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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 5th Oct 2022, 2:57 pm   #1
Goosegrass153
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Default Gradual failure of Scopex 4D 25

Earlier this year it was a fully functional cathode ray oscilloscope in daily use. One day the x time base ceased but I discovered that pressing the "Locate" button restored the x-scan. Whilst the vertical, y-direction, scale was distorted I could still make some measurements. Then that too ceased working and all I can get is bright spot in the centre. Can anyone suggest what to start looking at to effect even a partial repair?
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Old 5th Oct 2022, 6:38 pm   #2
frsimen
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Default Re: Gradual failure of Scopex 4D 25

Hello and welcome to the forum.

The best thing to start with is to check that the +110V, +20V and -20V supplies are correct. Be aware that the -20V supply tracks +20V supply, so a fault on the +20V will affect the -20V output too.

One further test is to see whether any of the shift controls can move the spot when adjusted.

Be very careful when working on this oscilloscope, the mains derived EHT can kill, so keep well clear of the high voltage areas.

Paula
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Old 5th Oct 2022, 7:05 pm   #3
G6Tanuki
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Default Re: Gradual failure of Scopex 4D 25

How has it been stored? I've had all sorts of odd issues with gear that uses high voltages when it's spent time in damp environments.

[I consider anything greater than 60% RH as unacceptably-damp for old electronics].

Can you put it in a room heated to at least 20C along with a dehumidifier for a week or so before investigating further?
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