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Heatercathodeshort · 14th Sep 2018, 9:00 am

The capacitors should be replaced. The linearity presets should be set half way with plenty of adjustment either way.
You cannot test them accurately with any test gear.

I came across this just yesterday. I was working on a KB/ITT VC200 series for display at the TV day.

Fault was frame hold control on end but locking and overall linearity pot on end with slight bottom cramp. 'Passable' but far from 100% as these excellent chassis should be.

The components are all of excellent make and quality, the ones I had the mystery with were Plessey .022uf and .047uf 1000v DC plastic types that have a very good reputation.

I lifted one end of each cap, all in the coupling and feedback path and measured them on my reliable cap bridge. All four read exactly correct capacitance and a 750V leakage test proved them to be as near perfect capacitors as you will find.

I must admit I spent far too long messing about with new PCL805 valves and checking components that were obviously nothing to do with the fault.

I then had a cup of tea and returning to the workshop did what I should have done in the first place. I replaced all four caps with good quality replacements. Switching on produced a rolling picture and a massive increase in height.

Adjusting the presets produced a very linear picture with them set mid way and yes the hold control was now centered as it should be.

Testing the capacitors again showed them to be perfect! So be warned, it might save you a bit of head scratching.

The 1400 should give a 100% linear picture easily with plenty to spare. Hope to see you at the TV Day. Regards, John.

14th Sep 2018, 9:00 am	#40
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Stuck on a BRC 1400! The capacitors should be replaced. The linearity presets should be set half way with plenty of adjustment either way. You cannot test them accurately with any test gear. I came across this just yesterday. I was working on a KB/ITT VC200 series for display at the TV day. Fault was frame hold control on end but locking and overall linearity pot on end with slight bottom cramp. 'Passable' but far from 100% as these excellent chassis should be. The components are all of excellent make and quality, the ones I had the mystery with were Plessey .022uf and .047uf 1000v DC plastic types that have a very good reputation. I lifted one end of each cap, all in the coupling and feedback path and measured them on my reliable cap bridge. All four read exactly correct capacitance and a 750V leakage test proved them to be as near perfect capacitors as you will find. I must admit I spent far too long messing about with new PCL805 valves and checking components that were obviously nothing to do with the fault. I then had a cup of tea and returning to the workshop did what I should have done in the first place. I replaced all four caps with good quality replacements. Switching on produced a rolling picture and a massive increase in height. Adjusting the presets produced a very linear picture with them set mid way and yes the hold control was now centered as it should be. Testing the capacitors again showed them to be perfect! So be warned, it might save you a bit of head scratching. The 1400 should give a 100% linear picture easily with plenty to spare. Hope to see you at the TV Day. Regards, John.