| Re: K200 Bright Channel is ALIVE... [message #28746 is a reply to message #28744] |
Sun, 21 August 2022 22:27   |
2beertom
Messages: 4
Registered: August 2022
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Junior Member |
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Hi,
Thanks for replying!
I had ECG123AP's on hand, put them in and the voltages are pretty close to the schematic.
I checked the DC voltages on Q300-Q307, everything is fairly close to whats on the schematic.
I changed many 10uf caps and one 33uf cap and still no joy with bright on.
My bench setup allows for a 1khz low level sine wave to be injected at the input jack, while an 8 ohm power resistor with distortion meter, audio voltmeter and scope monitor the output.
With the other channel of the scope on the center contact of the bright switch, with switch in off, I see a low level sine wave on both other contacts, one from the q305q306 circuit and the one Q304. Whats interesting is that when ti he put the bright switch to ON, both sine waves on those switch contacts drop in level by 25db!
For fun, I disconnected the center contact wire from the bright switch, the one that goes to Q307 and again scope the switch contacts....again interesting, the levels are 25db lower....what the heck! the circuit "need" to have that connection to work? I don't see any feedback loop...
Anyway, I pretty much stumped on this one, any insight would be really appreciated.
tom f
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