Colour monitor stuck in green screen?

[Jon]

Ok this might be a really obvious problem since I haven't used a CPC since 1991, but I can't seem to find an answer online.

I have dusted off my old Amstrad CPC 464 which has been in the loft gathering dust for years. My old green screen monitor simply smelt of burning plastic when I powered it on and didn't show a picture so I have disposed of it. Instead, a friend said he had an old Amstrad monitor which he swears was a colour monitor (he has no reason to lie, he's given it to me free of charge).

The computer now works great but, bizarrely, the monitor still appears to be green screen! On the front it says "Colour monitor CTM 644" and the back has model number CTM644-2.

Is there a way of switching the monitor between colour and green screen? Or is the CPC itself somehow set to use green screen? When I was a kid I previously used the CPC with an MP1 and had no issues with colour output on the TV.

Any advice welcome!

Thanks,

Jon

[Bryce]

Hi Jon, if the CPC was supplied with a green screen, then it only produces a green picture... Only joking, of course you should have a colour picture when you connect the CPC to a CTM644 and there's no switch to choose green. The colour signal is supplied with three separate signals, Red, Green and Blue. I guess the red and blue signals aren't getting through. Either you have a bad connection at the monitor socket of the CPC, or the wire to the monitor has breaks in it. Try waggling the wire and plug at the CPC and clean the contacts on the connector.

Bryce.

[Jon]

Thanks for the quick reply. I will have a look at the weekend and let you know how I get on.

[ralferoo]

model number CTM644-2

I think in Amstrad terminology, "-2" means "-red -blue"... 

[Gryzor]

But it would be quite strange for it to give a familiar green image, wouldn't it? Quite a coincidence...


Jon, can you post a photo of the monitor - both its case and its screen switched on?

[beaker]

Your mate doesn't have an evil streak in him and stuck green acetate over the screen? 

[Jon]

Lol I don't think so- I don't recall upsetting him that much in the past! I will take some pictures as requested.

[Bryce]

But it would be quite strange for it to give a familiar green image, wouldn't it? Quite a coincidence...

Usually the Red and Blue won't be completely off, just much weaker than the Green, so all the detail is there, just it has an extreme greenness to it.

Bryce.

[Jon]

Well now I'm gutted. Plugged everything in to take some pictures of what it looks like and now the CPC won't power on - no red light. Tried the tape functions to see if any power was getting through and it's dead. Monitor is working. Managed to find my MP1 after an hour rummaging in the loft but the CPC won't power on through that either.

[Jon]

By monitor working, I mean it has power. Whether it's colour or not I still have no idea!

[Bryce]

Is there power on the 5V plug to the CPC?

Bryce.

[Badstarr]

Yikes another 464 that has mysteriously died during its downtiime! Maybe we are experiencing the Amstrad CPC equivalent of the millennium bug? 464s seem to be having a bad run of luck if the (I presume) smashed in transit CPC I just received is anything thing to go by!


The modulator was known to be working before it was stored away I presume? The only thing I can think of is checking the fuse in the plug attached to the modulator, having never owned one I'm not sure if it has a "power on" LED. If you have a multimeter check the voltage on the 5v output. Beyond that, checking that the 5v socket hasn't become detached from the PCB is probably the next port of call

[endangermice]

Sonds to me like there could be a loose connection on the motherboard for the power, that could be the problem with the monitor too, for it to lose power completely unless it is a fuse that's gone I'd say there's a problem somewhere with the power getting into the board considering you checked with both monitor and modulator - do check the outputs of these though, just in case!

[Bryce]

The good thing is, although people regularly speculate about Gate Arrays being faulty, ASICs malfunctioning or AYs having strange short circuits... 95% of "dead" CPCs have a simple power supply problem or a dodgy capacitor, so most of them can be easily brought back to life

Bryce.

[00WReX]

Could even simply be the on/off switch on the CPC that is a bit dusty/grubby or the contacts are tarnished etc.
I had this happen when i got one of my CPC's...thought it was dead initially.
After flicking the on/off switch a few times I noticed a flicker on the power LED.
So I unplugged the CPC from the monitor and proceeded to flick the switch a few more times.
This CPC has been fine since, that was almost 10 years ago.
Must have just been grubby contacts within the switch.
As Bryce indicated, you definately want to start at the basic's first.
Cheers,
Shane

[CanonMan]

Grotty power switches?

Squirt some Servisol Super 10 in there and waggle the switch backwards and forwards a dozen times.... that usually does the trick

[Jon]

Thanks all for the advice. I tried the trick with the switch but no joy so I took the whole thing apart, cleaned the dust off (using only antistatic materials), used a LED light and magnifying glass to check the circuit, power connector, etc but can't see anything wrong. Have put it all back together but still no joy.

Over the weekend I found a replacement fully working 464 with colour monitor and joystick for £50 on ebay, picking it up on Thursday. Will sell my broken one for spares on ebay, hopefully someone who knows what they're doing will pick it up for a few quid and will be able to breathe new life into it.

Thanks again.

Jon

[Badstarr]

Doh! I have a working main board that I would have been able to sell you instead! Never mind I'm sure you will enjoy your new 464 ! I think you should store your dead 464 away to donate parts to the new one as and when they are required. I would wager its more useful parts are still intact and you have a cassette unit and possibly a keyboard as backup units too ( the keyboard maybe a different style connector though but still possible to use just a bit more fiddley to do ) It may very well save you having to shell out 50 quid for another one in the future! And you can claim you have a collection of CPCs too!

[Bryce]

I doubt there is very much wrong with it and would probably be very cheap to repair. Completely dead computers usually have a supply problem and all those parts are cheap and plentiful. It's when the computer runs but gives strange screens, then you can be sure that it's usually one of the custom ICs, so expensive and difficult to get sometimes.

That's why I usually buy that type on ebay.

Bryce.

[ralferoo]

I would wager its more useful parts are still intact and you have a cassette unit and possibly a keyboard as backup units too ( the keyboard maybe a different style connector though but still possible to use just a bit more fiddley to do )

Be careful swapping tape units between machines too as the pinout of the connector changed slightly between revisions. I forgot which way round it changed but on some there is an extra 5V pin, shorted on mainboard and daughter board with the main one and on the other revisions it's an extra GND pin shorted on both sides. So, you can either disconnect that pin or just be careful!

[Gryzor]

Be careful swapping tape units between machines too as the pinout of the connector changed slightly between revisions. I forgot which way round it changed but on some there is an extra 5V pin, shorted on mainboard and daughter board with the main one and on the other revisions it's an extra GND pin shorted on both sides. So, you can either disconnect that pin or just be careful!

Very useful advice, as I'm going to be replacing one pretty soon and I had never heard of that before...

[Bryce]

Yup, Pin 6, I think it's usually a brown wire. Most of the time it's connected to GND. I've also heard of versions where it was connected to the 5V line, but I've never seen one of these. There are also many CPCs where there's no wire there at all. The easiest solution is to remove the wire completely, the tape drive works fine without it. If you connected non-matching parts it would short the 5V supply. It wouldn't damage the CPC or the tapedeck, but it might destroy parts in the Monitor or the 5V supply you were using.

Bryce.