Advice needed re Roland JC-60—power/polarity switch and safety

[ga20t]

Picked up an old metal corner Roland JC-60 with a few issues:

- previous owner said it was blowing fuses. I looked at the fuse assembly and it was melted together and still operating...
- when I tried it out, it was quite noisy
- took it home, played it a bit, and my strings felt "live". Shut it down, unplugged it, and then noticed the 3rd prong (ground) was snapped off.

I've taken it in to set it right, but I'd like to know what to have done re the ON/OFF/ON polarity/power switch.

- Did these JCs with the ON/OFF/ON switch originally ship with a 3-prong?
- If not, and I'm having a grounded 3-prong reinstalled, I'm assuming one would no longer want the ability to switch polarity? Perhaps I should have it changed to an ON/OFF?

I can't read schematics myself, but I did manage to find this one for a JC-60/60A. No idea if the revision is the same as my amp. http://music-electronics-forum.com/a...oland-jc60.zip

Any help is appreciated!

[Enzo]

Polarity is a separate issue from grounded. No reason you can't have polarity swapping on a grounded chassis. Leave the switch alone. In some situations it will allow you to reduce hum.

In the file you linked, look lower left corner of page 2, it shows the 120v wiring as a diagram rather than schematic. They call it 117v. Note the mains wiring includes a green ground wire to the chassis. Right next to this is the 220/240 volt wiring if that is your part of the world. Trust me, they never made an amp with a three prong cord with a snapped off ground prong. Someone snapped it off later.

[DrGonz78]

My JC-60 (Older 1978 or so) came with a 2 prong Kawasaki branded power cable. There was not a safety ground at all and installing one was the first thing I did to start off restoring the amp. I remember having to drill a hole in the chassis to mount the ground lug terminal while installing a 3 prong. My thought process on the polarity switch was to keep the HOT AC wire to always be the in line with the fuse. So yes I disabled the ON|OFF|ON function of the switch so one of the ON options on the switch were removed. Sure Enzo makes a great point though that polarity switch and to be able to still use it in certain situations. For me though I want to keep that hot wire in line with the fused side of the AC primary. Stuff like that is really about how anal you want to get about stuff as it is not such a huge deal.

Please look for any caps that might go from Hot or Neutral wires straight to chassis ground. You are going to want remove those old possibly leaky caps if you find anything like that.

Edit: BTW the one Doctor posted were for the older JC60 type that I had and it show 2-prong wiring examples with a cap that goes from AC wiring to chassis ground. Click the 2nd link below to see that wiring diagram. Plus does your amp have a separate Effects board or is it just one long circuit board?
http://music-electronics-forum.com/a...160-p.6-9-.pdf
http://music-electronics-forum.com/a...160-p.4-5-.pdf
http://music-electronics-forum.com/a...160-p.1-3-.pdf

[ga20t]

Polarity is a separate issue from grounded. No reason you can't have polarity swapping on a grounded chassis. Leave the switch alone. In some situations it will allow you to reduce hum.

In the file you linked, look lower left corner of page 2, it shows the 120v wiring as a diagram rather than schematic. They call it 117v. Note the mains wiring includes a green ground wire to the chassis. Right next to this is the 220/240 volt wiring if that is your part of the world. Trust me, they never made an amp with a three prong cord with a snapped off ground prong. Someone snapped it off later.

Yes, I'm aware that the ground prong was damaged and never produced that way. I'll consider leaving the polarity switch. As long as it can be safe, I'd like to keep it as close to spec as possible. Thanks for the thoughts.

My JC-60 (Older 1978 or so) came with a 2 prong Kawasaki branded power cable. There was not a safety ground at all and installing one was the first thing I did to start off restoring the amp. I remember having to drill a hole in the chassis to mount the ground lug terminal while installing a 3 prong. My thought process on the polarity switch was to keep the HOT AC wire to always be the in line with the fuse. So yes I disabled the ON|OFF|ON function of the switch so one of the ON options on the switch were removed. Sure Enzo makes a great point though that polarity switch and to be able to still use it in certain situations. For me though I want to keep that hot wire in line with the fused side of the AC primary. Stuff like that is really about how anal you want to get about stuff as it is not such a huge deal.

Please look for any caps that might go from Hot or Neutral wires straight to chassis ground. You are going to want remove those old possibly leaky caps if you find anything like that.

Edit: BTW the one Doctor posted were for the older JC60 type that I had and it show 2-prong wiring examples with a cap that goes from AC wiring to chassis ground. Click the 2nd link below to see that wiring diagram. Plus does your amp have a separate Effects board or is it just one long circuit board?
http://music-electronics-forum.com/a...160-p.6-9-.pdf
http://music-electronics-forum.com/a...160-p.4-5-.pdf
http://music-electronics-forum.com/a...160-p.1-3-.pdf

Hi DrGonz78,

My amp is a 3-board version. That scheme I linked didn't seem quite right to me—I was having trouble opening the others on my mac but I've figured it out now and had a look.

The reasons I am uncertain as to whether mine had a 2-prong originally are 1) I know nothing about these particular amps, date of manufacture etc. 2) First thing I did when I got it home was do a visual inspection for any mods, fresh solder etc. This is when I noticed that the 3-prong in mine didn't have a star connector for the ac wire ground, the solder to the punched chassis tab where it is soldered (perhaps an indicator a 3-prong was original equipment?) looks fresh compared to the rest, and the ac cord, inside the chassis, has been strapped to the other transformer wires with sandwich bag twists ties, which is inconsistent with the silicone type bands throughout the rest of the chassis.3) not sure of the date of mine, but having done a little research it's looking more and more like mine is an earlier '70s-'80 model (metal corners, access holes through rear panel for jacks & chorus adjust trim). Wish I had it with me at the moment so I could access the serial and try and date it better.

I'm definitely leaning towards safer, but if the original setup is reliably safe I might leave the polarity option. As for the caps, I might have to put that on hold for a bit (unfortunately) as the amp is with a mom and pops shop at the moment for the fuse assembly and 3-prong. The knowledgeable guy I usually have service my stuff is a couple hours drive, expensive, and takes months at times. But I definitely want to have any of those replaced asap, as I normally would with any old tube amp I've taken home over the years. I'll see what they can do where it is. Would you suspect that that is the likely source of the noise, possibly the electrified strings?

Cheers, and thanks for the help people!

[olddawg]

If it's a beater, I would have just screwed a $3 generic replacement 3 prong plug on the end of the power cord and checked continuity from the ground prong to chassis in every polarity switch position. If it was there and there were no other issues with the amp... I'd call it a day.

[ga20t]

It's pretty mint, otherwise I would have done as much. Still need to sort the noise, why it was blowing fuses for the previous owner etc. Perhaps looking over and wiring the new 3-prong & fuse assembly will solve these issues? I'm not counting on it, but maybe.

[ga20t]

UPDATE

I received my amp with the safety issues resolved. It now runs dead quiet and sounds beautiful (wow!) and clean. A few issues though:

1) When the chorus or vibrato are engaged there is noise. The chorus is making an ocean sound that pulses with the vibrato time of the effect. It's not present when notes are played lightly and the gate(?) doesn't engage the chorus, but when the effect is pronounced, then the noise comes. Could/would/might this be the BBD chip or something else common on the FX board that might need replacing?

2) It's noisy when the reverb is engaged and turned up past noon. Sometimes. It's variable, even though I'm not really changing anything; playing position, effects etc. Strange.

3) Since it's been repaired (new fuse holder, grounded 3-prong as per schematic), the distortion being engaged nets a volume drop and no distortion. It sounded awful when it did work (I understand they were this way), but it's a bit of a weird symptom.

I'm going to try it with another speaker asap just to see if it cures the noise issues by chance. My Roland/metal dust cap speaker is a little beat up. I plan on having a filter cap job done in the very near future. I'll ask him to hunt down and address the known quirks it has, but it's always nice to go in knowing a little about where to look to begin with.

Thanks all.