Stagepass 300 troubleshooting (Yamha)

[g1]

I'm a bit puzzled by the 'troubleshooting' flow chart on pg.27 and 28. Maybe I'm misunderstanding but it seems they are saying if any of the first 3 conditions are true (blown fuse, missing +VB or missing -VB), you are supposed to skip to the end and replace the entire power board?
(pwr. supply schem is pg.50)

[The Dude]

That's the way I read it, but it doesn't mean you can't try to repair the power board. I think some of these repair manuals are written primarily for service centers, and the company would rather you just replace the board than pay the extra labor to repair it.

[g1]

When I was removing the board a chunk of IC802 fell out. I hadn't noticed that it had it's face blown off. It is the switching controller for T1.

I am missing +VB, yet I have -VB, +15V and +5V supplies that all run off same transformer, how can this be if IC802 is broken? (-15V supply is only giving -11V)
The unit is functional except for the power amps.

[The Dude]

There is also IC804. It looks like +VB is derived from IC802 & T1 and -VB from IC804 & T2. It also looks like +&-15V are derived from parallel windings (through rectifiers) of both transformers. So, unless both supplies are down, you'd probably have something close on the 15V supplies.

[g1]

The diodes and tx winding for the +VB check out ok so I guess I will gamble that there was nothing causing IC802 to blow and try replacing it.

[The Dude]

I would also check +VB to ground and to -VB to make sure the output section of the amp doesn't have a short before you fire it up.

[g1]

Unfortunately they are non-repairable small modules. I can check what you mentioned but they could still both end up being bad so kind of tough to give an estimate for repair.

[The Dude]

Well, IMO, it's worth a shot. Get a spare, they're cheap.

https://www.digikey.com/en/products/...iAAEgLeEPD_BwE

[x-pro]

If IC802 is missing, relay RY801 will not operate. This means that the mains supply is limited by the TH802 thermistor.
Everything in this SMPS can be repaired. I don't see any problems at all.

[g1]

Forgot to close this one out. Replaced the TOP249 (IC802) and that did it. Unit has not come back.
However, in the mean time I remember reading that nearby cap being weak will cause the chip to blow like that. I think in this circuit that would be either C834 or C841.

[x-pro]

Unit has not come back.

The device doesn't work?

[g1]

The device doesn't work?

No, I meant it has not come back for repair again. It worked, and as far as I know, it is still working.