820-2796 - Odd intermittent behaviour.

[gcain]

Customer said laptop was dead, no damage to it besides being a bit old.

The board was clean and the only damage was some corrosion on a TP on the trace from U4900::40.

Behaviour;

The board will sometimes boot and is sometimes completely dead. I have seen the screen brightness going up and down like someone is playing with the brightness, it's not flickering though. Moves up and down smoothly then the board cuts out.

Sometimes the green light goes on and off while it's just sitting on the desk.

Usually what happens though is that it turn on and off (like it's doing an RTC reset) and then eventually just stays off.

All power rails seem to be present 9it's tricky to measure when it's playing up). SMC_ONOFF & SMC_RESET are steady.

Any suggestions?

 

[dukefawks]

Corrosion on the Hall sensor, J6955 or crap in the trackpad connector. Trackpad and flat cable are suspect too.

 

[gcain]

I have nothing plugged in, bench testing.

J6955 looks nice and clean

 

[gcain]

Should I just remove the sensor and see?

Your intuition is usually fairly accurate.

 

[dukefawks]

Flux and heat, but if no corrosion is there then probably not the issue. Corrosion on/in trackpad connector? Possibly under SMC?

 

[gcain]

Trackpad connector looks clean.

I fluxed and heated the SMC, same behaviour.

 

[Alan.L]

Have you try another camera module and cable?

 

[gcain]

Nothing is plugged in. Just bench testing at the moment.

 

[dukefawks]

Check what SMC_LID is doing. It is probably being pulled low and then the computer cannot power on and when on it will go to sleep.

 

[gcain]

I can't see SMC_LID moving when it power loops.

SMC_LID is 3.4v when off and 3.363 when on.
It does move around a tiny bit when it's running.

 

[dukefawks]

Tried a known good IO board and flat cable as you said green light is affected too.

 

[gcain]

You might have been on the right track with the new DC Board.

Unfortunately it started the single RAM beep, so I've shelved it until later. Possible power related, going by the single beep.

 

[dukefawks]

Beep has nothing to do with power. If it beeps that means it is time to junk this board, this old crap is not worth messing with if it starts doing that.

 

[gcain]

I mean a single beep usually means no ram installed, which is likely power failure to the ram circuit making it /think/ there is no ram installed.

This makes me think there is probably a single point that has failed; as opposed to a three ram beep, which means it knows ram is there but faulty. Which would be a more complicated failure.

Either way, this is one of those boards plagued by this issue, so it's at the back of the queue.

 

[dukefawks]

One beep can be much more than just RAM. One beep is usually MCP failure.