Fisher PC50187-9 Tone module question (Electra VIII console)

[Rey1]

Hello everyone,

I recently acquired an Electra VIII console. It works but the right side tone control is wonky (static and poorly pitched treble). My tech says the above mentioned packaged electronic circuit is bad. These seem to be hard to come by. Is there a way to construct one with appropriate discrete resistors and caps? If so, does anyone know the component values and configuration of these?

Thanks

 

[fred soop]

You can build a small pc board and probably mount it by the wires at the tone controls. 4 capacitors, 2 resistors, and 7 wires from the module. You should probably do both channels while you have it open. Schematic should be a 49T tuner/preamp. Here is an example of the technique with a slightly larger circuit (phono preamp).

1418

1419

 

[larryderouin]

Fred's right. Get the 49A/49T manual. The values are right on the schematic. (Everything inside the dotted rectangle for "PC3" and "PC4" are the parts you would need to replace.

Caps (250V will be fine).
750pf X2 (2 channels)
3300pf X2
3600pf X2
.015pf X2

Resistors 1/2W 1% 250V
27KΩ X2
120KΩ X2

PC 4 is identical

 

[Rey1]

Wow,
That's fantastic! Thanks so much for this info. I really want to get this console back working again. Your help is greatly appreciated.

 

[fred soop]

If you are using 1% resistors they will be E96 values. 120K becomes 121K and 27K becomes 26.1K (if using every 4th value to map to E24 values) or 26.7K (closer to 27K). Be careful when reading these as the coloring can get confusing if you are used to typical 5% and 10%. Based on problems experienced by a fellow model railroader, it turns out that it is good to measure ALL parts before installing.

Building the board will be a slam dunk as there are no more than 2 components at any node.