820-2936 fan spins then stops 3 second loop

[Jimmy Spangle]

This one has got me a little. Just bought this board yesterday (for pennies). I have not come avcross this before. Green light, fan spins for a moment (few turns) then stops, 3 seconds or so later repeats in an endless loop.

So far:
PPBUS_G3H is 12.58v
PPBUS_S5_HS_COMPUTING_ISNS is 12.55v
PPBUS_S5_HS-OTHER_ISNS is 12.58v
PPDCIN_G3H is 18.50v
PP3V42_G3H is 3.48v
PPVRTC_G3H is 3.48v
PP5V_S5 is 4.92v
PP5V_SUS is 4.41v

Replaced U7200 and all joints look like a work of art they are that nice. Pin 6 is 0.771v. Pin 1 is 0.00v

Any ideas guys?

 

[2informaticos]

If fan spins, at least 3/5V present at that moment.
Usually all the coils pulse too (maybe not CPU).
So check for pulse on the secondary coils.
Also check if ALL_SYS_PWRGD pulses too...

 

[JohnB8812]

History liquid drop etc?

 

[Jimmy Spangle]

Yes, it pulses. For example at L7220 you get a quick burst that is around 3.3, but it is so quick I cannot tell anything without an oscilloscope. If I keep the meter probe on L7220 nothing happens again until I remove the probe.

History? None that I have been told. It has unfortunately been worked on before and ultrsonic cleaned before I got it. Frankly, I would rather have it withy all the crap still on as that always gives clues at lest.

It is effectively trying to start, sensing something wrong and shutting straight off, then sensing it is all fine and looping.

I am going to check Q7221 again tomorrow. I am unwell and can only do som much in a day. From memory, Pin 2 had 4.94v and pin 1 had nothing, but if you check at the right moment you get a spike of 3v or so and if you keep the meter on there it does nothing until released. Same with pin 1 of U7200 as it turns out. My guess is that Q7221 is OK.

Never come across this before. Had plenty that sort of work, don't work, dead etc. But this is irritating although rewardig if solved I am sure.

 

[2informaticos]

"Usually all the coils pulse too (maybe not CPU).
So check for pulse on the secondary coils.
Also check if ALL_SYS_PWRGD pulses too..."
No response yet...

Check for pulse on ALL secondary coils!

 

[Jimmy Spangle]

Ok. here is the update:

L7030 is 12.58v constant
L7630 pulse
L7100 pulse
L7260 pulse
L5801 pulse
L7220 constant 3.3v
L7330 pulse
L7550 no pulse
L7510 no pulse
L7520 no pulse
L3895 hard to tell without oscilloscope. multimeter from 35mv to 13mv and back to 35mv loop

ALL_SYS-PWRGD pulse

Q7221:
Pin 1 is 0v
Pin 2 is 3.458v
Pin 3 is 0.742v
Pin 4 is 0v
Pin 5 is 0v
Pin 6 was 0.887v for a few moments then 0v now.

 

[Jimmy Spangle]

Anyone got any ideas?

 

[2informaticos]

Check traces and resistors around SPI chip.
See if U7400 gets power and enable.
Also check if R7402 is OK.

 

[Jimmy Spangle]

I will check first thing tomorrow. I am ready to win either with logic solving or a large 4lb hammer now

 

[Jimmy Spangle]

R7402 is 91k (in circuit)

74000:
Pin 40 3v or so pulse
Pin15 3v or so pulse
Pin 1 3v or so pulse

Seems everything on this board is pulsing.

 

[2informaticos]

Any drop pulse at pin2?

Check what I told you about SPI chip...

 

[Jimmy Spangle]

I did check all traces and all resistors around SPI chip

drop pulse at pin 2

 

[2informaticos]

Could be everything, like CPU, crap underneath, PCH, or just a corroded resistor/trace.
No pulse of any CPU coil?

You can try BIOS now.

 

[Jimmy Spangle]

Thanks for all YOUR help. I note that nobody else offered any at all, so I appreciate your efforts.

I am calling it a day with this old board.

 

[Paul Daniels]

You got PPVRTC_G3H in multiple locations across the board? As opposed to just off the chip (U2800) itself?