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I have in this old JC120 which is foxing me. It's one of the first models to have ICs, they are old types including TA7122 TA7200 C1458 MN3002. None of the web schematics fit this model. If anyone has a schematic with those ICs I would be deeply grateful.
The faults are - hard gating on the chorus side (is this meant to happen to cut down the swishing noise when not playing? - it's very noticeable and takes a moment too long to open the gate when you play a note), no distortion, no vibrato.
I found two open diodes around the C1458 on the chorus effect board. I replaced a good few ICs in desperation! I checked all the transistors (quite a few 2SK fets on there but managed to squeeze beeps out of them) and diodes. The supplies are ok.
Any ideas?
The faults are - hard gating on the chorus side (is this meant to happen to cut down the swishing noise when not playing? - it's very noticeable and takes a moment too long to open the gate when you play a note), no distortion, no vibrato.
I found two open diodes around the C1458 on the chorus effect board. I replaced a good few ICs in desperation! I checked all the transistors (quite a few 2SK fets on there but managed to squeeze beeps out of them) and diodes. The supplies are ok.
Any ideas?
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