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Re: MC1 Switched Power Supply
Hi Hansjo. You may find that if one capacitor has failed, then there may be more. If you see any signs of bulging, leaking, or pushing the bottom out of any caps, then It is a good idea to just change them all. For the small expense, it is worthwhile knowing that your power supply has fresh caps. Try the amp and then see how it goes. If you still have problems, get back to me here and we can talk about it more.
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Fuses blow when there's an overload. This is most likely caused by a semiconductor device(s) shorted. In amps this is often cuased by speaker wires that have touched while on power. The main culprits are the devices on the heat sink. If they are transistors then connecting an Ohm Meter accros the terminals of the transistor(s) (amp switched off) will show as if you have touched the test probes together! More than one device might have blown!!
Replace the power supply capacitors and most of the electrolytic caps at the power amp
These are fairly cheap at mouser or digikey
Also resolder any areas associated with the power supply and the power amp
Does the unit work ok with headphones?
I think ,with the issues youve stated , that it's actually some solder joints that make a connection AFTER the amp has heated up a bit.
The issue could also be a Large power supply capacitor that is starting to fail.
You have an overload in either the power supply section or Main amp section. Culprits in the power supply are the transformer, the Large Capacitors, rectifier, voltage regulator.
In the Main amp anything on the heat sink.
Look carefully for burnt or damaged parts. If there's more than one fuse, follow the path of the one that is blowing it might lead you to the suspect.
Identify the main area on the pc board, and look around for a odd shaped Electrolytic capacitor. It might even have odd printed board number IE: mc500, not c500, for example.
If you find one it could be a Memory Retention Capacitor. They often have a low value 0.22uf and low voltage 5.6 for instance. It could have failed and so not supply the chip that stores the information, with power when switched off.
I can't say it will have one, but it's worth a try. They are in the Maplin catalogue for under £5!
You have an overload in the power supply or audio output stages. Look around sometimes a part may be burnt, have a hole in it etc... In the power supply it could be a diode, the large Elec Caps, Bridge Rectifier, Voltage Regulator. In the Audio Output, one or more large transistors, on the heatsink, or an IC if it uses one.
The desk itself is discontinued, however if you have a ring round the Behringer dealers for your area, they might have stock, or be able to obtain a spare power supply for the desk. Failing that, you're in the second hand area, so a popular online auction site, or google for people selling one. Unless they have a broken desk though, you might find that they only come together with the desk.
With out make and model, I can not supply parts information. Please update this with that info. Also, depending upon the age of the unit, parts may not be available. Are you sure that the problem is the transformer? This part is rare to fail.