JC-120 in need of a lot of love

[laurie]

The mystery of why the chorus didn't work but the vibrato works is solved. The chorus circuit takes an input from the left channel amp output, and the left channel board was removed.

I won't know for sure until I get the whole thing back together, but it looks definitive based on the schematic.
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JC-120 chorus signal.jpg (142.98 KiB) Viewed 8552 times

[Pepe]

A missing board? Well, at least not one with zillion components, eh? Seems like you can build something on a simple stripboard. Are the trasistors of a common type? And what is L1? A coil?

[laurie]

The board came with the amp... just not IN the amp
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JC-120_4.jpg (328.06 KiB) Viewed 8544 times

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JC-120_3.jpg (193.21 KiB) Viewed 8544 times

[Pepe]

Ah, good!

And what is "L1" now?

[laurie]

Ah, good!

And what is "L1" now?

Oh yes - it is a small inductor. To stop high frequency noise getting to the speakers.

[laurie]

I'm having trouble finding a serial decoder that works. If anyone can help - the serial on the amp is 400363.

Any idea about manufacture date?

[laurie]

For future reference - amp board connections in case anyone needs it.

Note that the labels do not necessarily follow the wiring diagram - the labels are as written on the trace side of the PCB.
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Early JC-120 amp board connections.jpg (363.1 KiB) Viewed 8534 times

[laurie]

For future reference. FX board connections.

Note that the labels do not necessarily follow the wiring diagram - the labels are as written on the trace side of the PCB.
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Early JC-120 FX board connections.jpg (257.04 KiB) Viewed 8532 times

[laurie]

Working out all the internal connections. Quite a few were incorrect from previous repairs (speaker jacks, line out, etc.). And a lot were unknown because the left channel amp board had been removed.

Additionally, the schematic is incorrect - the connection points on the boards are incorrectly named. I've had to trace the circuit on the PCB for most of the connections.

This restoration is "getting up there" in hours now.
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Early JC-120 all connections.jpg (322.02 KiB) Viewed 8428 times

[Pepe]

This restoration is "getting up there" in hours now.

I keep my fingers crossed for a perfectly working Jazz Chorus at the first time that you power it on.