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CPC 464 Out of spec Video?

Started by OldScot, 23:03, 07 January 24

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I finally acquired my first Amstrad, a CPC 464, and I've got it to the point that it is producing a video signal.
It seems the signal is out of spec as my composite PAL converters can't lock onto the signal. (I'm in the Chicago area.)
When I first tested the machine there was no video signal. ( I made a composite cable as I it didn't come with a monitor. Using a Meanwell 5V2A supply.)
Initially the VDU wasn't creating Vsync or Hsync so I assumed the VDU wasn't being configured by the cpu.
I replaced the Z80 and the VDU creates now Vsync and Hsync but while my PAL->VGA and PAL->HDMI converters occasionally claim to see a PAL signal, the claim is very brief and it displays nothing.
I do have a very accommodating NTSC composite monitor that will display (badly obviously) anything it can see.
It looks to be displaying the boot up screen (in a rolling, stretched, distorted way) so I wondered if the signal timings were off.
I compared the video signal to the one produced by my Acorn Electron and the frequencies looked quite similar, just a little different.
(Also verified my converters worked with the Electron. Normally I use an Electron RGB to VGA cable I made.)
Finally took some pictures of the screen so I could actually read it. (Should have done that earlier. :doh: )
The text is a garbled mess and reminds me of other posts here where it seems the Gate Array was the culprit.
I have an early model with the 40007 and large heat sink.
Pictures of the video and motherboard are at the link below.
At this point I presume the problem is with the VDU or 40007 but I'm leaning towards the 40007.
I understand there is a replacement for the 40010 but not for the 40007 and no translation board is available?
Where can I source a replacement 40007?
I watched one youtube repair video where it was demonstrated that after boot, hitting the 'Delete' key results in a beep. Unfortunately I'm not getting a beep either.
Thanks for any and all assistance!


1. The Video output from the CPC is an RGB output with Composity Sync. It also has a Composite monochrome output. I never tested it to attach the monochrome output to a composite to VGA converter, so this might not work at all. It does not output a PAL signal. It outputs a 50hz or 60hz RGB video signal.
2. Where did you source your CPC from? It might be that it is actually a 60hz model. It was available for both markets.
You can check this with your CPC @ home:
It has 4 "bridges" on mainboard.
the first 3 are to set the computername.

The one to the right is for changing between 50/60hz.

3. It does not look like a GA problem to me, more like a generic display connection problem.

What you need is a CPC Scart cable and then a SCART to VGA/HDMI converter. That should give you a picture.

Also the GA 40007 replacement is now available:
Proud owner of 2 Schneider CPC 464, 1 Schneider CPC 6128, GT65 and lots of books
Still learning all the details on how things work.


Thanks for the feedback SerErris, very helpful!

Eventually I plan to move to RGB but for initial testing purposes  I'm using this cable: (using pins 5 and 6 of the video connector)
I found it on this web page:

My 464 is a PAL model, vertical sync is 50hz.
I'll check the "bridges" on the mainboard in case anyone has monkeyed with it, but it doesn't appear anyone opened this machine previously.
I recall seeing the bridges on the schematic.

I'm judging the output by the characters. Even when the video is "torn" the characters should still make sense.
The two lines in the middle aren't torn and should be legible. See
In this case the characters are gibberish.

Thanks for the 40007 link! I hadn't found that previously. Always better to check with people that are familiar with the tech!
I'll order one straight away!


Is the monitor capable to display a 256p signal? because the CPC does not send a interlaced video, but actually the same frame.

The video signal looks like you have two frames overlapping and also somehow the characters are stretched (each pixel doubled?).

It can be the GA, yes, but I am still not convinced.

Proud owner of 2 Schneider CPC 464, 1 Schneider CPC 6128, GT65 and lots of books
Still learning all the details on how things work.


Quote from: SerErris on 12:20, 08 January 24What you need is a CPC Scart cable and then a SCART to VGA/HDMI converter. That should give you a picture.
But make sure that the SCART2VGA/HDMI is a RGB model and that the Scart cable properly provides the voltage to switch to RGB mode. A composite model will not help and most converters will stick to composite if the RGB switch signal is not provided (also the "capacitor hack" will not work with most).

Quote from: OldScot on 02:05, 09 January 24My 464 is a PAL model, vertical sync is 50hz.
Regarding PAL/NTSC: It's a common misunderstanding to talk about PAL/NTSC when actually 50/60Hz is meant. PAL/NTSC are TV signals and unless you are using the antenna connector, PAL/NTSC does not play a role. If you have a composite video signal or a RGB signal, it's just about 50/60Hz and no longer about PAL/NTSC.

Quote from: OldScot on 23:03, 07 January 24my composite PAL converters

What exact converter is that? Composite input? and which output?

Afaik the luminance signal is not a real composite video signal. It's close enough so most composite inputs work, but I could imagine that not all converters will accept it. 

btw: please upload pictures directly in the forum. If they are kept outside they will vanish at some point and we lose information for the future. (instead of quick reply, click on "Reply", then also the upload area/button will be available - or click preview in the quick reply - then also the upload will be possible)

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