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I have a Roland XP-50 synthesizer in because there’s no sound output. I can't upload the service manual due to size limitations of this forum and I don't remember where I found the one I have but it's out there on the internet somewhere, hope you can follow along.
Upon power up the synth looks to be starting up fine, the menus are navigable.
A quick look at the mainboard schematic shows that op amp pair U4 are the line out amplifiers so I scoped the inputs to the dual op amp and I can see signal when a key is pressed however there is nothing on the outputs. I figured that the dual op amp was bad so I replace it but this did not fix the problem. I disabled the mute circuit thinking that it may be faulty canceling the signal but this proved not to be the case. I finally did the check that I should have done first and that was to see if the +-15 rails were working. When I checked pin 4 of U4 it was at about -15VDC, but when I checked pin 8 of U4 I read -13.5VDC and not the +15VDC you would expect. So, U4 has 1.5VDC running it, no wonder it would not pass signal. Aside from this I found that all op amps on the mainboard had the same rails voltages.
I traced down the +-15VDC source to the mainboard at connector CN7 so I disconnected it and checked the power supply side of the connector and it was indeed putting out a clean +-15VDC.
I see that most of the +5VDC this board uses is derived from the +15 volt side of the +-15VDC rails and this is where I’m seeing a problem. I have some bizarre rails short or leak in this circuit, but where is still a mystery. To add insult to injury, this mainboard has 4 layers… the outside layers are signal and stuff while the inside layers are power and ground planes… very difficult to trace let alone find a short or partial short.
I guess in a nutshell has anyone see this before? If so, where was the fault?
I guessing that a component on the rails is misbehaving but methodically removing parts until the fault is cleared is just crazy with this board… lots of SMD, parts on both sides, inner layers, when installed and cabled up to the synthesizer it’s virtually impossible to remove parts so you have to extract the board, remove the part and re-install it to test… the connectors will not hold up to this kind of repeated abuse. Any help or hint would be greatly appreciated.
Upon power up the synth looks to be starting up fine, the menus are navigable.
A quick look at the mainboard schematic shows that op amp pair U4 are the line out amplifiers so I scoped the inputs to the dual op amp and I can see signal when a key is pressed however there is nothing on the outputs. I figured that the dual op amp was bad so I replace it but this did not fix the problem. I disabled the mute circuit thinking that it may be faulty canceling the signal but this proved not to be the case. I finally did the check that I should have done first and that was to see if the +-15 rails were working. When I checked pin 4 of U4 it was at about -15VDC, but when I checked pin 8 of U4 I read -13.5VDC and not the +15VDC you would expect. So, U4 has 1.5VDC running it, no wonder it would not pass signal. Aside from this I found that all op amps on the mainboard had the same rails voltages.
I traced down the +-15VDC source to the mainboard at connector CN7 so I disconnected it and checked the power supply side of the connector and it was indeed putting out a clean +-15VDC.
I see that most of the +5VDC this board uses is derived from the +15 volt side of the +-15VDC rails and this is where I’m seeing a problem. I have some bizarre rails short or leak in this circuit, but where is still a mystery. To add insult to injury, this mainboard has 4 layers… the outside layers are signal and stuff while the inside layers are power and ground planes… very difficult to trace let alone find a short or partial short.
I guess in a nutshell has anyone see this before? If so, where was the fault?
I guessing that a component on the rails is misbehaving but methodically removing parts until the fault is cleared is just crazy with this board… lots of SMD, parts on both sides, inner layers, when installed and cabled up to the synthesizer it’s virtually impossible to remove parts so you have to extract the board, remove the part and re-install it to test… the connectors will not hold up to this kind of repeated abuse. Any help or hint would be greatly appreciated.
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