Rolandd jazz chorus 77, bad hum how do i rid it

I've included a link which provides information on some of the possible causes for hum in an instrument amp. If all else fails to locate the hum, the hum may be caused by a bad filtering capacitor, possibly in the power supply. I suggest you have the amp diagnosed by a reputable musical instrument shop. Troubleshooting Guitar Amplifier Hum eHow

1976 -77 it depends on originality and condition a store will give less for resale private buyers are better but it must be 100% on both orig/condition in the 2000's

Sounds to me like low-end gear. You honestly get what you pay for. If it happens to be high-end then you have either bad cables or just a bad effects processor. If you have on-board effects built into the amp, then get better equipment.

Hope this helps.

Sounds like a resister is bad..

You take it in for electronic repair. Unless you are electronically adept at troubleshooting and repair this is not DIY. Probably one side of the PA transistors has shorted. You can blow the speaker if you keep trying to use it this way.

It sounds like the bypass contacts on the pedal are not working... this may be right in the pedal switch itself. With unit in off position, use an ohmmeter to check continuity between in and out cable tips.

Start by unplugging anything attached to the amp to eliminate simple things such as a broken shield on an input cable.
If you still have the pronounced hum with nothing connected, then the amp's power supply may have a failed filter capacitor or diode bridge. Either of those would have to be sought by a tech with the right gear.

https://www.amazon.in/Roland-JC-120B-Chorus-Guitar-Amplifier/dp/B00S0J6IS6


JC-120B 1975 or later

JC-120UT After 1984 - I haven't found the way to identify your serial number online. You may need to post a message on one of the many internet boards shown.

https://www.ssguitar.com/index.php?topic=2243.0

http://music-electronics-forum.com/t35754/https://www.gearslutz.com/board/so-many-guitars-so-little-time/181432-roland-jc-120-tough-date.html

JC=120UT /JA sold in Japan only.

https://www.gearslutz.com/board/so-many-guitars-so-little-time/181432-roland-jc-120-tough-date.html


ervicerepairmanuals.net/others/roland-jc-120ut-searvice-manual/






http://ervicerepairmanuals.net/others/roland-jc-120ut-searvice-manual

SING THE FIRST VERSE OF THE SONG, THEN PASTE THE CHORUS, SING THE SECOND VERSE OF THE SONG THEN PASTE THE SECOND COURSE.