Power supply blown on Zeppelin air speaker

[Nodw]

I am trying to fix a fault on my Zeppelin air power supply which has blown a fuse and visibly a couple of components, namely one of the mosfets (T3), and an R500 resistor (R31).
initially I was just going to replace the fuse, resisitor, and both the mosfets T2 and T3 and see what happens but I see from some previous postings a few years back that the a driver should also be replaced but I am not sure which component this is. There is also some suggestions that the triac should be removed as it appears that this could be the route cause of failure on this particular board. Again I am unsure which component this is and if it is ok to just remove this component without affecting anything else on the circuit. I will only be using this speaker on 240V so I am assuming that removing the triac it will just run on this voltage. Can anyone provide any guidance on the best action to take to provide a permanent solution to fix this power supply.
It would also be very useful if anyone can advise where I can get hold of these components at a reasonable cost, I see that there are some Chinese suppliers advertising on Ebay but I am very wary that there may be additional handling and import duties attached, does anyone have any experience purchasing parts from China via ebay?

 

[BradtheRad]

Generally a triac is used in an AC power supply, turning it on for a portion of the cycle. The effect is to reduce voltage or current to components.
Often it reduces house voltage to a lesser value. To remove it is risky. Can you tell which circuitry the triac is in, whether it's 240 VAC?

Your safest solution might be to disconnect the internal power supply, and hook up an external supply.

 

[Nodw]

Hi, thank you for the reply, here is a link to the circuit diagram which someone posted in a previous thread which may answer your question on which part of the circuit the triac is in.
**broken link removed**
I would not know where to start with an external power supply as the board has two connectors coming of it with 3 and 6 wires respectively

 

[BradtheRad]

Okay, here is the complete link. 6-page thread.

www.abcelectronique.com/forum/showthread.php?t=92915

Someone posted hand-drawn schematics of the power supply (smps, looks like a flyback). Apparently provides positive and negative DC rails.

It's hard to tell where regulation is done, whether via the triac, or elsewhere.

board has two connectors coming of it with 3 and 6 wires respectively

A few posts mention voltage around 16-18V. Maybe there's another supply 5v to controller circuitry on another board (wireless, input select, tone control, etc.)?

The 3 wires are probably one bipolar supply (positive, negative, ground).
The 6 wires are a tough one to figure out.

Can you find printing on the board which indicates volt levels? One guide is the volt rating on capacitors. The 16V wires may only be needed at the output stage. Before it's fixed you need to make sure the output devices are not faulty. Sustained loud volume is a prime cause for a fuse to blow, due to overmuch current going through output devices.

 

[Nodw]

Cannot see any printing on the board that relates to voltage levels, the caps have various voltages from 10 to275v,
was there a particular one I should look at?
when you say output devices are you referring to the speakers, if so how can these be tested?

 

[BradtheRad]

If you wish you can replace the visibly burned components in the power supply, and it might make the unit work.

We can assume those components burned prior to the fuse blowing. It's possible they were the root cause, nevertheless it's equally likely they failed because of a component elsewhere. Not necessarily a short circuit, but something bad happened yet it didn't blow a fuse right away. That may be a clue of some sort. Any unusual event at the moment of failure is a clue.

when you say output devices are you referring to the speakers, if so how can these be tested?

I meant a transistor array or IC which drives each channel.
Good quality hi-fi usually has tweeter, woofer, sometimes midrange. Therefore several output devices.

It could all be contained in a module to serve all the speakers. Look for a block of metal with fins exposed to carry away heat.

Is there a chance the output module was overdriven? Not that I know anything. In fact there's nothing wrong with going ahead with what you intended to do, since it's a few inexpensive components. It may be sufficient, although more diagnostic testing is wise before you apply full voltage to the unit. Such tests require knowledge of the circuitry, points to connect power, points to feed audio, etc.

As for buying from Ebay, sellers in your own country often offer free shipping on small items. (Can we bargain hunters resist even if it's a depot distributing Chinese products?) To play it safe, bid only to sellers who have better than 96 percent positive feedback.

 

[BradtheRad]

caps have various voltages from 10 to 275v

Then at least one power supply is less than 10V.

275 may be a working voltage rather than an absolute peak value. Notice that 240 VAC house voltage is a sinewave with peaks at 340V. It raises concerns about the results if you remove the triac.

This power supply may be light and compact (those are popular features in smps type), however it's not designed to be user serviceable. Consumer electronics appear designed for short lifespan nowadays. Not so long ago a power supply just needed a transformer, diodes and capacitors.

the board has two connectors coming of it with 3 and 6 wires respectively

There are power modules (available via Ebay or your favorite mail order house) which could be spliced onto the bundle of 3 wires and 6 wires. First you must determine which wire carries which voltage. Then you'll know which power supplies suits your purpose.
Tentatively one is +16V -16V bipolar.
And I believe the schematic has labels +5 -5V bipolar.

 

[Nodw]

Thanks Brad, unfortunately i do not have the necessary skills or equipment to investigate the circuitry or establish the voltages and specification of an external supply so will buy the components indicated and give it a go and hope there are no bangs. Although these components are inexpensive in bulk when your buying one or 2 they are a lot more expensive approx £18 for the visibly blown parts hence the question about Chinese supply.
Anyway thank you for all your help, stay safe and well, thanks Gordon