PowerBook 165 – Backlight turns off after a few seconds (CPU board issue)

[LeSpameur]

Hi everyone,

I’m experiencing a strange issue with my PowerBook 165. The machine boots and works perfectly, the screen comes on with proper contrast and image… but the backlight shuts off after about 5 seconds. The image remains visible under strong light, so the LCD itself is fine — it’s clearly just the backlight that’s turning off.

After swapping parts with other machines, I’ve been able to narrow the issue down to the CPU daughterboard. If I install a known-good CPU board (e.g. from a PB160), the backlight stays on without any problem. But when using the original 165 CPU board, the backlight consistently shuts off a few seconds after startup.

Additional info:

• The 165 CPU board is in excellent condition, no battery leakage or corrosion whatsoever.
• The issue is clearly hardware-related — it happens regardless of OS, and there’s no software control of brightness on this model.
• I’ve tried looking for schematics for the PowerBook 165 CPU board, but so far I haven’t found any available online.
• My suspicion is that the CPU board isn’t properly holding the backlight enable line high (maybe a weak transistor or open resistor), but without a schematic it’s hard to trace.

If anyone has:

• a copy of the 165 schematics,
• or has encountered this issue before,

I’d really appreciate your help.

Thanks in advance!

 

[croissantking]

That’s a new one. Just before you go any further, can you check all the pins are straight and clean on the interconnect socket?

Unfortunately there are no schematics for this model to be found on the internet.