I looked it up at Wikipedia and now I understand it. The case is one of the pins, isolated from the heatsink, but having a solder leg on the other end of one of the screws. And on the Roland SH-1000's circuit board it is connected to a solder point via a toothed washer.
JC-120 in need of a lot of love
-
Pepe
- Posts: 2276
- Joined: Thu Aug 16, 2018 2:19 pm
- Location: Germany
- SBZ: Multi Platinum
- Bossarea: Double Platinum
- Contact:
Re: JC-120 in need of a lot of love
-
laurie
- Posts: 2246
- Joined: Fri Aug 17, 2018 2:07 am
- Location: Canada
- SBZ: Multi Platinum
- Bossarea: Multi Platinum
Re: JC-120 in need of a lot of love
Powered up the amp board that I repaired. Sound is coming out, but the distortion is high (is the non-distortion channel) and DC bias voltages aren't (yet) making any sense.
The other amp board (the one that was working when I got the amp) now doesn't work
Gotta love electronics. Fortumately nothing went "bang" when I powered it up. And no smoke came out...
More work to do! But I think I'll put it aside and work on something else for a while - need to use fresh eyes later.
The other amp board (the one that was working when I got the amp) now doesn't work
Gotta love electronics. Fortumately nothing went "bang" when I powered it up. And no smoke came out...
More work to do! But I think I'll put it aside and work on something else for a while - need to use fresh eyes later.
-
Pepe
- Posts: 2276
- Joined: Thu Aug 16, 2018 2:19 pm
- Location: Germany
- SBZ: Multi Platinum
- Bossarea: Double Platinum
- Contact:
Re: JC-120 in need of a lot of love
Good luck with the repair when you feel ready for it!-
laurie
- Posts: 2246
- Joined: Fri Aug 17, 2018 2:07 am
- Location: Canada
- SBZ: Multi Platinum
- Bossarea: Multi Platinum
Re: JC-120 in need of a lot of love
Both amplifier boards tested and working. I had wired the switching on one of the input jacks incorrectly, hence one of the amps didn't work. The distortion levels in the other amp are actually OK. With the correct level input the signal path is working properly.
The substitute transistors are functionally OK.
Amps have been tested on dummy-load, then with guitar.
Next is to reconnect the FX board and see if any issues with that...
I know I've said it before with other repairs, but I would not want to be doing this "for money". The effective hourly rate would be about $1/hour
.
The substitute transistors are functionally OK.
Amps have been tested on dummy-load, then with guitar.
Next is to reconnect the FX board and see if any issues with that...
I know I've said it before with other repairs, but I would not want to be doing this "for money". The effective hourly rate would be about $1/hour
.
- JC-120_10.jpg (287.01 KiB) Viewed 9188 times
-
Pepe
- Posts: 2276
- Joined: Thu Aug 16, 2018 2:19 pm
- Location: Germany
- SBZ: Multi Platinum
- Bossarea: Double Platinum
- Contact:
Re: JC-120 in need of a lot of love
Great to hear that you found the error in the wiring!
-
laurie
- Posts: 2246
- Joined: Fri Aug 17, 2018 2:07 am
- Location: Canada
- SBZ: Multi Platinum
- Bossarea: Multi Platinum
Re: JC-120 in need of a lot of love
Everything connected back up. It all works!
The depth of the chorus isn't great, and not adjustable. Not sure if that is how it is supposed to sound - I haven't owned one this early before. Will dig into the schematic tomorrow.
The depth of the chorus isn't great, and not adjustable. Not sure if that is how it is supposed to sound - I haven't owned one this early before. Will dig into the schematic tomorrow.
Re: JC-120 in need of a lot of love
Great news to hear Laurie. A big job and a successful one. Give it a try with some dirt pedals but turn the treble down !
-
Pepe
- Posts: 2276
- Joined: Thu Aug 16, 2018 2:19 pm
- Location: Germany
- SBZ: Multi Platinum
- Bossarea: Double Platinum
- Contact:
Re: JC-120 in need of a lot of love
Congratulations so far! Good luck on fixing/solving/investigating the chorus part.
-
laurie
- Posts: 2246
- Joined: Fri Aug 17, 2018 2:07 am
- Location: Canada
- SBZ: Multi Platinum
- Bossarea: Multi Platinum
Re: JC-120 in need of a lot of love
I'll do more measurements tonight.
This is what I think the historical sequence of events has been with this amp.
1) Chorus failed. 20+ years ago?
2) Someone who did not understand the circuit started hacking at it.
3) The hacking caused one of the amplifier boards to fail.
4) The amp was shoved into a corner, out in the weather somehow. From the debris and corrosion, for maybe 10+ years. The original speakers were destroyed by weather/water damage, or maybe they were sold to recover some money against the failed amp.
5) A new hacker got the remaining amp board working and put a single Yamaha speaker in the cabinet.
6) The guy I bought it from used it as a mono keyboard amp for a few years.
This is what I think the historical sequence of events has been with this amp.
1) Chorus failed. 20+ years ago?
2) Someone who did not understand the circuit started hacking at it.
3) The hacking caused one of the amplifier boards to fail.
4) The amp was shoved into a corner, out in the weather somehow. From the debris and corrosion, for maybe 10+ years. The original speakers were destroyed by weather/water damage, or maybe they were sold to recover some money against the failed amp.
5) A new hacker got the remaining amp board working and put a single Yamaha speaker in the cabinet.
6) The guy I bought it from used it as a mono keyboard amp for a few years.