Sonance DSP 8-130 schematic

[ubxf]

Hello,
i just got one of those amps but it won't power up. I called the company for support but they don't repair or have the schematic .
It has 8 Hypex UCD250LP so it should be pretty good. My repair skills are quite basic and i'm more comfortable around tube gear , this
is definitely over my head.
I opened it up and looked at the power supply and didn't see any obvious burned component, the fuse is ok, is there anything else to look for.

 

[Khron]

Mains input fuse? NTC? Any smaller transformers in addition to the main one, in case the power supply is a switchmode one?

 

[ubxf]

Thanks, the main fuse is ok, when i apply power no current is being drawn

 

[Khron]

Those symptoms would lead me to believe that the standby supply may very well not be working. I see the small capacitors are of the "wonderful" JH brand (some nearly random chinese crap, wouldn't trust them as far as i could throw them), so the first step i'd take is investigating that area (C950 & co. on the primary side, and C955 and its neighbour, on the secondary.

And/or the PWM controller of the standby supply itself, the 7-pin hidden behind U906 in the second picture. What part number IS U906, by the way?

 

[ubxf]

Thanks Khron, i'll investigate according to your suggestions. Here is a picture unfortunately not great of U906. I'll get a better one later today

 

[ubxf]

U906 is a KA78R12

 

[ubxf]

So i changed the the JH electrolytics (955,954,950,949,927,920,926and the 2 10uf 400v) and the 7pin THY287PG that is behind U906 and unfortunately the situation is the same. If you have any other suggestions could you please let me know and i would be happy to give it a shot.

 

[Khron]

Is D921 ok?

 

[ubxf]

D921 IN5822 is ok (was ok but i put a new one in just in case)
still no change unfortunately. When i power up i reconnect everything to provide a load then i bring it up slowly on a variac and monitor the voltage and current. Would it be better to try the power supply by itself?

 

[Khron]

It can't hurt. Not sure winding the voltage up slowly is the best idea for switchmode supplies though; a series-bulb tester might be more useful.

Did you at least wind it up to full mains voltage? And is everything else on the primary side ok? Fuse, common-mode chokes, varistors, bridge rectifier?

 

[ubxf]

Yes a bulb tester would be better, i brought it to full mains voltage. Everything seems ok on the primary. Now it powers up but it is in a weird cycle loop, the relay keep clicking every 3 or 4 sec and the lights flash (that is with everything connected)

 

[Khron]

Can you connect the power to each of the 8(?) amplifier modules individually? Might be worth trying one at a time, to begin with.

 

[ubxf]

i was about to dismantle everything so i could test each amp by themselves but i noticed that the power supply is only good on +55V the minus 55V side is giving 0.7V .
btw i finished recapping and the supply is not cycling anymore.

 

[izackary]

Hey OP, I thought I'd try and see if you found success repairing this amp. Thanks!

 

[ubxf]

No unfortunately i couldn't but all the amps are ok by themselves . The power supply is still not working correctly.

 

[izackary]

Sorry to hear. Sadly there seem to be very very few on the internet who are repairing and posting about it anywhere. :/