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Hoping to get some help with this tricky problem.

I’m trying to repair a Wharfedale powercube SPC 12. The fault is that it just doesn’t power up.

I can’t seem to find a service manual or schematic.

The fault appears to be with a circuit intended to shut the PSU down if there is any DC detected at the amplifier outputs.

On the amplifier board there is a high pass filter and 3 transistors which it appears should pull the “dc_ps” line low if any DC I present on the output.

Between this line and the +15v line on the PSU PCB there’s an optocoupler, on the other (mains) side of the optocoupler seems to be where the issue lies.

Even though the optocoupler isn’t on (I have even tried lifting it to see if it was leaking) the circuitry (a set of smd transistors, diodes, and zeners which are proving difficult to trace out) seems to be pulling what measures as a 5v5 zener diode – it’s surface mount and lacks any markings – low which in turn pulls the vcc line low on the power supply driver IC. The driver (ir2153d) needs enough current to pull it’s internal zener all the way to 15v5 to operate.

If I lift this 5v5 zener, the PSU and amplifier seem to work just fine. There’s no DC on the output, just a small 500kHz signal as expected for a D class amp. Rails measure ok too.

I guess I’m hoping someone has had experience repairing this problem or can at least point me to a schematic/service manual. My searching has turned up nothing. I’m not sure how forthcoming Wharfedale are with service manuals so I haven’t gone that route yet.

Happy to provide any details / probing as needed. If I need to I could trace that circuit out but it will be tricky it’s a 2 sided PCB and the layout is a bit all over the place.

The diodes and transistors all seem to test ok, at least using diode mode on my meter (in circuit) but the fault must be here somewhere surely…

Thanks in advance!