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Trevor Wilson[_4_]

On 29/11/2019 11:13 pm, wrote:
Its a Sansui 5050 receiver. The power amp works, the radio tuning meter
moves, so it seems that works. But the preamp board is dead. Not a
single transistor or any other component on that board has voltage.
There is 44vdc on a wire from the power supply. It goes to a resistor.
No voltage on other side of this resistor. Multimeter on ohm scale
confirms resistor is open.

The problem is that resistor is red red brown @ 5% (gold). Thats 220
ohms. Yet an online schematic shows R601 as 100K.

OK, I know that resistor is dead, but how can the actual color code be
so different from schematic? The resistor is not burnt, but may have
gotten warm. Yet the color code is plain to see, except the gold band is
kind of greenish.....

My plan is to clip in a resistor, but where do I start with such a
conflict of values....

Yes, I triple checked this is R601. Unless the schematic is labeled
wrong????

This appears to be the only voltage source to this board.....

Any ideas or suggestions?

Thanks

**R601 is a 220 Ohm 0.5 Watt resistor. That is what is indicated on the
schematic from Hi Fi Engine.

As others have stated, you need to use your noggin when fault-finding.
For a 100k, 0.5 Watt resistor to show signs of stress (not burning) it
would need to dissipate at least 0.5 Watt. That would suggest a Voltage
drop in the order of 250 VDC across the resistor. Do you see 250VDC
anywhere in that amp?

--
Trevor Wilson
www.rageaudio.com.au