looking for technics to replacing the IC4 FST3253


David R. Hassall WA5DJJ
 

Dear Members,

 

I have to replace IC4 FST3253 on my QCX+.   I killed it by accident and so I am on the hook to replace it.   I have a repair part and looking for a technique that someone has used to replace this surface mount IC.

Any suggestions greatly appreciated.  

 

Take care and have fun.

73 Dave Hassall WA5DJJ  Las Cruces, New Mexico

Website: http://www.zianet.com/dhassall/

QRSS SUPER GRABBER WEBSITE: http://www.qsl.net/wa5djj/

 


Dean Smith
 

Hi, Dave.
I had to replace fst3253 here.
Technique I used is to desolder pins and lift one at a time down one side of ic. Then I flood other side of ic with solder and lift ic gently to remove. I then clean up the pads, making sure it's all looking good, and insert ic.
Next tack one of the edge pins with solder. Check ic pins are now neatly aligned, if it looks OK continue to tack the rest of ic pins to board with a light dusting of solder.
Once finished reinspect each pin for contact and neatness (quality control) :).
With respect to si 5351a this ic is easy on the eyes and a doddle to replace.
Good luck.
Dean aka G7EOB.


Alan G4ZFQ
 

Technique I used is to desolder pins
Another way is to slide a piece of enamelled wire under the IC. Anchor one end and pull it out under each pin as you heat them.

Don't worry about shorting pins when you refit, solder braid will clean it up.

73 Alan G4ZFQ


mike.carden
 

The main thing is to be kind to the PCB. The 'best' method here is to have a hot air surface mount rework station, but if you're asking about this, it's a virtual certainty that you don't have one.

The next best (and cheap and easy) method is to acquire some low melting point solder (I've heard it called 'Chip Quick' but I'm sure there are other brands). It's superficially expensive but you only need a tiny amount of it. The sticks I bought about 20 years ago are still useful. You just flood the chip's pins with it and float it off. Simples.

Failing that, just cut all of its pins (dremel tool?), remove the body then clean off the soldered pins with solder wick, flux, and maybe a touch more solder.

--
MC
VK1MC



geoffrey pike
 

I haven't used this low melting solder technique yet but know others who have and its brill, check out the Youtube videos for
this.And yes the biggest problem by far is pcb damage if it does come clean, i would also suggest flooding the area with
liquid flux then use GOOD desolder braid if you use cheap stuff you have made more work for yourself.
best of luck
Geoff
GI0GDP


On Monday, 9 November 2020, 08:44:58 GMT, mike.carden <mike.carden@...> wrote:


The main thing is to be kind to the PCB. The 'best' method here is to have a hot air surface mount rework station, but if you're asking about this, it's a virtual certainty that you don't have one.

The next best (and cheap and easy) method is to acquire some low melting point solder (I've heard it called 'Chip Quick' but I'm sure there are other brands). It's superficially expensive but you only need a tiny amount of it. The sticks I bought about 20 years ago are still useful. You just flood the chip's pins with it and float it off. Simples.

Failing that, just cut all of its pins (dremel tool?), remove the body then clean off the soldered pins with solder wick, flux, and maybe a touch more solder.

--
MC
VK1MC



samuel@...
 

Dave

When I started working with SMD I bought this from off Amazon.co.uk:  MG Chemicals 8341 No Clean Flux Paste, 10 ml Pneumatic Dispenser (Complete with Plunger & Dispensing Tip) -  I see it costs $16 on Amazon.com.

Three weeks ago I had to replace a FST3253 - I put 10V instead of 5V on the circuit I was playing with  - back to the "feeling stupid corner".

A small spread of flux on one row of legs allows you to get the all solder that is already there on this full row of pins, to flow simultaneous which lets you slightly lift the IC onto its side by bending against the row of legs still attached.

Then repeat on the other row and lift the IC off the board.  Clean the pads with good quality desolder braid (I use https://www.mouser.ie/ProductDetail/5168-80-2-10 - beware of cheap alternatives) and follow Deans advice.

Samuel


Mike Berg
 

Agreed. Hot air rework station @$125 is the best investment for removing sm ICs.

No clean flux and solder wick will do wonders for the pads to prep for the new part.

Mike  N0QBH


Bob M.
 

If you're going to be doing ANY SMD repair, definitely buy a Chip-Quik kit. It comes with liquid flux, which you apply before removing the IC, and before soldering on the new one. As the old IC is already bad, there's no real reason to save it, so you could just cut the leads off and remove each lead separately from the board, but with Chip-Quik it much easier to heat all the pins on one side and have them stay molten while you bend the chip up slightly. Remove the rest of the solder with solder wick or a vacuum desoldering tool. With the use of Chip-Quik, you CAN reuse some components, even though some mfgrs don't recommend it.

I found it difficult to re-solder some new SMD parts due to the closeness of the pins. You can flood all the pins with solder, then use solder wick to suck up the excess, leaving a thin film between the pins and solder pads. Just use a low enough iron temperature so it melts the solder and doesn't do any further damage.


Mont Pierce KM6WT
 

David,

A Hot Air SMD "Rework" gun is the way to go.  And, can be a lot of fun.
Don't be afraid to give it a try, you might find it as much fun as I do.  :)


On Mon, Nov 9, 2020 at 03:20 AM, Mike Berg wrote:
Hot air rework station @$125 is the best investment for removing sm ICs.
Amazon has several in the price range of $30-$50 (click here). 
The Kohree 858D for example is about $36 on Amazon.
The inexpensive ones, although not being the best on the market, should be adequate for the job.


Use the small nozzle, and only need to heat the one part.  Once solder is melted it will come right up, easy.
If you have some junk boards around with SMD parts, have a go at them for practice.


Also, soldering new part is very easy with the heat gun.

Clean the pads with solder wick.

Then, using solder paste in a syringe (also available on Amazon) put a bead of solder paste "ACROSS" the pins 1 thru 8, and another bead ACROSS pins 9-16.  Just like your crossing a series of ts  like this    tttttttt

Here's a YouTube example, starting at 3:44 thru 4:08   https://www.youtube.com/watch?v=RODp8HSlFPA
except he uses A LOT MORE solder paste than is really necessary...     
(this is NOT the best example, but just one I found quickly...)

VERY LITTLE solder paste is needed.  It only takes a paper thin amount of solder between the leads and the pads.


The FUN PART is watching the solder paste as it melts.   The Solder Mask, and Surface Tension of the melted solder will pull the solder on to the pads, and away from the solder mask.  Surprisingly, there will be NO Bridges most of the time, unless you put down way too much solder paste.


I really have a lot of fun building SMT kits, or kits with some/most SMD parts. 


73
km6wt


David R. Hassall WA5DJJ
 

Dear Mike,
Your probably correct in all you said.  I have the solder wick and the no clean flux solder.   Not sure about the investment in the hot air rework station.  I think I am going to try to replace it without buying one of them.  The part seems to be big enough that with a small pair of fine cutters (which I have ordered from AMAZON) I think I can clip the chip leads individually and remove the body, then remove the legs one my one. Then solder wick clean the pad and reinstall the new part manually.   If I screw it up, a whole new radio kit is about $56 plus postage.    I have done things like that in the past and they were successful.  But I was a bit younger then HI HI.    Good to hear from you Mike.   Thanks for the message.
73 Dave WA5DJJ
SUPER GRABBER http://www.qsl.net/wa5djj/


David R. Hassall WA5DJJ
 

Thanks Dean,   I think your method will work.  Studying the rest of the answers and will form a strategy after reading them all.  Appreciate the answer
73 Dave WA5DJJ
SUPER GRABBER http://www.qsl.net/wa5djj/


David R. Hassall WA5DJJ
 

Thanks Alan,
I have also used a very thin feeler gage to do the same trick but no room for that in this situation.  Thanks for the hint.
Take care and have fun.
73 Dave WA5DJJ
SUPER GRABBER http://www.qsl.net/wa5djj/


David R. Hassall WA5DJJ
 

Thanks Mike,
I understand that being kind to the PC board is the main goal.  I have a dermal tool but not a hot air workstation and the place it is in, I personally am not confident that the Hot air workstation is the right tool.   I ordered from Amazon some small cutters hoping that they will be small enough to clip the existing chips leads so I can remove the body and then remove each leg easily. If that works, the new chip reinstallation should be easy.  I appreciate your suggestions and thank you for the message.
Take care and have fun.
73 Dave WA5DJJ
SUPER GRABBER http://www.qsl.net/wa5djj/


David R. Hassall WA5DJJ
 

Thanks Geoffrey,   I appreciate the comments
Take care and have fun.
73 Dave WA5DJJ


David R. Hassall WA5DJJ
 

Dear Samuel,
To make you feel better, I hit the 5V line with a quick 13.5V.  I think FST3253 got hit then.   I still may not be out of the "stupid corner" yet.    But working on it.   I have the braid and some no clean solder flux.  Ordered some fine cutters from AMAZON and hoping I can clip the leads, remove the body and then the legs individually.  Trying to be as kind to the PC board as I can.
Thanks for the comments.  I appreciate the message.  Don't beat your self up to bad.  We learn new things when we make mistakes. As a fall back, I am ordering an new QCX+ today. Just in case.
Take care and have fun.
73 Dave WA5DJJ


David R. Hassall WA5DJJ
 

Dear Mont Pierce
I agree with your comments.   I have done some surface mount building but I didn't have all of what you have to do it.   But the kits worked.  Since this is only JUST ONE PART, I am going to try  to do it simply. My fall back is to just order a new QCX+ kit if I screw up.   That is cheaper than all the extra tooling I would need to buy.  If I was going to do this stuff more in the future your suggestions would be an excellent way to go.   I appreciate your comments and suggestions.  We shall see how this plays out.

Take care and have fun.
73  Dave WA5DJJ


David R. Hassall WA5DJJ
 

Dear Bob,

Thank you for your comments.   I appreciate your suggestions.
Take care and have fun.
73 Dave WA5DJJ


Dean Smith
 

No problem Dave so many good and valid answers here now. I have hot air rework here, but Im a little lazy. Hot air generally requires prepping the board against unwanted heat on other components resident around the faulty piece. On high density packages you have little choice. All down to experience and comfort.
Dean.


David R. Hassall WA5DJJ
 

Dear Group,

To add insult to injury, I went back into my workshop this morning and did some more analysis of my radio and found that the SI5351 CHIP is also blown.  So my immediate backup plan is to order a new QCX+ kit from Hans so I can get my 2200M Grabber back on the air.   It looks like what really happened is that a short circuit for a modification I was working on put +13.5 volts on the 5 VDC bus.   Post mortem indications is that I killed the FST3253 mux and the SI5351 Synthesizer.  The amazing thing is that the 25MHz TCXO seems to have survived. (it also runs on the 3.3V bus derived off of the 5VDC bus through two 1N4148 diodes)  The Main Processor seems to have also survived.   So even with all the great suggestions I have received, and I thank you all, I will save this QCX+ for a future repair after gathering up all the stuff to do it with and order me another $56 kit as a quicker option to repair the grabber.  


I am also revising my testing of my modifications procedures so that I won't have to sit in the DUMB STUNT corner again.   Thank you all for your help and support.  
Take care and have fun.
73 Dave WA5DJJ
SUPER GRABBER http://www.qsl.net/wa5djj/ 


Ronald Taylor
 

Dave, you may also find IC3 bad when you get back into it. I've fixed 4 QCXs that had 12v on the 5v line and all had destroyed IC1, IC3 and IC4. Only one destroyed the microprocessor. When you get IC1 and IC4 removed from the board and all cleaned up, take a look at the resistance to ground on the 5 volt line. If it is fairly low steady resistance and doesn't look like a capacitor charging up that settles into the low kilohm range, then it's likely IC3 will have to be changed as well... I've had 100% success using SMD Removal Alloy and flux to remove the little chips and solder wick and flux to clean up the mess. ... Good luck ...Ron


On Mon, Nov 9, 2020 at 10:36 AM David R. Hassall WA5DJJ <dhassall@...> wrote:
Dear Group,

To add insult to injury, I went back into my workshop this morning and did some more analysis of my radio and found that the SI5351 CHIP is also blown.  So my immediate backup plan is to order a new QCX+ kit from Hans so I can get my 2200M Grabber back on the air.   It looks like what really happened is that a short circuit for a modification I was working on put +13.5 volts on the 5 VDC bus.   Post mortem indications is that I killed the FST3253 mux and the SI5351 Synthesizer.  The amazing thing is that the 25MHz TCXO seems to have survived. (it also runs on the 3.3V bus derived off of the 5VDC bus through two 1N4148 diodes)  The Main Processor seems to have also survived.   So even with all the great suggestions I have received, and I thank you all, I will save this QCX+ for a future repair after gathering up all the stuff to do it with and order me another $56 kit as a quicker option to repair the grabber.  


I am also revising my testing of my modifications procedures so that I won't have to sit in the DUMB STUNT corner again.   Thank you all for your help and support.  
Take care and have fun.
73 Dave WA5DJJ
SUPER GRABBER http://www.qsl.net/wa5djj/