I fully examined the 8500 ohm resistor and did not see anywhere that the outside was scratched off so it could make contact with the band, However, with the band removed I get a reading of 6,850 ohms.
Well, I think my Bias pot is trashed. It is R7 (3,000 ohm pot, schematic posted in response above).
I tested it before cleaning and in certain areas around settings 40 – 80 I get alternating spots that show open and spots where the resistance can jump as high as 15K.
I then fully disassembled it:
I then cleaned the restive element with non-residue contact cleaner. Here are the results:
I then put it back together and tested just the element. It was 2.98K:
I then tested it off-line and got all kinds of spurious readings. Disregard the settings as the dial scale was not set properly:
I then reinstalled it, set the dial scale properly, and hooked the wires back up.
Very strange results. When installed in the chassis and the chassis is in my makeshift chassis holder I seem to get better results but things still jump around a lot between settings of 40 – 80. However, when I rotate the chassis so that it is laying flat like it would in the case it shows open most of the time between settings of 30 – 80. In other words, it behaves much worse when laying flat.
So it looks like this pot is trashed. Not sure why as the wiper seems to be making good contact. What’s everyone else’s opinion? Would it behave better if I were applying power to it? If I need a replacement would a generic 3K ohm pot work? Anyone have any recommendations where I could get one?
Thanks,
Geoff