dropped electronics repair

[UrQuan]

Any tips on the kinds of things that dropping electronics is likely to damage? Ideas on what to check?  I'm a neophyte here... I'm good for through-hole soldering and measuring resistance/capacitance, but clueless about diodes and ICs.

I dropped my TI-85 calculator once upon a time, and it never turned on again. Now that I'm starting to learn a little bit about electronics, I thought it might be fun to try to troubleshoot it.  I got it open and don't see any visible problems -- no cracked solder joints or traces or anything.  If the problem is a bad cap or something, it might be fun to try my hand at SMD soldering.

Thanks.

[saturation]

Many things can break with a fall, but the general class are items with least flexibility or ductility and high brittleness, and many things can fail depending on the height of or force of the fall.  This will causes cracks and separations and poor connections.  Common culprits are glass parts like LCDs.

The next are non-locking connections and cables that rely entirely on friction to hold true, they will pop off.  For example batteries, ribbon cables, membrane connectors.

Its unlikely that a SMT component fractured from a fall if other parts did not break too.  That's because they have less mass and the solder joint often has more mass and strenght than most SMT parts.

[kamilon]

Another really good thing to look for are things that stick up off the PCB without support. Things like linear regulators or TO-220 packages with no heat sink. Things like that will want to spring over and can break off or damage tracks etc.

[BillWojo]

I'll never forget a service call I made at a plant that made cellphones. This was about 15 years ago when cell phones were like bricks. Just one solid piece, no flips, or sliding keypads. I was there setting up a small machine shop in a room that was empty except for drop testing of cell phones. They dropped them from a height of 6 feet onto a concrete floor and recorded it with a high speed camera. After each drop they would see if the phone turned on and worked. If it did, drop it again. Each phone was matched to the video recording so they could study the impact. They were working to make the phones even more rugged.
All well and good until I stopped to take a break and looked at some of the playback of the high speed camera. My jaw dropped when I saw a ridged cell phone flex back and forth into a banana shape along with major twisting along it's long axis. There is no way in hell that I could bend or twist one of those phones like that short of clamping one end in a vise and going at it with a pair of channellocks.  All from a 6 foot fall. The shock wave could be seen as it danced twisting and bending. Just unbelievable. So I would also expect damages to traces, damage to almost anything.
That was a real eye opener.

BillWojo.

[elliott]

Measure the current consumption when trying to power it up. It might be working, but not displaying anything.

[SL4P]

Physics.
Look at mass, places where masses meet.
Types of materials - where materials meet.
Angles of moment (rotation and potential energy)
Almost all force/stress induced issues will occur here.

[Psi]

Check all ferrite inductors carefully.

When crashing quadcopters the little ferrite inductors on various PCBs tend to be the first things to fail.

Quite often you touch them and a corner falls off.

[tautech]

Seen many broken PCB's and components from falls.
Look at the heavy parts first,often that is where damage is most likely, PCB pins pull out, broken solder joints, cracked PCB's, torn off pads etc.
With the PCB removed and in a very quiet location flex the PCB and listen for the cracked joints "clicking".
Sometimes I have never found the cracked joint but a full re-solder returned the unit to life.

[UrQuan]

I feel like I'm getting an excellent education here... thanks everyone!

[Refrigerator]

I haven't had anything stop working after being dropped *knock on wood*. TI calculators seem so ridgid, i remember when i bought mine about three years ago, it was -15C cold on a garage sale, it was a beautiful looking blue TI-82 Stats, it had frost on the screen and snow everywhere else, for the two bucks the guy was asking i didn't expect it to work but i got it home set it on the table and after giving it about five hours to warm up i installed the batteries and the thing powered right up! I used it everywhere since then.

[jlmoon]

Physics.
Look at mass, places where masses meet.
Types of materials - where materials meet.
Angles of moment (rotation and potential energy)
Almost all force/stress induced issues will occur here.

This statement took the words right off my typing fingers!  I was going to suggest the exact same thing.  Mass kills & destroys!

[UrQuan]

I haven't had anything stop working after being dropped *knock on wood*. TI calculators seem so ridgid...

Yeah this was a first for me. I'd dropped it numerous times on linoleum school floors. This was no higher, and onto a carpeted office floor. Surprised the heck out of me that it wouldn't turn back on. But to be fair, it did have almost 20 years of service under its belt!

[G7PSK]

Look at the connection between the display and the board first as this is the most likely thing to have failed, the mass of a calculator is a lot less than one of those brick phones which weight around a kilo.

[Neilm]

Its unlikely that a SMT component fractured from a fall if other parts did not break too.  That's because they have less mass and the solder joint often has more mass and strenght than most SMT parts.

True for small parts, but larger SMD components can be damaged if the PCB flexes. I have an MP3 player where that has exactly happened, one of the BGA connection under the main chip has fractured meaning it won't talk to the PC. I suspect that there is damage to the PCB as reflowing it hasn't helped.

[rob77]

Its unlikely that a SMT component fractured from a fall if other parts did not break too.  That's because they have less mass and the solder joint often has more mass and strenght than most SMT parts.

True for small parts, but larger SMD components can be damaged if the PCB flexes. I have an MP3 player where that has exactly happened, one of the BGA connection under the main chip has fractured meaning it won't talk to the PC. I suspect that there is damage to the PCB as reflowing it hasn't helped.

try to re-ball the BGA - sometimes plain re-flowing doesn't help. and while the chip is out, take the opportunity to inspect the PCB. it's unlikely that one of the inner layers got damaged (the outer PCB layers are suffering the most during flexing).

[Neilm]

Never tried re-balling. The only facility I have for dealing with BGAs is at work (IR workstation) but it is U/S at the moment.

[rob77]

Never tried re-balling. The only facility I have for dealing with BGAs is at work (IR workstation) but it is U/S at the moment.

for small BGAs you don't need too much (and i assume that chip in the MP3 player is a small BGA package).
for small BGA packages you can get along with tin balls (from e-bay), tacky gel flux , IPA or other stuff to clean flux,  fine tipped tweezers , steady hand and hot-air.
desolder the BGA with hot-air, clean the PCB and BGA with flux and solder wick, clean everything with IPA,  apply flux to the bga, place the balls with tweezers, reflow the balls with hot air, clean up flux , apply fresh flux to PCB - place the BGA and reflow with hot air.
for bigger BGAs it won't work that way because of placing the balls with hand  and incorrect heating with hot-air - you would need a stencil to place the balls and IR rework station to desolder/solder.

[UrQuan]

Got the TI-85 back up and running. It was just the ribbon cable to the screen. Thanks everyone!

[SL4P]

Physics.
...

This statement took the words right off my typing fingers!  I was going to suggest the exact same thing.  Mass kills & destroys!

If you guys are ever designing something to be 'drop proof' - not only the above, but look at really well engineered MIL-spec stuff.

They include deceleration and torque damping at various rates as well as addressing the integrity of the device itself.

I know I'm a nerd, but did something similar 10 year ago for the kids in primary school --- showed them how to design and build their own 'force distributor' using zig-zag folded and laminated paper sheets (like corrugated cardboard)  at different wavelengths and thicknesses - in layers to save humpty-dumpty from a bad fall.  Ended up as a triangular pyramid with one side 'accessible' - and a cozy 'capsule' for humpty to sit in...

It worked. Son is now studying industrial design.