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820-01958 A2179 no power

J

jadao

Member
This board came with no liquid damage. It was stuck at 5V. Noticed a short on the PP1V1_S3 it was coming right from U2300 ddr chip.
When I removed the shorted chip the short was gone, I had to replace both of them as it was Micron 8GB ddr and I had only Hynix 8GB ddr known working donnour.

I did the replacement and adapted the strap resistor accordingly with Hynix set up, so I added RAMCFG0_L (R1490) and RAMCFG1_L (R1491).
Board is now charging and negotiating 20V. but it is stuck at 100mA and I noticed PP3V3_S5 is missing bu not shorted (0.320 diode mode).

PP3V3_G3H, PP5V_G3S, PP3V3_G3H_RTC are present.
All voltage on coils at u7800 are present except L7821 L7822 L7820 an L7819.

Is there something to check before blaming U7800?

Thanks!
 
J

jadao

Member
I just checked and compared. Diode mode on L7819 and L7820 is 0.474 and 0.457 on L7821 and L7822.
Values compare perfectly with good board :unsure:
 
J

jadao

Member
On the working donnour board, even without the 2 ddr chips I notice voltage on L7819-20-21-22. PP3V3_S5 of course present.

On the faulty board, I have the idea to replace U7800 because it outputs PP3V3_S5 but I don’t have a strong reason to assume it is faulty. As it maybe just need to satisfy some conditions to output PP3V3_S5. If no other suggestion I can just replace it and see from there.
 
2informaticos

2informaticos

Administrator
Staff member
Did you test removing R1490/1.
1 1 straps means high level on both.
Adding mentioned resistors, you've pulled them down to 0V.
 
J

jadao

Member
Yes i tried removing them but nothing change.
With original shorted chips 8GB Micron, straps conf are1 1 so R1490 and R1491 were no stuff on the board.
With Hynix chip 8GB, strap conf for CFG1 CFG0 according to the chart in page 3 of schematic are 0 0, witch means to me signal low asserted so I added mentionned resistors to pull signals down to 0V.
 
2informaticos

2informaticos

Administrator
Staff member
Ah OK, original was Micron.

The RAM chip got burnt because an overvoltage.
That probably damaged CPU also...
 
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