Keyboard or Mainboard problem

[talrek]

Hi,
here is my problem, i hope someone will be able to help me.


I have a Qwerty CPC6128 which has "Keyboard" problems, in fact i think it isn't a keyboard problem.
When I hit the DEL key for example, it makes a lot of strange characters on the screen, other keys are OK.
And when i use a joystick i don't have the Arrow characters, but strange characters instead.


I changed the Z80, I change the keyboard to see if it was related.
Every thing else is working great : Disc, Parados, Megaflash when connected.


Any clues ? 

[CraigsBar]

Can you swap the ay? I had a similar issue once, and a new ay fixed it.

[Bryce]

Dodgy Firmware ROM?

Bryce.

[talrek]

Can you swap the ay? I had a similar issue once, and a new ay fixed it.

Ok, i will try tomorrow with a new AY (if i have one...)

Dodgy Firmware ROM?

Bryce.

I will try also ;-) , i must have a Parados Eprom somewhere 

[Bryce]

It's very unlikely to be the AY, no AY failure could cause those effects. Only try a different AY if it's already socketed. It's also more likely to be the Firmware/BASIC ROM, not the AmsDOS (where ParaDOS goes).

Bryce.

[talrek]

Ok,
i'm going to desolder the Basic ROM first just to try a "good" one !
Thank you again

[TFM]

If it isn't the ROM or the AY, then it could be the PIO8255.


Good luck!

[talrek]

Well in order :
The basic, the AY and then the PIO
Got a lot of work ;-)


Thank you

[TFM]

Yes, but later you got a socket for all of them! And that's awesome! 

[Bryce]

Yes, but later you got a socket for all of them! And that's awesome! 

Yes, but it also means that you have destroyed perfectly good hard to get parts if you just blindly swap them all.

Bryce.

[TFM]

Yes, but it also means that you have destroyed perfectly good hard to get parts if you just blindly swap them all.

Bryce.

He only swaps the broken parts.[nb]Or the parts having been suggested here.[/nb]

[Bryce]

He only swaps the broken parts.[nb]Or the parts having been suggested here.[/nb]

Not all the parts suggested here are broken. The AY is very unlikely to be broken.

Bryce.

[TFM]

Well, we will see at the end... we could actually do some bets 


I guess the AY has a bigger chance to be broken than the PIO. Also if the Basic-ROM would be broken, you would rater get random effects or just altered keys, but the way he describes it the problem is located in key scanning, in particular the AY reports a bunch of keys not pressed.


One quid on the AY 

[Bryce]

He says the DEL key produces "lots of characters". Any AY problem can give you wrong or no character, but no AY failure would cause lots of characters to appear. You get two characters if an AY internal pull-up resistor fails, but it still gives the correct character first. Even if they all failed, I don't think it would cause that and it would effect all keys the same.

Bryce.

[robcfg]

Dirty keyboard membrane or failing membrane contact to the motherboard, maybe?

[Bryce]

Dirty keyboard membrane or failing membrane contact to the motherboard, maybe?

That still wouldn't cause multiple strange characters to appear.

Bryce.

[ZbyniuR]

My friend once repaired 464 and 6128 which had problems with kays with bigger numbers than 70. Sequences of characters on screen in each of them were different, but, after changed AY problem disappeared.
He said that it looks like AY had a gates that PIO uses to operate the keyboard and joystick. But such AY which making problem in CPC still playing well in sound cards for ZX Spectrum.
I guess cause was test connecting something strange to joystick port.

[TFM]

He says the DEL key produces "lots of characters". Any AY problem can give you wrong or no character, but no AY failure would cause lots of characters to appear. You get two characters if an AY internal pull-up resistor fails, but it still gives the correct character first. Even if they all failed, I don't think it would cause that and it would effect all keys the same.

Bryce.

I bet you a beer it's the AY! Because if it fails, it can start delivering random bits so you get lots of characters when pressing one key. 

Dirty keyboard membrane or failing membrane contact to the motherboard, maybe?

He exchanged the keyboard already. 

[talrek]

yes i tested the keyboard, so it is not that.I just removed the 40025 today, so i will solder the socket tomorrow and test it    First answer tomorrow     Who will win ?   

[TFM]

My best wishes! Hope it will work again soon!

[Bryce]

Hi Talrek,
     just fixing a CPC+ at the moment and it has a similar problem to what you describe. Is this the series of characters you get when you press DEL? If so, changing the AY doesn't solve the problem, nor does changing the ROMs. Unfortunately, this is a plus, so it doesn't have a 8255 PIO, but I'll let you know as soon as I've found the issue...

Bryce.

[talrek]

   I was just going to reply that i changed the Basic and AY and it doesn't work 


All this work for "almost" nothing  (in fact i have the luck to have now a CPC with two more sockets  [size=78%])[/size]



Then i saw your message : it is EXACTLY the same characters when i hit the DEL key.


Do you want that i try to change the 8255 PIO (even if i think it isn't the cause...) ??

[CraigsBar]

Hi Talrek,
     just fixing a CPC+ at the moment and it has a similar problem to what you describe. Is this the series of characters you get when you press DEL? If so, changing the AY doesn't solve the problem, nor does changing the ROMs. Unfortunately, this is a plus, so it doesn't have a 8255 PIO, but I'll let you know as soon as I've found the issue...

Bryce.

If that was one of the boards I sent you then it looks like the AY swap did not fix it for me 7 years ago and my memory is failing


Sorry.

[Bryce]

  I was just going to reply that i changed the Basic and AY and it doesn't work 


All this work for "almost" nothing  (in fact i have the luck to have now a CPC with two more sockets  [size=78%])[/size]



Then i saw your message : it is EXACTLY the same characters when i hit the DEL key.


Do you want that i try to change the 8255 PIO (even if i think it isn't the cause...) ??

Ok, so we have exactly the same issue, good to know. The plus doesn't have a PIO, so that's not going to be the issue. However, I have noticed that this PCB also has problems with the floppy drive, does yours too? Also one other thing that I noticed. Mine has a French keyboard and an English ROM, what about yours?

Hopefully I can check it some more today and maybe find the solution.

Bryce.

[arnoldemu]

Bit 7 or D7 is stuck. All these keys are on the same bit but over multiple keyboard columns. Is there a short somewhere between keyboard and ay?