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Old 8th Feb 2020, 10:35 am   #1
meter pan
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Default Faulty Microvitec Monitor help please!

I am trying to repair a 1431MS4C "BBC" monitor with an E-W fault (see picture).
The HT voltage is correct and the EHT is OK at 24kV. I would be grateful for some ideas as to the cause of the fault.
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Old 8th Feb 2020, 10:52 am   #2
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Default Re: Faulty Microvitec Monitor help please!

I would start by looking at the soldering with a magnifying eyepiece to see if there were any 'dry joints'.

Start with the large resistors and transformer connections.
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Old 8th Feb 2020, 11:50 am   #3
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Default Re: Faulty Microvitec Monitor help please!

Could be corrosion on the scan coil windings causing shorted turns.

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Old 8th Feb 2020, 12:11 pm   #4
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Default Re: Faulty Microvitec Monitor help please!

It does look like faulty scan coils, but yes check for dry joints first.
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Old 8th Feb 2020, 2:13 pm   #5
Red to black
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Default Re: Faulty Microvitec Monitor help please!

Almost certainly faulty scan coils unfortunately, seen it many times before.
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Old 8th Feb 2020, 4:09 pm   #6
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Default Re: Faulty Microvitec Monitor help please!

I was wondering about the scan coils.I've been through the joints and tested/replaced components.
Thanks for the replies!
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Old 10th Feb 2020, 4:40 pm   #7
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Default Re: Faulty Microvitec Monitor help please!

What make of CRT is it? I imagine it'll be one of the red label type fitted to Orions with the corroding scan coils. Unfortunately, as it's a monitor, scan coil repair will be unlikely to give a good enough display. I'm sure all my CRT coils are long since gone, but I will have a look just in case.
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Old 12th Feb 2020, 2:54 pm   #8
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Default Re: Faulty Microvitec Monitor help please!

A replacement scan coil should work, though only after careful adjustment.

Repairing the scan coil should be attempted first anyway. There's a chance of geometric distortion due to the winding position being different after repair but you may be able to keep it to a minimum.
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Old 12th Feb 2020, 3:27 pm   #9
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Default Re: Faulty Microvitec Monitor help please!

Measure the resistance of the coils and check/replace any capacitors at the deflection outputs. I once got lucky with a PC monitor with similar symptoms to yours.
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