CTM640 Bowed Picture

simondo · 14:41, 14 September 15

Hi,

My CTM640 monitor has a bowed image and misaligned text. Apparently this is not an uncommon fault on CRT displays.

Does anyone know if this can be repaired? I have the service manual so if anyone can point me in the direction of the faulty component(s) that would be great. Otherwise I will sell on for spares.

Thanks in advance.

Bryce · 14:54, 14 September 15

Can you post a picture of the screen please.

Bryce.

CanonMan · 16:38, 14 September 15

Deflection coils!

Bryce · 20:11, 14 September 15

Doesn't have to be the coils. It's most likely a capacitor or two that need to be changed.

Bryce.

CanonMan · 21:47, 14 September 15

Quote from: Bryce on 20:11, 14 September 15
Doesn't have to be the coils. It's most likely a capacitor or two that need to be changed.

Bryce.

True. We'll all have a better idea when the photos show up.

simondo · 18:24, 15 September 15

Here you go.

I should have post picture with new topic.

By the way it's a CTM664 not a CTM640.

arnoldemu · 18:55, 15 September 15

Quote from: simondo on 18:24, 15 September 15
Here you go.

I should have post picture with new topic.

By the way it's a CTM664 not a CTM640.

so it wasn't caused by a heavy box sitting on top of the monitor?

CanonMan · 19:22, 15 September 15

I still think it's the deflection coils, unfortunately.

simondo · 15:03, 16 September 15

Looks like it's off to auction as non working or for spares for this old friend then.

Thanks for help guys.

Bryce · 15:25, 16 September 15

Did you get the monitor in that condition? Or did it suddenly fail that way? The problem you have is known as Keystoning. This can usually be adjusted inside the monitor, but it seems like each colour has moved to a different position. If someone hasn't messed with the settings inside, then I'd guess that the coil has fallen off or become dislodged at least.

Bryce.

CanonMan · 17:45, 16 September 15

Yep, the only thing that's going to mess up the convergence that badly is either shorted windings in the deflection coils or the coils have moved on the back of the CRT. They're usually glued and clamped in place though, making it quite unlikely.

Bryce · 21:33, 16 September 15

The confusing bit is that some colours have drifted in one direction and others in the other direction. That can't happen from the coil becoming loose. Everything would go in the same direction. Maybe the CRT driver IC has failed? Eitherway, it's not an easy fix.

Bryce.

Devilmarkus · 23:46, 16 September 15

For me looks like the 30 years CPC megademo...

hmmm no but like too less power in the magnet fields which sort the lines... (Dunno the English expression for "Ablenkeinheit" sorry)

simondo · 08:11, 17 September 15

Like you say, not an easy fix. Had the monitor for 25 years and was going strong last time I used it 15 years ago. Got it out of loft recently with my 464 and found it to have this issue.

TV repair shops either will not look at it, or advise that the cost for investigation & repair will exceed value of monitor.

I have my CPC464 connected to a LCD via scart so it's not as though I can't use CPC. It would have been nice to have a working monitor though.

simondo · 08:16, 02 October 15

Does anyone know if any of the CTM664 ICs are still available e.g. CRT driver IC, convergence IC.

In the meantime I am going to check all electrolytic capacitors and replace as necessary.

CanonMan · 10:13, 02 October 15

Quote from: simondo on 08:16, 02 October 15
Does anyone know if any of the CTM664 ICs are still available e.g. CRT driver IC, convergence IC.

In the meantime I am going to check all electrolytic capacitors and replace as necessary.

Change all the electrolytics if you like, I still don't think it'll make any difference.

dragon · 13:03, 02 October 15

This happen to me time ago, after ten years of the monitor stored. But its not alone it made a sound "frezzzzzzzzzz" and the screen varies with the sound and the screen is more littel, and then one day it return to normal screen.

Now the monitor its autoself repaired o.k. Only i think it not draw the vertical line o.k. As if you compared the up right coner with the down right corner the downcorner is a litte displaced to the right.

I took it to the g.u.a one day. They said is normal effect(the vertical line) the capacitors are o.k, and about the story of the screen deformed, they looked me as i was crazy jajaja.

An x-files.

Bryce · 20:09, 02 October 15

Quote from: simondo on 08:16, 02 October 15
Does anyone know if any of the CTM664 ICs are still available e.g. CRT driver IC, convergence IC.

In the meantime I am going to check all electrolytic capacitors and replace as necessary.

Yes, but they so rarely fail, that you don't need them. There are three things that fail on the PCB: 1 - Capacitors. 2 - HT Transformer. 3 - Transistors. I've fixed so many monitors that I've lost count and I've never had to swap an IC.

Bryce.

simondo · 07:29, 07 October 15

Thanks guys.
Will check electrolytic capacitors on pcb and leave it at that.

Munchausen · 07:48, 07 October 15

I had this exact issue with my original 644, which saw heavy use as a TV using the MP3. Eventually the image disappeared completely. I've had 3 since then (gave two to guys on this forum) and never seen any issues.

roy bates · 11:36, 07 October 15

i would repair it for you,but,you would have to ship the entire monitor to me:)

simondo · 12:37, 29 October 15

Thanks for offer Roy. Posting to you, and something for your time & parts would probably not be economical. Thanks anyway.

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CTM640 Bowed Picture