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My Philips DCM 378 12 mini HiFi system stopped functioning some time ago. I remember it popped when I plugged it in. I thought it was a fuse, but when I opened up the unit, I didn't like what I saw, and I'm not a specialist.

Here are some images of the power board. There seem to be some leaks of brownish fluid everywhere. There were signs of burns on the other side of the board (I guess that was the pop sound I heard.)

enter image description here

enter image description here

I have two questions:

  1. Can this board be repaired? Can it be done by a novice?
  2. Is there some place where replacement boards like this can be ordered?
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    \$\begingroup\$ Source another supply - what were the output specs? \$\endgroup\$
    – Solar Mike
    Dec 30, 2022 at 12:09
  • \$\begingroup\$ Yes, no and, yes are the answers but, the 1st yes may be uneconomical. The last yes is a best guess. However, questions like this are usually deemed off-topic: Questions seeking recommendations for specific products or places to purchase them are off-topic as they are rarely useful to others and quickly obsolete. <-- site rule. Your question may also be off topic based on this: Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired \$\endgroup\$
    – Andy aka
    Dec 30, 2022 at 12:15
  • \$\begingroup\$ @Andyaka: Sorry if this question is not appropriate. I understand your points. I'll try finding a new power supply. \$\endgroup\$
    – Beni Bogosel
    Dec 30, 2022 at 12:18
  • \$\begingroup\$ @SolarMike: As seen in the photo, there are two outputs: 32V and 5.6V on the 4 pin side and 5V on the two pin side (this is for an Iphone dock). The unit has 2x80W amplifiers. \$\endgroup\$
    – Beni Bogosel
    Dec 30, 2022 at 12:20

2 Answers 2

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This stuff is probably not a problem:

enter image description here

That is most likely a sort of glue used to keep the parts from moving around.

This stuff probably is a problem, though not the cause:

enter image description here

Those resistors appear to have burned. If so, they are no longer OK. They are not, however, the cause of the problem. Something else went bad and caused too much current to flow through the resistors. That something else is the cause - and it may be something you can't see just by looking.

It can probably be repaired. Whether a novice could do it or not is a toss-up. Maybe, maybe not. It depends on how much time and effort you can spend on it. It also depends on how careful you are. That circuit works with the AC line voltage - making live measurements would be dangerous.

Philips probably sold a replacement at some time. Whether they still do is something you'll have to discover on your own.

There's a service manual available here.

These are the burned resistors:

enter image description here

Most likely, Q2 has failed short (it is short circuited inside.) It may have simply failed, or the driving circuitry may have failed.

You'd have to check and replace Q2, maybe also Q1 and Q3. You'll also need to replace those burned resistors. You might also have to check transformer T1 - if it is shot then you'll probably have to give up because it will be custom made. There's a fuse where the AC power connects to the board. It should have blown when the resistors burned out - that's probably the pop you heard. You'll need to replace it.

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  • \$\begingroup\$ Thank you very much for the detailed answer. I will see what can be done :) \$\endgroup\$
    – Beni Bogosel
    Dec 30, 2022 at 13:27
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The board can be repaired, but that depends on how much you know and how skilled you are. Even a novice can do it with sufficient amount of skill and knowledge. The burned parts are small value resistors used for current sensing through the main transistor and transformer primary. I have the complete schematic screenshot below. (Before I was even done with my answer, @JRE got it mostly answered for you. I will still add what needs to be added, without repeating the resources he kindly provided for you.) The parts pointed at with red arrows are definitely burned out. The orange ones are very likely to have burned out as well. You would also need to check other components in the primary, like the input diode bridge (BD1), the fuse (F1) and the thermistor (TR1). Q1 and Q3 could be bad too. I also suspect that the LD7575 might be bad, unfortunately that is harder to verify. I actually have a board with the same IC which I suspect is bad. The safest way to try the power supply after you have replaced all the bad components is to use an incandescent light bulb in series with the power line (make sure you insulate it properly so that you don't touch live wires!). The main transistor (Q2) model is not specified, you could use the same one you find on that board or you could use almost any TO-220 power MOSFET rated for 10A and 600-650V. If you know how to read schematics and test the components, you should be able to do it.

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  • \$\begingroup\$ Thank you very much for the detailed answer and for suggesting which parts are faulty. I will see what I can do :) \$\endgroup\$
    – Beni Bogosel
    Dec 30, 2022 at 15:04

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