Replacing QFP144 chip on vintage (ca. 2009) Asus X83Vb laptop board

[pplaninsky]

Hi,

TLDR;
Is it difficult for a begginer to replace a TQFP 144 pin chip in my home lab. Any tips?

The long story:

Recently I started looking into how to replace a dead battery on old laptops.
A lot of the laptop batteries use TI chips (bq20z90) that communicates with the laptop over the SM Bus (I2C compatible) using SBS (Smart Battery System) protocol.
I had a lot of fun, but actually you can't replace the dead Li-Ion cells, because the TI chip in the battery locks itself and you need special tools from TI to unlock it (if you have such tools - let me know.) I am not actually sure that it is unlockable at all.
So, I used my DSO to reverse engineer the I2C communication and Arduiono with software like: https://github.com/PowerCartel/PackProbe to hack it.

I was almost ready, when I accidentelly shorted the SDA line to 12 volts. I hoped some buffer or MOSFET had burned out, but it turns out that on this mother board the SCL and SDA lines are almost directly connected to the Super I/O controller (ITE-8752TE). The lines have some ESD protection, which obviously did not help in my case.

Now the SDA line has a permanent path to ground of around 11K. I desoldered the pull up resistor to measure that. Naturally, I think the open drain otput of the chip fused and created permanent path to ground, so the chip cannot drive the line. See, schematics.

The chip is TQFP-144. I have no experience desoldering and re-soldering such chips. As the whole mother board is otherwise functional I am worried to take the risk of repair.

Any hints on how to proceed. How easy/difficult is to desolder such chip and what tools I need for that? I've seen a lot of videos of people using hot air and Kapton tape to do it. It seems easy, but I think it just looks like that and I do not wish to damage the mother board further.

Thank you!

[pplaninsky]

just adding the schematic if someone is interested

[amyk]

That's the EC. It needs to be programmed with firmware too, if you replace it. Hot air is the method of choice for doing so.

[pplaninsky]

I thought about that firmware thing. It seems I am lucky here. There are a few variants - some of them with internal flash - some of them with external. This model seems to be with external flash.

[jmelson]

OK, assuming that you KNOW the chip is toast, and without fancy hot air desoldering tools, what I'd do is get an X-acto knife and slice all the pins off at the chip body.  Take the knife and just slide it down the rows of leads until they start to break off.  At this point, use the blade as a wedge and snap the leads off the body.  The reason for this is if you keep cutting the leads along the side of the body, you push them sideways and could rip the pads off the board.
When using the wedge technique, just break the lead free of the body, and don't bend it any further.

Actually, do this on 3 sides of the chip only.  On the 4th side start the slicing motion, but just do a few swipes and stop.
Now, you can bend the chip up and down a few times and the 4th side leads will all break off.

Now, use a small temperature-controlled soldering iron and sweep all the leads off the pads.  Use desoldering braid to remove excess solder and clean up the pads.

Place a tiny bead of solder on two corner pads.  Place the new chip in place and tack the corner leads down.  Check alignment on all 4 sides, and if not good enough, you can "walk" the chip into better alignment by heating one corner pad at a time.  When alignment is good, solder the rest of the leads.  I put liquid flux on the rows of leads by dipping a wire in the flux and wiping down the rows of leads.  Then, you just work the soldering iron down the rows, and add solder sparingly, if needed.

This is all made MUCH easier with a stereo zoom  microscope.

Jon

[pplaninsky]

Hey jmelson,

thanks for the advise.
I can try that. No microscope available, but I have a good magnifying glass with LED lighnting, which tends to the the job.

[agehall]

I would not attempt this without a microscope. Good vision is everything when soldering stuff like this.

Other than that, watch a lot of Lous Rossmann’s repair videos and use tons of flux would be my advice!

[jmelson]

I would not attempt this without a microscope. Good vision is everything when soldering stuff like this.

Other than that, watch a lot of Lous Rossmann’s repair videos and use tons of flux would be my advice!

Yes, I really have to agree.

Jon

[pplaninsky]

Hey jmelson,


You said it would probably need programming. There is no much documentation available for these ITE ECs.
I found this PDF (https://comsystem-tlt.ru/files/Vertyanov/Instruction%20Vertyanov%20JIG%20ver3.pdf) of a programmer that mentions it can program some ITEs. This thread here mentiones that some are self-programmable: https://www.badcaps.net/forum/showthread.php?t=72494
Is there anyway for me to know what kind of EC I have, say by looking at the motherboard. Obviuosly, datasheets are scarce.

Anyhow, theorhetically, how do you porgram an EC? Can I obtain the original firmware from the current EC? It is mostly functional, except one SDA line.

[amyk]

Programming algorithms and interfaces are usually undocumented even if you have the non-public documentation for the EC itself. BIOS updates may also flash the EC firmware too, and the non-public nature of the interface suggests there's probably no read protection. You'll just need to do lots of research and reverse-engineering.

That said, looking at the datasheets for other IT87xx, it seems you may be lucky and this is just a SuperIO instead of an EC with firmware. IT85xx are the ones that need programming.

[pplaninsky]

So, potentially it would be best to desolder the original one carefully and preserving it.
Try a new one, if it works - we are in.
If not - re-solder the original one - which mostly works.

[wasyoungonce]

I'd never re-use a de-soldered IC...unless it was so unique and not available...but wait there is more.

Trying to remove a QFN144 (edit QFP144) IC for a novice is in the realms of "fantasy" as you will damaged pads.  I do LQFP144 ICs and have decades of experience and they challenge me.   One damaged pad can be game over.

Its almost impossible to remove such IC without bending some PINs on the IC removed so there is almost no way to re-fit it....from the POV of heat let alone.

Your only chance is to use ChipQuik low melt solder and lots of flux...bridge all IC pins...also include std solder, use 2 irons and a helper to do 2 sides while you do the other 2.   Bridge the pads till the IC shifts.   PICK it up remove.

Remove LQFP ICs with chipquik:


Thoroughly clean all IC pads with with lots of flux and soder wick....do not over heat do not scrape the pads to twist them or apply mechanical force that damages the pads.   Quick, less heat is your goal.

There is a trick method using enamelled wire to lift legs off the PCB but the danger in this is lifting the pad as well. 
https://electronics.stackexchange.com/questions/51616/is-this-desoldering-hack-likely-to-work

Cutting IC legs...will twist the pads and they will degrade.

You may be able to clean the old IC legs with lots of flux, solder and soder wick but more likely you'll bend legs.

Tack in new IC at corner pins.  Use a hellva lot of good flux and drag solder the pins.  Look up vids on this.  Best you actually use a drag solder cup tip.  Heat attracts the molten solder so don't fret on multiple pin bridges....more flux and hot iron will draw that away...or some soder wick.

Drag solder techniques   Note he's using kimwipes...they are a must to clean pads. 


I solder LQFP 144 with magnifier head band and inspect (after cleaning) wit ha video magnifier.  You would be surprised at the number of "mistakes".

Remember Flux flux and more flux.  Is see users using just a flux pen.....I use far more than that.    I prefer rosin but I found Gel is best on these as it doesn't evaporate as quickly wrt rosin.   I find I can only get half of one side with rosin before I have to re-apply.

There are Hakko tips that are square 20mm so you can heat all legs at once...but they are not cheap and I'm yet to be convinced they work.   I've seen them use in the military in micro-min repair on aircraft PCBs but they also have pre-heaters and the best equipment.

I can solder with my ADSM302 but its not good for these ICs due to DOF and limited FOV.  But its excellent for inspection.   Dave has reviewed better digital microscopes...but nothing beats a binocular optical microscope.

There is so much to say but......for a novice to R&R successfully is impossible for a novice.  I'm sorry...It tests good solderers!   I'm definitely not the best and I can manage them, they do test me (I aim for zero pad faults and keep the PADs as cool as possible for future repairs) ...after decades as an Airforce Avionics Tech now doing telescope computers that use similar LQFP144s.

Oh it should have a programming port....probably JTAG. 

I'd be looking for a method of trying to read the firmware prior to removal.  Not you need a suitable programmer and knowledge of the key chain.....All this cannot be learned in a year or 2!

Look if you do need help PM me and I can advise as much I can but put it this way ...I have 2 vac de-solder dual iron stations, 2 Hakko 936 stations, 3 royel single stations, resistance solder gear, hot air stations......use high quality 63/37 solder enough spare tips solder and flux to last 2 life times...all this is experience and minimum equipment...to me.

[amyk]

Trying to remove a QFN144 IC for a novice is in the realms of "fantasy" as you will damaged pads.  I do LQFP144 ICs and have decades of experience and they challenge me.   One damaged pad can be game over.

If you are using a regular soldering iron I can definitely see why you think it's hard. Much like trying to solder a BGA with one

This is definitely a job for hot air.

[pplaninsky]

Hi amyk,

what would a not standard soldering iron?
I have a Weller station with different tips and digital temp
regulation

[pplaninsky]

Hey wasyoungonce,

thank you for the details. I will send you some DMs definately.

[pplaninsky]

so, after reading all of the above, anyone in Berlin area (Germany) with willingness to help and proper tools?