Roland D-Bass 210 PS Issue

[misterc57]

Fuse was blown. PS is pegging current with just a small amount of AC applied.

Read another thread on this and I am experiencing the same issue of not being able to find a schematic on the PS section.

I will see if I can step through the PS section without the schematic and check for damage. Nothing visibly looks bad. Suggestions welcome!

Attaching the service manual which has no diagram or schematic of the PS.

Thank you

Roland D-Bass 115, 210 Service Manual.pdf

[Jon Snell]

I would check the switching transistors and if short circuit, check/replace the snubber network.
Before powering it up, I would check all secondary diodes as a matter of course.

[misterc57]

This is going to be a challenge (for me) without a schematic to follow. I think it has been 5 years since someone here has worked on one of these. Any chance someone found a PS schematic?

I did find that the negative side of the large capacitor (I assume it is the filter cap) had a bad solder joint. The cap tests good. The solder would not flow into the hole so I ran a jumper wire to secure it.

Weird thing is that the negative side of that cap does not have a connection to ground, as far as I can tell. Anyway, still have the high current draw.

I think what I see for a PS flow in that section is

AC --> coils --> bridge rectifier --> filter cap --> (I need to figure out the rest)

Not sure which are the switching transistors. There is a transistor on each large heat sink.

Wondering which components I should remove in order to test properly? Bridge rectifier, transistors, diodes. What order to follow.

Thank you!

[The Dude]

You are likely looking for a short if the fuse blows, so it's not necessary to remove anything, YET. Check those transistors (probably FET's). If they measure shorted in circuit, then remove them and retest.

[misterc57]

Just getting back to this. Those two FETs look to be 17N80C3. I did not see any shorts between any combination of legs. Also no shorts on the diodes in that area.

[misterc57]

I have disconnected all connections to other boards. Problem still exists.

[misterc57]

There is a short between the two AC legs of the bridge rectifier. Is that normal?

[misterc57]

removed the rectifier. I have a short between + and AC

[g1]

Short between AC legs may be normal if in circuit, as you are measuring through transformer winding.
Bridge rectifier short between + and AC leg when out of circuit is a bad rectifier.

[misterc57]

Thanks for the confirmation. Both AC legs are also shorted out of circuit. Mouser has this bridge rectifier in stock. May be a while before I place the order.