Roland VA-5 Power Supply (SWM 80)

[musictronics]

Hi y'all,

We have a Roland VA-5 arranger synth in for repair... power supply (SWM 80) is no good, and a replacement has not been obtainable for at least 6 years or more. I am a Roland service agent, and have the service manual for this model, but there is no schematic for the PSU, as it was only to be replaced as a complete unit. Customer is keen to have the instrument repaired, and the only option is to attempt to repair the PSU. Does anyone ever traced a schematic for this, or has anyone worked on one of these beasties before...?

Any info gratefully received...

[Enzo]

With a part number like SWM, do I correctly assume it is a switcher?

Generically, when I see a dead switcher, I start by checking for shorted rectifiers on the secondary side. A short there often shuts them down rather than blow a fuse. On the primary side there is usually an onrush limiter, check for opens, check that your mains is getting to the rectifier bridge and the HV DC is being made. If there is a controller IC, the data sheet may have a similar schematic. Also, if you can identify the controller IC< look through your files for other SMPS that use the same controller IC.


And just what voltages does this supply? How hard would it be to just create a replacement supply?

[musictronics]

Yes, a switcher, manufactured by a third party... no service info available.
Normally we would just replace the entire SMPSU as Roland suggest, to expedite the repair... but as they are NLA, the only option is a repair.
The HV side is good & healthy, 5v rail is good... problem is with 12V rails +/-, I'll do a little more digging. Not much room inside for a linear PSU, although I have done that in the past!

[Enzo]

Are both 12v rails doing the same thing, and then likely at the same time? Do they use the same winding with branching rectifiers or does each have its own winding? What exactly is the symptom?

If the primary side is OK and working, as your good +5 tells you, then ther is only so much the 12v supplies can be. Are there 12v regulator ICs or are the two supplies just 12v by design?

And does disconnecting the load make a difference?