Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all
except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all >>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power
dissipation, when in use and is expected to run warm.
What is the actual current draw? Is your bulb dim?
You should be able to identify parts from board designators
and the reference manual.
That's an NTC inrush limiter. It has roughly constant power
dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on
the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
On Sun, 06 Nov 2022 16:05:00 -0500, legg <legg@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com> >>wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all >>>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power
dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on
the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
What is the actual current draw? Is your bulb dim?
4x40W bulbs for 160W all together and they're all full-on.
You should be able to identify parts from board designators
and the reference manual.
On Sun, 06 Nov 2022 21:29:37 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Sun, 06 Nov 2022 16:05:00 -0500, legg <legg@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com> >>>wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all >>>>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power
dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on
the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
What is the actual current draw? Is your bulb dim?
4x40W bulbs for 160W all together and they're all full-on.
You should be able to identify parts from board designators
and the reference manual.
Then it's time to find the short cct.
RL
by virtue of there being a multi-pronged jumper which interconnects
certain sections and by removing that you can drastically reduce the
number of parts to take a closer look at if the fault then clears,
which it has. Fingers crossed, eh?
The list is quite lenghty, but is at least limited
by virtue of there being a multi-pronged jumper which interconnects
certain sections and by removing that you can drastically reduce the
number of parts to take a closer look at if the fault then clears,
which it has. Fingers crossed, eh?
OK - if the fault clears when a jumper is removed, then you know that the fault is in the removed section, correct? Not the other way around?
Too many individuals think it works the other way, sadly.
On Sun, 06 Nov 2022 21:29:37 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Sun, 06 Nov 2022 16:05:00 -0500, legg <legg@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com> >>>wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all >>>>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power
dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on
the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
What is the actual current draw? Is your bulb dim?
4x40W bulbs for 160W all together and they're all full-on.
You should be able to identify parts from board designators
and the reference manual.
Then it's time to find the short cct.
RL
This kind of fault would be so much easier to detect if we had IR
glasses to view the suspect areas with. Someone really needs to invent those.
On Sun, 06 Nov 2022 19:52:50 -0500, legg <legg@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 21:29:37 +0000, Cursitor Doom <cd@notformail.com> >>wrote:
On Sun, 06 Nov 2022 16:05:00 -0500, legg <legg@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com> >>>>wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes >>>>>and fired up the faulty 'scope, this component gets hot. I'm not >>>>>really sure what it is, though and there are no markings on it at all >>>>>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power >>>>dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on
the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
What is the actual current draw? Is your bulb dim?
4x40W bulbs for 160W all together and they're all full-on.
You should be able to identify parts from board designators
and the reference manual.
Then it's time to find the short cct.
RL
This kind of fault would be so much easier to detect if we had IR
glasses to view the suspect areas with. Someone really needs to invent
those.
On Mon, 07 Nov 2022 23:22:26 +0000, Cursitor Doom <c...@notformail.com> wrote:
On Sun, 06 Nov 2022 19:52:50 -0500, legg <le...@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 21:29:37 +0000, Cursitor Doom <c...@notformail.com> >>wrote:
On Sun, 06 Nov 2022 16:05:00 -0500, legg <le...@nospam.magma.ca> wrote: >>>
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <c...@notformail.com> >>>>wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes >>>>>and fired up the faulty 'scope, this component gets hot. I'm not >>>>>really sure what it is, though and there are no markings on it at all >>>>>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power >>>>dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on >>>the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
What is the actual current draw? Is your bulb dim?
4x40W bulbs for 160W all together and they're all full-on.
You should be able to identify parts from board designators
and the reference manual.
Then it's time to find the short cct.
RL
This kind of fault would be so much easier to detect if we had IRYou should be able to track a short this close to the
glasses to view the suspect areas with. Someone really needs to invent >those.
AC input with a multimeter on diode test mode.
brodge rec,
inverter fets
bulk caps
to start.
RL
On Mon, 07 Nov 2022 23:22:26 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Sun, 06 Nov 2022 19:52:50 -0500, legg <legg@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 21:29:37 +0000, Cursitor Doom <cd@notformail.com> >>>wrote:
On Sun, 06 Nov 2022 16:05:00 -0500, legg <legg@nospam.magma.ca> wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com> >>>>>wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes >>>>>>and fired up the faulty 'scope, this component gets hot. I'm not >>>>>>really sure what it is, though and there are no markings on it at all >>>>>>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power >>>>>dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on
the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
What is the actual current draw? Is your bulb dim?
4x40W bulbs for 160W all together and they're all full-on.
You should be able to identify parts from board designators
and the reference manual.
Then it's time to find the short cct.
RL
This kind of fault would be so much easier to detect if we had IR
glasses to view the suspect areas with. Someone really needs to invent >>those.
You should be able to track a short this close to the
AC input with a multimeter on diode test mode.
brodge rec,
inverter fets
bulk caps
to start.
RL
On Tuesday, November 8, 2022 at 12:09:23 PM UTC-5, legg wrote:single component (sort of the brute force way to check), but judicious studying of the schematic and identifying appropriate points to isolate and subsequently test can prune away a number of branches in the tree fairly quickly so as to speak.
On Mon, 07 Nov 2022 23:22:26 +0000, Cursitor Doom <c...@notformail.com>
wrote:
On Sun, 06 Nov 2022 19:52:50 -0500, legg <le...@nospam.magma.ca> wrote:You should be able to track a short this close to the
On Sun, 06 Nov 2022 21:29:37 +0000, Cursitor Doom <c...@notformail.com>
wrote:
On Sun, 06 Nov 2022 16:05:00 -0500, legg <le...@nospam.magma.ca> wrote: >> >>>
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <c...@notformail.com> >> >>>>wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all >> >>>>>except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
That's an NTC inrush limiter. It has roughly constant power
dissipation, when in use and is expected to run warm.
That's what I thought too. But there's no such component visible on
the schematic:
https://disk.yandex.com/i/UhxATIy-6Y0LIA
What is the actual current draw? Is your bulb dim?
4x40W bulbs for 160W all together and they're all full-on.
You should be able to identify parts from board designators
and the reference manual.
Then it's time to find the short cct.
RL
This kind of fault would be so much easier to detect if we had IR
glasses to view the suspect areas with. Someone really needs to invent
those.
AC input with a multimeter on diode test mode.
brodge rec,
inverter fets
bulk caps
to start.
RL
yes, and actually, tracking down the short on the downstream sections (modules) should not be that difficult either, using the same approach. After all the faulty component is SHORTED which should be easy to find. Yea, it is a PITA to check every
Maybe bounce over to the tek google groups and ask if there are any common component failures that should be targeted first?
Otherwise, enjoy getting intimate with the guts of your scope....
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all
except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this?
On Thursday, November 10, 2022 at 9:57:16 AM UTC-8, Cursitor Doom wrote:
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this?
That'd be 'silicone' grease; the picture showing studs over the power package indicates
that an L-shaped or Z-shaped pressure arm (maybe three separate ones) was designed
into the system. Why else would there be a threaded rod there?
<https://e2e.ti.com/resized-image/__size/1230x0/__key/communityserver-discussions-components-files/196/7888.Mounting-a-TO220.png>
<https://media.rs-online.com/t_large/RD504059-01.jpg>
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all
except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
Got 'er!
I'm not at all familiar with the topology they've used in this PSU,
but I believe it's the chopper transistor (I should have guessed)
that's gone low-resistance: Q1050. It was releasing quite a bit of
heat even at only 18VAC supply with the current limited via 4x40 bulbs
to boot. I removed it from circuit to check and it was dead. So I'm
hoping that's the only part that's been damaged. It's an IRF820 and I
have a bunch of IRF840s so will press one of those into service in
place of the burnt-out one. Pin-outs just the same, just a lower Rdson figure, which is no bad thing.
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this? It doesn't seem like a very good way of ensuring
thermal conductivity. :-/
https://disk.yandex.com/i/cJDolujNfYucYw
On Fri, 11 Nov 2022 00:35:03 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:
On Thursday, November 10, 2022 at 9:57:16 AM UTC-8, Cursitor Doom wrote:
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this?
That'd be 'silicone' grease; the picture showing studs over the power package indicates
that an L-shaped or Z-shaped pressure arm (maybe three separate ones) was designed
into the system. Why else would there be a threaded rod there?
<https://e2e.ti.com/resized-image/__size/1230x0/__key/communityserver-discussions-components-files/196/7888.Mounting-a-TO220.png>
<https://media.rs-online.com/t_large/RD504059-01.jpg>
If that's the case, maybe it was removed at some time, shortening the
life of the chopper. I'll do something about that regardless. BTW, the >threaded rods are there to retain plastic covers which encase the 3
devices (don't ask me why as I haven't a clue what purpose they serve
but certainly not to press bear the transistors to the heatsink, that
much is certain).
On Fri, 11 Nov 2022 12:41:19 -0500, JC <Chipbee40_SpamNo@yahoo.com>
wrote:
Cursitor Doom wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com>look at the third photo, you will see that you have a lot of parts
wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all
except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
Got 'er!
I'm not at all familiar with the topology they've used in this PSU,
but I believe it's the chopper transistor (I should have guessed)
that's gone low-resistance: Q1050. It was releasing quite a bit of
heat even at only 18VAC supply with the current limited via 4x40 bulbs
to boot. I removed it from circuit to check and it was dead. So I'm
hoping that's the only part that's been damaged. It's an IRF820 and I
have a bunch of IRF840s so will press one of those into service in
place of the burnt-out one. Pin-outs just the same, just a lower Rdson
figure, which is no bad thing.
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this? It doesn't seem like a very good way of ensuring
thermal conductivity. :-/
https://disk.yandex.com/i/cJDolujNfYucYw
missing.
https://bradthx.blogspot.com/2017/05/tektronix-2465b-capacitor-replacement.html
Not sure what you mean by "a lot of parts missing" as I do have the individual plastic transistor covers shown in your photo but not in
the one I posted of mine. Apart from those covers (which were out of
shot in the picture I posted) there's nothing else missing AFAIK -
apart from whatever fastening they used to hold the trannies against
the heat sink (assuming they used something at all which they
certainly *should* have, I'd have thought).
you should also change out the 0.01uf cap, it has tendency to burn up
that area.
Yes, that and the two other RIFAs on that board. They all look end of
life AFAICT.
On Fri, 11 Nov 2022 15:31:20 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Fri, 11 Nov 2022 00:35:03 -0800 (PST), whit3rd <whit3rd@gmail.com> >>wrote:
On Thursday, November 10, 2022 at 9:57:16 AM UTC-8, Cursitor Doom wrote:
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this?
That'd be 'silicone' grease; the picture showing studs over the power package indicates
that an L-shaped or Z-shaped pressure arm (maybe three separate ones) was designed
into the system. Why else would there be a threaded rod there?
<https://e2e.ti.com/resized-image/__size/1230x0/__key/communityserver-discussions-components-files/196/7888.Mounting-a-TO220.png>
<https://media.rs-online.com/t_large/RD504059-01.jpg>
If that's the case, maybe it was removed at some time, shortening the
life of the chopper. I'll do something about that regardless. BTW, the >>threaded rods are there to retain plastic covers which encase the 3
devices (don't ask me why as I haven't a clue what purpose they serve
but certainly not to press bear the transistors to the heatsink, that
much is certain).
The 'plastic' covers may serve the purpose of forced device retension.
Depends on material composition and design.
'just leaning' is not what is intended here.
...
Diode test for other shorts.
Check resistance gate to source pads of empty fet location.
Should read diode drop minimum, or gate drive cct is
compromised.
RL
Cursitor Doom wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com>look at the third photo, you will see that you have a lot of parts
wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all
except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
Got 'er!
I'm not at all familiar with the topology they've used in this PSU,
but I believe it's the chopper transistor (I should have guessed)
that's gone low-resistance: Q1050. It was releasing quite a bit of
heat even at only 18VAC supply with the current limited via 4x40 bulbs
to boot. I removed it from circuit to check and it was dead. So I'm
hoping that's the only part that's been damaged. It's an IRF820 and I
have a bunch of IRF840s so will press one of those into service in
place of the burnt-out one. Pin-outs just the same, just a lower Rdson
figure, which is no bad thing.
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this? It doesn't seem like a very good way of ensuring
thermal conductivity. :-/
https://disk.yandex.com/i/cJDolujNfYucYw
missing.
https://bradthx.blogspot.com/2017/05/tektronix-2465b-capacitor-replacement.html
you should also change out the 0.01uf cap, it has tendency to burn up
that area.
Cursitor Doom wrote:
On Fri, 11 Nov 2022 12:41:19 -0500, JC <Chipbee40_SpamNo@yahoo.com>The plastic covers hold the transistors against the ceramic heatsink >insulator. They are bolted on as shown in the photo.
wrote:
Cursitor Doom wrote:
On Sun, 06 Nov 2022 20:48:15 +0000, Cursitor Doom <cd@notformail.com>look at the third photo, you will see that you have a lot of parts
wrote:
Gentlemen,
Having put together a dim bulb tester for current-limiting purposes
and fired up the faulty 'scope, this component gets hot. I'm not
really sure what it is, though and there are no markings on it at all >>>>> except for two tiny blobs of paint.
Anyone know?
https://disk.yandex.com/i/jmR716xUNBt8OQ
Got 'er!
I'm not at all familiar with the topology they've used in this PSU,
but I believe it's the chopper transistor (I should have guessed)
that's gone low-resistance: Q1050. It was releasing quite a bit of
heat even at only 18VAC supply with the current limited via 4x40 bulbs >>>> to boot. I removed it from circuit to check and it was dead. So I'm
hoping that's the only part that's been damaged. It's an IRF820 and I
have a bunch of IRF840s so will press one of those into service in
place of the burnt-out one. Pin-outs just the same, just a lower Rdson >>>> figure, which is no bad thing.
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this? It doesn't seem like a very good way of ensuring
thermal conductivity. :-/
https://disk.yandex.com/i/cJDolujNfYucYw
missing.
https://bradthx.blogspot.com/2017/05/tektronix-2465b-capacitor-replacement.html
Not sure what you mean by "a lot of parts missing" as I do have the
individual plastic transistor covers shown in your photo but not in
the one I posted of mine. Apart from those covers (which were out of
shot in the picture I posted) there's nothing else missing AFAIK -
apart from whatever fastening they used to hold the trannies against
the heat sink (assuming they used something at all which they
certainly *should* have, I'd have thought).
you should also change out the 0.01uf cap, it has tendency to burn up
that area.
Yes, that and the two other RIFAs on that board. They all look end of
life AFAICT.
On 2022-11-11 16:31, Cursitor Doom wrote:
On Fri, 11 Nov 2022 00:35:03 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:
On Thursday, November 10, 2022 at 9:57:16 AM UTC-8, Cursitor Doom wrote: >>>
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this?
That'd be 'silicone' grease; the picture showing studs over the power package indicates
that an L-shaped or Z-shaped pressure arm (maybe three separate ones) was designed
into the system. Why else would there be a threaded rod there?
<https://e2e.ti.com/resized-image/__size/1230x0/__key/communityserver-discussions-components-files/196/7888.Mounting-a-TO220.png>
<https://media.rs-online.com/t_large/RD504059-01.jpg>
If that's the case, maybe it was removed at some time, shortening the
life of the chopper. I'll do something about that regardless. BTW, the
threaded rods are there to retain plastic covers which encase the 3
devices (don't ask me why as I haven't a clue what purpose they serve
but certainly not to press bear the transistors to the heatsink, that
much is certain).
I would guess insulation - is that part connected to mains?
On Fri, 11 Nov 2022 00:35:03 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:
On Thursday, November 10, 2022 at 9:57:16 AM UTC-8, Cursitor Doom wrote:
One question, though: they've mounted these transistors without using
a screw through the mounting tab of this TO-220 package. The devices
are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this?
That'd be 'silicone' grease; the picture showing studs over the power package indicates
that an L-shaped or Z-shaped pressure arm (maybe three separate ones) was designed
into the system. Why else would there be a threaded rod there?
<https://e2e.ti.com/resized-image/__size/1230x0/__key/communityserver-discussions-components-files/196/7888.Mounting-a-TO220.png>
<https://media.rs-online.com/t_large/RD504059-01.jpg>
If that's the case, maybe it was removed at some time, shortening the
life of the chopper. I'll do something about that regardless. BTW, the threaded rods are there to retain plastic covers which encase the 3
devices (don't ask me why as I haven't a clue what purpose they serve
but certainly not to press bear the transistors to the heatsink, that
much is certain).
On Sun, 13 Nov 2022 23:17:29 +0100, "Carlos E.R."
<robin_listas@es.invalid> wrote:
On 2022-11-11 16:31, Cursitor Doom wrote:
On Fri, 11 Nov 2022 00:35:03 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:
On Thursday, November 10, 2022 at 9:57:16 AM UTC-8, Cursitor Doom wrote: >>>>
One question, though: they've mounted these transistors without using >>>>> a screw through the mounting tab of this TO-220 package. The devices >>>>> are just 'leaning' against some white pad mounted on the heat sink
(see photo). Is there some special grease required to mate the
transistor to the white pad or can I just use the regular silicon
grease for this?
That'd be 'silicone' grease; the picture showing studs over the power package indicates
that an L-shaped or Z-shaped pressure arm (maybe three separate ones) was designed
into the system. Why else would there be a threaded rod there?
<https://e2e.ti.com/resized-image/__size/1230x0/__key/communityserver-discussions-components-files/196/7888.Mounting-a-TO220.png>
<https://media.rs-online.com/t_large/RD504059-01.jpg>
If that's the case, maybe it was removed at some time, shortening the
life of the chopper. I'll do something about that regardless. BTW, the
threaded rods are there to retain plastic covers which encase the 3
devices (don't ask me why as I haven't a clue what purpose they serve
but certainly not to press bear the transistors to the heatsink, that
much is certain).
I would guess insulation - is that part connected to mains?
We eventually got to the bottom of it. The plastic covers are supposed
to bear against the transistors underneath and hold them tight against
the heatsink assembly. But it's a really unsatisfactory approach,
because they're not secured at the bottom in any way, so the devices
are not pressed evenly against their pads. I'm looking into whether it
can be improved whilst waiting for the spares to arrive. Perhaps I can
get some of those clips that Whit3rd posted a link to.
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