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Dolch C-P.A.C. 386-33C (DP386-33C) portable system LCD problem

Half-Saint

Experienced Member
Joined
Apr 21, 2004
Messages
322
Location
Ljubljana, Slovenia
Hey guys,

I don't really know where to post it, here or in Tech. Support but here goes.

I bought the abovementioned computer knowing that there's some kind of a problem with the LCD. Received it today and can confirm that the LCD backlight turns on but the screen is all white. However, the built in VGA card works fine with an external monitor. So the problem is either in the LCD itself or somewhere between the LCD and the VGA card.

Anyone have any experience fixing those or maybe even have a service manual? I'd really like to get it fixed but finding parts will be a challenge.

Many thanks,
Bojan
 
If this were my system, I'd first start by inspecting the cable between the LCD and VGA adapter. It could be something as simple as the cable not being connected. After that, things get more complicated.
 
If this were my system, I'd first start by inspecting the cable between the LCD and VGA adapter. It could be something as simple as the cable not being connected. After that, things get more complicated.

I started disassembling the computer today and it's gonna be a real PITA. The engineers obviously didn't have easy access in mind when they designed this chassis. The LCD is behind the motherboard which will have to be removed. I also have to figure out how to remove the FDD/HDD cage first.
 
I got to the cable and it appears to be intact. Tested each wire with a multimeter and continuity was fine. I removed a small interface circuit that contains two connectors, a couple of resistors and capacitors as well as a 74LS123N and UPRMA2A05B chips. Sadly the chips aren't socketed and I don't have the equipment to desolder them effectively anyway or the means of testing them. Nothing looks burnt tho so it might be just that the LCD itself is bad.
 
I had a much later (Pentium 200) Dolch, and while its LCD worked it had serious issues with frizting out if the cable was moved/touched/just felt like it. I never completely localized it before I gave the thing away, but it felt like oxidation or maybe a bad solder joint somewhere. A 386 is going to be about twice as old now as that Pentium was when I had it, so I’d probably say your best initial course of action is to just disassemble the whole thing and examine/clean all the steps in the chain.

Also, although generally I don’t like going straight there, bad capacitors *could* be a thing. Depending on exactly what LCD panel you have in there, anyway. I’ve heard the active matrix monochrome panels in some old PowerBooks haven’t been aging well.
 
I had a much later (Pentium 200) Dolch, and while its LCD worked it had serious issues with frizting out if the cable was moved/touched/just felt like it. I never completely localized it before I gave the thing away, but it felt like oxidation or maybe a bad solder joint somewhere. A 386 is going to be about twice as old now as that Pentium was when I had it, so I’d probably say your best initial course of action is to just disassemble the whole thing and examine/clean all the steps in the chain.

The flat ribbon cable looks solid, I don't think that's it. I'm currently in the process of disassembling the rest of the machine. We'll see what comes up.

Eudimorphodon said:
Also, although generally I don’t like going straight there, bad capacitors *could* be a thing. Depending on exactly what LCD panel you have in there, anyway. I’ve heard the active matrix monochrome panels in some old PowerBooks haven’t been aging well.

SMD capacitors, right? I need to start learning how to use my hot air station anyway :D
 
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