I'm interested in the nuanced release structure of the early 1990s IBM Thinkpads. Whereas the enterprise and business range of 7xx models was fairly sequential and linear (the model numbers from 700 to 770 are chronologically ordered and each machine is a new iteration of the last), the consumer 3xx models have a convoluted, non-linear development and release timeline.
It's also interesting how these two different model ranges interact when it comes to sharing designs, technologies and parts. You can see by some of the tiny details that there were probably lots of very detailed product meetings, where management poured over how one machine might rob sales from another or the unwashed masses might regard a cheaper IBM Thinkpad-branded machine as a 'better deal' than another Thinkpad at twice the price.
This makes restoring and preserving machines quite difficult, fraught with traps and gotchas.
What led me down the path of the title of this article is that I encountered a somewhat unusual 750 (9545-006/8) machine with a monochrome STN panel. I suspect this machine was not popular as by the time this machine was released in September 1993, both DSTN and TFT colour screens were considered infinitely more cutting-edge and quickly became de-facto standard of portable machines. I'm generally not happy to own a machine that doesn't work - unless it really really has tested me to the limit of writing the whole model off as a lost cause - and so I set about trying to make this machine work.
The 750 was really when the 7xx series got goooooood. The 700 and 720 machines are blighted with a terrible hinge design which is destroying every last one of them. And whilst some of the design ideals of the 700 and 720 are lost in the 750, it's certainly an revelation. Inside the circuit boards have clearly moved on a generation from the somewhat 'mechanical' look and feel of the 700 and 720. We have lost the front-loading floppy, battery and hard drives hot-swap ports, but these have now been almost as conveniently moved underneath the lifting keyboard design - retaining the idea of not elbowing your fellow passenger on a bus, train or plane whilst switching out your battery or HDD - a concept which would remain for many more generations.
In this case of this particular 750, this is how the machine looked on ebay - bloody awful. So I suspected I would get it for what it's worth - not a lot. And I did - about £21 and shipping fees from across the Atlantic. Vintage laptop aficionados will instantly recognise the vinegar syndrome LCD - a problem where early LCDs use a formula of adhesive to affix the two layers of polarising film inside and outside the glass LCD screen, which breaks down and fails - particularly in warm and humid environments. Secondly, it had no guarantee of actually working.
I received the machine and quickly checked the machine powered on - which it did, booting via the external SVGA port to a few error codes. I decided then to see if the rare monochrome STN LCD panel was salvigable. There are very few resources which give -true- details on what panel was used in what machine. It's clear that through the evolution of the IBM thinkpad, they uses a wide range of manufacturers - Sharp, Toshiba, Hitachi, Epson and others - so often the only way to know is to look.
It's a Toshiba display which cannot be found anywhere. So a direct replacement was out of the question and I set about Plan B - to remove the spunky dried up adhesive and replace the two polarising films. This takes about 3 hours of applying IPA, letting it soak for 30 seconds and then scraping as much of the glue into the centre of the screen and then lifting it off. After doing this for hours, you've left with what looks like a simple pane of glass, which you can insert polarising films either side (usually at 45 degree angles) to get the mono display working again. And after all this, it was totally dead.
So, Plan C. I knew that the 360 was a cost-reduced, consumer-end alternative to the 750, sharing lots of the same design and technology, However, there was also no clues online as to which display this used either. And I didn't own one. So, Plan D - the 340-series was released the same year as both the 750 and 360, and whilst it shares almost none of the same technology of those machines, it did have a mono display which was the same size. And crucially I owned 3 of them! So I took apart one of my 340 machines and the display was the exact same dimensions, connector, inverter, but a completely different make and model:
So would it work?
YES! It did! These LCDs are actually much more readily available, except at a higher cost than a 340. Much as it pains me to turn a working 340 into a non-working, no-display 340, this project is to restore a rarer 750 to working condition.
However, it would be worth noting that the 340 has a completely different internal video connector (specifically not via an interposer as used by the modular 750 and 360-series machines) and therefore whilst the ribbon connector from the mainboard to the LCD and Inverter is almost exactly the same, the connector onto the mainboard is completely different and cannot be used.
I believe the inverter is interchangable.
I'm also happy to report that the Optiplex 340 panel shared all the same dimensions and fit quite easily as a replacement for the 750's Toshiba panel. The only difference was that the 340 LCD had a thick, bendy RF shield all around it which could not be accomodated in the 750 lid as it has plastic strengthening strips preventing the RF shield laying flat.
The inverters only had 1 small side-mounted electrolytic cap on them which didn't appear to have been leaking but if you can be bothered, it might be worth replacing with a new one.
With the 750 lid back to full working order, I decided to crack on with the mainboard. The first oddity is that it would show the usual memory count and 161/163 (cmos dead) errors, but would not allow me to hold F1 to enter easy setup. I tested the F1 key and it was definitely working.
So I tried booting from an early IBM utility disk (used to update the BIOS) and it worked. However if you didn't have an IBM utility disk in, it would not enter easy-setup and would not boot off any drive, just showing an error I9990303 error.
There have been quite a lot of people over the years asking about this error, which is certainly related to the system board, but nobody ever appears to have fixed it.
I thought I would update the BIOS to see if that might fix it, but when you try, even with a charged battery, you get an error saying that 'power management has been disabled' preventing the BIOS update to take place.
The closest we have to an answer is "Bank–2 flash ROM check sum error." as described here.
So the machine has been parked. Waiting for a busted up 750 to come on the market, with a working system board.