Replacing LMS7002M on LimeSDR USB

#1

I seem to have damaged the RX input on CH A of my LimeSDR. How hard would it be to replace the LMS7002M IC. Is it worth it or should I just put up with RX on CH B only for the time being ??

#2

How much would it cost for a replacement chip ?

#3

Probably not that easy, unless you have the right tooling. Someone else who has had a go at DIY QFN replacement may be able to better advise. DigiKey stock the RFIC.

#4

Check if all inputs are damaged. For some reason my LimeSDR has half of RX1_W input damaged. Probably one pin of differential pair is damaged or badly soldered. Problem persists from the beginning. Signal level is 10dB smaller than RX2_W. Although one input is damaged other ones are working properly. RX1_L RX1_H have the same level as RX2_L and RX2_H.

#5

It would be not easy unless you already have an experience of soldering QFN packaged ICs. However if you managed to find a replacement chip some guy in local smartphone/laptop repairing service could probably solder it for you. Or yes, just use only CH B.

If I may ask, what happened, how exactly did you damaged a chip? Any advice how to avoid the same problem?

#6

~ 110 USD https://www.digikey.com/product-detail/en/lime-microsystems-ltd/LMS7002M/1434-1003-ND/5012880

Frankly for similar price you may consider to buy a brand new LimeSDR Mini instead.

#7

I leave my LimeSDR powered up and with antennas connected all the time. I believe that static build up on the longwire antenna I had on RX1_W did the damage as the LNA on that input is no longer working. The LNA on RX1_L is still working but the signal levels I am receiving are way down on what they were before the damage. I suspect I have blown the LNA on RX1_W and also done some damage to the ic circuit after the LNA.

I recommend people use some sort if input protection if using antennas that may build up a static charge.

#8

I do have some experience replacing SMD ic’s but not QFN type. I might practice on a few old video cards etc before contemplating replacing the LMS7002. I’ll just use CH B for now.

#9

Thanks for the reply Andrew. I might look into getting the chip once I have practised enough on some old video cards (removing, cleaning and refitting ic’s). I’ll let you know how I go if and when I get around to it.

#10

The LMS7002M is aQFN 261-pin package (BGA), not an easy part to remove without the correct tools and a lot of experience and not an easy part to replace without damaging other parts. It is not impossible, just at the high end of extremely difficult.

#11

I like a challenge :grin:

#12

There are videos of people doing similar work on other board on youtube which may help a tiny bit. But it is not easy, if it was not a $100 BGA replacement part, I’d probably give it a try though.


#13

By the time I take into account exchange rate and postage, I’ll probably be looking at about AU$150 or so.
I have watched a couple of BGA replacement videos and I feel that with a bit of practise, I should be able to do it.