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820-3476 Board gets warm, no fan spinning, not booting up, Corrosion around U7501

S

SamMac

New member
Hey another A1502 board for repair.

The board came in with not booting up and saw corrosion around U7501 with Pin 12 without a track which I made a jumper to pin 1 of R8140 and also replaced U7501. Unfortunately it hasn't made any changes and I also didn't take a complete list of the voltages I was getting before attempting the repair so I've only got the measurements after the repairs.

The CPU is getting warm and I've check all the traces and rails but don't see anything else wrong with the board. Hopefully someone can advise what I could check on next.

PPBUS_G3H1.150V
PPDCIN_G3H16.92V
PP3V42_G3H3.39V
PPVRTC_G3J3.39V
PP5V_S50V
PP5V_S40V
PP5V_S00V
PP3V3_S00.565V
PP3V3_S30V
PP3V3_S51.686V
 
2informaticos

2informaticos

Administrator
Staff member
Post resistance to ground on all these rails:
PPBUS_G3H, PP5V_S5, PP3V3_S5.
Check allso if you have short between PPBUS_G3H and any big coil from secondary supplies...
 
D

dukefawks

Administrator
This does not sound good! PPBUS is low and CPU is getting warm. I suspect PPBUS is shorted to some secondary rail. Probably RIP.
 
S

SamMac

New member
PPBUS_G3H is 60Ohms
PP5V_S5 constantly going up towards infinity.
PP3V3_S5 around 0.483 KOhms

Short can only be seen when put between PPBUS_G3H and L7130
 
2informaticos

2informaticos

Administrator
Staff member
L7130 is on PPBUS_G3H line; check with other coils...
Any other big coil shows 50-60 ohms to ground?

Remove F7140 and see where the low value remains.
 
S

SamMac

New member
okay somehow I find that L7520 is actually showing short with PPBUS_G3H aswell.

ANd no some coils are showing 80 Ohms and some are showing way above that L7520 is showing around 2-5 Ohms.

I'll double check the situation with the fuse tomorrow.

Appreciate any help, thanks.
 
S

SamMac

New member
Pin 6/7/8 is showing short even with the IC taken off

EDIT: above mesaurements with regards to Q7520
 
S

SamMac

New member
trying to check every component on the lines but removing the capacitors still showing the P5VS4 rail as short.

Any component in particular do you reckon i should check out?
 
S

SamMac

New member
Checked if U7501 is shorting the rail, but that seems like its shorting it even with that chip removed.

Removing F7140 I can see that Pin 2 is showing the 60Ohms (low resistance value)
 
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J

JohnB8812

New member
That seems like a short on pin 2 of PPBUS...inject voltage to see what heats up. Start low at 1 volt in case it's the CPU.
 
2informaticos

2informaticos

Administrator
Staff member
So you have 60 ohms at PPBUS_G3H?
Any secondary power rail (big coils) with same value?
If only L7520, then remove U7501 and check again.
Do NOT power up the board without U7501...
 
S

SamMac

New member
without U7501 attached PPBUS_G3H is still showing 60 Ohms

Every other coil is showing the same or similar resistances when put against PPBUS_G3H

With Q7520 also removed it doesn't show any significant changes and no coils showing the same resistances as PPBUS_G3H (which is showing 35Ohms)
 
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