Keyboard hardware repair help request

[MacShrike]

Ls,

I'm cleaning and fixing my old a1200.
It has a Zorro II expansion with 2 RAM bars. An FPU and MPU.
I can vaguely remember being able to afford this beast back in the days.
I'm just getting into microelectronics because of this, I'm a software guy mostly. And unemployed now.

Because of a simultaneous double fault; it failed to reboot sometimes and I spend a lot of resets to pin-point the problem, yet there may be two (please let it be just two)
Some help would be greatly appreciated.

I will describe my "diagnosis" below:

At first the machine worked although not booting up correctly every time.
I tried different variations of hardware on start-up before discovering that the awkwardly bent capacitor under the IDE plug on the motherboard was loose, and eventually came off. The loose IDE cable was sometimes making it connect I guess, until it came off.
Since It came loose. It's starts fine but the caps light blinks three times and no keyboard (Lost the mouse and still waiting for the usb replacement and I WAS using the kb left amiga cursor interface.)

Shortly before this,
I noticed type to type "Y" at exit game that the key didn't respond. Checking in Shell a whole column wasn't responding starting at R (or E cant remember now sorry) also some numpad keys weren't typing..

So I checked and cleaned the membrane. It looked like it had 1 broken line somewhere a bit blackish.
After putting it back it was worse.

Now when I hit "d", or any key in that column, it spits out the entire row (asdfghjkl sometimes with an escape character. Pretty the same every time but its hard to see sometimes.

So I ordered a new membrane, placed it but still, and exactly, the same.

So Question:
Can this KB issue have to do with the loosened capacitor?
and/or
Is the KB chip perhaps shorting?, I had cleaned the motherboard.

It does boot up, I accessed the HD and a CD-drive. Played a game... before I started cleaning.
I haven't resoldered the capacitor yet.
I was hoping it might also affect the KB troubles because, although I bought an old analogue scope to be able to try and learn and repair, I'm not feeling lucky.

Thanks for reading and regards,
Mac

[Leon Besson]

Yo Bromigo!

First things first.

If the mainboard hasn’t been recapped. Then I would start with that first. You may have old caps leaking if that haven’t been done. Any fishy smells from the mainboard will indicate this if you can’t see them.

If the cap has come away then replace this when doing a recap.

[MacShrike]

Horalez Leon

I don't want to sound lazy.... but I am
With smelling fishy do you mean actually smelling of fish?
They all look shiny, flat and OK.
Not counting the one I tore off.
Couldn't I quicker test them with a multimeter?
I'm about to go out and buy one anyway.

Thx for the reply

[Leon Besson]

Originally Posted by MacShrike

Horalez Leon

I don't want to sound lazy.... but I am
With smelling fishy do you mean actually smelling of fish?
They all look shiny, flat and OK.
Not counting the one I tore off.
Couldn't I quicker test them with a multimeter?
I'm about to go out and buy one anyway.

Thx for the reply

MacShrike Mang!

Yes a leaking cap actually smells like fish. Don’t just go off looks as I’ve had leaking SMD caps that looked good, but we’re leaking.

L8rs Bromigo!

[MacShrike]

So maybe I should get a cat to help me too then

[MacShrike]

Originally Posted by Leon Besson

MacShrike Mang!

Yes a leaking cap actually smells like fish. Don’t just go off looks as I’ve had leaking SMD caps that looked good, but we’re leaking.

L8rs Bromigo!

Bro,

I have recapped the thing, only 1 blister on finger.

The caps light keeps blinking three times,.
Found this:

Check IC's:
74LS123
74LS27
or
HD74HC00D
HD74HC123

Just can't find them on the a1200 motherboard.
Downloaded the Channel Z a1200 Rev1 schematic, still can't find them.
Please assist

[MacShrike]

Hi.
Thanks for all the advice.
I decided to send it to professionals after discovering a loose track and missing foot on 2 of the caps.

Close this thread if you will.

[A3000T]

Originally Posted by MacShrike

Ls,

I'm cleaning and fixing my old a1200.
It has a Zorro II expansion with 2 RAM bars. An FPU and MPU.
I can vaguely remember being able to afford this beast back in the days.
I'm just getting into microelectronics because of this, I'm a software guy mostly. And unemployed now.

Because of a simultaneous double fault; it failed to reboot sometimes and I spend a lot of resets to pin-point the problem, yet there may be two (please let it be just two)
Some help would be greatly appreciated.

I will describe my "diagnosis" below:

At first the machine worked although not booting up correctly every time.
I tried different variations of hardware on start-up before discovering that the awkwardly bent capacitor under the IDE plug on the motherboard was loose, and eventually came off. The loose IDE cable was sometimes making it connect I guess, until it came off.
Since It came loose. It's starts fine but the caps light blinks three times and no keyboard (Lost the mouse and still waiting for the usb replacement and I WAS using the kb left amiga cursor interface.)

Shortly before this,
I noticed type to type "Y" at exit game that the key didn't respond. Checking in Shell a whole column wasn't responding starting at R (or E cant remember now sorry) also some numpad keys weren't typing..

So I checked and cleaned the membrane. It looked like it had 1 broken line somewhere a bit blackish.
After putting it back it was worse.

Now when I hit "d", or any key in that column, it spits out the entire row (asdfghjkl sometimes with an escape character. Pretty the same every time but its hard to see sometimes.

So I ordered a new membrane, placed it but still, and exactly, the same.

So Question:
Can this KB issue have to do with the loosened capacitor?
and/or
Is the KB chip perhaps shorting?, I had cleaned the motherboard.

It does boot up, I accessed the HD and a CD-drive. Played a game... before I started cleaning.
I haven't resoldered the capacitor yet.
I was hoping it might also affect the KB troubles because, although I bought an old analogue scope to be able to try and learn and repair, I'm not feeling lucky.

Thanks for reading and regards,
Mac

My Amiga 1200 keyboard had 12 - 15 keys pads that were failing. I found replacements keys on many websites and were $2 to $4 plus shipping, too much, $30 - $50 to fix my keyboard. Note these are old used pads and may fail in a short time.

I found $5 to $12 to do all keypads many times. This will work on all conductive pads round or rectangle. The circuit membrane must be good, and all keys must work to some degree.

You can check the pads with an ohm meter on 200-ohm range and must be 80 ohms or lower across the black conductive pad to be ok, use slight pressure not to damage the pad.

Tools and parts.

1 Small tweezers.

2 Scissors

3 Small roll of aluminum tape used on forced air duct systems. You can go to a business that does heating and AC and ask them for a 20 mm piece. It MUST be aluminum and have zero ohms across the foil.

4 Caliper or a way to measure 7.5 mm x 2.5 mm.



Wipe the circuit membrane with a paper towel to lightly clean the black conductive pads, do not rub.

Cut the aluminum tape to the size above, use the tweezers to remove the paper from the aluminum tape and apply it to the bad keypad and press it down.

Do this for all bad keys.

On round keypads you may be able to use a paper punch, but small squares will work.

[Jope]

I just wipe the rubber pad under the stem against a piece of office paper from my printer, a good 5-10 wipes will do it. Then blow off any dust with compressed air and see if the key works again.

I have not had to replace a single pad ever since I started doing the paper trick. One C128D keyboard was almost totally inoperative, I got all the keys working with this method. Some took more than 10 wipes to come back. :-)

[A3000T]

Originally Posted by Jope

I just wipe the rubber pad under the stem against a piece of office paper from my printer, a good 5-10 wipes will do it. Then blow off any dust with compressed air and see if the key works again.

I have not had to replace a single pad ever since I started doing the paper trick. One C128D keyboard was almost totally inoperative, I got all the keys working with this method. Some took more than 10 wipes to come back. :-)

Yes this can work but I got tired removing 21 screws. I used this repair on my C64. So when you get to use a hammer to get the S key to work try my repair.

[Jope]

You only need to undo and redo all the screws once? When testing, if you don't want to hold it together with your other hand, you can put it together with 2-3 screws.