My point was there's no reason to be scared of the HV, it won't kill you and if you have any sense you won't even get a shock, just be careful. I've been repairing CRT equipment for ~25 years and haven't hurt myself yet. 240V mains is far more dangerous than 15kV at a milliamp or so for a CRT.
Im 92, anything can kill me, like pokeing around the HV while having Parkinson hands! Surely you would not advice such unless you wanted cause a death covered up as death by Parkinsson?! I'v actually zapped my self with a HV cap
several times , it's not nice, but i do lick 9V batteries as to se if they contain charge!
I do not doubt your experience with CRT's.
The first thing to do is see if you can find the service manual for it - you haven't given us a model number yet.
Well GW GOS622 i had assumed most old analog scopes is more or less same in the back end drive circuitry.
If it has steadily got worse over the last 30 years then something has aged rather than suddenly failed.
My fault there, what i should have said is 30 year old scope that faded past 2-3 years, sorry!
It might be the tube, but it could also be something as simple as a resistor changing value. The fact that the brightness control has "zero effect" is interesting though, was that sudden?
Nope faded for 2-3 years then just stuck in one level. Somethinmg silly like solder joint/cable off etc? Last time at least 10 years ago when i repaired H amp driver i recall the wave soldering in the beast look properly.
Does it not make any difference at all, or is it just too dim at maximum brightness?
No difference at all, trace is visible at evening light and scope can actually be used. No max intensity only low.
The observation that the trace is still in focus is interesting too - the brightness and focus controls are usually part of the same resistor chain.Does the focus control have any effect?
Yes over it's range dim focus dim again like when it was new.
If the horizontal and vertical deflection has not changed, then the high voltage has not changed either.
OK interesting to hear.
Low cathode emission can be tested by increasing the brightness and watching for "double peaking" where the brightness decreases before increasing again. This is accompanied by widening of the trace.
I have the schemo for GOS620 630 i assume 622 is similar i presume.
Sometimes the CRT grid bias adjustment drifts and all that is needed is a z-axis calibration.
Some trim pot?
CRTs are just like any other thermionic tube,---- the cathode only has a finite number of hours before the emission falls off enough to become unusable.
Im aware of that and also though that could be the case, but since its still usable in evening light (not daylight)
and focus works, well?
If it is possible, you could try increasing the heater voltage a bit, which might give a bit more life.
OK, il keep that in mind.
Here are the GOS620-630 schemos for Z amp and supply.