JP-8000 - potential power supply issue? (Hum & injected MIDI data)

Synth Repair
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Hi all. Something appears to be a bit unusual about my recently-acquired Roland JP-8000, and I’m really not sure if this is a fault or maybe a common issue.

I have observed the following two issues, and both kind of sound to me like the power supply is involved and may be faulty in some way or another (bad caps?).

Issue 1: 50 Hz ground hum. That in itself is not unexpected - if the synth is turned on. But I can even hear it on the stereo outs when the synth is turned off and even when the power switch of the power strip it’s connected to is interrupted (of course it only interrupts one of the two power wires, so the ground and either hot or neutral wire is still connected - rotating the power plug and thus swapping hot and neutral does not change anything). Granted, it’s low in the noise floor, but it still means I need to remember to mute this mixer channel for a clean recording of other synths (or use a DI box, which may alter the JP’s sound). If I put the gain all the way up on my analog mixer (+15dB) I get a noise floor of around -70dB, which is really quite bad for the synth not even being turned on. For comparison, unmuting all my other synthesizers on the mixer makes the noise floor go from below -100dB to -98dB or so. So this is quite a huge difference.

Issue 2: Phantom MIDI messages. Again, the synth is not even turned on, and the power strip’s switch is interrupted. Whenever I use on the light switch in an adjacent room (it’s one of those setups with a relay in the circuit breaker box, to allow for multiple switches controlling the lights in the room), my MIDI interface picks up MIDI messages from the JP. It’s always a single-byte FF (System Reset) message, making me think that there’s probably a series of short pulses on the power line, and they somehow propagate to the MIDI out. Again this does not happen with any other synth in my collection. I use the same MIDI cables for all of them (but using another cable from a different brand also didn’t help), and I have multiple MIDI interfaces which all expose the same issue. As I think the light switch cabling runs through the wall behind my MIDI interfaces, I thought that maybe the cable acts as an antenna (it’s 6 meters long), but given that there are two seemingly related issues here with the JP-8000, I’m not so sure that any external components are at fault.

Does anyone have an idea what could be the problem, or what further things I could try to help analyzing the issue?

1 Like
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It sounds like you have a shorted RIFA (Y class) capacitor across the power switch. When they fail from age, they short the on/off switch so the unit is always on, even though the switch is turned off.

It could also be the source of the hum, so unplug the unit before anything else and look for a capacitor going across the power switch. Replace it with a new type from Digikey. when ordering get the type with the same lead spacing.

They are there by government regulation to filter any electrical noise from feeding back onto the mains power.

If its not a RIFA capacitor, then there’s a chance the power switch is shorted.
If that’s it, then replace the switch, you may have to buy that from Roland though.

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Thanks for the reply. I will be checkout out those ideas the next time the synth is open. I doubt that there’s an issue with the power switch itself, since the synth still turns on and off as intended. I’ll also check all the other caps on the power supply.