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I had been working on this 465 (SN B175976) for a few days. I had replaced
a burned out input resistor on one channel and tightened a shaft coupling.
After that it was more or less working, but I was checking something else
(can't recall) when I noticed that suddenly I had no trace, and pressing
the beamfinder shows nothing. So I suspect that I accidentally shorted
something. A visual inspection shows nothing obviously burned or open.

My trouble shooting and electronic skills are pretty minimal, so I could
really use some help fixing this. I do have another scope, a recently
acquired 2213A. I'm using a 465 manual that is close but not exactly for my
scope- the manual's Tek number is tek-070-1330-00 (some other manuals seem
to cover a later model- B200000 and up). I can't find a trouble shooting
chart in this manual that I read other people referring to.

I have been reading through a past thread that seems related:
/g/TekScopes/topic/7656979#126934, and using that as a
starting point I have checked the following:

All low voltage supplies are within tolerance, and ripple on each seems
close to within tolerance.

Fuse F1419 is good.

Tantalum C1419 seemed fine, but I went ahead and replaced it with a 100uF
50v electrolytic.

I do have a high voltage probe, so I checked TP1423, it measures only -82V
(should be -2450V)

Q1418 seems good. Following a comment by David Hess in the previous
thread, I looked at the collector with my 2213A- it shows a slightly
distorted wave approx 1.5 volts p-p (Horiz on my 2213A set to 10uS). It's
base voltage measures about .47vdc using a VOM. David's comment was: "If
you have a secondary working oscilloscope, the collector of Q1418 on
schematic 10 will show if the high voltage inverter is operating."

Albert suggested to check C1416- mine measures .48vdc, way off from what
it should be. Alberts past comment was: "The best indication for output of
the oscillator circuit is the voltage at C1416, shown as -4.5 V in the
schematic. Roughly speaking the AC peak-peak voltage across the base
winding in T1420 is twice this voltage. Since the average voltage across
that winding is zero (neglecting the small resistive loss) you should also
measure about -4.5 V at the base of Q1418. But a measurement load at the
base might influence the oscillation."

The collector of Q1404 measures about 3.3v, should be around 4.4v?

I don't know what the above indicates, or what to do next.

tmillerdems had said: "First thing I would do is lift the input lead from
the HV multiplier that connects to T1420 transformer. That will isolate the
HV multiplier that is known to cause HV problems. The regulation comes from
sampling the -2450 volt cathode supply. You should still get some display
if you get the cathode supply going sans PDA supply. "

I don't see where/how to locate the "input lead from the HV multiplier
that connects to T1420 transformer" - can I access that from the main
board? Both T1420 and the HV multiplier are located beneath (and hidden by)
the main board, correct? I also cannot locate CR1421 (using the image on
page 160 of the manual).

If either the T1420 or the HV multiplier are toast then that probably
makes the scope unrepairable (at least by me, I'm guessing).

Oddly enough, I also have 464 that I recently acquired with the same
problem (no beam)- at least I didn't cause that one!

Thanks if you can help,
Keith Ostertag

Also, one manual says in order to isolate the HV multiplier one needs to unsolder "dummy resistor"... huh? illustration points to near R1449,R1447, R1448... but maybe that's also not relevant to my scope?

On 28 May 2018 at 16:26 Keith Ostertag <stuff@...> wrote:


Thanks! That's jumper P1445, I believe.

What's the "PDA lead "? I don't recognize what PDA stands for...

So... if I remove that ground strap, and I still don't see anything on the
screen (not even using the beamfinder)... that suggests the HV multiplier
is NOT the fault that's causing my problem?

Is this the ground strap you mean? /g/TekScopes/
photo/49286/0?p=Name,,,20,1,0,0

Doesn't seem likely to me, as it isn't under the HV cover, but near the
front end... but it is the only ground strap visible on that side of the
main board on my scope.

Here is a photo of the area under the HV cover, and I don't seen anything
resembling a ground strap coming up between the "main board and the
vertical amplifier board" as you describe:

/g/TekScopes/photo/49286/1?p=Name,,,20,1,0,0

My 465 SN is B175976.

I am looking at a manual marked "tek-070-1330-00" (236 pages, with yellow addendum pages added in the back), as well as a manual for later version 465's (070-1861-00, B250000 & up, says Rev B, June 1975, 291 pages).

I think the first is the correct one, but it is more limiting (for instance, no trouble shooting flowchart).

Thanks! That's jumper P1445, I believe.

What's the "PDA lead "? I don't recognize what PDA stands for...