Name the MISSING Part, PLEASE!

[the dude of dudes]

Hello everyone. Recently I've acquired a very old Commodore 386SX-LT laptop, made ~1990. I can get it to power up, the HD Power and FDD lights come on, and the LCD display lights as well. It even seems to POST with a single beep. However, nothing is displayed on the screen. It has a VGA port in back that I've connected to a monitor, but still black screen. I opened it up to find an empty socket on the motherboard, so now I'm thinking someone plundered the graphics chip. Problem is, there is VERY little info out there on this machine, nevermind a schematic. So I'm hoping someone out there can help identify what this empty socket is for. Here's the only specs I could find on the graphics abilities of this dinosaur:

9,5" monochrome LCD (VGA)
640 x 480 pix
80 x 25 chr
8 gray shades

If it is a VGA chip thats missing, I'm hoping someone can tell me what model it might have been. This is right around the time (I think) that the VGA standard was being adopted as the standard, so I don't think there was a lot of selection for graphics adaptors. Heres a photo of the board, the empty socket is in the upper right corner.

 

[hjames]

Hmm, trip down memory lane. So on the lower left we've probably got the BIOS EPROM next to the processor. The surrounding 4 rectangular chips are probably the chipset. Then a memory bank, along with sockets for 2 MB modules. The Sanyo chip in the middle is either a floppy controller - or the LCD controller. And that leads to the socket on the upper right.

I assume the flex connector is the keyboard, where does the LCD connect up?

But in general, I have No Idea....

 

[kchriste]

There is usually a special function key that switches between the LCD and the external monitor. Did you toggle it?
It is possible that the empty socket is for the optional math co-processor (387) and has nothing to do with the video at all. Just a hunch.

 

[hjames]

There is usually a special function key that switches between the LCD and the external monitor. Did you toggle it?
It is possible that the empty socket is for the optional math co-processor (387) and has nothing to do with the video at all. Just a hunch.

I initially thought it was that as well, but the only 387 pictures I saw had them as PGA packages... but it looks like the 387SX's were in 68 pin PLCC packages - so that is probably it.

 

[the dude of dudes]

The ribbon cable IS for the keyboard, the LCD is connected with a ribbon cable farther up (the keyboard is flipped upside down covering it). I couldn't find a toggle switch anywhere on the case. None of the keys are marked for anything video related either. Okay, so the empty socket is probably for the co-processor. Unfortunately, this means this laptop is paperweight to me.

 

[Hero999]

Does it matter?

Can't you get hold of an old laptop off ebay or from a second hand shop?

 

[the dude of dudes]

It was more the fact that it's a Commodore laptop, and I'm kinda becoming a C= collector it seems.

 

[the dude of dudes]

Well it seems I have a display after all (grin). However, it's far from perfect. If I leave the machine on for a minute or two, the LCD display eventually warms up and displays. After another minute or two, it starts to flicker then goes very bright and nothing is displayed any more. I have to fiddle with the contrast and brightness to keep the picture legible, until it fades to bright. Is this a dead/dying LCD, or is it easily repaired (guessing not)?

 

[zevon8]

First two things that come to mind are: dirty controls for the contrast and brightness ( slider pots or maybe the 2 black circles in the pic? ) second would be bad capacitors in the switching supply that powers the backlight for the display. The switching supply may be potted, if so you can't fix it. There may be a small box with a high voltage warning label somewhere that will identify the power supply.