Keyboard issue

[iturbez]

Hi!

My ZXpand has just arrived... I´m happy now!

But... when I've got my Zeddy to try it, I've found my keyboard is not working well: The following keys does not work:

5 6 T Y G H J K L newline V B

What may I look first?
The flat cables?
The connections to mainboard?

I'm displeased...

Thanks in advance.

[RWAP]

It is invariably the tails leading from the keyboard to the motherboard which will have cracked either where it bends under the keyboard, or where they go into the two sockets on the motherboard.

Replacement keyboards are very simple to obtain and fit - http://www.sellmyretro.com/offer/detail ... rd%29-1516

It may also be the molex connectors (that the keyboard tails push into) on the motherboard itself, although these are less likely to fail.

http://www.sellmyretro.com/offer/detail ... _ZX81-1487

[Paul]

5 6 T Y G H J K L newline V B

What may I look first?
The flat cables?

I am afraid I have to agree to what Rich says.
From my experiences it is no use to try to repair this by cutting the end of the leads.
It will not work or last long.
The best way is definitely to replace the membrane by one of Rich's new membranes.

[iturbez]

It is invariably the tails leading from the keyboard to the motherboard which will have cracked either where it bends under the keyboard, or where they go into the two sockets on the motherboard.

And that is the truth... I'll buy a new keyboard as soon as possible...

[Paul]

I use this Thread as it matches perfectly.
I built one of Martins ZX80 boards. It works quite good except for keyboard row
YUIOP. I tried the rwap foil, a switch, and an external memotech keyboard.
I used 47k resistors and schottky diodes instead of 1N4148
In order to use the memotech keyboard I have to pull the IC 10.
All chips are 74HTC. I checked with 74LS too. Everything else works just fine.
Any ideas? I checked all connections I checked a13 for any short circuits, I checked d8 it's working with a loss of 0,258V.
Is it possible that the z80 is broken?
It's a zilog z84C0006.
Are the resistors and diode used when I connect the memotech keyboard ?
I have no schematics of it.
I hope someone can help.

Greets
Paul

[sirmorris]

Hi Paul,

My 'Martin' ZX80 is now working fine after Prime traced a fault with a connection on one of the lines leading to a buffer chip.

As it's the the row of keys not working, as opposed to a column, this indicates there may be a connection issue between diode d8 and a13 somewhere - you checked for short circuits but did you check for open circuits? Does a13 reach its destinations? Does the connection on the row of keys reach the diode?

I don't think it's a short circuit as it would cause the zeddy to fail as a13 becomes corrupted. The Memotech keyboard has its own diodes, resistors etc. It simply drives the address and data lines in the same way as the foil would, which again shows some connection problem with the keyboard matrix itself.

It will work very similarly to Wilf's k/b interface - I built most of one of these. I left out the joystick and comms port and it worked beautifully.





C

[Paul]

It was a broken Z80
its working now.
I'm glad the problem is solved. And the Z80 is still for sale. So i can refill my stock.