A bit of history, about 3 maybe 4 years back I picked up a JX-3P in good shape. The first thing I did was replace the electrolytic caps, as I’ve done many times when purchasing old equipment. I always use quality caps when doing this. I also installed the Series Circuits Midi Kit. I calibrated it afterwards and it’s worked great since then, until recently.
The other day I fired it up and had a dead voice channel. After digging around for a bit it was a bad trace, damaged by a leaky cap (yes, one of the new ones.)
After further investigation it seems that all the caps (every single last one) on the main board were leaking. All caps are from the same brand (Nichicon) and from the same batch though some were different lines (i.e. some were “audio” grade caps, some are bipolar, some are simply power filtering.) Strangely, all the caps on the panel board and on the power supply are all good.
I’ve ordered some 25v caps to replace the 16v ones, but I don’t expect over voltage is the problem. The 15 volt rails are 14.5 (+ and -) and if the issue was voltage I’d expect to see the problem in the filter caps on the power supply board.
My question, seeing as I’ve never run into anything like this before, what could cause all the caps on the main board only to leak prematurely like that? Especially when caps everywhere else in the synth are fine (though I am replacing those as well, just to be safe.)
I don’t want to have to open this up again in another 2 years and have to do this again.
The bipolar caps in the signalpath (C109-C112) are specified for 16V, but C104 is 50V according to the servicemanual. I have here a spare mainboard, where C101 is 35V (in the service manual it is described as 16V).
I’d recommend 25V or 35V definitely.
Well the black Sanyo caps that Roland used from about 1980 onwards are top notch and have held up great unlike the previous purple Matsushita which are “replace on sight”. Sanyo rarely have problems except in rackmount modules because of the lack ventillation and heat eg MKS series. I never blanket replace them. They are still underrated though 16v is not enough margin. There are transients that are always present at power up. Your other mistake is to replace all of them with audio grade, that’s not what they’re for. Audio grade is for the audio path only, for the powersupply decoupling you use good brand (Nichicon/Rubycon/Panasonic etc) general purpose (not low ESR) capacitors.
Florian, appreciate the reply. This gives me a chance to say thanks, I likely got my schematic of your site in the first place, it’s great that you keep that info available.
Ivan, I get what you are saying about the “Audio Grade” caps. I had a bunch left over from a recap / rechip on an old Tascam console. I had assumed they would be OK. This got me worried and I pulled a few channel strips out of the board and checked them, all the same caps used in the mixer are fine.
Either way it’s just strange that the only bad caps were on the main board. Some of the caps used were the same on the power supply board and the panel board, they were all fine, but replaced with higher voltage ones anyway.
The power rails all look very solid, I don’t get the impression anything is oscillating. I’m thinking of spending an afternoon sending it midi and seeing if I can spot anything odd.
Otherwise I have this working again and will put it back into the synth rack. I’m going to check it every 6 months or so, just to keep an eye on it. If I see any further issues I will share what I find.
When choosing power supply capacitors, Digikey for example lists Ripple Current as a feature most don’t consider. Ripple current is the average current the capacitor sees during normal operation of the circuit. If the current through the capacitor exceeds the ripple current, that too will damage and over stress the capacitor. Shorts and timed out components causing higher than designed current draw will damage the caps.
It seems there are a combination of reasons why these capacitors failed.