Keyboards - More Interesting Than You Think.

OK, so keyboards might not be THAT interesting.

I've been floating around the Amiga Facebook group for a while now and recently had a bit of a conversation with a couple of the guys about the different keyboards that were used on the Amiga, specifically on the A500(+).

A little bit of history. When the Amiga first launched it was known as 'Amiga'. Later, this first model was renamed as the Amiga 1000*. This model had a separate keyboard that slid neatly under the case to keep everything tidy. Allegedly, this design 'feature' was one of the reasons for the high cost of production. Another debatable point. The keyboard itself was a compact design, smaller than a standard IBM XT/AT keyboard but it was mechanical i.e. each key had a switch that when pressed sent that character to the computer. According to Deskthority.net, these keyboards were manufactured by Mitsumi. They also had the familiar 'A' Amiga keys, but with the 'A' printed in red.

A1000 Keyboard - Note Red Amiga Keys
Pic from Deskthority 

*There is some debate about this. Some say that it was always the A1000, some that it became the A1000 later to distinguish the models. I don't know the exact answer.

Fast forward a year or so. Commodore made a brilliant business decision (one of few) to release a cut down Amiga that would make it available to a much wider audience. This was the Amiga A500 which was the brainchild of Jeff Porter at Commodore. It incorporated the keyboard into the case and a floppy drive in the side in a form factor that was familiar all the way through the late eighties and early nineties. The Amiga, Atari ST and Archimedes all followed this design and it was highly successful.

From the information I have been able to find, the first Amiga A500s were actually released with Revision 3 motherboards. They also included keyboards that closely followed the design of the A1000 in that they used mechanical switches. They were actually Hi-Tek Series 725 and are affectionately known as 'space invader' keyboards. This is because, when a key cap is removed, the shape of the switch closely resembles the space invader characters from the 80's arcade classic.

Space Invade Keys
Original image from Deskthority

These early keyboards are easy to spot for a slightly fortunate reason. The plastic keycaps are made of polybutylene terephthalate (PBT) which, according to Deskthority.net is the hardest material used for keycaps. If you know anything about the Amiga you will know the problems with 'yellowing' caused by the bromide used in ABS. This doesn't happen with PBT so these keyboards make themselves obvious by being completely un-yellowed compared to the A500 they sit in. If you find an A500 for sale with an almost perfect white/grey keyboard then the chances are, it's a space invader type. They were only used on Revision 3 and some Revision 5 motherboards (Revision 4 isn't really a thing for the A500).

Another feature of the early A500s is that the case badge is moulded into the case itself rather than being a recessed plastic badge. These are known as 'chicken lips' cases since the Commodore logo looks like a stylised drawing of a chicken. Allegedly. So, the upshot of all this is, if you happen to be perusing a car boot sale in your local muddy field and happen to see a chicken lips A500 with a pearly white keyboard at a decent price it's well worth getting as it will almost certainly be a rare, early model.

While the 'invader' type of keyboard is very nice to use, and is comparable with some of the best mechanical keyboards available even today, they also had a bit of a cost problem. They were not cheap and kept the price of the A500 high. To get around this, new keyboards were developed with a much lower price point and subsequent drop in 'niceness'.

There were two main types of this reduced cost keyboard, Samsung and Mitsumi. Yes, Samsung made keyboards for the A500.

However, the Mitsumi keyboard is by far the most common used on the Amiga A500. It was so successful - if not very good to use for long periods - that the same basic design was used for the A600 and A1200 keyboards as well as some A3000 keyboards. Mitsumi keyboards use 'hybrid switches' which are basically a plastic post that contacts with a membrane that completes a circuit. A spring underneath the keycap provides the 'return' of the key when pressed. The Samsung keyboard was similar but the spring was held inside the keyboard so that the springs are under the posts rather than directly under the keycaps as per the Mitsumi.

Samsung Keycap, Post and Spring

The above pic is of a keycap, post and spring from an old Samsung keyboard. The spring is REALLY small. And to make matters worse, if you need to replace the membranes (if you can find any new ones!) then you'll need to remove the rear plate of the keyboard and run the gauntlet of losing:

a) the worlds smallest screws
b) the worlds slipperiest springs
c) your sanity when you try to put it back together

Mistumi Keycaps - Note the bigger springs
Original image from Amigos Retro Gaming

You'll notice how much bigger the springs are for the Mitsumi keyboards which you would expect would give a better feel than the Samsung but they both feel very, very similar. Also, it is surprisingly easy to lose even these larger springs when you try to remove the keycaps. They fly out at an alarming speed when the cap finally pries loose, and instantly vanish into any carpet nearby...but they're nowhere near as fiddly as the Samsung.

Neither the Samsung or the Mitsumi keyboard offer a particularly good typing experience. The keys travel a little too far, there isn't any real tactile feedback and the general feel is quite spongy and unsatisfying. Both also suffer from the dreaded yellowing mentioned above as all of the keycaps are made of ABS. Despite this, it is relatively easy to determine the make of keyboard an A500 probably has.

Any A500 UK keyboard with a 'small' return key is ALWAYS Mitsumi*. This includes all A500+ and any A500 that has the larger A500 badges rather than the small square Commodore logo. The same basic keycap design is used on the A500, A600 and A1200.

*European keyboards always had a small enter key to allow for additional language characters. I've never seen a Samsung keyboard with a small enter key but they could be out there.

If the return key is the large 'L' shaped key then it could be any of the three available types, so ask yourself the following questions:

Q) Are the keys still very white?
A) Likely to be a 'space invader' keyboard.

Q) Does it have a 'C=' key instead of the usual 'A' Amiga key?
A) Likely a 'space invader'.

If the keys are yellow, take off the top case (if you can).

Q) Does the control board have a single white membrane connector?
A) If 'yes', it's a Mistumi. If 'no' it's a Samsung.

Samsung - Dual Connector (excuse my dust)

Mitsumi - Single White Connector

If you can't take the top case off to look at the control board then look at the keycaps themselves.
The Samsung keyboards use keycaps that are more angular than the Mitsumi. The Mitsumi keys appear softer and more rounded. This may sound a bit vague but if you see the two different types together, the differences become obvious. You might be able to make it out in the two pictures above.

Keyboards. More interesting than you'd think. Possibly.

Yet Another A500+ Motherboard - Finale

Only two parts to this one. This is because the board is actually in pretty good condition overall. There are a couple of things.

First, the missing pads at JP7A and J9. Just to be absolutely clear, the pads were loose when I got the board. They were also like that when the previous owner got the board. Fortunately, I was on hand to sort that out with a hot metal stick and some de-solder braid and a solder sucker. Poof! They're gone! The loss of these isn't critical but does mean certain modifications would be a bit more tricky in future...

Next, the dodgy ROM. It's dead. It's expired and gone to meet its maker. It's bereft of life. It's shuffled off its mortal coil. It is an ex-ROM. I stripped down my own A500+ and nicked the ROM from that for a few tests. It went straight to the familiar boot screen with no problems. This meant I could plug in an external drive and test it with that rather than stripping down my A500+ any further. And test it I did. I ran the Frontier game demo and just left it for a few hours. No problems.

“Don’t cry because it’s over, smile because it happened.”

Next, the joystick and mouse ports had pins broken. I'm certain that one pin was missing from the joystick port when I got the board but I'm fairly sure I broke off a couple more with my incessant waggling of the mouse plug trying to get it out. Oops. As luck would have it, I have a big bag of connectors that I 'over ordered' a while ago. They're not as good quality as the originals but they fit, they work and I have plenty....

Broken ports - oh dear. :(

The first thing to do with the old ports is, rather obviously, remove them. This was a bit of a pain but not as bad as I expected. With lots of de-solder pump action, some input from de-solder braid and a lot of patience they were eventually persuaded to come out. The hardest bit is the two anchor pins which provide mechanical stability to the ports when they're on the board. The solder joints are rather large and needed a much hotter iron than normal as well as lots of suction and a big waggle to get them to release. They both came out with no damage to the board though which was a good result.

Joystick Port Removed

Mouse Port Removed

Next, I had to solder in the new ones. This was surprisingly easy. After cleaning the board thoroughly with isopropyl alcohol and cotton buds, they just slotted straight in. I soldered one corner pin first while holding it firmly to the board, then did the opposite corner. This held the thing place while I did the rest. The larger joints for the supports were also fairly simple and just needed a hotter iron and a lot (a LOT) of solder to fill the holes. Rinse and repeat.

New ports loveliness

And from the back..

I'm really pleased with how the ports turned out and the only way you can tell they're not original is because the hex screws are a different thread to the originals. This was something I only realised as I was putting them in. Oh well. You can't have everything. A quick check with the standard Amiga test disk (courtesy of Kier on the Amiga Facebook group) proved that they are working correctly.

The final repair was to the cluster of resistors and diodes in the AUDIO FILTER section of the board. The pad on the underside of the board had been destroyed so the leg of the resistor and diode was just sticking through the hole.

Pad gone - leg with no connection

To repair this I took a piece of kynar wire and threaded it through the hole. I made sure it was long enough to extend along the leg of the diode on the other side.

Kynar wire in place - to be trimmed once soldered

I carefully soldered the wire along the exposed track, making sure that wire also joined nicely to the leg of the resistor. The I turned the board over and soldered the other end to the leg of the resistor/diode combo. Finally, I trimmed off the excess wire on the underside.

Repair complete on this side

Repair complete on underside of board

And that's about it. I did a final test to check that the audio filter still works (it does) and that I hadn't broken anything else (I hadn't that I could see). Pending the acquisition of a 2.04 ROM, it currently has KS1.3 installed. Another A500+ motherboard saved and almost ready to be released back into the wild. Thanks for reading. :)

Yet Another A500+ Motherboard - Part 1

This is getting to be habit... Another A500+ motherboard has arrived. This one just gives a black screen despite the best efforts of the previous owner.

Next patient please!

On first inspection the repair wires look to be correcting the classic signs of battery damage. They were pretty well done but a bit thick for my liking and, as I have some uber thin kynar wire knocking around, I decided to remove them with the intention of replacing them.

Previous Repairs

Then I inspected the board again. To my surprise, it looked very, very clean. There's not much damage from the battery. I poked around with a screwdriver to expose where the battery had leaked and remove the damaged conformal coating.  Where the copper was exposed I ran a smidgeon of solder across the tracks. But there wasn't really much damage at all.

One of the least damaged I've seen...

Continuity testing revealed that the only issue seemed to be from the cluster of resistors/diodes near the AUDIO FILTER section on the board. On the opposite side of the board one of the pads has fallen off probably through exposure to the battery leak and then a hot soldering iron. No biggie to sort this out but it shouldn't cause a black screen. Hmmmm.

Missing pad - no problemo!

I tried testing around Gary who is another prime candidate for causing a black screen, especially if his socket is corroded by the battery. No problems.

Strange.

Black screens are listed as being a CPU fault but, in reality can be caused by any number of things. Dodgy logic chips, broken tracks at Gary's socket (as mentioned), busted ROM etc.

Anyway, just to be sure I swapped over the CPU with a spare but this made no difference. Then I swapped Gary with a spare but this still made no difference. I don't have a spare 8375 Agnus or a 2.04 ROM but I do have a couple of 1.3 ROMs. Just out of interest - I wasn't even sure the 1.3 ROM would work on an A500Plus - I swapped out the ROM for one of these.

And it booted.

Well, this is awkward..

This is a surprise to me as I would normally expect ROM faults to give a red screen. In any case, the board boots to the familiar KS1.3 white screen. This is good news but is a bit of a pain as the 1.3 ROM with only boot from an internal floppy drive i.e. DF0. The big advantage with 2.04 is that it will happily boot a bare board from an external floppy drive. To do any more testing I have to dismantle my own A500+ and swipe the drive from it for a while which is a bit of a pain...

Before I start dismantling I decided to carry on looking over the board in case of any other issues. There were a couple of minor things. The pads at jumper 9 and jumper 7A are gone. This is partly my fault. Slightly over exuberant cleaning, battery acid and the heat of a soldering iron were too much for them. They were there when I started cleaning and, well, you can see the result. They were in poor condition but had been that way since before the previous owner. Their non-existence is not really an issue for a standard Rev 8A board though.

JP7A - Gone, but not forgotten.

J9 - Missing, presumed gone.

The mouse and joystick ports have pins that are damaged. I'm not sure if I did this. Oops. Again, it's not a big deal as I have a big bag of these connectors that I accidentally over-ordered a couple of years ago...

It wasn't me...honest..(probably was actually)

In part 2 I will dismantle my A500+ and attempt to test whether there are any other problems on this board. I might also replace the mouse and joystick connectors. 😀

Even More Memories...

Well it seems my detective work was correct. After testing the 512Kb memory expansion that was very kindly sent to me by Neil, I'd come to the conclusion that one of the four DRAM chips was dead.

After posting the blog post to the Amiga Facebook group one of the other guys there offered a DRAM chip to see if I was correct. I gladly accepted and guess what arrived in the post today? Yes, a bill from RS Components. But also, a small envelope with an expertly packed 20pin DRAM chip. Yay!

Well Wrapped DRAM

This DRAM chip is different from the others on the expansion board in a couple of respects. Firstly, it's made by Motorola (just like my phone). Secondly, it is rated at a speed of 70ns. That's a lot faster than the ones on this board which have a speed of 120ns. Hmmm. Not sure if that will make a difference or not..

Just to be sure I found the data sheets for the old DRAM and the new DRAM chips, and checked that they have the same pin out. Which they do. Nice.

Motorola DRAM Pinout

V53C DRAM Pinout (original on board)

So, time to just bite the bullet and put this sucker in there.

New Chip Inserted

Moment of truth....

No magic smoke released. Phew. White screen. OK, patience - there's no internal floppy attached to this test motherboard but there is an external drive. It boots and runs the test disk no problem.

Memory test shows 1.5Mb of total memory, just like before. This time though:

Success!

It works! This has been running through 84 iterations of the memory test with no problems. Nice! Huge thanks to Michael for the DRAM and Neil for the originally broken RAM expansion.

PS Memory test is now over 150 rounds with no faults. Oh, yes. ;)

More Memories...

As I was perusing the Amiga Facebook pages I came across a post by a chap who had dragged his A500 out of storage and was going to give a young relative a lesson in retro gaming. Sadly, this was not to be as the A500 refused to start.

With the quantity of helpful people on the group several pieces of advice were given and it transpired that the memory expansion was the cause of the non-boot. The OP (that's 'Original Poster' for you non-hip and trendy people out there..ahem) was about to throw it in the bin but I asked if he could send it to me instead as I was looking for another repair project. And he did.

Package Arrive Safely

It's a fairly generic 512Kb RAM expansion as was the trend in the late 80's and early 90's. It has four 256k x 4 bit CMOS dynamic RAM chips and, bizarrely, three of them are socketed. The battery was left on too but this was quickly despatched.

Argh! Curse you Varta!

Varta removed - clean up on aisle 5

I took some vinegar and applied it liberally to remove the battery residue (fizz-tastic) and then washed away the vinegar with some distilled water and allowed it to dry thoroughly. After a bit more clean up I was ready to test.

First test...

I used my A500+ spare motherboard with an external drive and the excellent Kier's test disk. There is an intermittent fault with this motherboard in that it sometimes won't boot and I get a yellow screen. Normally, I have to re-seat Agnus and then it works. Sometimes it works just by breathing near it. That's for another time. At this point, the motherboard is working...

...and so is the RAM expansion. Well that was easy.

Before I got too cocky I decided to run the RAM test and see what transpired. It was not necessarily good.

Aw, crap.

I re-seated the three RAM chips and got the same result. It looks like there is one dodgy chip in there but the question is, which one?

So I labelled them 1, 2 and (duh) 3. Then ran the RAM test again and took a picture of the board and the results. Then I moved the chips around and did it again. Rinse and repeat. Very quickly, I honed in on chip number 3.

Okay so I did 2, 1, 3.

Error on FEDC

Order now 3, 1, 2

Error now on 7654 - it's either chip 2 or 3.

Order now 3, 2, 1

Error still on 7654 - It's looking like it's chip 3 at fault

Order now 1, 2, 3

Error moved back to FEDC - It's chip 3 alright..

Whenever chip 3 moved, so did the RAM errors. I think we have our faulty RAM chip. Although I am not an expert in this, what  happens is the chemicals from the battery leak and attack the metal legs of the chips. In some cases it's just superficial but sometimes the corrosion can creep up the legs and into the actual chip destroying it completely with no chance of repair.

Rather annoyingly these are of a later vintage than the chips I was playing with here and I don't have any others that might be suitable. I guess I need to get on eBay to look for a replacement chip and see if that recovers it. But in the meantime, I will be doing some more reading up on this type of chip, just to be sure that my rudimentary detective work is correct.

Special thanks to Neil for providing the RAM expansion. :)

Re-purposed Laptop Screen

Recently I posted on the Amiga Facebook group a picture of my A500+ setup (as below) which generated a few comments, specifically about the screen.

Real Hardware - no emulation here...

The screen in question is actually from a Compaq laptop that died several years ago. It was, allegedly, affected by a faulty GPU from nVidia, caused by crap soldering between the GPU chip and the circuit board. It was particularly widespread and even prompted a class action lawsuit in the US.

This laptop got thrown into a bag and forgotten until a couple of years ago. I wondered if I could use the screen somehow on my Raspberry Pi. To cut a long story short, yes, yes I can. It requires a couple of relatively inexpensive circuit boards and a bit of hacking at the screen but nothing too complicated.

The hardest bit was getting the screen out of the laptop which required totally dismantling the whole thing. When dismantling, there is a cable called the LVDS cable (I think) which is a bit delicate. It's the one the connects the LCD to the main board. Take extra care when removing it.

There are three main bits to the driver board I bought (remember that the screen has been removed wholesale from the laptop body).

The Back of my professionally modified screen*

*Not professional(!)

First, there's the main board itself. The one I got hold of has VGA, HDMI and Composite inputs.

Main board - top view so you can see the model number

Main board - HDMI, VGA and composite inputs

Then, there's the control board which has several simple push buttons for the menu functions of the main controller board e.g. brightness, source input etc.

Control board

Finally, and most importantly, is the inverter board. This takes the low voltage from the board and inverts it to a level suitable to light the backlight in the LCD panel. This bit comes covered in thick insulating plastic for a reason. The voltage is high enough to make sure anyone touching it will have a bad day.

Inverter board - look but don't touch

With the board I acquired I also needed to acquire a power supply. This I got from a UK supplier who is subject to the strict regulations around electricity etc in this country. This is preferable to getting one from a supplier in China who isn't. It looks like a simple laptop replacement power supply and has a fairly standard 5mm barrel connector.

And that's basically it. I had to hack a hole in the back of the screen cover to get the backlight connector through and I drilled a few holes to mount the boards (blu-tack works fine for the control board).

DISCLAIMER - NONE OF THE INFORMATION BELOW IS INTENDED TO BE A RECOMMENDATION OR ENDORSEMENT OF ANY PRODUCT. I AM NOT RESPONSIBLE FOR YOUR ORDERS, ACTIONS OR YOU BLOWING UP YOUR CAT. THE INFORMATION IS PROVIDED IN GOOD FAITH AS AN INDICATOR OF WHAT I MANAGED TO DO. YOUR MILEAGE MAY VARY. SO THERE.

Sadly, I can't find the original listing on eBay that I bought this from as it was actually nearly two years ago when I did this (is it really that long?). They are still available in various forms though, just search for 'LCD Controller kit' and you'll see various results pop up.

A few points to note when ordering:

1) Remember to get one that includes the inverter board. Without it the backlight won't work.. I'd expect to pay around £25 (around $35 ish) for a complete kit.

2) Find out the make/model of the LCD panel you have before ordering. If in doubt, email the seller and ask if they support that particular model. Most LCDs have a white label on the back with this on (mine was an LG something or other).

3) Check what inputs are supported - mine does HDMI, VGA and composite which allows me to use my Amiga (composite), Raspberry Pi (HDMI) or even my work laptop (VGA). YMMV depending on which board you find.

3) Don't forget a suitable power supply!

Good luck.

Voyager Model Build

A long time ago, in a galaxy far, far away...

No.

A long time ago, my wife bought me a model of Voyager from Star Trek. This has followed us through two house moves and two children (one now at University). I thought it was about time I actually made it.

Voyager - nice

Instead of the usual paint it, glue it, paint it, display it I though I would try and do a bit more. One thing that I always wanted to do was use lights inside one of this type of model beacause:

a) it looks cool
b) do I need another reason?

So, first things first. The windows. On this model they're all there but filled in. The larger windows should, in theory be three separate panels but, for this model, I won't worry too much about that as I have a 'workaround' that might work. Every window needs to be drilled out and sanded to shape.

I tell you what, there's a lot of windows on Voyager...

Windows started..

Windows on this side finished

After a few nights of drilling, trimming and sanding, all the windows had been cleared out.

Next thing, get some LEDs. In this case, eBay is my friend and I managed to get a batch of 50 super bright 3mm LEDs for about three quid. A bit of a wait for them to arrive from China but they're cheap and they work.

To see what affect they produce I hooked up three LEDs and powered them up inside one half of the main body of the ship. The result was, to say the least, disappointing. The lighting was very harsh and it was easy to see the LEDs. To get around this I took a sheet of thin plastic (similar to a laminating pouch) and sanded one side. Then I cut a couple of small pieces and stuck them to the inside with double sided tape. When the lights were switched on again I got a much more pleasing effect.

LEDs held on with Blu-tack

Exterior view

Another Exterior Shot

With all this I was well on the way. I need to make sure that there are no light leaks when I glue the thing together and I also need to plan where exactly through the whole ship I will be putting the LEDs. Even though I have 50, that's not as many as you'd think.

I also need to consider what current these LEDs will draw when they're switched on. Assuming that each LED takes 20mA and there are 50 of them then the supply needs to be at least 1amp (say 1.5 for safety). I also need to consider what heat might be generated inside. Somewhere, I have a spare 2A USB power supply for a mobile phone which might do the job and provides 5V. More thought on this is required...

Also, what I would like to add is:

a) Flashing navigation lights
b) Blue nacelle lights on the engines
c) Red ramscoop lights at the front of the nacelles
d) A light for the main deflector

More next time!