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Power supply problem

Alchad

Jul 29, 2017
15
Joined
Jul 29, 2017
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15
Update - just couldnt read the numbers on most of the devices. Have ordered some replacement capacitors and when I take off the big one should be able to read them.

Will update then.

Regards

Alan C
 

Alchad

Jul 29, 2017
15
Joined
Jul 29, 2017
Messages
15
Hi,

Replacement capacitors have arrived and I've replaced the large one and the medium size one that was looking a bit dodgy on the top. Hasn't made any difference!

I've been swapping the good and bad DAC unit around just to confirm the problem:-

The good DAC unit allows the motherboard CPU fan to spin by shorting out the relevant switch pin connection. ALSO, when connecting the test bulb to the power supply from the DAC unit to the motherboard I get a strong light with NO flashing.

Swapping over to the faulty DAC, the CPU fan will not spin and checking the power supply with the bulb I get a pulsing light, almost on/off .

I'm getting convinced that somehow the DAC board is passing through some AC voltage to the motherboard - presumably indicating failure in some of the votage regulation side of the DAC ??

Re the 5 devices connected to the heatsink, 4 appear identical
CQ526 MBR 2045CTG

the fith, could be M50PO3HDLG CQ550 - very difficult to read?

Any thougths?

Regards

Alan C
 
Last edited:

kellys_eye

Jun 25, 2010
6,514
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Jun 25, 2010
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6,514
Clearly some form of current limiting is being implemented and since the CPU etc works normally when powered from the good board then the 'bad' board itself has an issue.

You need to identify the on board current limiting circuitry - I think I can see a sense resistor in the 12V line but cannot see anything else due to lack of detail.

Post some close up hi-res pictures of the board (both sides). We need to find the control electronics in order to point to areas where test measurements can be made.
 

kellys_eye

Jun 25, 2010
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R37 is the current detection resistor - what is the device number of the 8-pin chip below it?
 

kellys_eye

Jun 25, 2010
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Hmmm, not a device I can readily identify... looks like a 10-pin device too???

Any chance of a clearer close up? Even 'blown up' the image is blurry.
 
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