avatar_mrbee

CTM 644 Monitor, no picture even after replacing flyback

Started by mrbee, 10:42, 18 September 23

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mrbee

My CTM 644 monitor worked fine until one day the screen went really dark (lost colours) and then warped and shrunk into a wavy diagonal display until it faded out and that was it..

I checked the fuse, this is fine, the monitor led comes on, ive tested the power output to the 5v and 12v and they are spot on. it powers the cpc 464 just fine.
Thinking the flyback had died, I ordered 2x of them off donberg that arrived 2 weeks ago.
NOTE : This replacement flyback doesnt have a pin (usually a screen pin).

Powering back on.. no picture at all, it doesn't seem like the flyback is getting any power as you can't hear the tube working (no static on the screen etc either).

Just wondering if anyone knew the next step should be to try and rule out what it could be? I can remove each capacitor one by one and test them, which will take me some time but any advice would be appreciated. thank you


SerErris

As I have no clue as you, I can only advise to stop working on it.

It is very dangerous (if you do not know what you are doing) and it can make things worse.

Better seek help of a professional. I know this is getting harder and harder over time, as no one will repair CRTs anymore, but still it is dangerous - in the meaning of you can get killed.
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.

mrbee

Thank you for the warning, I have worked on a few arcade monitors before and replaced flybacks and capacitors and things like that. I have a proper discharging probe and that sort of thing. I'm pretty confident and safe when poking around these things but some old school knowledge on these things is very appreciated.

It's just time that is precious at the moment and just sitting there taking out one capacitor at a time and testing and all that, just looking to see if anyone knew of a common thing about it to get me testing in the right areas. You can literally spend hours testing these, case back on, power on, test, case off, discharge, disconnect and repeat. If it had no power at all I would suspect it was the transformer but thats testing all good!
As there is no pin for "screen", usually on a flyback if this is not connected it will power on but the screen will be blurry and very bright but because there is no power at all going to the flyback, but power going to the amstrad and transformer voltage is all good im thinking capacitors... but maybe its a chip? I have no idea :(

mrbee

Progress so far - I have another ctm 644 that works but it has a bad yoke, so i swapped the board from this one over and now this monitor is working again, but it needs new capacitors as the screen is faded to one side and the colours aren't good. 

I am currently trying to source the right capacitors to replace but it's taking some time. Online there is a list of capacitors, the capacitors on my board would say it is a 35v but the list online has this as 50v (which is fine to have a higher voltage as long as the uf is the same) but when looking online for a replacement - the tricky part is to buy one that is the same size as in the physical size and other things to get a suitable replacement.

Does anyone know of a place that sells a capacitor kit for these? 

darkhalf

There won't be a magic place I can think of selling specifically for these monitors. Digikey or Mouser will have a wide variety of parts which should meet the dimensions and voltage ranges you need

I would personally invest in an ESR meter and check them before replacing. The various monitors I have here show all my caps are within EGR range. 

You are lucky you still have correct power to the primary transformer. Both of my units have had the voltage regulator, diodes, fuses and 5.6 ohm resistor taken out by the flyback
CPC464/GT64, CPC464 Plus/CTM640, 2 x CPC6128/CTM644

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