Amstrad CPC 464 bought as parts, how do I restore?

[betpet]

After watching many videos of people fixing up broken computers and getting them up and running again, I fancied giving it a go myself.


I found one on eBay that seems to be in excellent condition albeit in need of a clean.  It has all the keys and there doesn't seem to be too much superficial damage to it.  It turned up on Friday and, after trying it, it doesn't even power on.  Not to panic, it's what I was expecting. I have a multimeter and will be getting a soldering iron in time but, as a complete newbie, I've no idea what I'm looking for when it comes to plugging it in and checking readings. I've enclosed some pics of the board and the model details.  I've not seen a short board before so that was a surprise to me.  The screws in the machine were clearly not the originals (not even a full set) so someone has had a look regardless of what may or may not be wrong with it.


I'm happy to buy the relevant chips, etc. as I find them to be needing replacing.  I'd like to almost make this a community project where we're taking a broken machine and fixing it. I post further screenshots and details as and when I try any suggestions and if we get it up and running, we have a record of what to do for future inexperienced restorers.


My question is, what should I do and what should I be looking for?  My priorities (in this order) are going to be:


Get it working.
Take it apart and clean the whole thing up.
Service what needs servicing (bridging commonly replaced chips, re-capping, etc.)
Retrobrite what may need de-aging

[Bryce]

Hi Betpet,
First off, a quick tip: Don't bend those flat cables to the keyboard like that, they'll crack and then you definitely have a problem. They can be gently pulled out so that you can open the case and work on it. The CPC (unlike some other retro computers) will boot without the keyboard connected.

The first thing to test is the voltage. Choose some random 74LSxx chip on the board and check that it's getting at least 4.75V (check the datasheet of the chip to find out what pins are VCC (+5V) and GND). It's probably not. Clean the power socket and check that it's really soldered to the PCB and not flapping about in the breeze. If there's 5V at the back of the socket, but a lot less on the PCB you'll need to clean inside the switch. All these things can be checked/done before your iron arrives.

Bryce.

[VintageAdvantage]

> It has all the keys and there doesn't seem to be too much superficial damage to it.  It turned up on Friday and, > after trying it, it doesn't even power on.

The first question should probalby be - how do you power it? Do you have a CPC monitor? Or other means of powering it? Did you measure the output from the monitor?

[betpet]

Cheers guys!


Bryce, where can I find the data sheet for the chip?  How would I go about cleaning the socket? Is there some solution I can apply? Is there some tool I can use to get inside it?  I'll disconnect the keyboard properly next time I open it up.  Sorry for the complete newbie questions, I literally have the bare basic knowledge.  Think wiring a plug if I look up which sides the blue and brown wires go level knowledge.


VintageAdvantage, I have a MP2 modulator. I checked the voltage coming out of it and it seems to be 5-6v which seems right.  I only know how to check because I watched someone do it on a video. Black connector to the outside, red to the inside of the plug pipe thing (stop me if I'm starting to get too scientific).

[VintageAdvantage]

Cheers guys!
VintageAdvantage, I have a MP2 modulator. I checked the voltage coming out of it and it seems to be 5-6v which seems right.  I only know how to check because I watched someone do it on a video. Black connector to the outside, red to the inside of the plug pipe thing (stop me if I'm starting to get too scientific).

Cheers to you!
Yeah, then do as Bryce said - trace the power from the barrel jack input all the way to the switch and finally to the LED and figure out where it is getting stuck.

[Bryce]

Cheers guys!


Bryce, where can I find the data sheet for the chip?  How would I go about cleaning the socket? Is there some solution I can apply? Is there some tool I can use to get inside it?  I'll disconnect the keyboard properly next time I open it up.  Sorry for the complete newbie questions, I literally have the bare basic knowledge.  Think wiring a plug if I look up which sides the blue and brown wires go level knowledge.


VintageAdvantage, I have a MP2 modulator. I checked the voltage coming out of it and it seems to be 5-6v which seems right.  I only know how to check because I watched someone do it on a video. Black connector to the outside, red to the inside of the plug pipe thing (stop me if I'm starting to get too scientific).

Google almost any chip with it's part number + "Datasheet PDF" and you'll find it. As for cleaning the socket and switch, there are electrical contact cleaner available to do this such as: https://wd40.co.uk/specialist/fast-drying-contact-cleaner/  which you can buy on ebay / Amazon or wherever.

Bryce.

[betpet]

Thanks for the replies.  I'll order the contact cleaner, give these suggestions a go and let you know how I get on.

[betpet]

OK, I received my contact cleaner this afternoon.  Gave all the main ports a spray and here are some images of the connectors and ports from the MP2 and CPC.  There's clearly some corrosion. What should I use to clean it up with? Inside the ports is my main concern really as it seens to be somewhere that'll be tricky to get to.

[Bryce]

That 5V socket is in a bad state! It would probably easier to just swap the entire socket. You can clean it with fine sandpaper for now (the plug too) to get it working, but I'd swap the socket.

Bryce.

[betpet]

How would I swap the socket?  Order a new one and replace it? What am I looking for?


I appreciate all the help

[Bryce]

Yeah, it's a pretty standard barrel socket which can still be bought new. You'd need to desolder that one from the PCB and replace it with the new one.

But before you do that, just clean it with sandpaper to get it working and check that the rest of the CPC is ok.

Bryce.

[betpet]

Will do.  I'll post my results when I have tried that

[betpet]

Can anyone confirm that this is a suitable replacement socket?


https://uk.farnell.com/gct-global-connector-technology/dcj235-05-a-k1-k/dc-power-jack-5a-20vdc-black/dp/2524129


It seems right but I really have no idea.

[Bryce]

Not quite, the pin diameter should be 2.1mm.

Bryce.

[betpet]

How about this?


https://uk.farnell.com/cliff-electronic-components/fc68148/socket-pcb-dc-power-2-1mm-pk10/dp/224959


I've watched some more videos and they showed it's possible to have dry joints or a loose socket. I checked and it doesn't seem the most stable of connectors. I think it's so mucky it would be better replaced but it's possible that the power socket could just be loose and it may be the main problem.

[Bryce]

That's the correct one.

Bryce.

[betpet]

Excellent!  Thanks


I'll post more info as and when I get any further.

[betpet]

OK, I've made a little more progress.  I've decided to clean up the machine before I try anything more er... permanent to it.  I saw in a video that the switch can be a major source of power concerns from poor conductivity to none whatsoever.  I took it out and took it apart.  Filthy!  It seems to be covered in some oily substance.  The switch was dirty in itself which was a clue as to how dirty it was going to be.  A cotton but and some 99.9% isopropanol and it come up nicely.  I put it back together and... nothing!

[betpet]

Next thing was to take the board out and give it a good clean.  There seems to be an oily coating on it.  Nothing major. A little Isopropanol 99.9% and some cotton buds seem to clear up the worst of it pretty quickly although each cotton bud lasted seconds. You wouldn't think it was as dirty as all that. I saw on another video saying vapour spray air fresheners could be the cause which makes some sense.   I think it'll take me quite a while to give this a full clean though.

[betpet]

Underneath the board provided a couple of surprises. Firstly, there was some kind of heat distortion on the edges.  Maybe I'm wrong (remember, I know nothing about this stuff really) but the plastic coating does look like it was attacked with a heat gun.


Secondly, it looks like an amateur repair has been undertaken to fix the power.Quite honestly I can't see why this has been done but, again, I am no expert. It doesn't look the most professional of jobs either.


For now, I'll continue cleaning it and I'll see if that helps. I have a new power connector I can fit if need be but I need to gain some soldering confidence before I try anything like that.


Does anyone have any observations or tips?

[Bryce]

The switch is assembled incorrectly. That metal disk should be facing down as far as I can remember. Also, you can just bridge the two contacts on the main PCB to bypass the switch completely and check if the switch is the issue. Connect pin 1 and 3 (red wire and white wire) to turn the CPC on, but be extremely careful that neither touches pin 2 (the black wire) or you'll short circuit your PSU.
The repair is because the copper pad has most likely detached from the PCB and broken the trace. This is a common fault from many years of plugging/unplugging the power connector. It's a messy repair, but should work.

Bryce.

[betpet]

Cheers Bryce.  I'll have a look at the switch next time I have an hour to myself! Please note that the picture is how I found the switch.  I replaced it exactly the same way.

[betpet]

OK, I had an hour to myself undisturbed so I've gone a little further...


I checked the power and a 74 chip as described in a video I watched. I'm either doing it wrong or there is no power coming through either.  I checked the switch I cleaned up and managed to get a change in figure when turning the switch off and on which indicates to me that the switch is working anyway

[betpet]

I decided to go ahead and replace the connector. It looked in bad shape anyway and I figured I had nothing to lose

[betpet]

I've soldered it in and it looks good. I've not soldered anything before so please feel free to critique my skills.  All constructive criticism welcome.


I tried the power.  Still nothing.  I left it for 10 minutes and touched the chips, stone cold.


Any ideas?