What are these mystery components (one of wire coil, another labeled "100-10L A9")?
I have here an acre-counter or crop counter device like the lykketronic shown below, using two AA batteries. It arrived without working.
Upon opening its case, I found that the PCB is missing two components, and the area where these components were is scratched, as though someone removed them carelessly.
Here is a photograph of the main PCB. The top part (cropped) is just the LCD.
And a close-up of the corner missing the components.
I was able to find another identical device, and the components are intact. One is a coil of wire on a black spool with a rectangular top. The other is a rectangular box labeled "100-10L A9". Here is a general view:
And again the close-up, including the mystery wire coil component:
Is this wire coil a filter of some sort? An impedance? What does it do?
And what is the black box to its left? It looks like an SMD capacitor like this one at mouser, but I don't know how to interpret its label.
I am hoping to either replace or re-make the components to restore the PCB.
2 answers
The black one is a tantalum capacitor. There are various weird ways to mark these (because typing out 100u instead of 100- would be too easy...). If I'm correct in this case, I believe:
-
100stands for 100uF -
10for 10V. -
Lis tolerance +/-10%. - From the size of it it looks like a "D package" aka EIA 2917. In plain SI units meaning 7.3mm x 4.3mm.
This would then be an equivalent part: https://export.rsdelivers.com/product/vishay/593d107x9010d2te3/vishay-100μf-mno2-tantalum-capacitor-10v-dc-593d/6844474?query=6844474
These are bulk caps for the supply and the exact value or tolerance won't be important.
As for the second part, it is some manner of inductor and that's all I can tell. It seems likely that the little black SOT (SOT-89?) IC marked 331 is a switch regulator. You won't be able to figure out the value of the inductor by looking at it, you have to look at the regulator requirements, then find an equivalent part.
You may have to reverse-engineer the board and produce a schematic to tell for sure what the 331 IC does.
I'm guessing since it runs on AA batteries that it's a boost regulator to 3.3V. There's several parts that might fit the bill, I can't be bothered to track it down.
(You could try to just smack on some inductor between 10uH to 100uH and hope for the best... not professional but I've been there, done that. Fully enclosed ones are preferred.)
Tantalum caps tend to explode with a spectacular pyrotechnic effect if you for example mount the backwards and provide enough power, or if you simply apply way too high voltage etc. So that could be what has happened here. Then some clumsy person tried to salvage the board but failed, removing the solder pads in the process.
You may be able to salvage the board if you are less clumsy, by carefully carving off the solder mask from the traces going to the pads with a scalpel or similar precision knife. Then attempt to solder a new cap there. If it is easier mechanical-wise, you could maybe pick a through-hole one of 100uF instead.
It might be easier to just desolder anything related to the regulator and patch in a brand new one there instead.
The component with the coil of wire is an inductor. Judging from the small size, it is probably only a few µH. There are lots of uses for inductors, like for filters, switching power supplies, tuned oscillators, and others. I would not try to guess the use from this scant information.
The component to the left of the inductor in second picture looks to be a diode. It only has two terminals. The stripe at one end probably marks the cathode.
Added
Lundin has pointed out that the black component on the left is probably a tantalum cap, not a diode. In retrospect and given the markings, I agree that it is a definite possibility that I just didn't think of earlier.
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