CPC 6128+ trouble

[RocketRanger]

Hi guys,


I have an Amstrad 6128+ which I rescued from a charity shop a few years back and has been a bit of a project for me on and off. I successfully restored the drive belt and invested in a power supply and Scart cable from RCS a few years back. Everything was working well and I put the computer into boxes and moved house.


I decided to pull the Amstrad out this week to give it some TLC again as it's been a couple of years since I last used it. Unfortunately it's developed a fault and I wondered if you guys might have seen anything like this before...


When I turn it on it beeps like someone is pressing a key continuously. I get the Basic/Burning rubber selection screen and I can choose either fine, however once Basic kicks in it continues to act as though someone is holding down minus '-' until I press return (see picture attached).

As you can see my LCD monitor is giving me some ghosting too, I don't think that's related and it works fine on my CRT although as I remember it, it used to work ok on this monitor.


My first thought was that maybe there was a power issue. I've run a simple test with a 5v multi-adapter and it has the same issue.


I'd be grateful for any advice guys before I open this baby up again. I was thinking maybe the keyboard membrane might just need a bit of a clean but wanted to see what you guys thought before I went down that road.


Many thanks!


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[keropi]

I am pretty sure you have to clean the keyboard membrane to fix the keyboard issue
As for the ghosting I had this too (I also have the very same LG monitor on my test bench  ) and that is because the scart cable you have uses the TTL SYNC signal as voltage for the SCART RGB-ON. A terrible idea but goes unnoticed on CRT screens - LCD ones do pick it up though...


I modified my 6128+ with a switch to select what PIN1 on the AV-OUT port is: 5v or TTL SYNC. Using 5V eliminates all ghosting and screen abnormalities. There could be some other solution but in reality the correct way is to use voltage for the RGB-ON signal and not a TTL signal of any kind... here is what I did: http://www.cpcwiki.eu/forum/technical-support/accidentally-used-a-9v-psu-on-the-6128-plus-what's-the-damage/msg129042/#msg129042

[RocketRanger]

Thanks keropi, that's interesting. The Scart cable is a Retro Computer Shack 6128+ Scart from Ebay - maybe I'm getting forgetful but I could have sworn I'd used it successfully with that monitor. However, that doesn't concern me so much as I have a nice Sony Trinitron CRT 16" widescreen that's rather lovely with the CPC. I guess I'll give the membrane a clean and report back.

[keropi]

Well the scart cable is good for sure and follows the decades old schematics... on CRT you can't notice anything funny so that's why noone bothered all these years I guess. But even though this works it doesn't mean it's correct    , LCDs being picky imeddiately show the side effects.
If you don't plan to ever use a real amstrad monitor (or don't have one) you can just lift R87 , patch a 5v signal on the via and call it a day. No need to modify your cable at all.

[RocketRanger]

I was feeling brave so decided to open her up and look at that membrane.


There was all kinds of interesting dust under there. I carefully hoovered it without touching the membrane and cleaned it a bit with a clean cloth and some solution.


After I figured out how to put it back together with the membrane holes correctly aligned I powered it up and the beeping had gone and no more minus involuntary keypress.


Amazingly, all keys are working correctly again!


I'll look into the Scart ghosting issue further, the suggestions are interesting, but at least it isn't a new issue with the Amstrad hardware itself. It isn't an issue for me as I have a nice clear CRT for this anyway.


Here's some CPC+ P0rn of the membrane...

[keropi]

Nice, had similar issues with my 6128 membrane, asked around here and passed down the knowledge... 
Like I wrote, you can easily do a wire jumper and solve all your issues - even if CRT works it's not correct to mistreat a TTL signal like that 

[||C|-|E||]

These things with the membranes happen all the time if you do not regularly use the computer  Nice to see that it is working again!

[keropi]

These things with the membranes happen all the time if you do not regularly use the computer  Nice to see that it is working again!

Any idea why is that? Is the conductive material dissolving or something due to age and makes contact when it shouldn't?

[Bryce]

No, the plastic is just getting more rigid over time. As well as that, the plastic absorbs moisture which means that the dust in the room will stick to it and become gunk. Using the computer just keeps the membrane regurlarly warm (slows the gunk build-up) and regular use also keeps the plastic more flexible.

Bryce.