Roland Jazz Chorus 120

[goldtop5]

Anyone have a schematic for a Roland Jazz Chorus 120?
I also need to find what replacement switch I could use for SW3 (Chorus/Vibrato selector). Or do I need to contact the manufacturer?

[Jazz P Bass]

As far as I know, that switch is no longer available.

Contact Roland to be sure.

[soundguruman]

you 'might'(?) get one from Roland
this is a special switch but you can use a DPDT center off as a substitute
the difference is the center off, which is actually a bypass set of contacts.
When you use DPDT you can't get the true bypass in center off position, but it still works just dandy without the true bypass..

[Mick Bailey]

Some of the obsolete switches found in Japanese equipment fail through contamination of the contacts and general oxidation. In many cases a switch can be removed and carefully pried open. Just take care not to over-stress any tabs or lose any springs or parts. Make a note how everything goes together.

I'd say I have a 90% + success rate in rejuvenating low-voltage switches. Repairing old Roland synths gives plenty of practice! There's rarely enough voltage to cause any burning or pitting.

I've found that reassembling with a contact grease intended for switch contacts ensures continued reliabilty once the switch is back together. It can also be used as a general mechanical lubricant. Just make sure not to abrade the contacts when cleaning. The stuff I use (Kontakt) removes oxide deposits. Lighter fluid will remove the grease.

[Amapola]

Hi there,

I have this jc120 and i find the ground wired to positive on "input" jack very strange and the schematics show the same thing ^^. It's seem a ground loop , no ?

I've always had a problem of hum in this jc120... Many years ago, i even pulled the transformer out the amp several meters away...but always hum.

Am sure it's come from these wrong imput...

So what do you think about it ?

Thanx in Advance for reply

Greetings

[Jazz P Bass]

Not too sure what you mean by the "positive on the input jack is grounded".

Both input jacks have a normally closed tab on the positive tip that opens when a plug is inserted and remains closed when no plug is inserted.

The 'High' input jack is closed to Ground.
While the 'Low' input relies on that closed contact (and it's own) to get to ground.

Here is a schematic crop of the input jacks.

Roland JC120' 84.pdf

[goldtop5]

Wow, this post is really old! I've already moved on to 2 different jobs since leaving the repair business in 2016. The shop closed shortly after I left, but my boss still owed me money. Not worried about it. Wasn't much anyways. I'll still do repairs, but only part-time on the side or whenever my schedule will allow. Mainly on my own stuff. I'll still come back to this site every once in a while.

[J M Fahey]

Well, visit us often