On 13 May 2007 04:06:03 GMT, Jim Yanik wrote:

Steve wrote in
:

The scope is a 465M, S/N is B056721 but it looks like that may not be
original, assemblies have been swapped etc..

The problem: the scope had been working fine until one day the crt was
dead. Fuse F558 was blown, (it goes from the 32V unreg to the HV
oscillator circuit). All other supplies are fine.

I first unsoldered pin 10 from T550 (feeds the 3x multiplier), but the
95V supply still wouldn't come up. I then checked Q556 & Q552, the
transistors driving T550, both are fine. I then checked the caps and
transistors in the 95V circuit, all fine. I then unhooked the jumper
leading from L582 to the rest of the scope, still no luck. I then
took out the crt (both the plug on the back and the anode lead), and
the supply came up with no problems. 94.5V, .07A, negligible ripple.

My readings are as follows.
Anode off & Rear Plug off: 94.5V @ .070A
Anode on & Rear Plug off: 64.2V @ .54A & climbing
Anode off & Rear Plug on: 26.7V @ .427A & climbing
Anode on & Rear Plug on: 21.6V @ .460A & climbing

Is this probably a bad tube? I don't have a whole lot of experience
with scopes, as this post would indicate, and don't want to get a new
crt if it's not going to fix it.

Also, just to make sure, there isn't any alignment procedure when
swapping scope crt's, is there?

Yes,the whole scope has to be recalibrated.

I don't figure there is, just want to
make sure.

I have another 465m, but the same fuse is blown, and I haven't gotten
into it yet.

All thoughts appreciated.

Thanks,
Steve



The CRT should not draw any appreciable current from the 95V supply.

You are right, the new tube only draws ~30mA extra. In the schematic
I have, 95V goes to geometry, 32V to astig. I am sure this scope has
probably seen many bumps. I didn't check the date code but I'm sure
it's at least 20 years old, probably older. However, it was sitting
still on my bench when it stopped working, so I guess something might
have just given out after being previously broken.

I agree with you, the case isn't rugged, I simply bought the pair
because they cost $20.00 each. I would much prefer a 465b, but I
already have seven scopes and have to stop collecting sometime.

Just out of curiousity, the supply was still drawing too much current
and the 95V was loaded down when I only had the anode lead connected.
Why would this be if the astig or geom elements were shorted? Is this
due to the absense of the anode at the other end? Just curious.

Luckily I work at a cal lab so I can probably put it on the bench for
cheap. Unluckily, I will be the one calibrating it and this procedure
looks a bit lenghty. Oh well, good experience.

Thanks for your help,
Steve