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View Full Version : Peter Chou Power Supply F10214288



immortal
3rd April 2009, 02:16 PM
This power supply is out of my Mortal Kombat 1 LAI Cabinet.

Problem:

+5 and +12 are ok but -5 was reading 2.36 with or without load on power supply

Repairs

2 Diodes D12 and D13 and replaced 4 rail caps

Found this problem last night when playing MK2. Sound would start getting static and fading away and coming back. Checked power supply and found that -5 was very low causing my sound issue.

Having a look inside the power supply look like some of the rail caps where a bit old . Removed 2 1000uf and 2 3300uf and found all 4 to be a very low so i replaced all 4 with new ones no change.

Traced the -5 rail back L1 coil which goes into 2 PR1504 diodes. Removed these 2 diodes which showed the fault. One was open and the other was reading both ways. Replaced these with 2 i had spare out of a damaged power supply repaired the power supply.

David_AVD
3rd April 2009, 02:39 PM
Just a quick note on replacing caps in switchmode power supplies; make sure you use "Low ESR" types. These are often brown (or black) in colour instead of the usual blue. Using "regular" type capacitors in switchmode supplies can lead to premature failure.

immortal
3rd April 2009, 02:41 PM
Hey Dave_AVD

All ready done mate. I always use low ESR ones in power supplies :)

cwispy
3rd April 2009, 09:55 PM
These are often brown (or black) in colour instead of the usual blue.

Not really an accurate statement. Yes you should use low Z caps, but I have plenty of esr caps of almost every colour, blue, black, brown, gold, white etc. The codes on the side of the caps will actually tell you what they are if you know the manufacturers production codes though.

David_AVD
3rd April 2009, 10:48 PM
True, don't want to be called a colourist! What I was getting at is that the ones you buy at Altronics, DSE & Jaycar are often blue. (and only 85 degree, instead of the more rugged 105 degree type)

There's even more to than that when you get into the nitty gritties. Some switching regulators need very specific capacitors. Too low an ESR value is just as bad as too high and leads to instability. It's no wonder there are so many shit design power supplies out there!