[time-nuts] KS-24361 Power Module Repair
doug at dougronald.com
Sat Apr 11 13:38:05 EDT 2015
Yes, and for those hams amongst us TN's, these switchers produce copious amounts of RFI all over the HF bands. I replaced my DC/DC converters with external linears, to stop the pollution.
>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...
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Chuck Harris
Sent: Friday, April 10, 2015 9:52 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] KS-24361 Power Module Repair
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...
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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