Ok. Now I know where the screws are. Under the plastic stickers on the back.

Now I will turn this into a repair thread and post progress how I get along.

Attached is a photo of the screw positions.

The bios battery is empty but it is some strange 3.6V lithium cell soldered directly to the board. I removed it and the solderpads look like maybe I can replace it with a normal 3V cell holder. 3V should be sufficient for some time. The old cell is at 120mV so absolutely flat.

Edit: I had a look on Ebay and those batteries sell for a furtune and only come from China. So I will definately use some replacement.

Removed the screen and the transformer fell off the inverterboard directly. Seems like the solder never really flow on the pads correctly. Resoldered it and it seems solid now. This could explain the fluctuation of the backlight when pressing down on the inverter board through the case.

As the floppy drive made strange noises when a disk is inserted and could not read any disks, I took that apart, too.
Looks like the drivebelt broke in half and so the motor was rotating endlessly without being able to seek.
Ordered some replacement on Amazon, but as it comes from China, it will take a Month or so to arrive...

Also removed the HDD. This seems to have a normal 44 pin mini ide connector, so replacement should be easy. Maybe with some SD card adapter. The Bios seems to have a limit of 512MB, so I need to find some small SD card. The HDD just clicks when trying to power up even on an adapter on my pc. Not sure if I will try to open it carefully and try to unblock the readheads. It is one of the 2.5" drives with full height (double the height of todays notebook drives).

That drive is guaranteed to have bad capacitors on it, the exact same types fail with 100% certainity in Sega Game Gears and other hardware using those.

Also here are some pictures of the completete motherboard. There even is an empty socket for a co-processor.
Not sure what the dual pinheaders at the lower right are. Maybe for a ram expansion? If anybody has an idea, let me know.
The upper male 44 pin connector is for the HDD. But I have no clue what the blue female one is for.

Tiido wrote:

That drive is guaranteed to have bad capacitors on it, the exact same types fail with 100% certainity in Sega Game Gears and other hardware using those.

Thanks for your post. In this case it could be that it can't provide the power to move the heads. I will definately try to replace them. Do you know where to source them from?

Here is the power supply board. Seems to be some old switchmode design. The electrolytic caps seem to be in good condition. May replace them anyway though.
I noticed a lot of bodge wires and added components (diodes, wires, transistors soldered directly to vias) all around this pc. Maybe this is some early model.

Just use anything with same or smaller physical size and capcitance ratings. There are no voltages above 5V there so 6.3V or higher voltage rating capacitors will do. I see two 100µF, two 68µF and one 10µF.

And the last post for today. There is the display assembly. The board unter the lcd has two potentiometers. One for brightness and one for contrast. Both were a little sticky so I cleaned them. The rest seems fine.

Tiido wrote:

Just use anything with same or smaller physical size and capcitance ratings. There are no voltages above 5V there so 6.3V or higher voltage rating capacitors will do. I see two 100µF, two 68µF and one 10µF.

Yeah, some of them look like they became a bit hot as the silkscreen is almost completetly destroyed. Maybe I can get some smaller round electrolytics that will fit. The ones that are on there seem to have the advantage that they don't seem to leak though.
The PSU board also has some of those. Will have to count and replace them all.

They absolutely do leak, I'm pretty sure you'll smell rotting fish when you try to desolder them... There should be 5mm of clearance and it is easy to find suitable capacitors that fit in place.

Got the new belts for the floppy drive today. It is back in working oder. Also replaced the harddrive with an SD Card adapter. Boots fine now. Still have to get a coincell holder and have to 3D print a new powerswitch as the old one is cracked.
Also replaced two capacitors on the display controller what made the contrast a lot more stable.

Great. Just when I was about putting everything together again, the backlighttube on the lcd seems to have died...
Now for another mod: LED Backlight....

Attached is a photo of the broken tube.
I had some 20mA constant current sources from another project. As there are 19V to drive the display on the display controll board, I just used that to drive two warm white leds placed in the gap where the tube used to sit.
Works great. Although not perfect as you can see on the other picture. There are darker spots as the leds have a more focused beam.
That doesn't bother me too much though as it is a hundered percent better than without backlight.

I like the warm white backlight. Adds some old Monitor touch. Maybe I will try amber leds in the future.

Now let's party like it's 1991!

Revisited the backlight part again. I wanted a better light distribution. So I cut an led strip from a salvaged led monitor to size and found that I can drive 3 of the leds (one led of those has 2 chips in series) in series with a 1k resistor to get sufficient brightness.
So I used a strip of 9 leds and modified it so that always 3 are in series. The original used a 40V supply to drive 8 in series.

Then soldered everything together. This should give a good lifetime as the leds are only driven by 1/4th of their rated current. The whole circuit draws 20mA what should also be a lot more efficient than the old tube at a similar brightness.