Re: Si5351A blown (IC1) QCX transceiver.


Hans Summers
 

Hi all

Lots of good SMD soldering equipment advice in this thread. 

But some reassurance for some of you who don't have all this stuff. Never fear! It's still possible. I'm proof of that. 

I don't have any flux. I don't have a desoldering station or any special soldering iron. I have a cheap 60W temp controlled iron with a 3mm chisel tip. 

To remove and replace an 8-pin SOIC such as the OPA2287, I first cut the four pins along one side with wire cutters. Then lift that side of the chip and wiggle up and down... after a couple of wiggles the pins on the other side break off cleanly at the chip body. Then use the soldering iron to remove the 8 pin remnants and clean up. Squeaky clean can be done with desoldering braid (or I hear, coax outer braid) but is not totally necessary. Then solder in the new component. Of course a 3mm chisel bit is too big but just rotate it 90° and use a corner, it works fine. 

General rule when replacing components: don't try to save the component, it is defective anyway (otherwise why are you replacing it?)... try to save the PCB. 

I solder components down to 0402 by hand like this. 

If soldering a fine-pitch IC like the Si5351A or an STM32 in LQFP format for example - i use solder paste spread on with a small screwdriver or any convenient sharp thing (since for me at least, the syringes get blocked almost immediately after the first use). And a dollar store type very cheap hobby hot air gun, held under the board for about 30 seconds. 

Solder paste has a limited shelf life but I usually find I can exceed it by quite a factor and it still works fine.

On some occasions such as when the bottom side of the component also has components on it, the hot air isn't possible... then I use the usual soldering iron - which of course bridges multiple pins together - then tidy up the bridges using desoldering braid to soak up the excess. 

So remember - for those of us poor underprivileged souls - sometimes a bit of perseverance and patience can substitute for the proper $$$ equipment. 

73 Hans G0UPL 

On Thu, Feb 25, 2021, 14:41 mick baldwin via groups.io <mickm3for=yahoo.co.uk@groups.io> wrote:
Dont forget plenty of flux    Mick

On Thursday, 25 February 2021, 11:02:28 GMT, Jim Mcilroy via groups.io <gts53=btinternet.com@groups.io> wrote:


Hi

Best to use a hot gun for small parts like that.

As it happens I've just removed a Si5351 from an old Elektor board and installed it on a uSDX PCB

I use an 863D work station and use hot air at 385 deg with the fan control at minimum. For removal I move the hot air gun above the chip in a circulating motion (saw that in a video) which stops parts getting really hot.

To install I add some liquid flux as there is often enough solder on the pads where the chip has to be placed and carefully use the hot gun as before.

I use a Flux Dispensing Pen type CW8400

Jim  G4EQX

PS don't forget the magnifying glasses and a cup of tea


On 25/02/2021 08:37, William Jenrick wrote:
Yea, but then if I buy another QCX kit and wind the "TOROID FROM HELL" and the chip fails again, then where am I.....? Besides It is not the mini I have, but the maxi....

On Wed, Feb 24, 2021 at 11:27 PM Ian VA7ITM <ian.mcalpine@...> wrote:
when replacing an Si5351A chip please be sure to purchase Si5351A-B-GT or Si5351A-B-GTR. Do not be tempted to buy a part number such as Si5351A-Bxxxxx-GT [R]
Wait... what?! C**p! Well that explains everything. Problem now is that in North America Digikey, Mouser, Arrow, RS, etc have no stock and a lead time of 20+ weeks! The one unofficial supplier that I did find was charging $18 for delivery...

... and alas the SI5351A is not available from QRP Labs shop either.

There's a lesson to be learned here... if you frazzle your Mini don't even bother trying to repair the SMD devices. By the time you've bought new SMD devices, paid for shipping and spent $20 on ChipQuik, you could have bought a new QCX mini main board with all components from QRP Labs for only $40!!


--
William Jenrick 

Join QRPLabs@groups.io to automatically receive all group messages.