rail, and it is playing as I speak. This series of amps has problems with the KIA7915 for some reason, I heard it was overheating. Maybe because of the plastic case...
In any case, I moved on to the AVR45, and for some reason the display won't come on. There is a -29V rail that is only -16V. The -29V comes from a voltage multiplier off of the transformer feeding the 5V rails. But I can't figure out what is wrong. I suspect the fluorescent display tube may be failing, since the -29V rail is suspended on the CT of the filament windings of the transformer. I tried to take a picture of what it looks like.
A service manual can be downloaded from here:
Harman/Kardon AVR35 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
Page 30 is the PCB layout and page 71 has the schematic for the power board.
Another possibility is that C992 is failing. I don't trust the service manual much. Look at the voltages at the emitter and collector of Q981 - makes no sense.
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