[time-nuts] KS-24361 Power Module Repair

paul swed paulswedb at gmail.com
Sat Apr 11 11:15:43 EDT 2015


Bob
Thanks for the pictures and clues. I have a bad lucent on a hp3801. It was
just 1 of the supplies so I adapted an alternate switcher and it works just
fine.
That said there is hope I can go back in and fix it and also if need be the
ones on the KS units I have. I have sensed there is a flake-y unit on one
of them.
Regards
Paul
WB8TSL

On Sat, Apr 11, 2015 at 12:52 AM, Chuck Harris <cfharris at erols.com> wrote:

> That is almost a carbon copy description of how I fixed a
> similar module in my Ball/Efratom MGPS unit on my GPSRb
> unit.
>
> An oven set to 140C is your friend when doing jobs like
> this.
>
> The guys that make these modules are trying to make them
> as small as possible, so they always use tantalum capacitors,
> and run them very close to their ratings... in this case, it
> was 18V on a 20V cap.
>
> This particular module had +/- 15V, and +5V on board.  I have
> never seen so many individual switching power supplies stuffed
> into a single module... They were all little 5 terminal IC's,
> with each running at whatever frequency it felt like...
>
> -Chuck Harris
>
>
>
>
> Bob Stewart wrote:
>
>> This is just a brief report, not a how-to.
>>
>> I got a KS_24361 with a bad Lucent power module.  Having nothing to lose
>> I thought
>> I'd see if it came apart.  After unsoldering it from the motherboard, I
>> found the
>> usual potting compound.  Fortunately, the compound was only loosely
>> attached to
>> the board in the brick and was easy to pick off.  After that, I used a
>> pair of
>> needle-nose pliers to work the board out of the casing.  In spite of the
>> pic
>> below, I first gently pried up on the corners, in succession, until the
>> corners
>> released.  Then I worked my way toward the middle, until the board came
>> out.  Be
>> aware that there are two small inductors on the top side of the board
>> that have
>> metal covers that will probably stay in the potting compound.  Just leave
>> them
>> there.  When you push it all back together the covers will go back on the
>> inductors.
>>
>> http://evoria.net/AE6RV/KS/OpenUp.jpg One corner of the brick was pretty
>> hot while
>> I had it on, so I figured there was a shorted component.  As it turned
>> out, it was
>> a 15uF tantalum cap with a big brown spot on it.
>>
>> http://evoria.net/AE6RV/KS/BadCap.jpg Here's the cap removed from the
>> board at the
>> upper left. http://evoria.net/AE6RV/KS/CapRemoved.jpg
>>
>> So, ordered the cap, put it on the board, then just pushed the pins into
>> the
>> motherboard for testing.  I didn't even bother soldering it.
>> http://evoria.net/AE6RV/KS/Testing.jpg Tests were good, so I stuffed the
>> board
>> back into the casing, and soldered it all back on the motherboard.  I
>> didn't
>> bother repotting the bottom surface of the board.  I attached the
>> repaired KS to
>> my good REF-0, and it's now working. Bob - AE6RV
>>
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