Roland Again

[mhuss]

Hi all, I have a Roland JC-77 (schematic: http://music-electronics-forum.com/t37207/) that I'm looking at for a friend. When the chorus switch is off, both speakers work fine, but when the chorus switch is on manual or fixed, the one side dies. It's seems as though there's nothing coming through the chorus circuit and when that gets connected to the amp, silence on that side.

Before I dig in testing and probing does this symptom sound familiar to anyone? Are those MN3xxx BBD chips still available anywhere?

Thanks...

[Enzo]

That is exactly what is happening. In plain mode, teh same signal feeds both amps, in chorus mode one side gets the dry signal, the other side gets the chorused signal. If the chorus circuit is not working, that speaker goes silent.

It may or may not be an MN chip, it could be anywhere in that circuit, including the JFETs that route signal.

[mhuss]

I had the chassis out and started probing around - and it started working again! A judicious amount of "chopsticking" and moderate banging on the chassis with a rubber mallet could not recreate the problem. Sigh.

I'm giving it back no charge, no warranty...