How to replace a Marvell PXA270 processor

[AlexMA]

Hello,

I have a handheld data collector, that runs Windows Mobile 6.1.  I have been having intermittent problems with the loading of the operating system.  Sometimes it completes, other times does not.  Sometimes the LCD touchscreen comes on, sometimes it doesn't.  It has been suggested to me that it could be a problem with the main processor.

My question is how to physically replace the processor.  I have no problem getting into the innards of the data collector, and removing the circuit board.  And, I have located the processor, which is a Marvell PXA270.

As you may see from the front side image below, the processor is marked as follows:

RTPXA270C5
G8104981.1
0824
TW

I believe from researching this processor that the unit was manufactured by Marvell in Taiwan, and that it was made in the 24th week of 2008.  Otherwise, it appears the model number of the chip is expressed on the first line, and I have found that replacement chips having the same model number are available at very reasonable cost.

I researched how to replace a processor, and found some videos describing how to remove them from a desktop or laptop computer.  in each of the videos I found, the processing chip was removed by lifting a latch, or turning a screw, or some similar mechanical technique.  However, on this unit, I find no similar mechanism or latch.

I suspect, then, that the processor is soldered onto the circuit board, although I don’t see the actual connections.  How is removal and replacement done?  Is the entire processor heated to remove?  How?

I would be perfectly willing to pay a reasonable fee for someone to do this for me, as I believe it may be beyond my reach.

Thanks in advance for any advice or suggestions,

Al

[JacobPilsen]

Why do you believe, that the PXA270 is defective???

[abraxa]

What you describe sounds to me like there's a brown-out during the boot process, putting the blame on the power supply instead of the processor. It could also be a flaky connection on one of the pins, particularly the flash ICs. Either way, unless the BGA soldering is of poor quality, the main processor is the last thing I'd suspect to be faulty. Do you have a scope to look at the voltage rails during boot-up?

So I'm with JacobPilsen on that one: why do you believe the main processor is defective?

[AlexMA]

 Thank you both. The only reason that I suspect the processor is the reason for the failure is that I spoke with a repair technician at the manufacturers facility, and he told me that it was likely. However, since they didn't have any processors  in stock, but had only the complete circuit boards, they advise replacement of the latter at a cost of around $1000. It is an older unit, and hard to justify such an expense repairing it, especially since they only give a 90 day warranty on the repair.

[AlexMA]

abraxa,

I don't have a scope. I've never used one.

If I were to purchase a used scope for this purpose, can you suggest a make and model of an older reliable scope that might not cost too much?  Looks like Tektronics are popular.

Thanks,
Al

[abraxa]

Well, this is not an easy task, I'll be honest. You correctly noticed that there is no simple way of changing the processor - that's because it was never intended to be changed in the first place. The connections are on the underside because the kind of packaging the processor uses is called BGA - a grid of solderable "balls" on the underside makes the connections. Those balls however melt at a high enough temperature and make the connection virtually permanent. Due to the nature of this difficult process, problems can arise after a certain time as cutting costs on the manufacturing side may have introduced faults that may worsen over time. Usually, such faults however only show up when the ICs connected in such fashion become warm/hot during operation as the hot/cold cycling puts mechanical stress on the connections (think shrinking/expanding material).

Maybe the engineer told you it's the processor because they discovered this to be the issue with other units, there is no real way for us to verify or falsify this. Assuming that the processor is at fault, I would put my bets on the BGA connections, not on the IC inside the package. What I mean is that it may be sufficient to bring the balls back to melting temperature so that any cracks disappear. Replacing the processor completely is a difficult task because there are parts on the opposite side of the board and because a new processor (if you were actually able to obtain one) would need to be perfectly aligned with the grid on the PCB before being heated. This is not trivial and I'd leave it to someone who does this on a regular basis.

Now, you seem to really want to get this working again. From my point of view you have two options (except for paying the manufacturer for a repair, obviously):

1) take the board to some phone repair shops. Some of them have suitable equipment for such a task because they replace BGA ICs on smart phones. Maybe you can find one who is willing to reflow the BGA (that's what the soldering process is called).

2) try reflowing in your (electric!) oven at home: https://www.google.de/search?q=nvidia+reflow
Also check https://www.eevblog.com/forum/repair/my-experiences-reflowing-videocards-(so-far-100-success-rate)/
The thing however is that the plastic connectors on the board *may* take damage during this process as they might overheat and warp a bit. Not heating up the board enough may not bring the temperature under the processor up high enough, however. It's a gamble, so only do this as a last resort.

Keep in mind that this is assuming that the connections to the processor are the issue. Without being able to examine the board in detail, I'm afraid there's not much more I can do. Buying an oscilloscope in the hopes that you can diagnose the issue is unfortunately ill-advised, simply because such a complicated board needs experience to debug and isn't trivial.

[Armadillo]

2) try reflowing in your (electric!) oven at home: https://www.google.de/search?q=nvidia+reflow
Also check https://www.eevblog.com/forum/repair/my-experiences-reflowing-videocards-(so-far-100-success-rate)/
The thing however is that the plastic connectors on the board *may* take damage during this process as they might overheat and warp a bit. Not heating up the board enough may not bring the temperature under the processor up high enough, however. It's a gamble, so only do this as a last resort.

Buying an oscilloscope in the hopes that you can diagnose the issue is unfortunately ill-advised, simply because such a complicated board needs experience to debug and isn't trivial.

if we will to concur with the statement that it "needs experience and isn't  trivial"
then avoid Item 2 at all cost because all the underside components will fall out and then with missing components, the board will be permanently written off"

[AlexMA]

I'm definitely in over my head, and I value your suggestion that it is not trivial exercise.  I am not inclined to do the processor replacement myself.

I'm looking over the history of correspondence I've had with the manufacturer regarding this unit.  Since purchasing the unit about 3 years ago at a cost of $1,000 (used), I have had this unit repaired 3 times, at a total additional cost of about $1,150.  In fully functional condition, I'd estimate the street value of this data collector at $800.  Given the chance that any further repair efforts may still be unsuccessful, I'd seek to limit the cost of any future repair to less than $200.

Prior to authorizing the last repair, the repair technician wrote the following:

I have just concluded my assessment and testing of your unit. It appears the main processor needs to be reflowed and other supporting componentry replaced on the main circuit board. In addition to this the LCD has gone out and will need to be replaced, we currently have our hardened touch screens in stock and ready to go. Attached to this email is a summarized repair quote showing the cost of labor for the parts and repairs needed to restore the unit.

I authorized that this repair be completed, and since then, the unit has failed again.  It would seem that the main processor has already been re-flowed, and that it might be unlikely that performing the same procedure again would do much good.

As abraxa has pointed out, it could be several other components besides the main processor that are causing the symptom.
 
Maybe I could find a phone shop that would try replacing the BGA processor with another.  Maybe it would work.  Or, not.

Thanks for the help.

[abraxa]

if we will to concur with the statement that it "needs experience and isn't  trivial"
then avoid Item 2 at all cost because all the underside components will fall out and then with missing components, the board will be permanently written off"

For two-sided PCBs, SMD components are usually glued to the board before reflowing both sides simultaneously, so there's no danger of them falling off. Otherwise, the manufacturer wouldn't be able to solder the board in the first place - unless wave soldering is used, sure, but I honestly haven't seen that done for any of the commercial two-sided PCBs I came across.

[abraxa]

I authorized that this repair be completed, and since then, the unit has failed again.  It would seem that the main processor has already been re-flowed, and that it might be unlikely that performing the same procedure again would do much good.

Indeed. If it failed once before due to faulty BGA connections, it's only a matter of time until it happens again. Eventually, the connections will fail permanently because of the repeated excessive thermal stress to the processor and board.

Maybe I could find a phone shop that would try replacing the BGA processor with another.  Maybe it would work.  Or, not.

Worth a shot if you can get such a processor but I'd assume that they're difficult to come by in small quantities. Maybe digikey has it, I didn't check.

I am curious as to why the repair technician thinks that "other supporting componentry" needs to be replaced. I guess we'll never find out

[Armadillo]

if we will to concur with the statement that it "needs experience and isn't  trivial"
then avoid Item 2 at all cost because all the underside components will fall out and then with missing components, the board will be permanently written off"

For two-sided PCBs, SMD components are usually glued to the board before reflowing both sides simultaneously, so there's no danger of them falling off. Otherwise, the manufacturer wouldn't be able to solder the board in the first place - unless wave soldering is used, sure, but I honestly haven't seen that done for any of the commercial two-sided PCBs I came across.

The problem is he is NOT the manufacturer and don't assume the temperature will be correct, evenly distributed or controlled. Don't assume that the board will not be knocked or mishandled when hot. You need to deduce his ability in making your suggestion. Unless you think that few drop out components will not be any problems at others pain.

But since you are in Germany, maybe you can help him to use your oven for the reflow to proof your point also