820-00165 Only power when U7090 gets some heat

[No-Clean]

Clean board has come in 2 times, U7100 was replaced and worked for about 2 weeks, back again and no power, but when I apply some heat to U7090 board turns on, I know that looks like U7090 may be the problem, but I dont want to replace that, have the board work again for 1-2 weeks and get it back in here again, any advice is greatly appreciated.

When board doesnt power on pp3v42 is 3.8v, there is no green light and of course no power.

 

[2informaticos]

Remove C7095 and change R7095/96.

 

[No-Clean]

Just to check I measured all those 3 components
C7095 is 0.256uf Not sure...
R7095 is 348k OK
R7096 is 200k OK

I will test after board cools off and report back

 

[2informaticos]

Change U7090, if its feedback pin is not steady 1.25V.

 

[No-Clean]

I have another one of this boards in here again, different one this time but same problem pp3v42_g3h is 2.5v if I apply heat around U7090 that line goes to 3.42v and board works fine until its shut down for a while.

So far I have replaced U7090 L7095 C7094 C7095 and R7095

U7090
1 1.27v steady
2 2.5v
3 5.4v
4 2.5v
5 Gnd
6 16.49v
7 0v
8 16.49v

Last time I got a board in for warranty with this same issues I replaced ALL components around U7090 and it did not come back again, but I want to find out what it could be so I only replace that part and not everything again.

 

[No-Clean]

The biggest problem here is that sometimes it will start up fine even when is cold and work fine for days, but eventually it fails and it comes back for warranty.

 

[2informaticos]

Usually Ra/Rb resistors affected by corrosion.
Sometime leakage on the cap in paralel with Ra; because of corrosion too.
Could be even internal problem of the chip, which doesn't control feedback correctly.

 

[No-Clean]

Thanks, on this one I did the same thing, replaced all components around U7090 and all is fine, next time I get another one in I will check more, so far I have seen about 3 of the same exact problem.