Fix a 1200 keyboard with a 500 keyboard

[magistral]

Hi,

Recently i've bought a 1200 miggy via mercadolibre (third world ebay). Unfortunately, the keyboard have a lot of broken keys (the seller "forgot" that). Anyone knows how to fit a 500 keyboard into a 1200?. I know almost nothing about electronic, but i can learn.

Thanks in advance.
Greets.

[amigakit]

They are different unfortunately.  The A1200 keyboard uses a ribbon cable and green membrane with carbon pads which is very difficult to repair.

However we stock new A1200 keyboards

[Piru]

@magistral

You can repair A1200 keyboard with A500 one, the only problem is that A500 keys are much darker.

If you decide to do this, you need to disassemble the keyboard completely (unscrew every small screw on the backside). Once the keyboard is open, you can remove the bottom metal plate. Under you can see the keyboard matrix.

If the keys are broken, just take the topside (keys) from the A500, use the matrix and bottom from the A1200 keyboard. This way you get the correct ribbon cable.

Here you can see external A1200 keyboard constructed of the A1200 case, A1200 keys and A500 keyboard matrix and metal bottom:

http://www.iki.fi/sintonen/tmp/keyb_front_1_s.jpg
http://www.iki.fi/sintonen/tmp/keyb_back_s.jpg
(If you look carefully you can see the dent on the metal bottom made by the stand holding the keyboard in place in A500 :-))

[magistral]

@Piru

Well, the problem is: I think the matrix is broken... any tips?

Thanks.

[Piru]

If the matrix itself (the film kind of thing) is damaged then you need to get a replacement one from a A1200 keyboard, or get a new keyboard altogether. The matrix itself is fragile and afaik quite impossible to fix.

I'd still check if the matrix is just dirty or if the buttons themselves are somehow damaged.

[Jope]

The matrix itself is fragile and afaik quite impossible to fix.

One option might be conductive ink, but that will be messy and difficult to do..

[_yak_]

When I was moving my A1200 to an ATX tower I've adapted A500 keyboard for this setup. The signals generated by the A500 keyboard interface can be found on the A1200 mobo. I simply connected them there and it was working flawlessly. However, I used it as an external keyboard so there may be some problems puting it into the A1200 case, there will be problems with A1200 LEDs for sure.

[magistral]

@_yak_ : Can you please explain a little more?. Any pictures?.

btw: I've examined the matrix and cannot see any damages on it, but it doesn't work...

@Jope: There is any way to use any other conductive part of the matrix to fix the broken keys?. The keys Ctrl, White Amiga and Black Amiga are broken, so i cannot reset!

Thanks a lot.

[Oliver]

Hi,

Are you sure that the problem is with the matrix, and not the keys?

I've never had cause to open the keyboard section of my 1200, so I'm not certain of its construction, but I have repaired a number of kepads of other devices, which are quite likely similar.  The aging of carbon contacts is quite often the cause of keypad failure.  

You could have a look here for an example of repairing an old synthesizer keypad.  There are carbon contact cleaner kits like this one available.  However, I have also heard of contacts which only used a kind of thin carbon powder coat on the pad, which can simply rub off whith wear (not sure if this is true though, as I don't think I've actually seen these).  If that's the case, probably they can't be cleaned too vigourously.  Such contacts can probably be replaced with a new coating.  The afore mentioned repair kit may do the job.

Of course, you should also make sure the contacts on the matrix are clean.

Anyway, if the key contacts are at fault, it is possible to trouble shoot this by using a contact which is known to be working well, on a key which has otherwise been problematic.  As you don't have much electronics experience, be careful, and it would also be a good idea to get help from a friend who may have a little more experience.

Good luck.

edit- For the trouble shooting procedure, you should also try using the carbon contact from a non functional key for the matrix contact of an otherwise functional key.  Hope the description makes sense.

[_yak_]

I forgot to mention that it was long ago and I don't have access to this Amiga now so I cannot provide you with any photos.

However, I've just collected some info found on the www. If you're going to do it then do it at your own risk, I cannot take any responsibility for any damage you may make.

So, the A500 keyboard pinout is listed on Amiga-Hardware site:

http://www.amiga-hardware.com/showhardware.cgi?HARDID=651

All you have to do is to connect the +5V, GND, CLOCK, DATA and RESET lines to the A1200 motherboard. The +5V/GND part is simple. You can get it from diskdrive power connector for example. Make sure you connect it to 5V, not 12V (!) as this would blow up the A500 keyboard controller (and maybe even more).

The other three signals, CLOCK, DATA and RESET, should be called KB_CLOCK, KB_DATA and KB_RESET and can be found on the chip marked U13 (KEYBOARD MPU) on the A1200 motherboard.

Here you can see the chip, it is located near the keyboard connector:

http://www.amiga-hardware.com/download_photos/a1200mb_rev1d4.jpg

The apropriate lines can be seen on the A1200 schematics found here:

http://www.amiga-hardware.com/downloads/a1200schem.lzx (page 9).

Here is the pin assigment (taken from the schematics):

KB_CLOCK - pin 14
KB_DATA - pin 13
KB_RESET - pin 38

If you're good at soldering you can do it yourself. If you're not, better ask someone who is as A1200 is made in SMD technology and the pins are very small.

Good luck!

[magistral]

@_yak_

The signals are the same?.
The data is encoded in the same way?.

Thanks a lot.

[Piru]

The signals are the same. The encoding is the same.

In fact A1200 mobo has the keyboard MPU on it directly, and at least I had to disconnect it (cut 2 pins) for the external keyboard to work correctly.

[magistral]

One more question about soldering...

I must solder it directly into the metal pins that are visible in the top side of the mother?

[_yak_]

Piru may be right, I did it a long time ago so I could forgot that you have to separate the KB_DATA and KB_CLOCK lines from the A1200 KEYBOARD MPU so it does not disturb the transmission.

Of course you don't have to solder to the chip. In fact, I remember soldering it to some other points. Take a multimeter, schematics and see where the signals go, on their way you may find some better place to solder and to cut them.

[dawiper]

When I made my external keyboard, I soldered kb_data and clock to legs of pin 43 and 44 on u7(cia). But like piru I had to cut pin 13 and 14 on the keyboard mpu(u13) to take the onboard controller offline.
I still used pin 38(u13) for keyboard reset.