Atari 130XE Keyboard issue

[Steverd]

I just got an Atari 130XE that is has some keyboard problems.

I tested the continuity of the keyboard membrane and could not find any breaks.

Keys 3,0,E,P,D,:,C and Start are not working, so that know that points to Pin 10, R151 and U24

The resistors to the chip all check out in the 270 range, so they are ok.

 

Should I just go ahead and replace the keyboard membrane? I see they are only $20 on ebay.

What is the chip in U24? It's labelled: NEC 8449B7 D40551BC

BUT I can not find it online. Thank you

 

[Beeblebrox]

Remember there are two different types of XE membrane. The one for the rubber caps version and the other fixed rubber plunger type. 

 

Sound like some tracks on the old membrane have oxidised or have tiny breaks. Happens a lot. 

 

The 4051 chips are involved in the keyboard functionality and faulty ones can cause issues. For example I just had an 800 where all of keys on the main keyboard didn't respond at all. I replaced both 4051s and it instantly worked.

They are easily sourced and cheap but tbh because some keys work and others don't I'd say replacing the mylar/membrane should help as I don't think failing 4051s is the issue. (I could of course be wrong). 

 

Take the keyboard apart and if you have the rubber cap version source the correct mylar for that, or get the other. Simius here on AA sells XE mylar. Pm him and he'll be able to advise. 

 

FYI if you have a rubber cap version keep the keyboard face down or they'll all fall out, and you don't wanna lose any of them!

 

Edit: if you do need to source 4051s look on ebay for:

 

CD4051BE CD4051 4051BE 4051

 

 

Edit 2: I should add you can fix tracks on mylars/membranes with conductive circuit paint, etc. Many a time I've done this after tracking down the issue on a mylar/membrane with my multimeter in continuity mode and a magnifying glass. They aren't always salvageable and a replacement is sometimes needed. Luckily given XE mylar/membrane replacements are reddily available at least you have replacements as an option. (Same goes for the 800XL mylar/membrane based keyboard variants too. 

 

On a related note for other mylar/membranes (like the mitsumi ones for 1200XL and some 800 keyboards), if you are based in Europe then fixing them yourself is really the only option. (I believe in the States you can by new ones but really not worth the postage for someone like me in the UK). 

 

Be very interested to see if you get any joy with Xrbrevin's excellent suggestion.

Edited June 25, 2023 by Beeblebrox

[xrbrevin]

you can short 2x pins on the 24pin header socket to generate a character on screen

try the co-ordinates for the broken keys to help find the cause

[Steverd]

57 minutes ago, Beeblebrox said:

Remember there are two different types of XE membrane. The one for the rubber caps version and the other fixed rubber plunger type. 

 

Sound like some tracks on the old membrane have oxidised or have tiny breaks. Happens a lot. 

 

The 4051 chips are involved in the keyboard functionality and fault ones can cause issues. For example I just had an 800 where all of keys on the main keyboard didn't respond at all. I replaced both 4051s and it instantly worked.

They are easily sourced and cheap but tbh because some keys work and others don't I'd say replacing the mylar/membrane should help as I don't think failing 4051s is the issue. (I could of course be wrong). 

 

Take the keyboard apart and if you have the rubber cap version source the correct mylar for that, or get the other. Simius here on AA sells XE mylar. Pm him and he'll be able to advise. 

 

FYI if you have a rubber cap version keep the keyboard face down or they'll all fall out, and you don't wanna lose any of them!

 

Edit: if you do need to source 4051s look on ebay for:

 

CD4051BE CD4051 4051BE 4051

 

 

I did not know there was two versions - Thank you

I have Mitsumi TF-02 56-3217a

Also thank you for the chip number. (I found HD14051BP as U24 in the Sams Computerfacts.)

So I will grab a few of those also.

 

Steve

[Beeblebrox]

No. Worries. 

 

Yup this is the single sided spring/plunger type:

 

 

 

 

 

And this is the rubber cup/dome type (double sided folded over) :

 

 

 

Edited June 25, 2023 by Beeblebrox