CTM 644 Vertical Hold Issues

[Wiggs1979]

Hello,

Firstly, just wanted to say thank you for such a great forum - I've been a long time lurker and read so many helpful posts on here that have helped get my 464's and 6128 fully functioning. I was never a CPC user back in the day, but I have a growing collection of retro computers!

I have a CTM 644 that wasn't working, but having replaced the HOT it seems to be back to life again. However, the vertical hold adjuster on the rear seems to need tweaking every time I power on the machine connected to it, else I have a rolling image or an image that is out of sync, split with part of the black border. If I leave the screen on for a bit, occasionally it'll start rolling very slowly too. The adjustment seems to be very sensitive, very small adjustments required, is that normal? Before I go desoldering and hunting for a suitable replacement 20k POT as I don't have anything to hand, I wondered if it's there's a common issue I might be missing? It's got the Z70215 PCB. Other than that, it shows a good, clear picture when it's not rolling!

Thank you!

[Devlin]

Hello,

Firstly, just wanted to say thank you for such a great forum - I've been a long time lurker and read so many helpful posts on here that have helped get my 464's and 6128 fully functioning. I was never a CPC user back in the day, but I have a growing collection of retro computers!

I have a CTM 644 that wasn't working, but having replaced the HOT it seems to be back to life again. However, the vertical hold adjuster on the rear seems to need tweaking every time I power on the machine connected to it, else I have a rolling image or an image that is out of sync, split with part of the black border. If I leave the screen on for a bit, occasionally it'll start rolling very slowly too. The adjustment seems to be very sensitive, very small adjustments required, is that normal? Before I go desoldering and hunting for a suitable replacement 20k POT as I don't have anything to hand, I wondered if it's there's a common issue I might be missing? It's got the Z70215 PCB. Other than that, it shows a good, clear picture when it's not rolling!

Thank you!

the pot's internals might be dirty - give it a good blast of contact cleaner and give it a spin the full range a few times while the monitor is off and see if that helps?

I've found a lot of issues with the CPC and accessories misbehaving *so often* being down to purely things being dirty.