[sdiy] Korg DW-8000 power supply help?

[Graham Atkins]

Hold on, we were talking linear power supplies just, not switched mode.

Graham

On 3 Nov 2010, at 20:06, Mike Pepper wrote:

>> I'm trying to troubleshoot a failed Korg DW-8000 power supply.
> Disconnected from any load it pops fuses as soon as it's powered up. I
> started with the bridge rectifier, it's fine; while it was removed I  
> checked
> the xformer, it's fine. There doesn't appear to be anything  
> irregular (trace
> damage, burns, blown bits, etc.) on the board.
>>
>> Do you guys have any techniques you can share for where I might  
>> start with
> this thing, since I can't power it up at all? It's not like there's  
> just one
> rail down and I can fire up the rest of it to test.
>>
>> And yes, I realize I'm dealing with potentially lethal voltages and I
> won't hold any of you accountable if I screw up my own handiwork.
>>
>
> I'd more likely supect a blown chopper transistor on the primary. At  
> least
> if the fuse is blowing, the ground resistor in the chopper is  
> probably OK,
> (choppers can be bipolar or MOSFET, and often have a current sensing
> resistor in the 'ground side' lead).
>
> Remember to put some kind of dummy load(s) on the output, a lot of  
> switch
> modes don't like working into an open circuit.
>
> The Old TV engineer's trick of putting a standard light bulb in  
> series with
> the mains live can save a lot of blown parts. If the bulb lights up,  
> you
> still have a short, if it just blinks, and the supply fires up, you  
> can
> remove it. I still somewhere have a box with a bulb holder, mains  
> lead and
> socket, big bright 'Power On' neons and a bypass switch. Harry is  
> right
> about shorted electrolytics. Prime suspect is the big high voltage  
> one in
> the primary circuit. Make yourself a discharger resistor, or solder  
> some
> on - those caps can stay charged for hours, and deliver a nasty bite  
> if you
> touch them.
>
> ||\/||ike
>
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