Author Topic: 6128 with keyboard issues (random chars on boot, half keys not working)  (Read 3010 times)

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Offline keropi

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hiya!


I have bought a new 6128 that I want to repair, this one on boot prints some random characters and most of the keys on the right side are not responsive.
I've read that this could mean that either the AY or a demux (what IC is that on the original 6128?) could be problematic, does that sound like the case?


TIA for any tips/help!
 :)

Offline Audronic

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@keropi
Plug in the Joystick,
tell us what is on the screen for " Up, Down, Left,right. Fire Button.
Thanks   Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Offline Bryce

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hiya!


I have bought a new 6128 that I want to repair, this one on boot prints some random characters and most of the keys on the right side are not responsive.
I've read that this could mean that either the AY or a demux (what IC is that on the original 6128?) could be problematic, does that sound like the case?


TIA for any tips/help!
 :)

Hi Keropi,
        the "demux" is actually just a 74LS145. However, I'd recommend just giving the membrane a good clean first to see if the problem is just gunk and dirt.

Bryce.

Offline keropi

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sorry for the late reply, I am away on a trip and I can't access the cpc until Friday... I do have though a *very quick* video of the problem:



https://www.youtube.com/watch?v=P2yNaB7twU8


you can see the auto-garbage on boot and the garbage that some keys produce  :laugh:


Offline keropi

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The friend that keeps the cpc for me did a small test, removed the keyboard completely and the CPC does not register garbage keys ... he will try later with his own good working keyboard and report back, tbh I hope it's not a membrane problem - I very much prefer to change some ICs rather than hunting for membranes  :laugh:

Offline robcfg

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Sounds like the membrane though.


Don't panic, the thing to try is to gently separate the two sides of the membrane and gently blow away dust or any other thing that shouldn't be in there.


If that doesn't work, you can worry a bit, but not too much  ;)
« Last Edit: 12:52, 02 November 16 by robcfg »

Offline ||C|-|E||

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As robcfg says you can usually rescue a membrane  :) There is even this varnish that has lots of silver particles and can be used to repair broken tracks. If you separate the two halves (they are sort of lightly glued) you can put them back together and then add a bit of sellotape on the outside to seal the membrane and prevent the dirt to enter again. I am saying sellotape because it is transparent, very thin and can be easily removed without damaging anything. Be careful when cleaning, though, do not use solvents, not even isopropanol.

Offline Bryce

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Sticky gunk. A decent clean should solve the issue.

Bryce.

Offline keropi

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I see... I will clean it then.
thanks for all the help guys!  :)

Offline keropi

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allright, I got the machine and plugged a joystick , it displays these characters when I press something on it:





LEFT is working like backspace, it deletes on character at a time
no idea if this is normal behavior or not  ::)

Offline VincentGR

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Is the keyboard attached on CPC?

Offline keropi

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yes it is
I am in the opening stage now, should I try with no keyboard attached?

Offline VincentGR

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Yes, check if the characters appear without keyboard.

Offline keropi

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I get the corresponding arrows now, up arrow for up , down arrow for down and so on... button1 is X.
so it's just the membrane, correct?

Offline VincentGR

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It seems to be.
Do you have a spare to try out?
Give a good clean to the membrane and try gentle to separate the two layers without cutting it.
Just slide your palms in circles, maybe the layers are stacked. Then plug the membrane without the keyboard.As for the keyboard, clean it well and use a brush underneath.

Offline Joseman

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It seems to be.
Do you have a spare to try out?
Give a good clean to the membrane and try gentle to separate the two layers without cutting it.
Just slide your palms in circles, maybe the layers are stacked. Then plug the membrane without the keyboard.As for the keyboard, clean it well and use a brush underneath.

I did just like this the last week, one 6128 with ramdon keys on screen.

I separate the two layers (be careful) and cleaned the contacts of the two layers with a cotton bud and alcohol isopropilyc.

the contacts seemed clean before, but the cotton was getting dirty and i finally use 10 - 15 cotton buds!!

Now the keyboard works like a charm, only 1 keyboard contact broke a little with the cotton, but the key still works!, this is why i recommed be very careful!

Offline keropi

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I'm on cleaning detail then! Will report back later  :)
the whole machine needs a GOOD cleaning, too much dust

Offline keropi

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All fixed, cleaned the membrane and it seems it did the trick , thanks for all the help guys!


Now all that remains is to fix the drive, I can see the disk is not spinning so I guess I'll have to wait for a new belt and take it from there


thanks again!  ;D

Offline Bryce

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Congratulations. A cheap repair. If the drive isn't turning at all, then you've probably got quite a bit of gunk removal and cleaning ahead of you. I'd start doing that while you're waiting for the drive to arrive. Make sure you remove every bit of rubber from the two wheels, especially the small one as even the slightest bit of gunk will cause the belt to fall off the wheel within seconds.

Bryce.

Offline robcfg

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Don't forget about the write protection pin!


When you open the disk drive, be sure that the circuit board is facing upwards, as there's a loose pin used to detect whether the disk is write protected or not and it's very easy to lose it. That will left you with a read only drive.


Not that it's not easy to replace, but better not to lose it in the first place.

Offline Bryce

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The pin is only in one version of the drive, the other versions didn't have one. However, if your drive has a pin, the chances are you're going to loose it :D
I wrote a guide here on the types with and without pins and where it goes: http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/help-i-changed-the-drive-belt-and-now-my-disk-drive-is-suddenly-read-only/

Bryce.

Offline keropi

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Thanks again for the tips, I'll be more carefull now  8)
ATM the whole setup is in pieces, both 6128 shell and CTM644 ones went to take a bath - they were really dirty but luckily in very good condition.


I am debating wether I recap the CTM644 chassis or not.


Offline ||C|-|E||

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I recently recapped a CM14 (I have a completely discharged CTM644 still waiting) and, certainly, when I checked the ESR of the old caps it had gone bonkers in quite a few cases. Actually, I recapped because I had some image issues. Problem with the CRTs is, as always, the danger when working with them. Does you screen have any problem? 

Offline keropi

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The only problem I detected was the brightness pot that when you adjust it you get lots of parasites - that's easily solved with some electronics cleaner AFAIK (had the same issue with 1084 monitor pots, cleaning did the trick)


I was more worried about the onboard 6128 PSU tbh. I'll just replace all the electrolytics with chemicon/panasonics and call it a day. Unsure about the motherboard caps now , maybe I replace them as well  ;D




Offline keropi

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it is done  ;D









edit:


OK, it did not catch fire - that's always a concern  :laugh: :laugh: :P :laugh:


« Last Edit: 18:36, 05 November 16 by keropi »