Acorn Electron Repair

ULA Shinangins

The Acorn Electron, the ones of you who are my age might not have even herd of the device. For those who don't know, its a computer! It came out before Christmas in 1983 but a manufacturing cock up caused the company major damage to which they never fully recovered, my model was made in early 1984. It's a shame because there's no English computer manufacturing any more. History lesson over, if you want more info on the history, many other sites explain it, so... there's no need for a another site to explain the history. Although it was an highly anticipated wait for the machine to arrive.

Any way, back on subject. I got this beast off eBay for dirt cheap, the person who sold it did not know its working state, this normally means don't buy it un less you can fix it.

Any way it arrived and after the third degree from my mum wondering what was in the package I was able to open it and see what had arrived. By open it I mean the device its self as well, just to see exactly what I had got.

Oh, if your wondering about the Nivea cream, a Geeks got to look after his face to!

After plugging it in and using the b/w composite video and firing it up, I was disappointed but un surprised to find the computer was dead and only displaying jargon. Thanks to research I had been doing on the computer before I got it, I had an idea on what was wrong.

It had to be something wrong with the ULA (Undedicated Logic Array). The rest of the computer looked fine and was built with good components, even the caps looked fine.

The ULA is a chip that Acorn squeezed most of the functionality of a BBC B into. It handles I/O, video, sound etc. I can not remember off the top of my head. Also there's an underused expansion port on the back which would be grate for hacks and interfaces when I learn more of the BASIC.

The computer did not make a sound, all I herd was the relay by the tape drive port clicking. The pattern was the same every time showing that the computer had only got partly through its boot sequence. (So its time to prepare the evil mad lab for another twisted experiment). HA HA HA HA (evil lath).

The list of things you will need is:

Lab Assistant

Some kind of lab assistant. Preferably one who does not pass gas every five seconds and then ditch you with the smell. But I guess you just make do with what you have got so, "GO TODD".

Todd, his use as an lab assistant is debatable!

He is sorly missed these days.

A Clear Space

Fuck that! Right move onto the desk for this one, although the tools are handy.

Right the check list is over, now time to actually tell you how I fixed the problem.

(Funny how some things don't change as I get older)

Ok so you will want to open the machine to reach the parts that need work. Now you can gaze into the magic that made your beloved computer work. 80s tech is so well built, unlike to days crap. Most people may stop here and start using anti static precautions, but to be honest I've never had a static problem, the thought is, that static discharge is built up on. I mean a lot of people make a fuss over nothing and it is only a minor danger. Although it does not hurt to be safe so if you want to take them precautions... then feel free. I'm not going to judge you for it. If you have spent a small fortune then its better to be safe. Once you have the device open you should check the capacitors to see if they have died. If they are bulging then replace them as they have died. If you have an ESR meter then you can check to see if they are still good. You may even want to check all the signal lines and frequency's of the machine just to make sure every thing is ok, but don't forget the ULA chip. All I did was look at the caps to see if they bulged as I do not have an ESR meter (oh how times have changed) and checked the ULA. It was the ULA that was the problem in my machine.

Just for good measure, here's the keyboard PCB. The only thing they seem to have shortcuted on is the ribbon cable that connects it to the Mobo.

Any good electronics enthusiast will inspect the inner workings, so that's what I did. The top right shot we've got a nice view of the TMS4164-15NL' RAM chips, the ULA and the 6502 CPU. The HN613256P023 ROM chip containing the OS and BASIC is just about visible behind the CPU out of focus. The Photo at the top left is the power supply that regulates the power from the transformer. It is a switch mode supply looking at it. Right is the ULA underside (one beautiful chip if you ask me). The bottom left image of the ULA in its socket with the clamp removed.

So I removed the ULA to take a look at the chip to give it a good clean when a website alerted me to also look at the connecters pins. I looked at the pins and "shit", two of them were victims of metal fatigue, they did not bend up like the rest of the pins when the chip was removed. They broke off when I tried to bend them back. So I was in for a "fun" repair.

I tried two methods to get the machine working. The first one was to cram silver foil in the gaps, in place of the pins. This worked at first, but as the chip got hot it expanded enough that when you switched the machine off and the chip contracted from the loss of the heat, the electrical connection was lost.

Method too was to put the original pins on top of the silver foil. This turned out to be the best solution and have fixed the fault to a very reliable condition. You only need to remember not to remove the ULA for anything except repair.

Eventualy a few years later I managed to source some of these ULA sockets & I repaired the Electron in this artical properly. I desoldered the socket & replaced the broken pins & soldered it back. Also repaired another Electron as I have five now by replacing the black blob ULA as I somehow found a ceramic one being sold on eBay, bought it, found the correct socket & repaired the Electron. Another electron I had got on eBay just needed new RAM, for it is always RAM. Quite a few Acorn Electrons use the black blob ULA chip.

The black blob ULA chip to the left is the one that failed, it was relapced by a new socket & the ceramic ULA I managed to some how find on eBay. Once I pluged that in & replaced the fulty RAM the machine booted as normal.

Sadly Ferranti is another piece of British industry that has died, it went down the bog in 1993. On the up side the company invented the ULA concept that has lead to the development of PLA (programmable logic arrays and similar devises).


The end result!

So after that victory I now have an Acorn Electron I can play on. I have now hacked and repaired an 1976-1977 tape recorder to run with the machine. I have also obtained the game Plan B for the machine and have been rewarde with a surprisingly capable machine for the lack of power it has.

I would highly recommend getting one of these computers as they are quite common on eBay. (Sadly not cheap anymore)

Any questions just ask.