On 2020/01/19 3:02 p.m., Jeff Liebermann wrote:
On Sun, 19 Jan 2020 18:18:49 +0000, Cursitor Doom
wrote:

Gentlemen,

Hardly.

Would I be correct in thinking that if you have an item of test
equipment with a CRT display and it's dim and when you try to turn up
the brightness it actually gets dimmer for the last bit as you get
towards maximum? And there's nothing you can do about it; it's only
fit for spare parts?

No. You would NOT be correct. Find the service manual of your
unspecified model piece of antique test equipment, and check the
voltages in the CRT and Hi-V section. Use a Hi-V probe if you value
your life and your DMM. My guess(tm) is that you'll find some form of
component failure or deterioration, such as a burnt resistor, leaky
capacitor, arcing flyback, sick hi-v diode, or the usual high ESR
electrolytic capacitor. Plenty of possibilities.

Also, some of us have CRT test fixtures that can also restore/rejuvenate
almost any picture tube/CRT - B&K model 490 for example.

If the image grows/shrinks when you change the brightness, then there is
usually a fault with the HV diode, especially in B&W CRTs.

I'd first look at the electrolytic caps in this unit - most are past
their best before date... When replacing the caps take care to use caps
specced for the circuit they are being used in. And try using a good
quality cap like Panasonic from Digikey or Mouser. Not crap from eBay...


Now, I have question. Is there some reason you chronically fail to
provide the maker and model number of what you are working on? I'm
wondering if you have a pathological aversion towards numbers, or
perhaps you might be embarrassed by your choice of test equipment.


That might be considered to be cheating - actually providing useful
background information...

John :-#)#

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