1973 AC Model 70 Invacar, Visitors & Occasional Distractions

Little been going on lately really as sadly boring responsible adult homeowner tasks have been keeping me very busy.

A little package arrived this morning though.



Lovely little IBM branded calculator paperweight. I wasn't expecting to win this to be honest as IBM memorabilia usually goes for silly money. Quite possibly because the calculator was dead so a static exhibit. I didn't really care either way as it's an interesting bit of desk furniture anyway and will look great next to the IBM keyboard (which is one of those bits of technology I can't ever see me replacing).

Oh...and one turned up on Saturday too. That was another £0.99 starting bid item that nobody else bid on so was less than a fiver delivered, so an Imperial 91S has also joined the calculator collection.



I don't have a problem...I can stop any time I want!

Of course being me the calculator built into the paperweight wasn't going to be left as a static exhibit if I could fix it was it? On removing the cover it was obvious no batteries were fitted, replacing those though did nothing so I pulled the board out.

Can you see anything wrong here?



Yes, that is indeed the front display polariser. Behind the display. Well that's not going to be helping anything is it. Sorted that out, cleaned the inside of the display window and put it back together and...



Success!

Have to wonder if that's a manufacturing defect and it's never worked since it left the factory in May 1984.

Tell you what though, by mid 80s standards it's a *slow* calculator. All 9s divided by 1 takes a good half a second. That's mid 70s territory! Guess that's the price paid for something so cheap as to be built into promotional novelties like this.

It's a lovely thing though and given I do tend to have a window open or fan in use a lot a paperweight is honestly something I'd been meaning to add to my desktop for a while.

*Hoping* I might actually get to touch the cars at some point later this week.

Between poor weather and lack of time I've really not touched the cars or anything relating to them this week. Poor Invacar hasn't been out of the garage in over two weeks at this point, given the looks of the weather forecast it doesn't look like that's likely to change this coming week either. For now have another brief foray into historic technological distraction as some of you have apparently found this interesting...we'll be back to the cars again as soon as time and weather allow.

Have had some quite major progress on one of my longer term historic computing projects though.

One of my favourite machines out of all those I've owned over the years was an old Toshiba T1200. An 80C86 based portable dating from 1988. I found it to be a really genuinely useful productivity machine, with a nice keyboard, form factor which made it actually easy to travel with, and a battery life which can put many modern laptops to shame. Sadly this came to a shuddering halt in mid 2002 when the power supply board developed a fault. Didn't take long to figure out that all it needed was replacement of a couple of capacitors and a good clean. Unfortunately due to a communication breakdown between me and my parents while they were doing a clear out, several key components were lost. The remainder was stuffed in a box in the hope that I could get back to it one day. Particularly of note was that I really wanted to recover several documents off the hard drive (I was young and stupid at the time and didn't have a backup regime in place), which meant getting this or an identical machine up and running as the hard drives are of a non-standard type so I can't just plug them into another computer.

Note the strange 26-pin interface connector.



It was then largely forgotten about for a good few years, until about ten years ago when I started to get back into the hobby of messing around with old computers. Unfortunately I discovered at this point that these machines are actually quite sought after, and the issues I had with the power supply in mine turned out to be one of those faults where it's a matter of when it happens rather than if it happens...as such working examples swap hands for several times more than I was willing to spend. Non working or those claimed to be untested seemed to have their pricing rather more determined by a random number generator.

The big problem with buying a machine that was non functional or untested is that the nature of the fault means that it's a complete lottery as to whether the machine is repairable, a good parts donor or nothing but a door stop. This is the power supply board used by the T1200.



By the standards of 1988 for a power supply board this is quite a complex bit of kit. That's because in addition to providing the voltage rails needed by the machine (12V, 5V - all normal there then, but also -9V and -22V more unusually), this board also does all the battery management and has direct control over power to the hard drive, floppy drove, internal modem (where fitted) and the display. It also interfaces with the screen closed switch to give the ability to suspend the machine state - which we take for granted on laptops these days, but in 1988 that was a truly cutting edge feature. One of the reasons that this thing was quite capable of getting north of 7 hours out of a charge with a bit of care on the part of the user.

The problem with these power supplies is with those electrolytic capacitors to the right of the board. Once they get to a certain age they tend to become physically leaky. In the short term this isn't a huge issue...It causes the power supply to trip out into a protection mode meaning that the machine won't work (you just get a flashing red status light) as it can tell something is amiss. The big problem however is that the electrolyte which leaks from those caps is corrosive, and if the board is left in that state (and when these machines stopped working they tended to just get stuffed away in a cupboard or loft and forgotten about) this causes the traces on the PCB to be eaten away. A pretty typical example of this is shown below. That photo is actually of the underside of the board...the traces on the top layer tend to fare even worse.



It would *probably* be possible to repair this...however I've never been able to find a schematic and layout diagram for the board so you'd need to reverse engineer it first. Trying to do that with half the traces and three quarters of the through board vias having dissolved is a bit like trying to do a crossword puzzle backwards while wearing a blindfold and a pair of boxing gloves. The *biggest* problem though is that due to the location where the corrosion tends to start, the first traces that usually seem to go are the output side feedback lines...meaning that when someone plugs a machine that they've just found in a box somewhere into the mains, the first thing that happens is that the output voltages from the power supply shoot sky high...Usually resulting in every chip on the motherboard being nuked about five seconds before the switching transistors in the power supply itself take exception to the situation and expire in a puff of acrid smelling smoke. Even figuring out what those are to replace them is a chore in itself as they seem to be stamped with only a Toshiba internal part number which doesn't match anything else anywhere. So you've quickly gone from a machine which needs £15 worth of capacitors and an hour's labour to sort...to a half dissolved, blown up power supply and a motherboard which is now a doorstop.

It's because of this situation that over the last couple of years I've ended up accumulating three parts machines in addition to the 3/4 I still have of my original one. The most recent of which arrived last week.

This was described by the seller as broken, with the light on the power supply initially being green when plugged in, but turning to flashing red as soon as the power switch was flicked. Having a pretty good understanding of how these machines work, I knew that was actually a VERY good sign. These machines don't like running without a battery installed - tending to trip out during high power events (such as the hard drive spinning up) if one isn't in place. If the supply had failed catastrophically and nuked the whole machine it would either do nothing or show a solid amber light (which isn't a valid state)...so the odds were that the PSU board in this machine was either working or in a state where it could be saved. The rest of the machine was missing a couple of bits here and there but nothing I didn't already have spares of.

Obviously the very first thing I did was pull the board out for examination and testing (which takes all of five minutes...oh how I wish modern laptops were this service-friendly!). Initial signs were very good. This is the area of the board which usually suffers by far the most badly.



I'm not entirely certain if these caps have just started to leak or if the grime on the board was just generally there from the fact that it's 33 years old (there is a small vent grill above the power supply in that area). However they're obviously going to be changed (along with every electrolytic cap in the entire machine) as a matter of course. After giving the board a good clean I did a bit of testing, sure enough the expected voltages were present in the expected places.

After a bit of head scratching I managed to figure out an arrangement where I could make all the necessary bits of wiring reach to allow me to do some testing without reassembling the case...and when powered up we got life on the screen showing that it was at least trying to work.



The hard drive that was actually in the machine at that point wasn't interested in working. It simply went "click" once and that was it. While having that drive working would be nice, I had another from the previous spares machine, plus the one I was really interested in was the one from my original machine. The other spare was successfully spinning up but kept shutting down again during the initial seek operation - it allowed me to confirm the right supply voltages were present on the right pins though and that I wasn't going to immediately fry my old drive by plugging it in...so it was time to do some testing of that. I had the camera rolling for the event. I had no idea whether the thing would even spin up, much less whether we'd be able to actually read data from it.



To my considerable surprise it spun up and worked absolutely fine on the first attempt...No untoward noises, no protest...just worked. Since that video I've managed to coax both of the other drives back into operation as well, though the one is still a little cranky about starting.

I had no memory of setting up a custom boot screen and a little system description that prints on the screen above the command line at start-up...but apparently I did! It's astonishing the things you find when digging through a drive you've not been able to look at for 15 odd years.

It was obvious though that something was amiss with the display...I had a *serious* lack of contrast.





I knew this wasn't right as I remembered the display on this as being pretty decent. A bit of examination quickly identified that this is a physical problem with the actual display itself - however I do have two good spares. Looking at it next to one of my spares it was really obvious that there's something wrong with the original panel. The "off" state of this display is dark, so in an unpowered state the display should be a uniform deep indigo colour - like the lower one in the photo below. You can clearly see how much paler the top one is, with the tan colour of the unlit backlight showing through.



Thankfully swapping the panels over on this - as with most parts - is a quick and simple job. The difference compared to the earlier photos is clear as day. While the response time isn't anything to write home about this display really isn't bad at all to use. Contrast is very good, viewing angle is fine and the backlight is more than bright enough in shady areas. When you're in an area with lots of light you can basically turn it off thanks to the nature of the screen.



At this point I put everything back together and set about copying the documents I wanted off the hard drive.



After that the system was depowered and everything unplugged. It won't be going near power again until such point as I've had a chance to replace all of the capacitors. Given it's taken me so many years to get to the point of having a working system again I'm being very cautious with regards to not doing anything stupid that might cause issues. Once the caps have been replaced there should be no reason that the system can't be put back to work.

I also gave the case a good clean. I may well transplant this into the case from my original machine as it's far, far less yellowed than this one is. That is if I can *find* the upper case moulding in the loft. I knew which box the innards were in...not so sure about the case! Sorting the loft out is a job on my list closely behind "sort the garage."





Another reason I'd like to swap the cases over is that the legend on the indicator lights above the keyboard clearly shows that this upper case half came from what was originally a dual floppy drive model which had the hard drive (and controller card) fitted at a later date, as it shows drives A and B on the legend.



Whereas factory hard drive equipped models have this legend showing A and C, like this.



Minor detail, but it would be nice to have that right if possible.

The battery in there is from the second parts machine which had obviously spent much of its life sitting next to a window and has one of the worst cases of yellowing I've seen! Despite dating from 1988 though that battery pack still took a charge!



While the capacity will no doubt be vastly reduced compared to its original figure it was still able to run the machine for more than the 15 minutes or so that I had it on test for. It shouldn't be too difficult to open this pack up carefully with a Dremel or similar and rebuild it though, if memory serves there are 6 2/3AA sized cells in there - and I've got a few of these packs so don't mind potentially sacrificing one in the interests of seeing how hard it is to rebuild. Having a useful battery life though is something I'd like to make sure this still has to offer though.

Just waiting on the capacitors to arrive in the post so I can give the machine a blanket cap replacement then it can be put back into use...and to have a bit of fun testing done on it. I know about and have a lot more DOS software in the library these days than I did back in 2002.

Feels like I've finally made some good progress on this one after ten years of false starts, setbacks and frustration.

Very interesting, the lucas efi module on my 87 range rover is of similar construction, when I got it it didn't realy idle properly and following advice from thr TR8 guys I soldered every joint, it now works fine for all except the first 30 seconds or so when it is very rich, I wonder if the capacitors in there are going the same way. I have a spare one which behaved exactly the same, might try re-soldering that and replacing any capacitors at the same time.

Are you going to reveal the content of the hard drive that you’ve wanted to recover; or are you going to leave us to our imaginations?

👍 Glen Anderson “likes” this... He doesn’t understand much of it, mind, 🤣🤣🤣🤣

If memory serves it's a low power CMOS based variant of the 8086.

Don't seem to recall it was all that widely used mainly for cost reasons... though given that this thing cost $6500 (in the US anyway, not seen a UK price quoted that I recall) when it was new, price wasn't a huge consideration on this model.

Zelandeth need any software (excel ver 3)

Talking about hard drives, many (many) years ago I worked for Burroughs Machines in a clean room building hard drives, back then they were somewhat larger than current drives. I found this picture on Google, very similar to the drives I worked on, in fact this could have been me at work (it's not, it was around 1971 I worked there) I can't remember the exact capacity of the drives I built, but I'm sure they were much smaller than 3Gb possibly smaller than 1Gb

That must have been quite an interesting place to work, especially around that time. The engineering on that sort of kit back then is something else.

Best I've got for ludicrously expensive when new hardware is a full height SCSI drive from 1991 with a capacity of 1.2Gb. Cost me a fiver around 2000!