On 2022-11-13 23:50, Cursitor Doom wrote:
> 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.

maybe drill a hole to put a small bolt?

--
Cheers, Carlos.