# 465m shorted 95V problems

S

#### Steve

Jan 1, 1970
0
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.

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? 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

S

#### Steve

Jan 1, 1970
0
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.

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? 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

Well, I replaced the tube with the one from the other scope, and it
works just fine. So, my CRT must have gone bad, and the other scope
must have some deeper problems (I'm not even going to attempt to fix
it, it's best suited to a parts unit). What causes a CRT to just die?
It was working fine one day, the next day it's causing fuses to blow.
Now I'm curious. I always though they just wore out, lost brightness,
filament burns up, etc..

Again, all thoughts appreciated.

Thanks,
Steve

J

#### Jamie

Jan 1, 1970
0
Steve said:
Well, I replaced the tube with the one from the other scope, and it
works just fine. So, my CRT must have gone bad, and the other scope
must have some deeper problems (I'm not even going to attempt to fix
it, it's best suited to a parts unit). What causes a CRT to just die?
It was working fine one day, the next day it's causing fuses to blow.
Now I'm curious. I always though they just wore out, lost brightness,
filament burns up, etc..

Again, all thoughts appreciated.

Thanks,
Steve
check the heater to cathode, it may have shorted..
that is a common problem in CRT's
Years ago, we use to isolate the heater circuit so that it wouldn't
ground any more and be able to still use the TUBE>
it's also possible a grid wire could have broke in side.

J

#### Jim Yanik

Jan 1, 1970
0
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.

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.

J

#### Jim Yanik

Jan 1, 1970
0
Well, I replaced the tube with the one from the other scope, and it
works just fine. So, my CRT must have gone bad, and the other scope
must have some deeper problems (I'm not even going to attempt to fix
it, it's best suited to a parts unit). What causes a CRT to just die?
It was working fine one day, the next day it's causing fuses to blow.
Now I'm curious. I always though they just wore out, lost brightness,
filament burns up, etc..

Again, all thoughts appreciated.

Thanks,
Steve

You can get CRT elements shorting to others in the electron gun structure.
I've seen CRTs with the glass rods cracked or broken,the mesh lens
collapsed,glass particles stuck to the screen phosphor making dark or
intensely glowing bright spots. I've seen geometry extremely distorted,so
when you put time marks up,the straight lines are warped terribly.

Sometimes people stand the scope on it's end while using it(field
service),and then accidentally tug on a scope probe,and the front of the
scope goes crashing down.

BTW,the 465M was a "ruggedized" scope to use in lieu of a regular 465,but
NOT the same circuitry,being more similar to a 455A2B2.

My experience was that they were not as rugged as a regular 465,the plastic
case/chassis flexed and caused problems.

J

#### Jim Yanik

Jan 1, 1970
0
check the heater to cathode, it may have shorted..
that is a common problem in CRT's
Years ago, we use to isolate the heater circuit so that it wouldn't
ground any more and be able to still use the TUBE>
it's also possible a grid wire could have broke in side.

you WANT the heater to be at the same potential as the cathode,so it will
not arc over.

Most likely,his geometry or astig elements shorted to another element.
IIRC,the +95 went to either one or the other.

The scope probably took a hard shock somewhere.

S

#### Steve

Jan 1, 1970
0
Yes,the whole scope has to be recalibrated.

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 S #### Steve Jan 1, 1970 0 BTW,the 465M was a "ruggedized" scope to use in lieu of a regular 465,but NOT the same circuitry,being more similar to a 455A2B2. My experience was that they were not as rugged as a regular 465,the plastic case/chassis flexed and caused problems. I've seen so many of them on ebay listed as the "ruggedized" version of the 465b. I guess because they look similar on the front panel the must be the same inside, right? (sarcasm) J #### Jim Yanik Jan 1, 1970 0 You are right, the new tube only draws ~30mA extra. the CRT is not drawing that 32 ma from the 95V,the geom element is an electroSTATIC element,and should draw only ua. 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
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.

Makes me wonder if you don't have a HV multiplier problem.
If the rear socket is off,the geom and astig elements are unconnected,and
the 95V is not going to the CRT at all.Nor the negative cathode V,just the
12-16KV anode supply.

Or the anode connection inside the bad CRT has some sort of problem,drawing
too much current from the multiplier,and that is why the HV was loading.
I suspect this is the real problem.
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.

Steve

Well,if you work at a cal lab,then you have all the proper cal equipment!
The procedure is not that hard.
You want hard,try a 7844 dual beam 7000 series mainframe,or a bistable
transfer storage scope like a 464/466. I HATED those 2 scopes.

S

#### Steve

Jan 1, 1970
0
Makes me wonder if you don't have a HV multiplier problem.
If the rear socket is off,the geom and astig elements are unconnected,and
the 95V is not going to the CRT at all.Nor the negative cathode V,just the
12-16KV anode supply.

Or the anode connection inside the bad CRT has some sort of problem,drawing
too much current from the multiplier,and that is why the HV was loading.
I suspect this is the real problem.

Well,if you work at a cal lab,then you have all the proper cal equipment!
The procedure is not that hard.
You want hard,try a 7844 dual beam 7000 series mainframe,or a bistable
transfer storage scope like a 464/466. I HATED those 2 scopes.

The 30mA I was speaking of was just the difference in draw on the 32V
unreg supply with no tube in vs tube in, so really just an observation
I guess.

I've never tried those two scopes. We see a lot of the TDS scopes, I
minutes, can't complain about that. I used to hate cal'ing the analog
scopes when I started, I was spoiled with the easy DSO's. I'm
starting to come around though, the amount of engineering that went
into them is amazing and they're interesting to work on.

This has sparked my curiousity. When I pulled the jumper off the 95V
rail, it didn't fix the problem. If the schematic is correct, that
should have isolated everything on the 95V supply, leaving the other
items sharing the transformer to blame (tripler, cathode, etc). With
no tube in, everything worked fine, so I would figure the HV module
was ok (maybe a bad assumption). So it must be in the tube (again,
maybe a bad assumption). With just the anode connected, the supply is
loaded down. With just the rear plug connected, the supply is loaded
down. With another tube, it has no problem. If it was just a anode
lead problem, shouldn't the supply have come up with just the rear
plug on? I may be beating a dead horse here, I just like to learn.

I think I'm going to pull the bad tube out of the bad scope I put it
in and see if I can't find the problem. Would doing continuity
measurements show anything useful, or would the likely problem be too
high in resistance for say, a Fluke 87?

Steve

S

#### Steve

Jan 1, 1970
0
The 30mA I was speaking of was just the difference in draw on the 32V
unreg supply with no tube in vs tube in, so really just an observation
I guess.

I've never tried those two scopes. We see a lot of the TDS scopes, I
minutes, can't complain about that. I used to hate cal'ing the analog
scopes when I started, I was spoiled with the easy DSO's. I'm
starting to come around though, the amount of engineering that went
into them is amazing and they're interesting to work on.

This has sparked my curiousity. When I pulled the jumper off the 95V
rail, it didn't fix the problem. If the schematic is correct, that
should have isolated everything on the 95V supply, leaving the other
items sharing the transformer to blame (tripler, cathode, etc). With
no tube in, everything worked fine, so I would figure the HV module
was ok (maybe a bad assumption). So it must be in the tube (again,
maybe a bad assumption). With just the anode connected, the supply is
loaded down. With just the rear plug connected, the supply is loaded
down. With another tube, it has no problem. If it was just a anode
lead problem, shouldn't the supply have come up with just the rear
plug on? I may be beating a dead horse here, I just like to learn.

I think I'm going to pull the bad tube out of the bad scope I put it
in and see if I can't find the problem. Would doing continuity
measurements show anything useful, or would the likely problem be too
high in resistance for say, a Fluke 87?

Steve

Well, not sure if it means anything at all, but I couldn't measure any
resistance with my meter between any pins. I know the meter puts out
small DC voltage, and things become a different story at kV, but I did
it anyway. Visual check of the tube looks fine.
I was going to hook up a little 8kV transformer I have lying around
between anode and cathode, put a couple volts on the filament and see
if I got a trace, but then I started thinking about XRays. Would
doing this out of the metal shield be a bad idea? Would this produce
XRays or radiation? I don't want to give myself cancer or cause
damage. Also, would this even produce a trace or am I just wasting my
time?

Thanks again,
Stev

S

#### Steve

Jan 1, 1970
0
Well, not sure if it means anything at all, but I couldn't measure any
resistance with my meter between any pins. I know the meter puts out
small DC voltage, and things become a different story at kV, but I did
it anyway. Visual check of the tube looks fine.
I was going to hook up a little 8kV transformer I have lying around
between anode and cathode, put a couple volts on the filament and see
if I got a trace, but then I started thinking about XRays. Would
doing this out of the metal shield be a bad idea? Would this produce
XRays or radiation? I don't want to give myself cancer or cause
damage. Also, would this even produce a trace or am I just wasting my
time?
And by trace, I mean dot. I know there would be no deflection or
focus or alignment or astigmatism or anything else applied.
And, the heater/filament measured about 13.4ohms.

Steve

B

#### bz

Jan 1, 1970
0
Well, not sure if it means anything at all, but I couldn't measure any
resistance with my meter between any pins. I know the meter puts out
small DC voltage, and things become a different story at kV, but I did
it anyway. Visual check of the tube looks fine.
I was going to hook up a little 8kV transformer I have lying around
between anode and cathode

You might want a diode in there and maybe a cap to smooth the dc a bit.
, put a couple volts on the filament

Be sure and tie the cathode and filament together, or at least keep the
voltage between them fairly low... 8kV might not be good for the
insulation.
and see
if I got a trace, but then I started thinking about XRays. Would
doing this out of the metal shield be a bad idea? Would this produce
XRays or radiation? I don't want to give myself cancer or cause
damage. Also, would this even produce a trace or am I just wasting my
time?

I doubt that you are likely to get xrays until you get up above 20 kv or
so. You might get some nasty UV or very soft xrays at lower voltages, but
the crt's glass will stop most, if not all.

But you can sure kill yourself with the voltage.

The metal shield is probably mu metal, to keep stray magnetic fields from
messing with the crt beam.

You have a strange problem!

When I pulled the base off of my 545 scope's crt, the HV supply didn't like
it at all. With no load, it started snapping and sparking from the
multplyer chain to the HV supply's case!

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

S

#### Steve

Jan 1, 1970
0
You have a strange problem!

When I pulled the base off of my 545 scope's crt, the HV supply didn't like
it at all. With no load, it started snapping and sparking from the
multplyer chain to the HV supply's case!

That would make sense if there was no "good" return path for the hv.
Interesting. I think I may just move on to bigger and better things,
the scope's working for now, and I have a spare with some really
serious issues (I was debating trying to get two working, now I really
don't think it's worth it)

Steve

M

#### [email protected]

Jan 1, 1970
0
That would make sense if there was no "good" return path for the hv.
Interesting. I think I may just move on to bigger and better things,
the scope's working for now, and I have a spare with some really
serious issues (I was debating trying to get two working, now I really
don't think it's worth it)

Steve

Yes, quite. I suspect a short from final anode to something else in
the tube is possible, though its not a common fault. If youre lucky
the short may be external, and a careful clean of glass round the
anode connection should fix it. If less lucky, it'll be an
accumulation of crud inside shorting it. Internal CRT shorts can often
be cleared by hitting them with moment of of high V high i, and
flicking the tube at the same time.

NT

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