Jazz chorus 120 fuse sizes?

[Rusty shackleford]

Hi all, I just picked up a not working jc120 s#574589 for cheap and I'm having trouble fixing it, (tube amps I can fix in my sleep but I don't have much experience with solid state). So, the external 5a fuse is fine, internally there are 4 fuse spots labelled 3.15a/3.15a/125ma/125ma, the 125ma's are fine and the 3.15a's are blown. Every schematic that I can find that lists the internal fuse sizes says the 117v version uses 2 6amp fuses on xfmr secondaries but mine are labelled 3.15a, it's definitely a 117v amp but it's clearly been worked on in that past so I don't know if the fuse block is original. So which fuses should I use? I don't wanna go on trying to diagnose it thinking fuses are blowing because something is wrong when it turns out they're blowing because they're too small, or the opposite using fuses twice as big as they should be. I'll try to upload some pics. Thanks.

[Rusty shackleford]

[Helmholtz]

Secondary fuse values should be the same for different mains voltages. Only primary fuses should be different.
Please post schematic.

[Rusty shackleford]

Roland JC-120 Jazz Chorus (2-79) Schematic.pdf
This one seems to be the closest match but doesn't show sec fuses that I can see.

RolandRoland JC120' 82.pdf
This one is different than mine but lists the sec fuse values. 100/117v 6a, 220/240v 3.15a

[Helmholtz]

I see, that's really confusing. But I think different secondary fuse ratings might be due to different local safety regulation.
I would use major brand 3.15A sloblo ("T") fuses.

[Rusty shackleford]

Ok, I'll go with the 3.15's and start the troubleshooting, probably won't be too long before I have more questions lol. Thanks for the help.

[Enzo]

Just stick with what was in it, especially if there are labels. There are so many JC120 variants it is highly likely your different fuse value is just a change, like a hundred other changes. WHen the factory labels a fuse holder as 3A, why on earth should we think, "Gee, maybe I ought to install something other than that"?

As to your reasoning, if it was supposed to have 2.6A fuses and we install 3A fuses, it surely won't be blowing them more often because of it. In fact, I might wager they upped the 2.6 to 3 because they were getting nuisance blows.

SInce you know the serial number, most JC120 schematics include the range of serial numbers it covers.

[g1]

[ATTACH]n926545[/ATTACH]
This one seems to be the closest match but doesn't show sec fuses that I can see.

Roland[ATTACH]n926546[/ATTACH]
This one is different than mine but lists the sec fuse values. 100/117v 6a, 220/240v 3.15a

attached schematic package includes proper schem. for your serial number. Power supply shown on pg.12 of pdf.

[Rusty shackleford]

Kinda what I was thinking, but I was unsure after seeing the higher values in the schematics. Just wanted to make sure I wasn't chasing my tail using undersized fuses. Stuck some 3.15's in and disconnected the speakers, fuses still good. Checked speakers, channel 1 good, channel 2 shorted. Hooked up channel 1 speaker and it works. Diode tested ch2 output transistors, they test ok. Swapped ch2 transistors to ch1 and they work. No visibly damaged components on any boards.

[Rusty shackleford]

Hooked up a cheap speaker to ch2, all controls at 0, power on and speaker cone extends out about 1/4" and sits there. Turned it off and that's as far as I've gone.

[The Dude]

When repairing the amp section of a solid state amp, always measure the speaker output for DC voltage before connecting a speaker.

[Rusty shackleford]

Thanks for the schematics g1, those will be a big help in figuring this thing out.

[Rusty shackleford]

It's fixed!! Took magnifying glass to the ch2 board and found that Q26 had a broken leg, it tested good so I soldered the break, put an old rola 12" in and everything works now. Just gotta find an appropriate replacement speaker and she's all done. Thanks to everyone for their help and suggestions.