Topics

465 - Successfully Replaced HV multiplier


Dave W1BVV
 

New member here. 2 Months ago purchased an older 465 scope on the auction site. It worked for approximately 2 days begore the trace went dead. After lengthy searches on this and other forums I traced the problem to the HV Multiplier after lifting it's ground and getting the -2450V back.

Long story short, I found a NOS Murata multiplier on Ebay and proceeded to swap it in. Searches yielded a number of Instruction/repair manuals for the 465 but none matched my serial number, all being newer. I did run across an excellent post here which added some very helpful insight, techniques and missing steps ( sorry, I'm at work now and can't seem to find that post, I wanted to thank him).

Yesterday I finished the reassembly and - success, nice bright focused beam.

Even with all that help, I found that there were many wires and screws that were not mentioned, techniques that worked and didn't, apparent miscounts of fasteners and numbers of wires identifying connectors. Probably all of which due to design changes over the different SN's.

Anyway, I took al lot of notes and photo's as I went and probably should write up the process but in the mean time I would be glad to answer any questions and/or provide tips for anyone deciding to start this project.

Dave W, W1BVV


Siggi
 

Hey Dave,

congrats on the fix, it's pretty gratifying to bring one of those old'uns
back to life. Beware that it can be addictive - I managed to put the brakes
on at 8 scopes or so after the first one, but I fear it might merely be a
temporary remission...

Siggi

On Tue, Jan 26, 2021 at 10:04 AM Dave W1BVV <dmwalker3009@gmail.com> wrote:

New member here. 2 Months ago purchased an older 465 scope on the auction
site. It worked for approximately 2 days begore the trace went dead.
After lengthy searches on this and other forums I traced the problem to the
HV Multiplier after lifting it's ground and getting the -2450V back.

Long story short, I found a NOS Murata multiplier on Ebay and proceeded to
swap it in. Searches yielded a number of Instruction/repair manuals for
the 465 but none matched my serial number, all being newer. I did run
across an excellent post here which added some very helpful insight,
techniques and missing steps ( sorry, I'm at work now and can't seem to
find that post, I wanted to thank him).

Yesterday I finished the reassembly and - success, nice bright focused
beam.

Even with all that help, I found that there were many wires and screws
that were not mentioned, techniques that worked and didn't, apparent
miscounts of fasteners and numbers of wires identifying connectors.
Probably all of which due to design changes over the different SN's.

Anyway, I took al lot of notes and photo's as I went and probably should
write up the process but in the mean time I would be glad to answer any
questions and/or provide tips for anyone deciding to start this project.

Dave W, W1BVV






Dave W1BVV
 

Siggi,

I'll try to keep it at one old'un. As probably with most of us, the 465 was the first scope I used in college and at my first job so it was a sentimental project. My real addiction is becoming Heathkit boat-anchor Ham radios. Anyway my retirement job is teaching HS physics, and I'm putting together an Intro to Electrical Engineering course for next year. Heavy on the hardware as most "CS" coursed these days are software. For the kids I just requisitioned 6 Rigol DS1054Z's. Heresy!!
But the cost for one is almost less than it cost to buy and repair the 465 (not including the fun factor).

Dave, W1BVV


quad@...
 

Dave , great work! Do post the pics of the fix, for future ref. tks!


Dave W1BVV
 

Working on the writeup and editing the pics.

Dave, W1BVV


randolphbeebe@...
 

I had both a 465 and a 465M have the same failure after a day or two of purchasing them. Both had
been unused for a long time. I am wondering if, just as a precaution it might help powering up and old scope gradually with a variac might help.

Randy


toby@...
 

On 2021-01-29 5:38 p.m., randolphbeebe@gmail.com wrote:
I had both a 465 and a 465M have the same failure after a day or two of purchasing them. Both had
been unused for a long time. I am wondering if, just as a precaution it might help powering up and old scope gradually with a variac might help.
I had a 466, purchased off ebay, lose trace within a few minutes of use.
I haven't tried debugging it yet but I wonder...

--Toby

Randy





 

randolphbeebe wrote:
I had both a 465 and a 465M have the same failure after a day or two of purchasing them.
Both had been unused for a long time. I am wondering if, just as a precaution it might help
powering up and old scope gradually with a variac might help.
Maybe I'm completely off-base here, but if the problem was that power was applied too quickly (and which would have been either remedied or revealed by gradual power up on a variac) wouldn't we expect the failure to be immediate, rather than happen after a couple of days?

I understand that gradual power up is a common tactic when working with certain kinds of old electronics, and I even used it myself (based purely on internet hearsay, not on personal experience or wisdom), but I also understand (also on hearsay) that gradual power up can harm more recent equipment that uses switch mode, rather than linear power supplies (I don't think that this applies to either the 465 or 465M, but I'm not intimately familiar with either scope, so again, maybe off-base).

Also, wouldn't the HV multiplier suffer MORE stress, not less, being powered from a lower input voltage?

If a variac would have helped I would have expected the failure to be essentially immediate. Am I wrong about this?

-- Jeff Dutky


n4buq
 

I may be wrong as well, but since the HV multiplier is fed from an oscillator, once the voltage is sufficient and the oscillator kicks in, then there wouldn't much difference between that point and when full line voltage is applied. Is that incorrect?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Jeff Dutky" <jeff.dutky@gmail.com>
To: TekScopes@groups.io
Sent: Friday, January 29, 2021 5:34:29 PM
Subject: Re: [TekScopes] 465 - Successfully Replaced HV multiplier

randolphbeebe wrote:
I had both a 465 and a 465M have the same failure after a day or two of
purchasing them.
Both had been unused for a long time. I am wondering if, just as a
precaution it might help
powering up and old scope gradually with a variac might help.
Maybe I'm completely off-base here, but if the problem was that power was
applied too quickly (and which would have been either remedied or revealed
by gradual power up on a variac) wouldn't we expect the failure to be
immediate, rather than happen after a couple of days?

I understand that gradual power up is a common tactic when working with
certain kinds of old electronics, and I even used it myself (based purely on
internet hearsay, not on personal experience or wisdom), but I also
understand (also on hearsay) that gradual power up can harm more recent
equipment that uses switch mode, rather than linear power supplies (I don't
think that this applies to either the 465 or 465M, but I'm not intimately
familiar with either scope, so again, maybe off-base).

Also, wouldn't the HV multiplier suffer MORE stress, not less, being powered
from a lower input voltage?

If a variac would have helped I would have expected the failure to be
essentially immediate. Am I wrong about this?

-- Jeff Dutky






Michael W. Lynch
 

On Fri, Jan 29, 2021 at 06:12 PM, n4buq wrote:


I may be wrong as well, but since the HV multiplier is fed from an oscillator,
once the voltage is sufficient and the oscillator kicks in, then there
wouldn't much difference between that point and when full line voltage is
applied. Is that incorrect?
Barry,

I would tend to agree with you. The HV Multiplier in the 465/475 and 455/465M are just failure prone parts. I have had them die right in front of me after just a few minutes of operation.

--
Michael Lynch
Dardanelle, AR


Michael W. Lynch
 

On Fri, Jan 29, 2021 at 05:34 PM, Jeff Dutky wrote:


gradual power up can harm more recent equipment that uses switch mode, rather
than linear power supplies (I don't think that this applies to either the 465
or 465M, but I'm not intimately familiar with either scope, so again, maybe
off-base)
Jeff,

Correct, the power supplies in the 455 / 465 / 475 and many others are linear, so they are OK to start on variac. You are 100% right about SMPS, like the 485 and other more modern scopes, should never be started on a variac as far as I have learned.

If you use a Variac, make sure that you know if your equipment uses SMPS or Linear supply.

--
Michael Lynch
Dardanelle, AR


Garth Daddy
 

Whats the recommended method with SMPS then? remove connections to main switching caps and regenerate them?


 

The HV oscillator is fed from the unregulated 15 supply so if you start out with low line voltage, the oscillator will be starved of its supply. Since it is a regulated supply and hence a constant power device, it will demand a very high starting current. This could put a larger stress on the oscillator driver. It might even pop the fuse in that supply (a 1.5 amp fast blow fuse).

On 1/29/2021 7:12 PM, n4buq wrote:
I may be wrong as well, but since the HV multiplier is fed from an oscillator, once the voltage is sufficient and the oscillator kicks in, then there wouldn't much difference between that point and when full line voltage is applied. Is that incorrect?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Jeff Dutky" <jeff.dutky@gmail.com>
To: TekScopes@groups.io
Sent: Friday, January 29, 2021 5:34:29 PM
Subject: Re: [TekScopes] 465 - Successfully Replaced HV multiplier

randolphbeebe wrote:
I had both a 465 and a 465M have the same failure after a day or two of
purchasing them.
Both had been unused for a long time. I am wondering if, just as a
precaution it might help
powering up and old scope gradually with a variac might help.
Maybe I'm completely off-base here, but if the problem was that power was
applied too quickly (and which would have been either remedied or revealed
by gradual power up on a variac) wouldn't we expect the failure to be
immediate, rather than happen after a couple of days?

I understand that gradual power up is a common tactic when working with
certain kinds of old electronics, and I even used it myself (based purely on
internet hearsay, not on personal experience or wisdom), but I also
understand (also on hearsay) that gradual power up can harm more recent
equipment that uses switch mode, rather than linear power supplies (I don't
think that this applies to either the 465 or 465M, but I'm not intimately
familiar with either scope, so again, maybe off-base).

Also, wouldn't the HV multiplier suffer MORE stress, not less, being powered
from a lower input voltage?

If a variac would have helped I would have expected the failure to be
essentially immediate. Am I wrong about this?

-- Jeff Dutky






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Get an ESR meter and find and replace the bad caps before power applied.

Regards

On 1/29/2021 9:21 PM, Garth Daddy wrote:
Whats the recommended method with SMPS then? remove connections to main switching caps and regenerate them?



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