Problem with a CTM644 monitor (edited: pictures were not properly uploaded)

[ago]

Hi!!
As you can see in the pictures, my monitor is not working properly. It was working perfectly one day, it went to the wardrobe for some months, and next time I wanted to use my real CPC it was like in the pictures. I remember it took a slight hit in the upper side with its own plug when I was putting it inside its box, but to be honest, it was a very soft touch and I have always been very careful with it, so it would be a suprise if that were the cause of the malfunctioning.

Do you think it is possible to repair it? If yes, could it be done easily? I mean, repair it myself considering I am not into electronics. I am not afraid of opening things and do some soldering (for example, I have modded my CPC to use an internal 3.5" drive, and have modded consoles and other basic stuff in the past), but I know that CRT's are a different world, so I if it is fixable but somehow complicated I can take it to a local technician.
I use my CPC with a 14" CRT since then, but it would be nice to be able to use it with its CTM again.

[TotO]

Nice demo. I love this effect! 

[ago]

Nice demo. I love this effect! 

And it is CPU free!! 

[Animalgril987]

Looks like at least 5 colours in Mode 1 !!


On a serious note, I think it's one for @Bryce

[Kris]

You have a defective Yoke.......


check: [size=78%]I burned the ctm 644 accidentally. (cpcwiki.eu)[/size]

[Nworc]

Nice picture!  Maybe the deflection yoke just came loose, but am not sure.

[Bryce]

Yup, the yoke has serious issues.

Bryce.

[ago]

@Kris @Nworc @Bryce

I see you all agree with the diagnostic, I will see what I can do. Thank you very much!!

[Bryce]

Be careful messing around in that area. There are high voltages present, even when the monitor has been unplugged.

Bryce.

[ago]

Be careful messing around in that area. There are high voltages present, even when the monitor has been unplugged. Bryce.

Thanks. I am aware of the dangers when manipulating CRT's, I won't be cheap about safety.

[Nworc]

Thanks. I am aware of the dangers when manipulating CRT's, I won't be cheap about safety.

:thumbsup:

Just in case you'd have a careful look inside - a picture showing the inside would be appreciated.

[RetroCPC]

I would suspect C436 & C437 - but as others have warned, these a located in the HV section so its best serviced by someone with electronics experance.

Other caps such as C424 / C425 / C402 could be suspect - but I'd start with C436 / C437

[tjohnson]

My CM14 did that, the yoke needed replacing, corrosion on the windings until it shorted out completely.

[Nworc]

Seems to be a common problem, here is another one with the same issue:

https://www.ebay.de/itm/373938226105

[RetroCPC]

I really suspect the caps I mentioned, I've just had a similure issue with a piece of Lab equipment - dryed out cap in the scan coil circuit...

[ago]

:thumbsup: Just in case you'd have a careful look inside - a picture showing the inside would be appreciated.

Seems to be a common problem, here is another one with the same issue: https://www.ebay.de/itm/373938226105

I don't know yet when I am going to check it, probably next weekend but not sure, but I will take some pictures and post here what I see.

I would suspect C436 & C437 - but as others have warned, these a located in the HV section so its best serviced by someone with electronics experance. Other caps such as C424 / C425 / C402 could be suspect - but I'd start with C436 / C437

My intention is to check if I am a lucky person and the problem is that the yoke is just loose. If that is not the case I will try to find someone around in my hometown who can repair it.

[roy bates]

the problem you have a shorted deflection yoke,unfortunalty its quite common on these monitors,seen too many of them die like this

roy

[roy bates]

to save you alot more time since i work on this sort of stuff alot,its not capacitors,if it was i would expecting vertical collapse,some sort of hoirzontal sync issue that sort of thing,siganl is going in fine,picture is there,its just messed up delfection because the coils are shorted

[Nworc]

to save you alot more time since i work on this sort of stuff alot,its not capacitors,if it was i would expecting vertical collapse,some sort of hoirzontal sync issue that sort of thing,siganl is going in fine,picture is there,its just messed up delfection because the coils are shorted

You are right - I found the specific problem description of a shortened deflection yoke in Heinz Lummers TV Service book, chapter 15.2.3, matching the scenario provided here very closely.

That chapter distinguishes between different types of short: inside the vertical coil, inside the horizontal coil, or between both of them. The provided image here matches a short between vertical and horizontal coil very closely. So, it is very likely that.

If that helps ... ?

[roy bates]

to save you alot more time since i work on this sort of stuff alot,its not capacitors,if it was i would expecting vertical collapse,some sort of hoirzontal sync issue that sort of thing,siganl is going in fine,picture is there,its just messed up delfection because the coils are shorted

You are right - I found the specific problem description of a shortened deflection yoke in Heinz Lummers TV Service book, chapter 15.2.3, matching the scenario provided here very closely.

That chapter distinguishes between different types of short: inside the vertical coil, inside the horizontal coil, or between both of them. The provided image here matches a short between vertical and horizontal coil very closely. So, it is very likely that.

If that helps ... ?

yes it does and thats right,i have seen exactly that personally itll help the op,and i wouldnt turn it on again because of the short it wont get better,only fix for this is replacing the deflection yoke which is the easier of the options,or remove the yoke and try to find the short and remove it and try to insulate it after,i have done that a  few times but its hit or miss,and i couldnt really advise that option,its not for the faint of heart,and success is very limited at best

if i had to guess exactly where it was shorted ,by the picture,as you look into the set from the rear,the short is probably in the lower or upper two coils and arcing between the insulation in the center of the two quandrents ,facing the tube,it could even be shorting to the tube itself at some points,itll be burnt and probably visable when the coil is removed,insulation is definetly gone
hense i wouldnt keep turning it on

[dragon]

I made a database time ago with what ctm 644 tubes mount what model of yokes. 

Some mounted various types. (equivalent). 

Should be here ost in the forum. But in her day I never find anyone as spare part in internet. 

[tjohnson]

As I said before my CM14 monitor did this I fixed it by getting the tube and yoke out of a 14" Philips TV and swapped them over.  Worked fine and probably actually had a clearer picture afterwards.

[ago]

Thank you all for your answers!! I didn't have time yet to open and check the monitor, hopefully I will be less busy after summer. Probably I won't be able to fix it, but I will take and upload some pictures.