Topics

465B soft start?

treasurer@...
 

Is there much to be gained by powering up my 465B with a variac, lamp dimmer or similar arrangement? It popped (shorted) its 1200 ufd C4429 at power on recently. This cap does not have much head room with its 100 volt rating and 70 volts sitting on it. I'm thinking a soft power up may help prolong the life of those caps. Any thoughts or past experience from the group using this power-on approach?
Bruce

Tom Gardner
 

Switching power supplies operate to keep the output power constant.
Hence if the input voltage is lower, the input current must be higher.

Increased current stresses components such as the rectifiers and
switching transistors.

On 18/11/2019, treasurer@... <treasurer@...> wrote:
Is there much to be gained by powering up my 465B with a variac, lamp dimmer
or similar arrangement? It popped (shorted) its 1200 ufd C4429 at power on
recently. This cap does not have much head room with its 100 volt rating and
70 volts sitting on it. I'm thinking a soft power up may help prolong the
life of those caps. Any thoughts or past experience from the group using
this power-on approach?
Bruce



 

On Mon, Nov 18, 2019 at 10:01 PM, Tom Gardner wrote:


Switching power supplies operate to keep the output power constant.
Hence if the input voltage is lower, the input current must be higher.

Increased current stresses components such as the rectifiers and
switching transistors.
The 465B has a linear power supply.
Low-spec'ed (if so) working voltage hasn't affected those caps for the past 35-odd years. Also, those are (were?) high-quality caps so I wouldn't bother. Epoxy-encapsulated (i.e. dipped) tantalum caps are another matter, especially those with little voltage headroom. The 465B is stuffed with those but slow-on won't help those much I'm afraid. Lots about all that to be found in this group.

Raymond
Power-on current surge puts a strain on the bridge rectifiers. That has been an issue with some 465's.

Tom Gardner
 

On 18/11/19 22:58, Raymond Domp Frank wrote:
On Mon, Nov 18, 2019 at 10:01 PM, Tom Gardner wrote:

Switching power supplies operate to keep the output power constant.
Hence if the input voltage is lower, the input current must be higher.

Increased current stresses components such as the rectifiers and
switching transistors.
The 465B has a linear power supply.
Doh! Too much time spent inside a 2465 :(

Apologies.

treasurer@...
 

Appreciate the thoughts from Tom & Raymond. Guess we should be thankful these 35 + year old scopes are still serviceable. I will need to confirm it is indeed the capacitor and not the bridge rectifier which is shorted, if that has been a past issue.
Cheers

DaveH52
 

I've got a 465M and I've had to replace several caps in the power supply. You will probably have problems getting an exact replacement, After the 30 to 40 years it's been around you can expect the caps to go bad. 70 V on a 100V rated cap is adequately derated. When you go looking for replacements consider the voltage rating, capacitance, size, ( you can probably get more C in the same size) and ripple current rating (higher is better) and ESR (lower is better). Get 105 degree rated parts. They will probably be good for another 30 years.
Just my 2ยข

david
 

Had same cap blow in my 465 two years ago, they don't last forever. Look up Capacitor Reforming on net, it will explain why aluminum caps go bad. I replaced all the filter caps in power supply section and power supply has been good since then. A Wise Man once told me "Machines are made to be run", "If you don't run them they stop working". The oxide layer that insulates plates in cap breaks down and eventually will short out cap if you don't run equipment.

radioconnection@...
 

I have had a few of the 5-volt power0supply bridge rectifiers fail in 465 scopes.

Mlynch001
 

I have heard that sitting idle is the worst thing one can do to a scope, such as the 465. I exercise all of my scopes regularly, by turning them on and feeding a signal through the inputs. I have no idea if this helps or not. But I had heard the same advice years ago and thought it made sense to run the scopes from time to time.

--
Michael Lynch
Dardanelle, AR

Abc Xyz
 

Worked on many 465B Scopes?

On Tue, Dec 10, 2019, 10:14 AM <radioconnection@...> wrote:

I have had a few of the 5-volt power0supply bridge rectifiers fail in 465
scopes.



DaveH52
 

I should have mentioned before that the capacitor can completes part of the circuit. So if you don't want to add some jumper wires, use a tubing cutter to cut the base off the old capacitors and use that as an interposer between the new caps and the circuit board. I don't recommend putting the can back over the new caps because it will hold in heat.

DaveH52
 

For what it's worth, the power transformer will provide some degree of current limiting. I suppose you could add an inrush limiting thermister, but that really doesn't seem necessary to me.

Andrew Stanworth
 

On Wed, Dec 11, 2019 at 10:20 AM, DaveH52 wrote:


I should have mentioned before that the capacitor can completes part of the
circuit. So if you don't want to add some jumper wires, use a tubing cutter
to cut the base off the old capacitors and use that as an interposer between
the new caps and the circuit board. I don't recommend putting the can back
over the new caps because it will hold in heat.
Interesting. I have been considering the options for replacing the PSU caps on this scope too - although currently mine seem to be working ok (haven't got around to measuring ripple yet but like a good boy scout wanted to 'be prepared'!). Desoldering those cans from the pcb seems pretty tricky with almost inevitable track damage from the inordinate amount of heat required. I was going to attempt this and then use those circular adapter boards you can get to mount the new caps. How easy is it in reality to cut the cans with a tubing cutter (I presume you mean like plumbers use to cut pipe?) - is there enough clearance to get a tool like this around the cans? Other suggestions I have read about include the use of some sort of saw (eg. a cutting disc in a Dremmel) but that would produce a lot of metal filings and swarf - not ideal in this enviroment! Also, how much gunk in the form of electrolyte etc comes out of these things when cut? Is it liquid or paste and is it manageable? Any photos of or links to this process would be interesting to see!

n4buq
 

I designed a board to help with this:

https://groups.io/g/TekScopes/album?id=64929

I have some of the boards if you're interested.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Andrew Stanworth via Groups.Io" <andrew.stanworth=ntlworld.com@groups.io>
To: TekScopes@groups.io
Sent: Thursday, December 12, 2019 8:42:36 AM
Subject: Re: [TekScopes] 465B soft start?

On Wed, Dec 11, 2019 at 10:20 AM, DaveH52 wrote:


I should have mentioned before that the capacitor can completes part of the
circuit. So if you don't want to add some jumper wires, use a tubing
cutter
to cut the base off the old capacitors and use that as an interposer
between
the new caps and the circuit board. I don't recommend putting the can back
over the new caps because it will hold in heat.
Interesting. I have been considering the options for replacing the PSU caps
on this scope too - although currently mine seem to be working ok (haven't
got around to measuring ripple yet but like a good boy scout wanted to 'be
prepared'!). Desoldering those cans from the pcb seems pretty tricky with
almost inevitable track damage from the inordinate amount of heat required.
I was going to attempt this and then use those circular adapter boards you
can get to mount the new caps. How easy is it in reality to cut the cans
with a tubing cutter (I presume you mean like plumbers use to cut pipe?) -
is there enough clearance to get a tool like this around the cans? Other
suggestions I have read about include the use of some sort of saw (eg. a
cutting disc in a Dremmel) but that would produce a lot of metal filings and
swarf - not ideal in this enviroment! Also, how much gunk in the form of
electrolyte etc comes out of these things when cut? Is it liquid or paste
and is it manageable? Any photos of or links to this process would be
interesting to see!



Tom Green
 

On Thu, Dec 12, 2019 at 10:19 AM n4buq <n4buq@...> wrote:

I designed a board to help with this:

https://groups.io/g/TekScopes/album?id=64929

I have some of the boards if you're interested.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Andrew Stanworth via Groups.Io" <andrew.stanworth=
ntlworld.com@groups.io>
To: TekScopes@groups.io
Sent: Thursday, December 12, 2019 8:42:36 AM
Subject: Re: [TekScopes] 465B soft start?

On Wed, Dec 11, 2019 at 10:20 AM, DaveH52 wrote:


I should have mentioned before that the capacitor can completes part
of the
circuit. So if you don't want to add some jumper wires, use a tubing
cutter
to cut the base off the old capacitors and use that as an interposer
between
the new caps and the circuit board. I don't recommend putting the can
back
over the new caps because it will hold in heat.
Interesting. I have been considering the options for replacing the PSU
caps
on this scope too - although currently mine seem to be working ok
(haven't
got around to measuring ripple yet but like a good boy scout wanted to
'be
prepared'!). Desoldering those cans from the pcb seems pretty tricky with
almost inevitable track damage from the inordinate amount of heat
required.
I was going to attempt this and then use those circular adapter boards
you
can get to mount the new caps. How easy is it in reality to cut the cans
with a tubing cutter (I presume you mean like plumbers use to cut pipe?)
-
is there enough clearance to get a tool like this around the cans? Other
suggestions I have read about include the use of some sort of saw (eg. a
cutting disc in a Dremmel) but that would produce a lot of metal filings
and
swarf - not ideal in this enviroment! Also, how much gunk in the form of
electrolyte etc comes out of these things when cut? Is it liquid or paste
and is it manageable? Any photos of or links to this process would be
interesting to see!





n4buq
 

Done my share of restuffing caps and considered doing that to the 465B; however, that requires both desoldering and soldering to the board, each time risking damage. I decided to only desolder the old ones, solder small jumper wires as needed, and use an auxilliary board. If the new caps ever need replacing, it won't involve soldering/desoldering to the main board. I have some of the discs which would have worked, but if the caps ever needed replacing for those, it would still involve work to the main board. Not pushing my boards, just explaining my reasoning.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Tom Green" <xman143@...>
To: TekScopes@groups.io
Sent: Thursday, December 12, 2019 9:38:05 AM
Subject: Re: [TekScopes] 465B soft start?

Old caps:

https://www.youtube.com/watch?v=WOlH5hVajco

https://www.youtube.com/watch?v=IYtu_2psK2I

There are many other videos on there as well.

Tom

On Thu, Dec 12, 2019 at 10:19 AM n4buq <n4buq@...> wrote:

I designed a board to help with this:

https://groups.io/g/TekScopes/album?id=64929

I have some of the boards if you're interested.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Andrew Stanworth via Groups.Io" <andrew.stanworth=
ntlworld.com@groups.io>
To: TekScopes@groups.io
Sent: Thursday, December 12, 2019 8:42:36 AM
Subject: Re: [TekScopes] 465B soft start?

On Wed, Dec 11, 2019 at 10:20 AM, DaveH52 wrote:


I should have mentioned before that the capacitor can completes part
of the
circuit. So if you don't want to add some jumper wires, use a tubing
cutter
to cut the base off the old capacitors and use that as an interposer
between
the new caps and the circuit board. I don't recommend putting the can
back
over the new caps because it will hold in heat.
Interesting. I have been considering the options for replacing the PSU
caps
on this scope too - although currently mine seem to be working ok
(haven't
got around to measuring ripple yet but like a good boy scout wanted to
'be
prepared'!). Desoldering those cans from the pcb seems pretty tricky with
almost inevitable track damage from the inordinate amount of heat
required.
I was going to attempt this and then use those circular adapter boards
you
can get to mount the new caps. How easy is it in reality to cut the cans
with a tubing cutter (I presume you mean like plumbers use to cut pipe?)
-
is there enough clearance to get a tool like this around the cans? Other
suggestions I have read about include the use of some sort of saw (eg. a
cutting disc in a Dremmel) but that would produce a lot of metal filings
and
swarf - not ideal in this enviroment! Also, how much gunk in the form of
electrolyte etc comes out of these things when cut? Is it liquid or paste
and is it manageable? Any photos of or links to this process would be
interesting to see!