820-3476-A chime but no display on both LCD and thunderbolt port

[protocold]

Minor corrosion around U8300 and U3210 and cleaned by some flux and hot air.

The board will chime but no display whatsoever via LCD nor thunderbolt port.

where to look?

 

[2informaticos]

Do you get 5V at pins 28-30 of J8300, at least in the first few seconds (when chimes)?

 

[protocold]

sorry do i need to have LCD plugged in to test the 5V at pin 28-30 of J8300?

 

[2informaticos]

It should appear even without LCD; but will disappear in 2-3s.
PCH needs to detect LCD, in order to maintain video voltages.

Are you not interested to check video related voltages with LCD connected?
What do you expect to get in such case?

 

[protocold]

I do, just that I dont have a A1502 LCD handy right now and need to get one.. I will have the A1502 LCD in a few days.. but I was trying to see if I can do some troubleshooting before that arrive. e.g. getting it to display via thunderbolt or something like that..

 

[2informaticos]

"Do you get 5V at pins 28-30 of J8300, at least in the first few seconds (when chimes)?"
As above mentioned, you can test that without LCD; a minimal test.

You've mentioned corrosion on U3210.
Resolder all its pins and check related components and traces.
Do you get any output from it?
TBT_A_HV_EN comes high?

 

[protocold]

Yes, I do have 5V for a few seconds at pins 28-30 of J8300 after resoldering all pins of U3210. Actually my LCD arrived and I have hooked it up and saw the flashing folder so it actually displayed via LCD now.

However, BOTH thunderbolt port are still not working, TBT_A_HV_EN is 0v.

 

[2informaticos]

Isn't more convenient to use HDMI instead of thunderbolt adapter?

I suspect something damaged by corrosion on thunderbolt area.
Check TBT_A/B_HPD on the port where you insert thunderbolt device.

 

[protocold]

how do I check those pin without causing a short into the metal shield?

 

[2informaticos]

These pins are available at U3220/320...

 

[protocold]

sorry, turns out this has more problem. keyboard not working (power on button seems to work) but other key has no response after boot up. Trackpad also not working and the known good IO board also not working.

something more serious upstream?

 

[2informaticos]

So trackpad/keyboard work in boot menu. but no in macOS?
Check R4800 and L4807 and all resistors around U4801.
BUTTON_DISABLE stays at 0V?