What can a broken infrared remote control tell me?
October 12, 2011 8:05 PM   Subscribe

Can I learn anything useful from the circuit board of a nonfunctional infrared remote control?

I have a cheap moon-shaped light with phases controlled by an infrared remote control with three buttons. The RC is broken, with no IR light detected by a camera. It also seems to be improperly wired: when batteries are inserted into the RC, a burning smell is produced and the batteries heat up very quickly. The online retailer has refunded my money but I still have the light and the defective remote.

I'd like to use the moon light. Perhaps I can program the necessary IR codes into my Harmony remote. Can I learn anything useful from the remote's circuit board? Is it likely that an electronics repair shop would be able to do anything to fix the remote, or would they just laugh me out of the place?
posted by kelly42 to Technology (13 answers total)
You won't be able to determine the codes sent by the RC by looking at the PCB. An electronics shop might be able to repair it, but it probably wouldn't be worth the cost.
posted by sanko at 8:09 PM on October 12, 2011

Probably nothing very useful to learn from the board - the codes etc will be generated by a chip you can't see inside of (and if you could, it still wouldn't make sense visibly).
posted by anadem at 8:12 PM on October 12, 2011

There's a possibility that the remote is built around some known chip and the part number would tell you what kinds of codes it sends. In that case you could probably look that up and program the codes into a programmable remote. It's more likely, though, that the remote just has an anonymous blob of epoxy which will keep its secrets to the grave.
posted by hattifattener at 8:46 PM on October 12, 2011

The heating up and burning smell is probably a short (duh). But if it's something you can fix, the rest of the remote might work. If the transmitter chip is fried, you're out of luck, but if it's some sort of power conditioner circuit on the input, it might be that you can bypass that and power the transmitter directly.

If you can get it working long enough to test the buttons, you could have a learning remote learn the codes and then use that to control your lamp.
posted by spacewrench at 8:53 PM on October 12, 2011

Best answer: If you'd like, open the unit up, shoot a good digipix of it (so that I can read the chip part number), and memail it to me. I'll see if I can find you a data sheet on the part. You can learn something, I'm sure, from a perusal of it.

Remotes aren't conceptually much more complicated than a flashlight. Most of the work is done in one chip, and there are usually few discrete components, some switching, and some really cheap circuit boards (phenolic as opposed to fiberglass.) A row/column switch matrix is usually employed, with gold plated contacts on the circuit board and conductive rubber buttons on the key pad.

If it stinks, it's probably (but not certainly) toast. Fixing it would involve replacing the chip but not before verifying that you have the batteries in right and that the unit is wired properly. If it once ran, then you can forget about it being miswired, but you can't be sure you're installing the batteries properly... that's up to you to assure.
posted by FauxScot at 9:25 PM on October 12, 2011

Best answer: FWIW a lot of such things I've seen over the years don't have a particularly sophisticated remote containing a chip programmed to produce complex multi-bit protocols etc. Many are simply a 38 or 40kHz oscillator + a 74-series counter strapped up to produce a couple of simple long-short or missing pulse trains, which the slightly-more-complex receiver interprets as up, down, & on/off.

They're usually also really poorly made, looking like they've been hand-soldered by a blind and untrained monkey with Parkinson's and a plumber's iron.

So, yeah, may as well open it up, have a look, and take some pics. Wouldn't be at all surprised to see that the problem is merely a big blob of solder bridging the battery terminals on the board.
posted by Pinback at 1:01 AM on October 13, 2011

You can always learn something by taking anything apart. Since your RC doesn't work, congratulations! You don't have to worry about breaking it. Part of the fun is figuring out how it comes apart. Then study what's inside, look for a short circuit, try to figure out what the various things are. Treat it as a puzzle. Take photos and post them, and add links here. We'll share in your fun!
posted by exphysicist345 at 5:59 PM on October 13, 2011

Response by poster: Thanks, everyone, for your help. This is my first AskMeFi post and I'm pleased I found the right place to ask this question.

I should add this wrinkle: I know this moon light works; I bought two identical units. I found this remote to be defective immediately, then tried the second unit which worked perfectly, and verified that the second remote did work using the first moon light. Unfortunately I then gave the working unit to a colleague's daughter for her birthday so I have little to no shot of borrowing back the remote for use in training the Harmony.

Interestingly, this moon light seems to be a cheap knockoff of an Uncle Milton brand 'Moon In My Room'. Lo and behold, the Uncle Milton product is in the Harmony database. My moon light doesn't recognise the Uncle Milton's IR codes. (That was upsetting to say the least! I thought I had a solution!)

I'm assuming this cheap knockoff was probably produced by the factory that makes the Uncle Milton units. Wouldn't the chances of the IR codes being changed between these identical moon lights be pretty slim?

I'm working on the requested pix of the remote unit; thank you for the offers to have a look. I only have an 18-55mm lens on my camera so it's proving difficult to get close enough to the chip to see the numbers; I'll post what I can get shortly.
posted by kelly42 at 1:29 AM on October 15, 2011

Response by poster: Photos are here. These are 1920 x 1080 pixels but I can produce larger images if desired.

overview of the front of the board, with 3 buttons

the battery compartment - note one extremely short spring which contains a section of wire differently coloured to the rest - indicates problem, I'm guessing?

closeup of the black chip containing text 'S8050 D 331'

the solder points, which don't look great even to my untrained eye
posted by kelly42 at 1:42 AM on October 15, 2011

Mm, that's the "anonymous epoxy blob" style I mentioned— the actual brains are under that unmarked hemispherical black blob in the upper-middle-right of the picture. A very common technique for high volume low cost circuits but not very hackable.

On the upside, I don't see any heat discoloration on the board. If the short is before the blobchip, then the blobchip might be fine and fixing the short might make the remote work again. Can you tell where the burning was coming from? (Are the leads of those two small capacitors on the right— the orange lentils with '101' printed on them— touching each other maybe?)

The S8050 seems to be a simple transistor, maybe the output driver or something.
posted by hattifattener at 12:53 PM on October 15, 2011

Interesting. What happens when you insert the batteries? Can you figure out what's getting hot? Any smoke? Sizzling?
posted by exphysicist345 at 10:06 PM on October 15, 2011


battery compartment is such that it eliminates you having the batteries in backwards.
also, no wiring, so it's not wiring.

You can see the parts count is really low and it is Chip-on-board tech. No visible damage present.

What I see is kind of odd. The yellow thing and the flat components at the end are a ceramic resonator (455 kiloHertz) and the two caps needed to make it run. There are pads on the board that were designed for surface mount versions of both of those. they are marked C1 and C2 and have values of 100 picoFarads. The resonator appears to have been meant to hang off the board, but the hack of adding the caps is a little wierd? Not wierd enough to keep it from working or explain the smell/non-function.

The part at the other end is probably a driver transistor, and used to pump the IR LED at higher currents than the epoxied chip can handle. It's common to do that, but I don't see the LED. If I were going to look for something bad, it would be this, though.

The part marked R1 on the pix which goes to the trace leading to the blob, it probably the signal from the remote transmitter. If you looked there with a scope, you might see the remote waveform and that would tell you if the driver is to blame or the remote chip. If the former, then you can fix it with a 2n2222 and an LED hack. If it's the chip, you're dead.

ham radio friend with a scope can help. 10 minutes of techie fun to see what's up. go for it.
posted by FauxScot at 6:43 AM on October 16, 2011

Response by poster: Thanks, everyone, for the help. I completely forgot that my best friend also bought one of these units, so I borrowed her remote control and taught its infrared signals to my Harmony remote. Problem solved, at least for now!
posted by kelly42 at 12:34 AM on October 30, 2011

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