130XE with some bad non registering key presses - not the keyboard itself and not 4051 - ideas?

[Beeblebrox]

So I've an odd issue with some keys not responding on a 130XE.

 

Namely: HELP, 7,8,9,0,Clear, Insert, delete, Break, both shift keys, Z, X, C, V and B.

 

Importantly the same keys that weren't working before I did work to this are still not working. They weren't responding when I first acquired the machine and still aren't.

 

So far I've ruled out the keyboard itself as I've put 2 x different keyboards from working XE's into it and have exactly the same issue. One keyboard as a new mylar also. Both keyboards work when placed back in their original XEs.

 

I've also since tried socketing and replacing the 4051 chips with brand new ones as I was convinced it would be a 4051 chip or two failing from past experience with my 600XL and 800 Atari's. Frustratingly it didn't make any different - same issue still, same keys not working.

 

Finally I checked the 24pin keyboard connector for continuity. All register.

 

So my thoughts have turned to the Pokey chip. It seems to work fine in terms of the sound side, (and joystick is fine so assume PIA is good). Also powering up holding down Start I get the tape bleep.

 

Not had a chance to test SIO function fully

 

The computer works fine otherwise, with my side3 cart running well and games like Prince of Persia loading, joystick working fine. Ram checks out.

 

• So before I desolder the Pokey and socket it does anyone think this could this be a failing Pokey?  

 

• Or alternatively could this be failing passive components or a 74 logic chip?

 

EDIT: Could this possibly be bad resistors on the lines from the 24pin connector for pin 6 and 13 as per the matrix - given the failing keys are on those two lines on the matrix?

 

Here is the matrix, but as I say the keyboard is good, as is the 24pin connector:

 

Here is the PCB:

 

 

 

 

 

 

Edited December 31, 2023 by Beeblebrox

[Rybags]

Did you check continuity from the relevant pins on the 4051s to the kb ribbon connector?   Maybe ensure the resistances are in the same range?

Swapping the 2 4051s is also a common diagnostic step but by the sounds of it you've eliminated them as the possible problem anyway.

So to me probably leaves just the board and Pokey itself.  Though if Pokey was at fault you'd probably expect more than just one row to be non responsive.

[TGB1718]

Having had a look at the circuit, there doesn't seem to be any other IC's involved in the keyboard scanning.

If you have a scope, you could check pins 18, 19 and 20 on Pokey and see all 3 lines are providing addresses to the

4051 chip (U25) as those lines select the 2 rows (6 and 13) that are not working.

 

 

[Overange]

Weirdly i cannot upload images so....

 

Have you shorted the KB Conn Pins using a peice of wire?

 

 

then check Continuity

 

Between KB Conn Pin 13 and pin14 of U25 ( 4051 ) =  270ohms ( via R144 )

Between KB Conn Pin 13 and pin5 of U25 ( 4051 ) =  270ohms ( via R140 )

 

 

U25 Pins 9 - Pokey Pin 18

U25 Pins 10 - Pokey Pin 19

U25 Pins 11 - Pokey Pin 20

 

May be worth checking R90 ( 100 Ohms ) Pin 3 to Pin 6 7 8  on U25

Edited December 31, 2023 by Overange

[Beeblebrox]

3 minutes ago, Rybags said:

Though if Pokey was at fault you'd probably expect more than just one row to be non responsive.

I was thinking this. Given the matrix shows all failing key responses are on lines 13 and 6, I just mapped and checked out the two resistors they connect to via traces on the underside of the pcb:

 

 

I took a reading of these 270ohm resistors and both are reading 265ohm. I took readings of the same value resistors nearby which read the same. 

3 minutes ago, Rybags said:

Did you check continuity from the relevant pins on the 4051s to the kb ribbon connector?   Maybe ensure the resistances are in the same range?

Will check now

[pseudografx]

If the POKEY is at fault and its audio part still works fine, it may still be a valuable chip to be used as a secondary one in stereo expansions.

[Beeblebrox]

36 minutes ago, Overange said:

U25 Pins 9 - Pokey Pin 18

U25 Pins 10 - Pokey Pin 19

U25 Pins 11 - Pokey Pin 20

 

May be worth checking R90 ( 100 Ohms ) Pin 3 to Pin 6 7 8  on U25

ok all the above check out ok

 

37 minutes ago, Overange said:

Have you shorted the KB Conn Pins using a peice of wire?

 

 

then check Continuity

 

Between KB Conn Pin 13 and pin14 of U25 ( 4051 ) =  270ohms ( via R144 )

Between KB Conn Pin 13 and pin5 of U25 ( 4051 ) =  270ohms ( via R140 )

Didn'y fully understand 🙂- which pins to short on the 24pin keyboard connector?  pins 6 and 13?

[Beeblebrox]

5 minutes ago, pseudografx said:

If the POKEY is at fault and its audio part still works fine, it may still be a valuable chip to be used as a secondary one in stereo expansions.

yup, if it turns out to me pokey I'll defo keep it for that. Done that with failing pokeys for stereo setups several times now.

[Overange]

Just now, Beeblebrox said:

ok all the above check out ok

 

Didn'y fully understand 🙂- which pins to short on the 24pin keyboard connector?  pins 6 and 13?

Na, it’s easy, go from pin 13 to say pin19 for 7 

pin 13 to pin 10 for zero

 

you see the pattern?

[Overange]

also, what is going on here?

 

Maybe worth seeing what it is supposed to be connected to?

 

maybe nothing to do with pokey🤔

[Beeblebrox]

1 hour ago, Rybags said:

Did you check continuity from the relevant pins on the 4051s to the kb ribbon connector?   Maybe ensure the resistances are in the same range?

I think these are ok. I only checked those for the aforementioned two resistors for lines 6 and 13

4 minutes ago, Overange said:

also, what is going on here?

 

Maybe worth seeing what it is supposed to be connected to?

 

maybe nothing to do with pokey🤔

I wondered what that is for also. It was in place when I first opened up the machine.

 

It connects pin 8 of the 74LS138 with pin 3 of the 74LS08 (resistor is a 1kohm)

Edited December 31, 2023 by Beeblebrox

[Peri Noid]

Check the keyboard socket itself. The pins may be bent and not contacting. 

[Beeblebrox]

10 minutes ago, Overange said:

Na, it’s easy, go from pin 13 to say pin19 for 7 

pin 13 to pin 10 for zero

 

you see the pattern?

sorry, not understanding what you mean at all heh heh. Are you talking about shorting Pin 13 on the 24pin connector with pin 19 on the same connector? (Don't under stand the ref to 7 or zero).

 

FYI I don't have a scope btw.  Just a multimeter.

[Overange]

16 minutes ago, Beeblebrox said:

I think these are ok. I only checked those for the aforementioned two resistors for lines 6 and 13

I wondered what that is for also. It was in place when I first opened up the machine.

 

It connects pin 8 of the 74LS138 with pin 3 of the 74LS08 (resistor is a 1kohm)

That is tying the O2 line to gnd with a 1K resisitor ?!?

 

 

[Overange]

15 minutes ago, Beeblebrox said:

sorry, not understanding what you mean at all heh heh. Are you talking about shorting Pin 13 on the 24pin connector with pin 19 on the same connector? (Don't under stand the ref to 7 or zero).

 

FYI I don't have a scope btw.  Just a multimeter.

You do not need a scope.

 

7 is Keyboard button 7 and Zero is keyboard button Zero

 

My images are now uploading ( PC Reboot ?!?!? )

 

Like this, so for button 7 short pins 19 and 13

for button zero short pins 10 and 13

 

 

[TGB1718]

1 hour ago, Beeblebrox said:

I took a reading of these 270ohm resistors and both are reading 265ohm. I took readings of the same value resistors nearby which read the same.

Gold band is tolerance on resistors which is +/-5% so for 270 Ohm +/- 13.5 Ohms all good in this case.

[Beeblebrox]

3 minutes ago, Peri Noid said:

Check the keyboard socket itself. The pins may be bent and not contacting. 

I already did that as per first post. All continuity checked out with the connector pins and the solder points........

 

However......a penny dropped and as a double check I just plugged into the ribbon cable again and tested continuiting between the ribbon on line 6 with the connector pin 6, as well as ribbon line 13 and pin line 13.  I had to do the ribbon cable half in the connector in order to be able to check continuity.

 

Well damn do I feel stupid!! 😵‍💫 Seems pins 6 and 13 metal contacts were very slightly dulled and bent a fraction more than the others deep down inside the connector. With the ribbon cable in situ I had to bend them downwards with a small sharp knife to get them to fully make surface contact and.....surprise surprise... instantly got those keys back! It's all working fine now.

 

They looked fine unless you use a super strong torch and peek deep down inside.

 

Doh!!!!!

 

Sometimes the way - you start down a route thinking it's gonna be a more complex issue ........and it turns out to be simply a mechanical issue!

 

Sorry to wasting everyone's time on this, feel a prize Turkey (apt for this time of year!) 🫢

 

😁

[TGB1718]

1 minute ago, Beeblebrox said:

Sorry to wasting everyone's time on this, feel a prize Turkey (apt for this time of year!) 🫢

Not wasted, someone else might use the helpful information in this thread to resolve their own issues

 

[Overange]

1 minute ago, Beeblebrox said:

I already did that as per first post. All continuity checked out with the connector pins and the solder points........

 

However......a penny dropped and as a double check I just plugged into the ribbon cable again and tested continuiting between the ribbon on line 6 with the connector pin 6, as well as ribbon line 13 and pin line 13.  I had to do the ribbon cable half in the connector in order to be able to check continuity.

 

Well damn do I feel stupid!! 😵‍💫 Seems pins 6 and 13 metal contacts were very slightly dulled and bent a fraction more than the others deep down inside the connector. With the ribbon cable in situ I had to bend them downwards with a small sharp knife to get them to fully make surface contact and.....surprise surprise... instantly got those keys back! It's all working fine now.

 

They looked fine unless you use a super strong torch and peek deep down inside.

 

Doh!!!!!

 

Sometimes the way - you start down a route thinking it's gonna be a more complex issue ........and it turns out to be simply a mechanical issue!

 

Sorry to wasting everyone's time on this, feel a prize Turkey (apt for this time of year!) 🫢

 

😁

 

We all have those days lol 

 

you just need to figure out that resistor mod

 

[Peri Noid]

2 hours ago, Beeblebrox said:

Seems pins 6 and 13 metal contacts were very slightly dulled and bent a fraction more than the others deep down inside the connector. With the ribbon cable in situ I had to bend them downwards with a small sharp knife to get them to fully make surface contact and.....surprise surprise... instantly got those keys back! It's all working fine now.

I'm not surprised. I simply had the same situation, that's why I mentioned checking the connector 🙂

[erichenneke]

Definitely not a waste of time, nor of "posting real estate"  here. Eventually somebody else will have same problem and benefit from seeing this. 🙂