Russound CA4 Power Supply Repair

[CMCM]

Hello Everybody,

Trying to repair a power supply from a Russound CA4 Multizone Controller (picture attached)

Russound no longer supports it but were kind enough to provide a schematic of the power supply (pdf attached).

The outputs marked 12v and 20v are all measuring only 1v.

The board is clicking, which I think means it is in something called hiccup mode when the flyback transformers switches because of an internal problem or something else on the board Overloading it.

The capacitors physically look clean (no bludgesor leaks) and are not shorted. The diodes seems to all be showing continuity only in one direction.

Someone in another forum suggested lifting a leg from the 2M 1/2W resistor at position R6 that triggers the TOP248YN (connected to the large heatsink) but it tested at healthy looking 1.994M.

Have enough skills to be dangerous, but am in over my head on this one.

Any guidance on how to pinpoint the fault Is welcome and appreciated.

Thank you!

[CMCM]

Success! Replaced the P6KE200, the TOP248YN, and three small capacitors that had high ear ratings and it now alive and kicking,
thank everybody!

[R_J]

A cap that can cause problems is C18 (4.7µf/50v) check that there are no shorts across any of the outputs

[CMCM]

Hey R_J,
Thank you for the reply!
The 4.7 uf 50v capacitor at C18 is not shorted. It tests as 124 uf in circuit. Does that mean it is bad or does it not test well when in circuit and I should remove it to test again?
No shorts when i check between 12v pin 3 and -20v pins 4/5 and 20v pins 9/10
Looking at the diodes, i did find a few anomalies: With the meter in diode mode, most gave a reading with the negitive lead on the cathode and ol when the leads were reversed... except these...
The two at D5 and D7 (between the black heatsink and the yellow transformer) reported 0.0 in both directions. The one at D3 on the short edge of the low power side reports about 0.4 with the negative lead on the cathode, and 1.5 when reversed.
Those don't seem right, but perhaps that is because it is in circuit?
Thank you!

[CapLeaker]

Probably that top248yn is just playing dead. Very common for these TOP, LNK, TYN etc to do that. Very troublesome devices those suckers. Btw if you replace it, make sure that the area is hospital grade clean, otherwise you may have to replace it again a short while after. Just my Canadian 5 cents. Gotta count for inflation…
how much DCV are you getting on that big main filter cap?

[CMCM]

Hey CapLeaker,
I was suspicious of the TOP248YN despite it looking immaculate. Can you tell me how to test it if i remove it?
Also the cap that R_J suggested i look at tested with some crazy value 1346nf when it is supposed to be 4.7uf/50v.
Still don't understand the strange reading on the diodes i mentioned previously.
Would really like to round up all the suspects before placing and order with digikey. So sad that there are no longer any local stores to pick up parts as needed.
Thank you!

[R_J]

If C18 is bad, as in open, the top248 will start and shut down repeatedly, this cap is meant to maintain the ic's vcc voltage, D7 is a tvs diode and might check open circuit, D5 should check as a regular diode, remove one end of these diodes to check them out of circuit, if one is shorted it could cause this problem as the primary of the transformer is not being switched
D4 might be the problem as it should not check 1.5 in reverse, remove one end and check it again. D3 should check the same as D4 (obviously D4 is installed for negative voltage)
The clicking sound is usually caused by the ic driving the transformer and shutting down due to a short in the output somewhere.

[CapLeaker]

If you get questionable component readings in circuit, either lift a leg or take the component out and re check it.

[Agent24]

Remove and test out of circuit the three small capacitors C18, C16, C8
Though C18 is the most likely to cause this issue, the others might too.

D2 could also be suspect, it maybe shorted/leaky.

Another fairly likely cause is the TOP248YN, I've seen a lot of these little integrated "offline" SMPS controllers fail, in various ways, and power-cycling is one of them.

[CMCM]

Pulled just about everything off the board to test out of circuit.
Turns out that it was none of the above.
It was the diode at D7, a P6KE200 testing as a 15.6 ohm resistor instead of a diode.
Thanks everybody.

[lotas]

It was the diode at D7, a P6KE200 testing as a 15.6 ohm resistor instead of a diode.
Thanks everybody.

P6KE200 - This is not a diode, it is a surge voltage suppressor (TVS)

[CMCM]

P6KE200 - This is not a diode, it is a surge voltage suppressor (TVS)

Hmmm, so you think it might be OK even though it tests as a resistor?
All i have is one of those basic TC1 testers (picture attached).
Do you know how I could test it properly?
Thank you.

[Agent24]

No, a TVS diode should not read as 15 ohms. It is effectively shorted.

The P6KE200 has a breakdown voltage of 200 volts. You would need a current-limited supply with over 200 volts to test one.

[CapLeaker]

Depending on what TVS, directional or bi-directional it should read either as a diode or totally open with your DMM on diode mode. Component testers don’t do TVS.

[CMCM]

Success! Replaced the P6KE200, the TOP248YN, and three small capacitors that had high ear ratings and it now alive and kicking,
thank everybody!

[CapLeaker]

Sweet little repair!

[CMCM]

Thank CapLeaker.
of course I ment high ESR not high EAR. Lol