Author Topic: Any way to fix CTM-644 misaligned red ghost image? (Photograph attached.)  (Read 252 times)

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Offline Jonathan

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My young daughter would like to have a "retro games day" for her birthday on Saturday.


Unfortunately I have just discovered that the CPC 6128's monitor isn't working - see photograph.


There is a red ghost image, and the screen display is (based on some quick Wikipedia research!) an isosceles trapezium rather than a rectangle.


Everything looks all right physically, except that the RGB connector is slightly dented.


Is there any way to fix this? Thanks in anticipation.

Offline tjohnson

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Thats what my CM14 did before it gave up the ghost this morning, no idea what it is and nervous to mess around inside it because of the high voltage.

Offline betpet

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I'm no electrical genius by any stretch of the imagination but I suspect that the CRT projects the three primary colours to the screen and the red projector seems to have slipped.


NB. This could be utter nonsense but possibly worth checking out.
Old Amstrad CPC 6128 owner. New Amstrad CPC 464 and 6128 owner. Getting back the love!

Offline Bryce

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There are 3 dark grey levers on the glass neck of the tube. These shift the 3 colour guns. You need to CAREFULLY adjust these so that the colours line up. Carefully, because there are high voltages very close to the levers.

Bryce.

Found a picture... Red circle on the left shows the levers.
« Last Edit: 17:13, 30 September 20 by Bryce »

Offline betpet

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Woah!  Does this mean I got the right idea without having a clue? :O
Old Amstrad CPC 6128 owner. New Amstrad CPC 464 and 6128 owner. Getting back the love!

Offline Bryce

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Woah!  Does this mean I got the right idea without having a clue? :O

Yes, congratulations! :D As the Germans would say: "Even a blind chicken eventually finds a grain".

Bryce.

Offline Jonathan

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Thanks. How easy is it to get to the levers? And what are the risks of this blind chicken electrocuting himself?


It turns out all three colours are out of alignment. It’s quite a beautiful effect (in a way) but the forum won’t let me upload a photo of it.

Offline Jonathan

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I found something about it here: http://cpc.sylvestre.org/technique/technique_reglage_ecran.html


My French can just about understand “théoriquement possible” and “bon courage”!



Réglage position RGB sur le tube
Il est théoriquement possible de corriger le décalage des couleurs les unes par rapport aux autres. Cela se fait sur les ailettes qui ceignent le tube :
Je n'ai jamais réalisé cette entreprise. On me l'a décrite comme étant une opération de la dernière chance car il est très difficile d'être précis sur ce réglage. Le principe est de les "décoller" du tube, car leur réglage est fixé en usine par une colle épaisse. En faisant jouer les ailettes, on casse cette colle pour modifier le réglage. Et quand vous en êtes là, bon courage... n'hésitez pas à me raconter votre expérience. Mais un conseil, ne faites ça que si quelqu'un d'autre est dans la pièce pour vous regarder agoniser si ça foire (et prendre des photos).

Offline Bryce

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Just be careful that you only touch the plastic levers. It's a simple process.

Bryce.

Offline gerald

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The brightness of this screen make me thing it's not a matter of colour alignment but more G2 voltage being too low.
Before touching any of these levers, try fiddling with the G labelled potentiometer on the back of the high voltage transformer.

Offline Jonathan

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If anyone happens to live in Yorkshire (England) I'd happily pay you to fix this for me!


I haven't worked up the courage yet...

Offline Bryce

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There are a few retro repair people near you. I'll send you a PM.

Bryce.

Offline Jonathan

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I feel obliged to keep you updated!

Retro games day went well yesterday even with the broken monitor. She liked Space Invaders from Auntie John%u2019s Twilight Zone disc, The Prize, Boulderdash, and some others. Dizzy worked very well because it%u2019s mostly green and red, so the misaligned colours caused minimal problems. We had a go on the emulator today but Dizzy on the real CPC remains the favourite!

Bryce has put me onto someone fairly local who is willing to try to fix the monitor, and Sid has sent me an adapter which might work with a Samsung monitor.
« Last Edit: 22:11, 04 October 20 by Jonathan »