Vacuum fluorescent display.

[Dave Plowman (News)]

The old car has a green vacuum fluorescent display for the clock and OBC. On a cold and damp day it tends to show all the segments until it warms up then comes good. The obvious thing would be to simply fit a spare - I have a couple - but my late car includes a dimming function for when the lights are on - the earlier units, and my spares, not. And it is uncomfortably bright at night without the dimming function. I've checked for dry solder joints - but some of it is thick film construction, which I don't really understand.

Any ideas?

[Andrew Gabriel]

I would guess damp/condensation, causing leakage to the grid connections to the tube (and/or the anode plates if it's a multiplexed display with multiple anode plates).

[The Natural Philosopher]

That is a cogent thought, in which case washing with alcohol and spraying with a spirit based lacquer might sort it.

[Brian Gaff]

A lot of theolder calculators seemed to suffer this way after some years. I think its due to degradation of internal insulation which lets the voltage leak to other electrodes. Certainly, I never found an external reason for it as those early things ere very very simply built. I got the feeling that the little inverter was the most taxing part. Maybe someone else knows what the problem is with those. I guess they are pretty high impedance, so any leakage will probably light the segments.

Brian

[Andrew Gabriel]

You can buy conformal coating sprays for this purpose. Obviously, need to make sure it's completely dry before applying.

If the car interior has got excessively wet, then driving with the heater on full blast and some ventilation might fix it, if it dries out the moisture inside the car.

[Dave Plowman (News)]

Thanks for the replies. The car lives outside all year long and isn't used every day. However, it didn't do this when newer. Perhaps I'll try giving it all a good clean and dry it out then use a coating.