KC Micro Tronix
Member
I got a water damaged 820-01987
came in with no back light. water damage around U8400, fixed trace damage and replaced U8400 Then found a blown fuse F8400. After this the
backlight voltage came back but it would quickly fade away and only went to 12v not 50. The CPU would quickly shutdown the backlight enable signal to U8400. Seemed like the buck was bad. Found Q8501 "FET" shorted source to drain. That explained the buck circuit problem. Replaced that and I had back light. Lots of chit chat between the driver and the screen then back to the cpu and then to the driver. Check all these circuits when troubleshooting backlight on these.
Then the next problem was no WiFI. WiFI not shorted and rail was good but thermal showed slight edge glow which usually means WiFi/Bluetooth module is bad. This is a underfilled part. I was concerned that it was married to the machine and that even if I changed it it would not work. Lots of labor on a underfilled part of this size. Well I changed it anyway and to my surprise the WiFI did work!
Lessons learned:
* Check that buck FET on water damaged no backlight. ( IF pulse only goes to 12v not 50v on startup )
* WiFi module can be replaced!
Hope this helps someone.
came in with no back light. water damage around U8400, fixed trace damage and replaced U8400 Then found a blown fuse F8400. After this the
backlight voltage came back but it would quickly fade away and only went to 12v not 50. The CPU would quickly shutdown the backlight enable signal to U8400. Seemed like the buck was bad. Found Q8501 "FET" shorted source to drain. That explained the buck circuit problem. Replaced that and I had back light. Lots of chit chat between the driver and the screen then back to the cpu and then to the driver. Check all these circuits when troubleshooting backlight on these.
Then the next problem was no WiFI. WiFI not shorted and rail was good but thermal showed slight edge glow which usually means WiFi/Bluetooth module is bad. This is a underfilled part. I was concerned that it was married to the machine and that even if I changed it it would not work. Lots of labor on a underfilled part of this size. Well I changed it anyway and to my surprise the WiFI did work!
Lessons learned:
* Check that buck FET on water damaged no backlight. ( IF pulse only goes to 12v not 50v on startup )
* WiFi module can be replaced!
Hope this helps someone.