Hi all.
I have a CPC 464, a CPC 664 and a CPC 6128.
I've always loved them since I had a 464 when I was at school. I actually wrote my O Level computer studies project on it.
Anyway, I know the 664 is rare, and as I'm saving up for something I've decided it's probably better I move it on as it seems a good time to do it.
Amazingly, it's like new. Totally original condition, no yellowing at all and the blue keys are as blue as the day they were made!
I powered it on using a modern power supply and it powers up fine. Only issue is the keyboard seems to be typing gobbledegook.
Some of the keys work fine, some type rubbish. For example, pressing the 'ctrl' key actually displays the PI symbol. Some of the number keys work, some display groups of random characters.
I assumed the keyboard membrane was faulty so I bought a reproduction one which arrived today. I opened up the 664 noting every screw is there and all the screws inside and out have never been undone before.
I changed the membrane for the new one, although the old one looked perfect.
Powered on, and I'm getting the same issue!!
I took the board out and looked at the back of it, and it does seem to have some residue all over the back of the board, yet the old keyboard membrane and inside of the case are spotless, so it's not had anything poured in. I'm guessing it's a protective layer of varnish or something?
Can anyone suggest what I try next? I'm guessing on of the chips is faulty, but can someone please point me in the direction of which one or how to run a test.. and if it's a chip, is it possible to get replacements?
I do have two 464's which if needs be means I could raid one for parts if it meant bringing the 664 into full working order.
Thanks everyone in advance.
(https://www.dropbox.com/scl/fi/3lvhmnebqwmid9eg4mxzh/IMG_5553.JPG?rlkey=xepixpv66tpe2moop4ayqrw11&raw=1)
Here's a picture of it.
@glynharper Can you take a photo of the Screen after typing " abcdefg " and show us what happens.
Thanks
Ps They are lovely machines the CPC664.
Keep Safe
Ray
Quote from: glynharper on Yesterday at 00:26Hi all.
I have a CPC 464, a CPC 664 and a CPC 6128.
I've always loved them since I had a 464 when I was at school. I actually wrote my O Level computer studies project on it.
Anyway, I know the 664 is rare, and as I'm saving up for something I've decided it's probably better I move it on as it seems a good time to do it.
Amazingly, it's like new. Totally original condition, no yellowing at all and the blue keys are as blue as the day they were made!
I powered it on using a modern power supply and it powers up fine. Only issue is the keyboard seems to be typing gobbledegook.
Some of the keys work fine, some type rubbish. For example, pressing the 'ctrl' key actually displays the PI symbol. Some of the number keys work, some display groups of random characters.
I assumed the keyboard membrane was faulty so I bought a reproduction one which arrived today. I opened up the 664 noting every screw is there and all the screws inside and out have never been undone before.
I changed the membrane for the new one, although the old one looked perfect.
Powered on, and I'm getting the same issue!!
I took the board out and looked at the back of it, and it does seem to have some residue all over the back of the board, yet the old keyboard membrane and inside of the case are spotless, so it's not had anything poured in. I'm guessing it's a protective layer of varnish or something?
Can anyone suggest what I try next? I'm guessing on of the chips is faulty, but can someone please point me in the direction of which one or how to run a test.. and if it's a chip, is it possible to get replacements?
I do have two 464's which if needs be means I could raid one for parts if it meant bringing the 664 into full working order.
Thanks everyone in advance.
Hi Glyn,
there are only 2 chips directly involved with keyboard scanning. The AY sound chip (IC102) and a 74LS145 (IC101). The most likely one to have failed is the AY.
Bryce.
Thanks everyone so far. I have it dismantled at the moment to look at the back of the board, but I'll put it back together later to take photos of the keypresses. I should have done that originally really!
the AY chip does sound doesn't it? It does beep at the right times, but if that's the suspect I can swap it out and socket it while I'm at it..
Any idea where I can source the AY chips?
The AY has two sections, the Analogue side that does the sound and the digital port that reads the keyboard. They are pretty isolated from each other, so one side can fail with the other side still functioning completely as it should.
There are two versions of the AY chip, one with internal pull-up resistors and one without. Make sure you get the correct version. You can find them on ebay, but be careful when buying them from China, there are a lot of fakes being sold.
Bryce.
Here's a picture of the keystrokes, when pressing 1-9 on the main keyboard.
Funnily though, whereas the ctrl key used to show the PI symbol it now doesn't, and actually works. So whatever it is seems to be intermitted or a different failure each time I try it.
Also, it appears the floppy disc doesn't seem to work. The red light is on, but it won't spin. I put a disc in, type cat, and it just comes up with unable to read.
(https://www.dropbox.com/scl/fi/os82tzk1kn6h0ps0w26z6/keyboard.jpg?rlkey=jo0ojokdul7kchf03ldbo6fky&raw=1)
The AY is expensive to replace but a known and common failure. So I agree with
@Bryce but surprised that you do not see random characters printed on power on even without pressing any keys. I would try some non destructive things first like cleaning the keyboard socket. Regarding the disk drive check the belt first.
Thanks. I've got some contact cleaner somewhere (but I've not long moved house so I need to find it) and I got two new drive belts today. One for this job and another in case my 6128 needs one.
I'll give that a go. Thanks.
Wow, you were right about the drive belt. It had literally turned to powder.
I've cleaned it all up, fitted a new one, but still no joy on the floppy drive. It doesn't even sound like it's trying to spin. the computer just goes straight to 'Drive A: Disc Missing' when there is definitely a disc in there.
| LS145 PIN: | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 9 | 10 | 11 |
| LS145 Line | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| AY PA Bit: | | | | | | | | | | | | | | | | | | | | |
| 7 -Pin7 | f . | f0 | Ctrl | > , | < . | Space | V | X | Z | Del |
| 6 -Pin8 | Enter | f2 | ` \ | ? / | M | N | B | C | Caps Lock | Unused |
| 5 -Pin9 | f3 | f1 | Shift | * : | K | J | F | D | A | Joy 0 Fire 1 |
| 4 -Pin10 | f6 | f5 | f4 | + ; | L | H | G | S | Tab | Joy 0 Fire 2 |
| 3 -Pin11 | f9 | f8 | } ] | P | I | Y | T | W | Q | Joy 0 Right |
| 2 -Pin12 | Cur.Down | f7 | Return | | @ | O | U | R | E | Esc | Joy 0 Left |
| 1 -Pin13 | Cur.Right | Copy | { [ | = - | ) 9 | & 7 | % 5 | # 3 | " 2 | Joy 0 Down |
| 0 -Pin14 | Cur.Up | Cur.Left | Clr | ^ | _ 0 | ( 8 | & 6 | $ 4 | ! 1 | Joy 0 Up |