Commodore 1084s monitor - smoking scan coil - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Maarten · 20th Dec 2017, 9:23 pm

Impressive indeed!

I would proceed by first adjusting it as good as possible by the procedure in the manual. Then you could do local corrections (presumably near the repaired section) by sticking permalloy strips between the yoke and the tube.

jay_oldstuff · 20th Dec 2017, 9:34 pm

very nice repair. I have one of these commodore monitors down in the celler with exactely the same issue, you've inspired me to have a go and see if i can fix mine too.

1955APREN · 20th Dec 2017, 9:38 pm

What a great job I hope that my ex service manger do not read this as he would have all of us making this type of repair in customers homes. Hope the repair last's if it does not my scan coils + crt here if you require them. Regards Derrickl

Boater Sam · 21st Dec 2017, 1:35 am

Excellent.
Bet working that out was no Yoke!

Clydeuk · 21st Dec 2017, 2:00 am

I think the way to I used to do the setting up on these was to display a red raster, remove the wedges and slide the yoke as far forward as it would go (pulling back sometimes works as well), adjust the purity rings to get the largest red patch in the centre, then slide back (or forwards if pulled back) to obtain a pure red raster. At this point the yoke clamp would be tightened. I left the wedges out and then adjusted the other rings for best overall convergence, then if there was any covergence errors left, tried rocking the edges of the yoke and wedging in the best position. I don't remember having one that I couldn't get spot on, or as near as damn it. I never tried repairing a yoke though, which might have an effect on how well you can get it converged, though I would expect it to only affect one corner.

I wouldn't reuse the old wedges as it is the chemical breakdown of these that caused this problem in the first place, and that will continue.

Welsh Anorak · 21st Dec 2017, 3:09 pm

Well, back in the day that yoke would have gone straight in the bin, no messing! Well done to even think about repair.
Get the red raster right first having demagnetised the CRT and go on from there. I'd be tempted to follow Maarten's advice and try those small strip magnets near the repair if you need to. I've always found that damage occurred at the 'ten past' wedge. I think the cause was not the wedges per se but the silicone sealant leeching corrosive acetic acid as it cured. I'd use non-acidic sealant when you've got everything right.
That's the sort of repair we all like to do - completely uneconomic but oddly satisfying - congratulations.
Glyn

20th Dec 2017, 9:23 pm	#21
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Commodore 1084s monitor - smoking scan coil Impressive indeed! I would proceed by first adjusting it as good as possible by the procedure in the manual. Then you could do local corrections (presumably near the repaired section) by sticking permalloy strips between the yoke and the tube.

20th Dec 2017, 9:34 pm	#22
jay_oldstuff Octode Join Date: Jan 2005 Location: Hyde, Greater Manchester, UK. Posts: 1,074	Re: Commodore 1084s monitor - smoking scan coil very nice repair. I have one of these commodore monitors down in the celler with exactely the same issue, you've inspired me to have a go and see if i can fix mine too. __________________ The light at the end of the tunnel is probably the headlight of an oncoming train

20th Dec 2017, 9:38 pm	#23
1955APREN Hexode Join Date: Nov 2010 Location: Market Drayton, Shropshire, UK. Posts: 485	Re: Commodore 1084s monitor - smoking scan coil What a great job I hope that my ex service manger do not read this as he would have all of us making this type of repair in customers homes. Hope the repair last's if it does not my scan coils + crt here if you require them. Regards Derrickl

21st Dec 2017, 1:35 am	#24
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Commodore 1084s monitor - smoking scan coil Excellent. Bet working that out was no Yoke!

21st Dec 2017, 2:00 am	#25
Clydeuk Hexode Join Date: Mar 2012 Location: Liverpool, Merseyside, UK. Posts: 453	Re: Commodore 1084s monitor - smoking scan coil I think the way to I used to do the setting up on these was to display a red raster, remove the wedges and slide the yoke as far forward as it would go (pulling back sometimes works as well), adjust the purity rings to get the largest red patch in the centre, then slide back (or forwards if pulled back) to obtain a pure red raster. At this point the yoke clamp would be tightened. I left the wedges out and then adjusted the other rings for best overall convergence, then if there was any covergence errors left, tried rocking the edges of the yoke and wedging in the best position. I don't remember having one that I couldn't get spot on, or as near as damn it. I never tried repairing a yoke though, which might have an effect on how well you can get it converged, though I would expect it to only affect one corner. I wouldn't reuse the old wedges as it is the chemical breakdown of these that caused this problem in the first place, and that will continue.

21st Dec 2017, 3:09 pm	#26
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Commodore 1084s monitor - smoking scan coil Well, back in the day that yoke would have gone straight in the bin, no messing! Well done to even think about repair. Get the red raster right first having demagnetised the CRT and go on from there. I'd be tempted to follow Maarten's advice and try those small strip magnets near the repair if you need to. I've always found that damage occurred at the 'ten past' wedge. I think the cause was not the wedges per se but the silicone sealant leeching corrosive acetic acid as it cured. I'd use non-acidic sealant when you've got everything right. That's the sort of repair we all like to do - completely uneconomic but oddly satisfying - congratulations. Glyn