T20 nothing on internal display.....

[solidpro]

Hi Everyone

I've been going through a bunch of T2x parts, testing to see what works and doesn't and I was using 1 'good' machine to swap out stuff with. After testing everything I went to rebuild the original machine and none of the working LCDs would work. So I hooked up an external monitor and it's booting just fine.

So I took out the original T20 mainboard and continuity checked every fuze I could find and all check out fine. I also checked the inverter in one of the LCDs.... I can't get it to output internally. Anyone got any ideas?!

Thanks

[RealBlackStuff]

LCD-cable?

[solidpro]

3 completely different working lids (combining the LCD, inverter and cable) and nothing displays on this machine that clearly is working.... flummoxed....

[solidpro]

Ok the plot thickens..... all three lids ARe actually showing a picture but with no backlight.... have all 3 inverters gone bad simulatenously!!??

Edit, I've given up for the time being and put them back on the shelf.

I ended up with 2 'perfect' bases but they would not display the backlight. I found a box with 4 'known good' inverters inside and they all do the same thing. The inverter on the T2x machines doesn't appear to have a fuse.

So with so many flat ribbon cables, inverters, LCDs thrown at these two machines I can only imagine something on the mainboard has failed, but I know not what it is! It's not a fuse.

[RealBlackStuff]

No backlight means, fuse F4 near the mobo LCD-connector is blown.
It's a very small 434002 fuse (2A/32V/fast).
Just solder a new one on top of the old one.
And T20 schematics can be found here: https://dokumen.tips/download/link/ibm- ... uence.html

[solidpro]

Bingo! Well, the no-backlight issue was actually F5 which is directly next to the LCD connector on the motherboard. On both machines, this was blown.

One of them worked fine after that and the other was displaying a white screen which was discussed by us all on another thread viewtopic.php?f=28&t=134100 and was a symptom of F4, which on this unit was also blown. Both are tiny - about 1-2mm wide and I had to replace them with a microscope....

Thanks for helping me solve it!