Memotech ZX81 keyboard + ZXPand

[palmheads]

Hi All

OK so finally my Memotech keyboard arrived!!! (WOO!)

Its a lovely bit of hardware!

Unfortunately the H-J-K-L keys don't work. It weird 'cos the '81 cursor blinks when I press the keys, but the characters don't appear on the screen.

On the I/F connector, I noticed with the 2 isoloted prongs on the left (while looking at the connector), the 2nd from the left prong are a little bent. Could that be the problem? If they went making a connection to the edge connector, does it make sense those 4 keys wouldn't work?

Here is a piccie:

IMG_20150121_222511.jpg

(1.57 MiB) Downloaded 492 times

cheers
Daryn

[RWAP]

I see the spacer is missing which means it would be easy to misalign the interface which could cause any sort of problem and even wreck some chips on the ZX81... Make a new one from a piece of cassette case and glue it in place before proceeding...

[Moggy]

Good grief A missing key way!!

Please do as Rich says and make a key-way at once before connecting again, as for the bent pins the bit of the pin that makes contact looks to be ok but perhaps closing the gap between the contact part of the pins wouldn't hurt, the part that's bent at the front doesn't make contact anyway so no worries there.

Should any of the gubbins inside the module be blown they are as far as I'm aware replaceable IE no custom chips etc.

[palmheads]

Cheers for the advice Moggy & RWAP!

Ok so put a wee plastic key-way/spacer in the gap, so that should be good now.

Still no go with the keys. I realised the Newline/Function key also is not working. So that makes 5 keys (H-J-K-L-NL).

Seeing there are 10 keys in a row, could this be a keyboard matrix issue? Maybe something on the PCB?

Funny, I wanted the Memotech keyboard to safeguard the membrane failing oneday (also have a membrane replacement stored away), but the keyboard has the failing keys issue! haha

cheers
Daryn

[palmheads]

HOLD THE PHONE!!!!!

I recalled seeing some memotech documentation on zx81.de.

http://www.zx81.de/memotech/_frame_e.htm

Clicked on the Keyboard I/F link

Read this:

"IS THE ORDER OF THE MEMOPAKS IMPORTANT?

Not terribly, but the 'big' Memopaks containing 16K, 32K, or 64K should
come last. If you've got a Memopak HRG (High Resolution Graphics),
it's best to put that first, next to the ZX81. All Memopaks come with
extender boards at the back, so adding on to your add-ons is no problem."

I had been putting the Memotech 16k RAM first, then the I/F. So just tried switching them....

IT WORKED!!! haha. WOO HOO!!!

How weird.

But anyway, all the keys work now!!!

Thanks all!

cheers
Daryn

[1024MAK]

The keyboard not working when the keyboard I/F "buffer" is connected behind the RAM module could just be a dirty contact on one of the edge-connector contacts (or another type of poor connection, like a dry solder joint). Or it could be a minor fault with the RAM module (it has circuitry to control any interfaces behind it to help prevent problems when more than one RAM module is connected up).

At least you now know that your your Memotech keyboard works okay

And you have learnt that the most important part of a edge-connector is the locating peg / pin

Many Sinclair ZX Spectrums have been killed when the locating peg / pin has broken or been lost from interfaces
It happened to me when I was school age

Happy retro computing

Mark

[Moggy]

Also if the ram pack DIP switches are set in a certain fashion anything, behind the ram pack tends not to be recognised.

The positioning seems more to do with the physical shape of the modules, small ones at the front with the larger ram pack fitting snugly behind.

[Moggy]

Many Sinclair ZX Spectrums have been killed when the locating peg / pin has broken or been lost from interfaces
It happened to me when I was school age



Mark

Take heart Mark it still happens to me and I'm retired!!

[palmheads]

Really happy with this set-up now. Don't think I need anything more!



cheers
Daryn

[rune]

A blue memotech keyboard Never knew they made then in anything other than black.

Enjoy!