[time-nuts] KS-24361 Power Module Repair

Bob Camp kb8tq at n1k.org
Sat Apr 11 11:31:08 EDT 2015


Hi

I’ve seen the same failure on Efratom LPRO Rb’s on the input bypass cap. 

It’s a pretty common failure in general. Tantalum’s don’t really like very high surge 
currents / rapid voltage ramps. In normal bypass applications, restricting current 
surge / voltage ramps may be a bit tough on the power input side of a system. 

Bob

> On 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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