Broken motherboard trace causing keyboard issues?

[NoMoreGreenScreen]

I have a CPC464, which was listed on eBay as spares and repairs, but had been listed as working and even showed the machine working. 

This revision is the low key, membrane based keyboard with the small motherboard.  

When I tested the 464, I noticed that the keys associated with Bank 1 (2,3,5,7,9,[, etc) didn't work.  I took a look at the membrane as the obvious issue and having cleaned and continuity tested the bank 1 line (amongst others), it seems fine.

My next point of investigation was the motherboard and having asked around, I understand that the keyboard signals travel through the AY through to the I/O chips.  There was a load of gunk of the board, and this gunk went across the traces from the AY, to what I presume is the I/O chip and so I cleaned this off with rubbing alcohol and noticed the trace from pin one of the AY is possibly broken (see picture below).  I am of course assuming that pin 1 from the AY is equal to bank 1 on the keyboard membrane.



I do not know where to go from here.  I have seen people (on various repair videos from other systems) running a 'patch' wire, but i don't know if that's an option and i wouldn't know where to start, if that even is the issue.  Please can i have some advice?

I dont know the history of this machine, other then it looks lie it has had quite a bit of liquid in, i can see that from the keyboard assembly and the motherboard and i think this may be why the power connector to the board has been re-soldered too. 

Thanks
NM

[NoMoreGreenScreen]

Have attached the image 

[Raft]

Hi!

Well, not sure what you show on the picture?
Anyway PIN1 of the AY is not connected to the keyboard

You can check the keyboard matrix and schematics in the service manuals (https://www.cpcwiki.eu/index.php/Service_Manuals)

Hope this can help

[McArti0]

Do you think the photo shows pin1 AY? 

[NoMoreGreenScreen]

Hi guys, thanks for responding 

This is why i came here - this is all very new to me and guidance is much appreciated.

@Raft - I have viewed the schematic and i can see that I was looking at the top tracings and not what is on the underside.  I have highlighted where i believe is where the bank 1 channel starts and ends - does this look right?  I guess i can check the solder connections on the the underside to see if it looks okay, but failing that I'm out of ideas.  I have also attached that photo above with what i thought was a broken trace and highlighted what i was talking about originally. 

@McArti0 - well, I was told that if the keyboard wasnt working, that it would go through the AY and IO chip.  As I said, this is all new to me.


Any ideas what I can do / try next please?

[McArti0]

Try pin14 AY to ground and next Pin13 to ground.

If AY Pin13 give You "97532" then Try cross pin13-AY to 74LS145 Pin 1,2,3,4,5,6,7   and 9,10,11

Try by multimeter continous Pin13 AY and all pins keyboard connector.

[Bryce]

Hi guys, thanks for responding

This is why i came here - this is all very new to me and guidance is much appreciated.

@Raft - I have viewed the schematic and i can see that I was looking at the top tracings and not what is on the underside.  I have highlighted where i believe is where the bank 1 channel starts and ends - does this look right?  I guess i can check the solder connections on the the underside to see if it looks okay, but failing that I'm out of ideas.  I have also attached that photo above with what i thought was a broken trace and highlighted what i was talking about originally.

@McArti0 - well, I was told that if the keyboard wasnt working, that it would go through the AY and IO chip.  As I said, this is all new to me.


Any ideas what I can do / try next please?

That trace isn't broken. The copper has just slightly oxidised under the stoplack layer. The AY chip has most likely failed on that particular io pin.

Bryce.

[NoMoreGreenScreen]

Thanks for your help guys...i will get the multi-meter out some evening this week and see what it turns up

[McArti0]

Try pin14 AY to ground and next Pin13 to ground.

@NoMoreGreenScreen

You really only need a piece of cable. A paper clip will do too.

Cross AY pin13 and pin6 (ground)

[NoMoreGreenScreen]

@McArti0 

okay, i misunderstood...


so run a small cable between AY pin 13 and pin 6, then power up the computer and test keys 2,3,4,7,9
Repeat test on pin 14 to pin 6 and test again.

Many thanks

[McArti0]

Almost good.
With CPC enabled. You short pin6 with pin 13 and the screen should immediately show 8 characters. Including 97532. In that order. Pin14 will give another 8 characters. As will pins 7,8,9,10,11,12. Each 8 different

If you have a long cable, you can touch the large mass around the mainboard.

[NoMoreGreenScreen]

Good news - I have a fully working CPC464  

(and i dont know what I did)

Yesterday evening I had the machine apart to follow the actions @McArti0 suggested.  In doing so i noticed i was straining the keyboard ribbon cables to try and accommodate the open case and room to get my paper clip in.  I ended up taking out the ribbon cables out and powering the machine up - except it would power up.   I put the ribbon cables back in and this time it powered up and the bank 1 keys are all working, the AY is working, everything (well apart from the pause button on tape deck, but no way am i taking that apart!!)

I dont really know what resolved it -   I had removed and reinserted the ribbon connectors multiple times prior and made sure they were bedded in each time so this was no different.  Prior to reconnecting, I had ran the multi meter probes in the keyboard connectors (maybe i scraped something off??), i had 'shorted' (but not if you get my drift) pins 13 to 6 with it powered off to practice with the paper clip but that was it.  

Irrespective, its working.  I retested with powering down and up and all was fine.  I don't know if this is permanent but at present as ts working, i wanted to take time to thank everyone who has contributed to this thread with advice; i really appreciate it.

[McArti0]

Have you ever done a pin13 to pin6 test?

[Bryce]

Good news - I have a fully working CPC464 

(and i dont know what I did)

Yesterday evening I had the machine apart to follow the actions @McArti0 suggested.  In doing so i noticed i was straining the keyboard ribbon cables to try and accommodate the open case and room to get my paper clip in.  I ended up taking out the ribbon cables out and powering the machine up - except it would power up.  I put the ribbon cables back in and this time it powered up and the bank 1 keys are all working, the AY is working, everything (well apart from the pause button on tape deck, but no way am i taking that apart!!)

I dont really know what resolved it -  I had removed and reinserted the ribbon connectors multiple times prior and made sure they were bedded in each time so this was no different.  Prior to reconnecting, I had ran the multi meter probes in the keyboard connectors (maybe i scraped something off??), i had 'shorted' (but not if you get my drift) pins 13 to 6 with it powered off to practice with the paper clip but that was it. 

Irrespective, its working.  I retested with powering down and up and all was fine.  I don't know if this is permanent but at present as ts working, i wanted to take time to thank everyone who has contributed to this thread with advice; i really appreciate it.

Check for dry joints on the keyboard connectors and AY.

Bryce.

[NoMoreGreenScreen]

Have you ever done a pin13 to pin6 test?

No, last night would of been the first  time of doing it but as mentioned after doing some practice running i turned the machine on to do the test but the keyboard was working

[NoMoreGreenScreen]

Good news - I have a fully working CPC464 

(and i dont know what I did)

Yesterday evening I had the machine apart to follow the actions @McArti0 suggested.  In doing so i noticed i was straining the keyboard ribbon cables to try and accommodate the open case and room to get my paper clip in.  I ended up taking out the ribbon cables out and powering the machine up - except it would power up.  I put the ribbon cables back in and this time it powered up and the bank 1 keys are all working, the AY is working, everything (well apart from the pause button on tape deck, but no way am i taking that apart!!)

I dont really know what resolved it -  I had removed and reinserted the ribbon connectors multiple times prior and made sure they were bedded in each time so this was no different.  Prior to reconnecting, I had ran the multi meter probes in the keyboard connectors (maybe i scraped something off??), i had 'shorted' (but not if you get my drift) pins 13 to 6 with it powered off to practice with the paper clip but that was it. 

Irrespective, its working.  I retested with powering down and up and all was fine.  I don't know if this is permanent but at present as ts working, i wanted to take time to thank everyone who has contributed to this thread with advice; i really appreciate it.

Check for dry joints on the keyboard connectors and AY.

Bryce.

that sounds like a solid idea.  thanks

[NoMoreGreenScreen]

hello again everyone   

@McArti0
@Bryce

Well, you guys probably are not surprised to hear that the CPC started playing up again

I havent actually been using the cpc in the week, only trying it again last weekend and the bit 1 associated keys were not working.   Did what both of you suggested - checked for dry solider joints and I couldn't see any around the AY or keyboard ribbon connectors -

Shorted pins 6 and 13 with the machine on and screen showed [-97532  (and the downward arrow)

This also started the keys working again. 

However, I misread the chip pin numbers and shorted pin 16 and pin 6 - the screen went black and now games dont finish loading - just a black screen at end of loading process or during loading the tape stops wit the black screen.   Ignore tis bit..the keys stopped working again and games are loading again!

So from this,
What does the pin 6 to 13 test result mean?

Thanks

 

[McArti0]

if grounded Pin13 then screen show [-97532

Pin13 as input is ok.

[McArti0]

I misread the chip pin numbers and shorted pin 16 and pin 6

you just little messed up the RESET signal.

are you still sure you want to do something about it yourself?

[NoMoreGreenScreen]

I misread the chip pin numbers and shorted pin 16 and pin 6

you just little messed up the RESET signal.

are you still sure you want to do something about it yourself?

IYea glad i haven't fried anything!!

I would like to try and get this working.  It is going to be a gift for my brother in law, who regrets selling his 464,  35 odd years ago (as he recently told me).  However, it depends what has to be done as my repair skills are limited, but if needs be, I will still gift it to him with instructions on what to do (he is good with electrical stuff).

So now we have established that Pin13 as input is okay  - what is the next step?

Thanks

[Bryce]

However, I misread the chip pin numbers and shorted pin 16 and pin 6 - the screen went black and now games dont finish loading - just a black screen at end of loading process or during loading the tape stops wit the black screen.  Ignore tis bit..the keys stopped working again and games are loading again!

Is this still the case? Or do games load again now?

As for the keyboard issue. There may be a crack in the membrane very near to the membrane connectors, or the connector and membrane contacts may need to be cleaned.

Bryce.

[NoMoreGreenScreen]

I think they are loading fine.  To be fair, i haven't  had much time this week to pick up my Amstrad story (only really having time on weekend - which is nearly here - hoooray!!)

"As for the keyboard issue. There may be a crack in the membrane very near to the membrane connectors, or the connector and membrane contacts may need to be cleaned."

I will clean the connectors and get the magnifying glass out to check the connectors for cracks.  What i have noticed though was when i'm shorting out pins 6 and 13 as recommended by @McArti0 then the keyboard started working  properly again (without touching the keyboard connectors), if only for a short while - so does that suggest that the issue may be more AY related?  Could a permanent short be made across pin 6 and 13 using a paperclip?

Thanks
NM

[McArti0]

was listed on eBay as spares and repairs,

It is going to be a gift for my brother in law

Tell him Do not use AY as spare 

[NoMoreGreenScreen]

was listed on eBay as spares and repairs,

It is going to be a gift for my brother in law

Tell him Do not use AY as spare 

@McArti0 - yea i think we have established the AY is faulty?

Well, if you tell me that the AY needs to be replaced, then i will gift him the CPC AND a replacement AY - 2 presents in one !!!  (I'm not comfortable unsoildering a chip)
If you say i can just create a permanent short on 6 and 13 to fix, then I can do that - he gets one present, but its not a DIY present!!

[McArti0]

Pin13 may be ending, but the keyboard may also have too much resistance.
Joystick no. 0 will not work Down. Worth checking.