820-01700 No Power, 5v rail missing

[Powerup]

I have an a2141 missing pp5v_g3s. 5v on ammeter and 1.6 amps. one port occasionally will negotiate 20v but still no power. I am stuck

[mon2]

Re: 820-01700 No Power, 5v rail missing

What is the history of this unit ? Liquid damage ?

pp5v_g3s is generated by U7650.

Remove all power (no adapter / no battery).

Meter in resistance mode (2k scale is ok).

Check the resistance to ground of pp5v_g3s (L7600 pin #1 or #2 - red meter lead; black to shield ground).

What is the resistance reading ? If it is low, then you may have a bad cap on this leg of the power rail. If not a low resistance, need to check if U7650 is being enabled.

Check the voltage of U7650, pin # 4 (P5VG3S_EN_R)

[Powerup]

Re: 820-01700 No Power, 5v rail missing

history:
cx came in with a no power device. claimed it was left in subzero temps overnight in a motorhome. When he retrieved it in the morning, He dropped it in the snow. device presented with minimal corrosion, only visible corrosion was on C6455, PPBUS_G3h_SPKRAMPL. I tested the resistance to ground after cleaning and it was in the milliohms.

[Powerup]

Re: 820-01700 No Power, 5v rail missing

checking voltages now as resistance is in the milliohms. thanks for the tips, Ill post back if lost. I'm also going to pull that one corroded cap as my g3h voltage is 12.3 not 12.6. not sure it is enough but im ruling out a parital short

[Powerup]

Re: 820-01700 No Power, 5v rail missing

enable voltage is missing.

[Powerup]

Re: 820-01700 No Power, 5v rail missing

Am i looking at a U7800 issue here?

[mon2]

Re: 820-01700 No Power, 5v rail missing

Check for the voltage @ R7691, pin #1.

See attached.

[Powerup]

Re: 820-01700 No Power, 5v rail missing

Well something has changed, my ammeter is now looping at im getting pulses of 3.3v at pin 1

[mon2]

Re: 820-01700 No Power, 5v rail missing

But you do not see this pulsing @ R7691, pin #2 ?

If not, remove R7691 and apply a solder blob to short pin #1 & #2 pads for this device. It is only a 0 ohm resistor - acting much like a fuse.

Perhaps corrosion ate away on this part.

[Powerup]

Re: 820-01700 No Power, 5v rail missing

UB000 and I assume the cd3217 on the underside are now heating up.

[Powerup]

Re: 820-01700 No Power, 5v rail missing

I see the same pulsing on both sides of r7691

[mon2]

Re: 820-01700 No Power, 5v rail missing

Too hot to touch or just warm ? The ACE controller(s) may be defective. Need to check the voltage of each LDO rail on each such controller.

[Powerup]

Re: 820-01700 No Power, 5v rail missing

hot to the touch. I will look into it. So check im getting the 3v3 and 1v5 LDO rails on each CD3217?

[mon2]

Re: 820-01700 No Power, 5v rail missing

There are a number of power rails including 1v1 for the BMC communication interface (CCx).

Check each.

Louis also suggests to check each rail with no voltage but meter in diode mode. Red meter lead to ground; black meter lead to the pin to test.

Post the readings. His forum has known good diode values for the CD3215 devices.

Hot to touch often means a defective CD3215 / CD3217.