Scope keeps blowing fuses...

[Cursitor Doom]

On Sun, 23 Oct 2022 05:34:30 -0700 (PDT), \"Peter W.\"
<peterwieck33@gmail.com> wrote:

>a) Do you have a VOM? And, if so, how good is it?

Several! Some professional ones too.

b) Not that testing capacitors in-situ generally accurate, but you can usually tell the difference between an open cap and a dead-shorted cap using the Ohms scale.
c) Similarly, transistors.
d) And it is possible that the RIFAs were symptoms, not the cause.

It would be very useful to know, but I cannot tell when they blew and
if they blew together or seperately. I can say is that they both went
catastrophically and blasted crap all over the surrounding components.
But we all know these caps \'let go\' after a certain time in service
anyway. You can pretty much guarantee it.

Which would be a start.

Yes. On the face of it, this should be simple to find and fix, but the
layout of the PSU on this model is just awful. Just one example, they
didn\'t leave enough room for the board! it\'s tight interference fit
with the casing and can only be withdrawn and inserted with
considerable force.

Peter Wieck
Melrose Park, PA

 

[Peter W.]

If the alternative is landfill, then heroic measures are justified.

If the alternative is \'sending it out\', unless you wish to did deeper - and all indications are that you do not - then go ahead and send it out.

There is no magic bullet.

Peter Wieck
Melrose Park, PA

 

[Cursitor Doom]

On Sun, 23 Oct 2022 09:36:24 -0700 (PDT), \"Peter W.\"
<peterwieck33@gmail.com> wrote:

>If the alternative is landfill, then heroic measures are justified.

I totally get where you\'re coming from here.

>If the alternative is \'sending it out\', unless you wish to did deeper - and all indications are that you do not - then go ahead and send it out.

I\'m not sure it\'s worth the expense, because there\'s another fault
with this scope that will most likely still be present even if the
present one is fixed. In fact, this \'other fault\' may well have caused
the current one. This \'other fault\' involved the displayed traces
suddenly turning extremely bright, accompanied by lines of dots. It
materialised only rarely, but I was out of the room when the scope
went *phut* so have no idea if there\'s any link to the current fault
or not.
I\'m beginning to suspect those caps may have failed at some time in
the past, because for them to go *bang* with that amount of crap
sprayed everywhere must surely have resulted in a great deal of acrid
smoke being released - yet there was none discernable. And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short) then the scope can contintue to
function pretty well as normal so long as the mains supply is
reasonably clean.

>There is no magic bullet.

How true!

 

[Jeff Liebermann]

On Sat, 22 Oct 2022 15:26:04 +0100, Cursitor Doom <cd@notformail.com>
wrote:

>Hi all,

Bah Humbug.

So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing
main fuses (the 2A one on the rear panel).

\"Oscilloscope Restoration Project - Repair Tektronix 2465B 400MHz\"
<https://cdn.hackaday.io/files/1638907011869760/Tektronix-2465A-B-Oscilloscope-Restoration-Repair.pdf>
\"Symptoms: This is my lab unit, which suddenly started blowing its
main AC fuse.\"

\"Amazing Tektronix 2465 Repair Information\"
<https://jestineyong.com/amazing-tektronix-2465-repair-information/>
Concerning my Tektronix 2465 repair I yesterday
replaced both 0.068uF 250VAC caps after I had
received the ordered new 275VAC caps.

Both caps are C1016 and C1018 in the Tektronix
service manual schematic on Board A2A1. And
only the C1016 0.068uF capacitor had blown
which also damaged the serie resistor R1016
of 68 ohm 5% which also was replaced.

They protect the Diode Bridge CR1011 (600V
3A Fast Recovery type RKBPC606-12) against
damage by high AC power voltages. The Diode
Bridge was not damaged. My oscilloscope is
happily working as new again. (48019 HRS of
service in 32 years or so).

Good luck.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[whit3rd]

On Saturday, October 22, 2022 at 7:26:11 AM UTC-7, Cursitor Doom wrote:

Hi all,

So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing
main fuses (the 2A one on the rear panel). I opened the case and found
two RIFA caps that had obviously blown, so replaced them, but it\'s
still blowing fuses. I can\'t be 100% certain, but I\'m pretty sure
there\'s a fault with the PSU board as I get the briefest whiff of
burning from that area each time I put a new fuse in and power up.

First thing to check is the rectifier; that diode bridge can fail, and
apply AC to the filter capacitors, and... that\'ll take out the fuse.
Not sure why the RIFA capa goes, though; maybe just a power surge some
time last week?

There seem to be some surge-suppressors (gas discharge?) in the diagram, they might
have failed short in a surge..

 

[Cursitor Doom]

On Sun, 23 Oct 2022 14:13:30 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Saturday, October 22, 2022 at 7:26:11 AM UTC-7, Cursitor Doom wrote:
Hi all,

So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing
main fuses (the 2A one on the rear panel). I opened the case and found
two RIFA caps that had obviously blown, so replaced them, but it\'s
still blowing fuses. I can\'t be 100% certain, but I\'m pretty sure
there\'s a fault with the PSU board as I get the briefest whiff of
burning from that area each time I put a new fuse in and power up.

First thing to check is the rectifier; that diode bridge can fail, and
apply AC to the filter capacitors, and... that\'ll take out the fuse.
Not sure why the RIFA capa goes, though; maybe just a power surge some
time last week?

There seem to be some surge-suppressors (gas discharge?) in the diagram, they might
have failed short in a surge..

Yes, they\'re each showing about 70k ohms, so can\'t be responsible.

One thing I forgot to mention in my first post was that a wire had
come adrift from the cooling fan\'s supply (poor factory soldering
clearly) so this unit had been running for an unknown length of time
with no fan. Not sure if that\'s relevant to the fault here, but it
certainly *could* be....

 

[Cursitor Doom]

On Sun, 23 Oct 2022 11:16:19 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sat, 22 Oct 2022 15:26:04 +0100, Cursitor Doom <cd@notformail.com
wrote:

Hi all,

Bah Humbug.

So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing
main fuses (the 2A one on the rear panel).

\"Oscilloscope Restoration Project - Repair Tektronix 2465B 400MHz\"
https://cdn.hackaday.io/files/1638907011869760/Tektronix-2465A-B-Oscilloscope-Restoration-Repair.pdf
\"Symptoms: This is my lab unit, which suddenly started blowing its
main AC fuse.\"

\"Amazing Tektronix 2465 Repair Information\"
https://jestineyong.com/amazing-tektronix-2465-repair-information/

Good luck

Thanks for the links, Jeff; I\'ll check \'em out...

 

[Phil Allison]

st...@swingnn.com wrote:
----------------------------------------------
Phil Allison

** Did both fail at the same time?

Those Rifa caps are bound to self destruct at some age, but two at once is suspicious.

.... Phil

Two capacitors in parallel can cause a problem when they both fail. I
had a computer power supply that had four smoothing capacitors in
parallel. It worked with just one so all four had to fail before the
fault was detected.

** So you have no clue what a piar of Rifa 68nF supreso caps do in an off line SMPS ?

It sure as hell ain\'t smoothing...


I was pointing out a common misunderstanding with multiple capacitors.
Rifa are alone, in parallel or in series and can all fail at the same
time as can smoothing capacitors in parallel.

** Shame how you own example contradict that idea.

.......Phil

 

[Phil Allison]

Cursitor Doom wrote:
---------------------------------

And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short)

** Really ? Where did you get that idea?

Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.

But those Rifa ones love to smoke and burn.

........Phil

 

[Jeff Liebermann]

On Sun, 23 Oct 2022 16:46:49 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

Cursitor Doom wrote:
---------------------------------
And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short)

** Really ? Where did you get that idea?

Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.

But those Rifa ones love to smoke and burn.

.......Phil

RIFA caps smoke, especially the old ones. This is typical for vintage
Tektronix scopes and RIFA caps:

\"Old RIFA capacitors and a disaster story\"
<https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/>

YouTube videos featuring smoking RIFA caps:
<https://www.youtube.com/results?search_query=rifa+capacitor>

I sometimes test the HV leakage in capacitors using an ancient Megger:
<http://www.learnbydestroying.com/jeffl/pics/Megger/Megger-Major.jpg>
<https://www.vintage-radio.net/forum/showthread.php?t=73265>
Unsolder the capacitor for testing. You really don\'t want a high
voltage power source connected to your oscilloscope.


--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[legg]

On Sat, 22 Oct 2022 15:26:04 +0100, Cursitor Doom <cd@notformail.com>
wrote:

Hi all,

So my main analogue scope, a Tek 2465A, has gone faulty. Keeps blowing
main fuses (the 2A one on the rear panel). I opened the case and found
two RIFA caps that had obviously blown, so replaced them, but it\'s
still blowing fuses. I can\'t be 100% certain, but I\'m pretty sure
there\'s a fault with the PSU board as I get the briefest whiff of
burning from that area each time I put a new fuse in and power up. The
new fuse blows again before I get to see any smoke coming from
anywhere at all. I\'m linking to a diagram of the PSU as I\'m not
familiar with this circuit topology. If anyone can spot a component
here that could have gone low-resistance and might be a good candidate
for out-of-circuit testing, by all means let me know.
Thanks,

CD.


https://disk.yandex.com/i/UhxATIy-6Y0LIA

Don\'t know your line voltage, but if it\'s 240, check the
input voltage setting on the scope.

If RFI caps are replaced and bridge is ok, check big
electros (C1021, C1022) and main switch (Q1050) for
shorts.

At 240V, a leaky bulk cap can blow the gas tubes.

Once a gas tube fires, it\'s breakover voltage will
reduce, so must be replaced, too.

RL

 

[legg]

On Sun, 23 Oct 2022 17:13:54 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sun, 23 Oct 2022 16:46:49 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

Cursitor Doom wrote:
---------------------------------
And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short)

** Really ? Where did you get that idea?

Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.

But those Rifa ones love to smoke and burn.

.......Phil

RIFA caps smoke, especially the old ones. This is typical for vintage
Tektronix scopes and RIFA caps:

\"Old RIFA capacitors and a disaster story\"
https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/

YouTube videos featuring smoking RIFA caps:
https://www.youtube.com/results?search_query=rifa+capacitor

I sometimes test the HV leakage in capacitors using an ancient Megger:
http://www.learnbydestroying.com/jeffl/pics/Megger/Megger-Major.jpg
https://www.vintage-radio.net/forum/showthread.php?t=73265
Unsolder the capacitor for testing. You really don\'t want a high
voltage power source connected to your oscilloscope.

The smoking caps were metalized paper construction. These were good
enough in their day, with a demonstrated mtbf and safe self-healing,
while seals lasted. The outer sealing body tended to shrink and crack
with age, allowing ingress of air and moisture, compromising
performance. They are no longer made.

Metalized film parts are usually less dramatic in self-clearing
of internal faults, but in extreme cases, you still get thermal
runaway, as the faulting area expands and eats away at succesive
layers of the wrapped structure.

Film parts will generally fail at the end schoopage joint, where
metalization and film stresses accumulate in mfring.

RL

 

[Charles Lucas]

Hi, everyone (including the original poster).

When the power supply unit fails, there can be a basic myriad of possible problems
and/or failed components.

Here are some things to look for:

Current limiting resistors, rectifier diodes, transformers, transistors,
caps., filters, coils, etc... Shorts and opens are common problems. Look
for bad connections, cold solders, etc... Lots to check for to \"pin in down\".
Especially with older devices. Since it is an analog device (as was said),
it is assumed the equipment is old, so we have to go to the old school
way of checking everything, looking for key things, in order to come up
with some accurate diagnosis.

Good luck and have a great day.

Charles Lucas

 

[three_jeeps]

On Sunday, October 23, 2022 at 8:14:05 PM UTC-4, Jeff Liebermann wrote:

On Sun, 23 Oct 2022 16:46:49 -0700 (PDT), Phil Allison
palli...@gmail.com> wrote:

Cursitor Doom wrote:
---------------------------------
And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short)

** Really ? Where did you get that idea?

Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.

But those Rifa ones love to smoke and burn.

.......Phil
RIFA caps smoke, especially the old ones. This is typical for vintage
Tektronix scopes and RIFA caps:

\"Old RIFA capacitors and a disaster story\"
https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/

YouTube videos featuring smoking RIFA caps:
https://www.youtube.com/results?search_query=rifa+capacitor

I sometimes test the HV leakage in capacitors using an ancient Megger:
http://www.learnbydestroying.com/jeffl/pics/Megger/Megger-Major.jpg
https://www.vintage-radio.net/forum/showthread.php?t=73265
Unsolder the capacitor for testing. You really don\'t want a high
voltage power source connected to your oscilloscope.
--
Jeff Liebermann je...@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

I know about the RIFA caps exploding - thanks for the interesting video tho.
What is the recommended replacement type? (assuming they can physically fit into the same space on the board)
I have a few vintage Tek scopes that I should do some preventative maintenance work on....
J

 

[Jeff Liebermann]

On Mon, 24 Oct 2022 09:46:18 -0400, legg <legg@nospam.magma.ca> wrote:

On Sun, 23 Oct 2022 17:13:54 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

On Sun, 23 Oct 2022 16:46:49 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

Cursitor Doom wrote:
---------------------------------
And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short)

** Really ? Where did you get that idea?

Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.

But those Rifa ones love to smoke and burn.

.......Phil

RIFA caps smoke, especially the old ones. This is typical for vintage
Tektronix scopes and RIFA caps:

\"Old RIFA capacitors and a disaster story\"
https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/

YouTube videos featuring smoking RIFA caps:
https://www.youtube.com/results?search_query=rifa+capacitor

I sometimes test the HV leakage in capacitors using an ancient Megger:
http://www.learnbydestroying.com/jeffl/pics/Megger/Megger-Major.jpg
https://www.vintage-radio.net/forum/showthread.php?t=73265
Unsolder the capacitor for testing. You really don\'t want a high
voltage power source connected to your oscilloscope.

The smoking caps were metalized paper construction. These were good
enough in their day, with a demonstrated mtbf and safe self-healing,
while seals lasted. The outer sealing body tended to shrink and crack
with age, allowing ingress of air and moisture, compromising
performance. They are no longer made.

When I test RIFA capacitors with the Megger, I sometimes see
capacitors the show some leakage for maybe 250 msec and then recover.
I\'ve been assuming that this demonstrates that self healing is
function. Known good capacitors don\'t do that. Since testing
required removing the capacitor from the PCB, I just replace any
capacitor that shows temporary leakage. (i.e. better safe than
sorry).

This video shows what might be two self healing RIFA capacitors in
action. Watch the current on the display:
\"40 Year Old Rifa Capacitors High Voltage Leakage Testing\"
<https://www.youtube.com/watch?v=m1nDrunJ1SE> (3:09)
The effect is more visible with a panel meter than with a digital
readout (except when the meter is moving because I\'m turning the crank
on the Megger).

Metalized film parts are usually less dramatic in self-clearing
of internal faults, but in extreme cases, you still get thermal
runaway, as the faulting area expands and eats away at succesive
layers of the wrapped structure.

I haven\'t bothered to perform a post mortem on a RIFA capacitor. I
have several suitable microscopes and would expect to find holed in
the dielectric (paper or plastic) and the metalization. The RIVA caps
that failed have warped, cracked, melted, or crumbled outer plastic
cases. For meaningful microscopy, I would need an old RIFA capacitor
in an intact case.

Film parts will generally fail at the end schoopage joint, where
metalization and film stresses accumulate in mfring.

RL

--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Mon, 24 Oct 2022 10:29:52 -0700 (PDT), three_jeeps
<jjhudak@gmail.com> wrote:

On Sunday, October 23, 2022 at 8:14:05 PM UTC-4, Jeff Liebermann wrote:
On Sun, 23 Oct 2022 16:46:49 -0700 (PDT), Phil Allison
palli...@gmail.com> wrote:

Cursitor Doom wrote:
---------------------------------
And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short)

** Really ? Where did you get that idea?

Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.

But those Rifa ones love to smoke and burn.

.......Phil
RIFA caps smoke, especially the old ones. This is typical for vintage
Tektronix scopes and RIFA caps:

\"Old RIFA capacitors and a disaster story\"
https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/

YouTube videos featuring smoking RIFA caps:
https://www.youtube.com/results?search_query=rifa+capacitor

I sometimes test the HV leakage in capacitors using an ancient Megger:
http://www.learnbydestroying.com/jeffl/pics/Megger/Megger-Major.jpg
https://www.vintage-radio.net/forum/showthread.php?t=73265
Unsolder the capacitor for testing. You really don\'t want a high
voltage power source connected to your oscilloscope.

I know about the RIFA caps exploding - thanks for the interesting video tho.
What is the recommended replacement type? (assuming they can physically fit into the same space on the board)
I have a few vintage Tek scopes that I should do some preventative maintenance work on....
J

\"RIFA - Replacement Choices\"
<https://www.eevblog.com/forum/beginners/rifa-replacement-choices/>

Kemet bought RIFA. My older Tek scopes survive 30 to 40 years and
usually blow electroltyics before RIFA caps. Rather than experiment,
I simply bought the same value/voltage X2 \"safety\" caps from Kemet
(via Mouser or Digikey):
<https://www.kemet.com/en/us/capacitors/film/safety.html?40=133>

I wasn\'t very careful when I ordered replacement caps many years ago.
I think I ordered \"metalized paper\", which in retrospect, was not the
best choice. Going down the list of dielectrics, only \"metalized
paper\" and \"metalized polypropylene\" are available for \"safety\" caps.
Kemet is recommending their R53 X2 caps with \"metalized polypropylene
film\" dielectric.

<https://www.mouser.com/new/kemet-electronics/kemet-miniature-emi-suppression-capacitors/>
<https://www.digikey.com/en/product-highlight/k/kemet/r53-film-capacitors>

X2 is for \"line to line\" filtering while Y2 is for \"line to ground\"
filtering.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Peter W.]

OK.
What is known:

a) Scope is blowing mains fuses.
b) RIFA -branded caps blew up.
c) The power-supply board was affected.

Suggestion:
1) Remove the power-supply board.
2) Replace all, repeat: ALL the capacitors on that board of any nature, type or style with the correct (but modern) replacement type.
3) Check each other component on the board. Diodes, regulators, transistors, whatever.
4) Replace any that are either bad or the slightest bit questionable.
5) Replace board - carefully (now might be an opportunity for a DBT to \'do its thing\' - but a metered Variac would be better).

I kinda-sorta think that will do it. KISS and all that.

Peter Wieck
Melrose Park, PA

 

[Jeff Liebermann]

On Sun, 23 Oct 2022 11:16:19 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
(chomp...)

When in doubt, replace everything.
I was wondering if someone sells a recap kit for the Tek 2465. Yep:
<https://www.ebay.com/itm/313637931679>
It includes some RIFA -> Kemet replacement caps.


--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Cursitor Doom]

On Mon, 24 Oct 2022 11:10:12 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Mon, 24 Oct 2022 10:29:52 -0700 (PDT), three_jeeps
jjhudak@gmail.com> wrote:

On Sunday, October 23, 2022 at 8:14:05 PM UTC-4, Jeff Liebermann wrote:
On Sun, 23 Oct 2022 16:46:49 -0700 (PDT), Phil Allison
palli...@gmail.com> wrote:

Cursitor Doom wrote:
---------------------------------
And if those
caps fail open circuit (which they both did despite being X2 safety
ones which are supposed to fail short)

** Really ? Where did you get that idea?

Plenty are found open or with low values after long times in service.
X2 dropping caps used in smoke alarms regularly fail open.

But those Rifa ones love to smoke and burn.

.......Phil
RIFA caps smoke, especially the old ones. This is typical for vintage
Tektronix scopes and RIFA caps:

\"Old RIFA capacitors and a disaster story\"
https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/

YouTube videos featuring smoking RIFA caps:
https://www.youtube.com/results?search_query=rifa+capacitor

I sometimes test the HV leakage in capacitors using an ancient Megger:
http://www.learnbydestroying.com/jeffl/pics/Megger/Megger-Major.jpg
https://www.vintage-radio.net/forum/showthread.php?t=73265
Unsolder the capacitor for testing. You really don\'t want a high
voltage power source connected to your oscilloscope.

I know about the RIFA caps exploding - thanks for the interesting video tho.
What is the recommended replacement type? (assuming they can physically fit into the same space on the board)
I have a few vintage Tek scopes that I should do some preventative maintenance work on....
J

\"RIFA - Replacement Choices\"
https://www.eevblog.com/forum/beginners/rifa-replacement-choices/

Kemet bought RIFA. My older Tek scopes survive 30 to 40 years and
usually blow electroltyics before RIFA caps. Rather than experiment,
I simply bought the same value/voltage X2 \"safety\" caps from Kemet
(via Mouser or Digikey):
https://www.kemet.com/en/us/capacitors/film/safety.html?40=133

I wasn\'t very careful when I ordered replacement caps many years ago.
I think I ordered \"metalized paper\", which in retrospect, was not the
best choice. Going down the list of dielectrics, only \"metalized
paper\" and \"metalized polypropylene\" are available for \"safety\" caps.
Kemet is recommending their R53 X2 caps with \"metalized polypropylene
film\" dielectric.

https://www.mouser.com/new/kemet-electronics/kemet-miniature-emi-suppression-capacitors/
https://www.digikey.com/en/product-highlight/k/kemet/r53-film-capacitors

X2 is for \"line to line\" filtering while Y2 is for \"line to ground\"
filtering.

Jeff, remind me to post a picture of the cap replacement I\'ve carried
out. You\'ll be both horrified and astounded. If I had more time I\'d
post it now, but it\'ll have to wait for the time being..

 

[Cursitor Doom]

On Mon, 24 Oct 2022 11:12:09 -0700 (PDT), \"Peter W.\"
<peterwieck33@gmail.com> wrote:

OK.
What is known:

a) Scope is blowing mains fuses.
b) RIFA -branded caps blew up.
c) The power-supply board was affected.

Suggestion:
1) Remove the power-supply board.
2) Replace all, repeat: ALL the capacitors on that board of any nature, type or style with the correct (but modern) replacement type.
3) Check each other component on the board. Diodes, regulators, transistors, whatever.
4) Replace any that are either bad or the slightest bit questionable.
5) Replace board - carefully (now might be an opportunity for a DBT to \'do its thing\' - but a metered Variac would be better).

I kinda-sorta think that will do it. KISS and all that.

I do have a metered variac, so plan to use that in series with DBT
current limiting, as the bulb can react to sudden over-current much
more quickly than I can. I\'ll slowly bring the variac up whilst
checking for anything getting warm on the board. That\'s the best I can
manage as I\'m no tech repairer; haven\'t got the necessary fine motor
skills, I\'m afraid.