820-3115, power, fan, optical cycles, no chime.

SMMRepair

Member
Working on an 820-3115 that had moderate liquid on top edge (as usual). Cleaned all liquid, replaced affected components, found 3v3_s5 shorted. Repaired short, got fan spin. Popped the board into a known-good test case, and it has the following symptoms:

1. Powers on, front LED comes on as normal (and goes off as normal--will turn on if I close the lid)
2. No chime
3. Optical drive cycles normally, as if it's powering up
4. LCD turns on--backlight turns on, but screen is black, so no video data.
5. Does not respond to PRAM reset. Nothing. Checked to make sure it wasn't EFI locked, and it isn't. Will respond to SMC reset.

I'm about to head out for the day (already stayed an extra hour working on this one), but will check VCORE and BIOS area in the morning. I wanted to go ahead and post, though, because would the LCD turn on (with backlight, black screen, no image) if VCORE and BIOS were not good? I think they will both turn out to be fine, but wanted to get an idea of what to check next. Thanks as always for any help in advance.
 

dukefawks

Administrator
If the backlight comes on the CPU and everything works. Pop a ROM on there that you know has had a PRAM reset and see if chime returns. Connect a HDD and see if there is boot activity.
 

SMMRepair

Member
Thanks, Duke. Yeah, it's weird; I tried a new ROM and new BIOS chip to be safe, and no change. Pulled one directly from a board that I had just reset the PRAM on to be sure, just for testing. No change. With board installed in full test assembly (hard drive present), there's no sign of activity beyond the optical drive cycling and the backlight coming on. I checked all diode readings for LVDS and all is normal. Confirmed vcore presence and checked all resistors related to it. Also checked to see if any rails were missing, and nothing seemed to be obviously not present. I'm thinking maybe a broken trace somewhere for a particular rail, specifically up near SMC. I've checked well and don't see anything amiss or questionable.

Might have to send this one to more experienced hands.
 
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