View Full Version : ?damaged I/O pin
While I was experimenting with the prop chip - I seem to have damaged the P-27.
When I switch the hardware to P-25 - it works correctly at times and erroniously at times - with the same hardware and the same code.
Does this mean I have to replace the Prop with a new one or can I still play with the other pins·-
P-0 to P20 or all the pins likely to malfunction - hence have no other option but replace the chip.
05-16-2008, 06:44 AM
I've done some terrible things to the Prop, but never saw just one pin give out... Have fried the entire thing once or twice...
Anybody seen just one pin go bad?
05-16-2008, 06:48 AM
Siri, you are in the best position to answer that one. If you can use another pin and everything seems to work, then fine. But if you do something and the chip doesn't behave the way you would expect then you might not know whether it's because some other part of the chip is damaged or it's your software. Because all integrated circuits have a common substrate it is quite possible that something else could be affected. Replace the propeller at your earliest convenience and save your hair which would have been pulled out trying to find a mysterious bug.
P.S. On saying all this I am assuming you KNOW that you have damaged a pin (like zapping it with 32 volts like I did). As you didn't describe the circuit etc then we can't really say.
I think you are right - it is easy to replace the chip than wreck my brain over it.
I· was looking to see whether others had similer issues.
05-16-2008, 09:06 AM
Yes, I've had a similar experience. I built a small circuit with a propeller driving a MOSFET to control the speed of a DC motor. I used an appropriate protection diode across the motor. This was for a friend, when it was in my possession it worked fine, but he called me shortly after I gave it to him to say it stopped.
I suspect that when mounting it, the back of the circuit board became shorted again the metal plate he was mounting it to (after I warned him to use some sort of spacers)
The result was 1 pin that didn't work, and a fried PLL. I changed IO pins and used no PLL multiplier and it worked fine. But I did not do any long term tests.
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I've fried two pins of my Parallax demo board. (P4 and P0).
One playing with RCTime...but I forget to place the 220 Ohm resistor in serial with the used pin. (that was P4).
The another one "P0"...I don't know how !!, but I never used inductive parts on it... http://forums.parallax.com/images/smilies/confused.gif
In my final designs, I never had to replace a propeller, neither in the LED screen, which has 17.
So now I'm looking for a way to replace the "QFP" of the demo board, will be easy...once I get a unsolder hot air tool.
05-16-2008, 10:28 AM
BTX, don't unsolder the chip the conventional way. Use a blade and push down and cut through the pins by pushing the blade (don't saw) against the pins right next to the body. You will be left with individual pins on the pcb which you can "desolder" by blobbing on some solder (all over) and running a hot iron along it. The pins will be stuck to the solder as it sticks to the iron tip, flick it off and continue. Turning the pcb upside down when you do this helps.
Thanks Peter for the tip. I would have unsoldered one leg at a time and bent them up, but your way sounds a lot quicker. Fortunately, I don't need this tip for my propellers yet;^)
It's just the other chips I burn out, or try to get out of the way when scavenging for parts.
Thanks so much Peter.
Good idea !!, just only one doubt, what is exactly a "blade", is it like a cutter ???.
ChipQuik is a lot easier and less likely to damage anything.
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
If you're refering to the "unsolder tape", it never was the better choice for me, after aplying that, the SMD chips remain attached to their PCB, unless you do some force to take each pin out, which can cause broken pads sometimes.
05-16-2008, 11:38 PM
REMOVING A DAMAGED QFP
I blew a qfp prop on one of my new boards and had to replace just a few hours ago. I used a small craft knife that had a blade long enough to cover the pins on one side then I simply pressed down at a slight angle which cut through in one go. I repeated this for all four sides then removed the chip.
Using a flat tip iron (best tip for smd work) I blobbed some solder onto the remaining pins and ran the tip along one side and flicked off the solder blob full of pins (they stick to the blob through surface-tension). After I got all the pins off I ran the clean tip like a scraper across several pads at a time from outside to inside to level the solder on the pads. I decided to clean it with a small squirt of isopropyl alcohol and not having a cotton tip handy I simply rubbed it with my finger.
HAND SOLDERING THE NEW CHIP
Next I dropped a new chip into place, lined it up and pressed the tip of the iron on one corner to tack it down (there is enough residual solder on the pads for this to happen) and did the same on the opposite corner. There is still an opportunity to correct any minor misalignment at this stage by touching the iron to one corner to loosen it and correct. You need to press down on the chip after this (if not before) and touch these two corners with the hot tip to make sure the chip is flat to the board.
After this I quickly blobbed fresh solder across the pins but avoiding the pins that were originally tacked till last. It looks a mess and the blobs are shorting out pins but if you tip the board upside down a bit you can run the hot tip along the edges and draw away the excess solder onto the tip and flick it off. There were a couple of pins still shorted after this but with a clean tip I touched the flat edge of the tip to the outsides of the pins and this tends to heat up the pins and the solder just migrates to where it needs to be or else onto the tip. Conical tips are useless for this type of work.
That was that, it only takes a few minutes and it all works again. No solder wick, no chipquik, no solder paste, no fuss. I did take some pictures of various stages just in case somebody wants to see them but I have to edit them first.
05-17-2008, 12:14 AM
Can you post the pics? I'm not sure how I could have blown my p23 line, but some pics may help my if I wish to replace the prop...
I would hate to have wasted $75...well not wasted I guess, but have a i/o pin that does not work...I'm just concerned that there may
be other damage...
I still don't know how or why this happened...could it be a bad chip?!
05-17-2008, 12:31 AM
Kam: Don't feel bad. We went through four proto boards because the prop mysteriously went bad (or was bad?). Some pins worked and some didn't. We were never able to explain what caused the damage. Since then we test every·proto board we use before adding components.
On the other hand, I have a demo board and a proto board that I have used over and over again for several projects and no damage to them.
Post Edited (Ken Peterson) : 5/16/2008 4:36:36 PM GMT
Thanks so much Peter !!
A "small craft knife" I understood that....!!
I'm agree with you, until take out all the cut pins with the solder.....
Then...I usually will use "ChemWick" tape at this time to remove all "Sn" from the pads, and then I clean all with isopropyl alcohol.
I put the new chip centered in the pads, and put a bit of solder in the corners too (without taking care about short circuits pins).
Then I use a "flux gel" which let solder the new chip without any care....just solder and voila !! no pins in short circuit.
After all, I clean again the board with a good quantity of isopropyl alcohol, and using a dental brush to take care of get all the flux out off the board.
Also could be usefull your picts.... I'm a bit afraid about, at the time to use the "knife", I never did it before...are the pins so soft to broke ?
If it works fine...it is a great and so cheap method to un-solder SMD chips !!!
05-17-2008, 12:55 AM
Did Parallax replace the "broken" boards?
05-17-2008, 01:05 AM
Well, I don't like to return stuff when I don't know for sure that I didn't cause the damage. That's why we now test them beforehand. Since then we didn't find any bad ones out of the box.
05-17-2008, 02:09 AM
Ya, I agree...I'm just going to assume that I *must* ( http://forums.parallax.com/images/smilies/confused.gif ) have done something (but what?!) to do this...Hopefully all I lost was one i/o pin.
sad sad me.
This was my very first usage! Hopefully it's not going to be a trend!
05-17-2008, 09:28 AM
I've never had a bad chip out of the box, of any description. Any that have failed have been directly attributed to the "idiot" factor (me).
I'll try and post those qfp rework pictures later as I've got a rather busy day.
05-17-2008, 08:40 PM
Here are some pics I did when I removed the QFP Propeller. I thought I did a video but it's a mystery as to what happened to it. Anyhow, this 5 pic sequence shows the chip being removed which is the main part of replacing the chip. If I get some more shots together I will post them up on this thread seeing it's relevant. It will probably be easier to post up a complete sequence onto some google pages once I organize it.
05-21-2008, 07:09 AM
It's difficult but not impossible to fry an I/O pin. I've done it once when stressing the heck out of the chip.
Peter's method is what I recommend to hobbyists who need to replace a qfp surface mount package. The only thing I do differently is use a small pair of wire cutters to snip the pins off the package, guess I don't trust myself enough with an xacto not to slip and damage another component or a trace.
Paul Baker (mailto:firstname.lastname@example.org)
Propeller Applications Engineer
Parallax, Inc. (http://www.parallax.com)
Post Edited (Paul Baker (Parallax)) : 5/20/2008 11:14:47 PM GMT
I replaced my QFP Propeller of my demo board succesufully !!!
Just I only use a "small cutter" to cut pins...... http://forums.parallax.com/images/smilies/smile.gif
05-21-2008, 09:47 AM
It's like dropping a new engine in your '69 Malibu! http://forums.parallax.com/images/smilies/smilewinkgrin.gif
05-21-2008, 12:11 PM
Good stuff! The reason I just press with the knife is so it doesn't cut through all of a sudden. In fact you can see I must use my thumb as a balance and as I cut at a slight angle the pins cut through easily. Cutters place a bit of sudden stress on the pins which may end up ripping up the pad so I would recommend this gentle press & cut method, the pads are never stressed in any way which is important since they are going to be stressed a little more when a new chip is soldered.
BTW, the chip I replaced had to be replaced again the next day. Just as well the pads weren't stressed and lifted. The board it's on has about 8 pin-driver modules that each handle 2 pins at 24 volts at up to 10 amps plus a high-side supply of 32V. It seems when I hot-socket these modules that I sometimes zap the prop http://forums.parallax.com/images/smilies/cry.gif Oh well, some things I can get away with, other things you can't, I'll be more careful in the future.
This is the first time I have ever zapped a prop and it's got all the classic signs of PLL or even crystal oscillator failure, but always works on the RCFAST. Most other chips just die in a horrible way so it's good to see the prop at least able to limp along. Perhaps I will make the prop startup in RCFAST first and check a status bit in EEPROM to see if it transfered ok to PLL mode previously and take necessary action from there. Of course a hardware watchdog is really needed but then again it shouldn't play up normally, it's just on the bench that the zap factor comes into play.