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820-3437 no fanspin

arnonabuurs

arnonabuurs

New member
Hi guys I have a 820-3437 that came in working, but occasionally it would reboot itself. A quick check with the microscope revealed corrosion on one of the pins of U7501 was corroded/burned (5v in). After removing the IC and scratch the dirt away I was able to fix the line as it was still there under the crap. Replaced the IC and now I got 3.3v on L7560 and 1.1v on L7520. It seems to powercycle, goes to 0v and then back to 1.1v stays there for a while and cycles again. Tried another IC same issie. Just because it looked crap, replaced Q7520 as well but still only get 1.1v on 5v line, seems something is pulling it down but if I check for short to ground I do not get a beep. I get 0.407 resistance to ground on both pins of L7520, any ideas?
 
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dukefawks

Administrator
If there is 3V on R7551 the 5V output should be switched on. Issue is certainly around U7501 then. Check for soldering and broken traces pin 23 is infamous. Could be you killed the chip too of course.
 
arnonabuurs

arnonabuurs

New member
I have replacedd the IC with a new one but the result is the same. No short on any of the rail going to it accept P5V_S4RS3_FUNC. What does this do? I got 0v on this line. Rest seems OK, 5V going into the IC and EN signal is 3.3.

R7549 = 0 ohm
 
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dukefawks

Administrator
P5V_S4RS3_FUNC is tied to GND, so that is fine.

Did you check the trace to pin 23, what voltage is there? Diode mode on pin 3 and 5 of Q7520? This must be a bad trace or bad FET, must be simple.
 
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