Repair adventure: A single white LED causing stuck keys on a RN988 keyboard | Hacker News Reader

Repair adventure: A single white LED causing stuck keys on a RN988 keyboard

halestrom.net

83 pointspanic24 comments

As someone who dabbles in electronics, I found this to be a cool debugging scenario. The "aha" of the LED doubling as a diode in the circuit, and the fix from that was really interesting to me.

It's a small anecdote, but inspiring since I hope to also get to the point where I can repair something on the component level one day.

I have repaired a number of things at the component level. If you're looking to get started, a lot of consumer electronics are "bad" when they simply need a through-hole capacitor replaced. They are generally visibly bad and bulging at the top, have visible markings to ID the part, and can be replaced with a cheap iron.

This is why my AV receiver still works. :-)

Ah yes I've read about the infamous capacitor plague :D.

So you start by just doing a visual scan of all the caps on a board to see if any are bulging? If nothing is apparent, where do you go from there?

AV receivers are nice because a lot of them have the schematics and parts list right in the service manual. This is the one that I repaired: https://yamahaservicemanual.com/wp-content/uploads/2020/02/y...

The part in question: https://i.imgur.com/hZDA08y.jpg

Repaired: https://i.imgur.com/IMbBUeN.jpg

Start with a visual inspection, looking for any components which appear to be visibly damaged. For capacitors this would be something bulging, but if something has failed thermally the chip might be burned. If you see anything burned, though, I would exercise caution before proceeding.

After that, measure the output of each power supply with a multimeter and confirm that it is at the appropriate voltage level. If you find something which is off, you need to confirm that all of the additional components supporting the power supply are present and functioning. You can measure resistors on the PCB with a multimeter.

Some AV Receivers will also fail after a number of heating / cooling cycles. In this case, the solder joints on the relays have gone bad (physically disconnected) and they can just be soldered again to correct the problem.

Honestly, AV Receivers are a great place to start since they are generally both well documented and designed to be serviced.

edit: one other thing -- you can check the clock output of different crystals / oscillators, etc, if you have an oscilloscope. This can be useful to know if the clock is operating at all, and, if it is, confirm that it is clocking at the appropriate rate.

That's really useful to know, thanks!

The capacitor plague was real. I had a 22" monitor that died after four years. Some enterprising person had set up a webshop where you could put in your model number and they'd send you a little bag of capacitors that matched. I paid $15 for what was probably a few cents of capacitors and that monitor lived on for many years, despite my sloppy soldering.

There were a few that were visiting bulging or had leaked, but I replaced all of them just in case.

"Oh no, they’re not… are they?"

It seems fairly sensible to me to double up the lighting leds as diodes, from an extreme cost-engineering perspective.

Of course, it does mean you can't turn the lighting off ...

I have an optical-switch k/b. If you need a diode per key anyway you may as well have an optical sensor instead, and have no key debounce, it could be waterproof, spark-free, separation of concerns between sensing and the mechaical switch itself for easy hot-swap switches, etc. To me it's the obvious future, but it seems true mechanical k/b fans aren't with the program yet.

Wrt TKL (and smaller) vs full-size keyboards; you can easily also get separate numpads these days. You might wonder what is the point of getting tkl keyboard and then separate numpad, the answer being that you can then position it more ergonomically, for example on left side of keyboard or right side of mouse.

> that’s a decade of $20 keyboards lasting a year each.

Whole lot less landfill tho.

Yeah, I don't quite understand this attitude. If you use a computer as much as I do, you deserve to have a nice keyboard. Maybe not $2000 USD nice, but still decent.

I had gotten nearly two decades of use from the three of my Microsoft Natural keyboards (the original one). They weren't that expensive at the time.

I'm currently running a pair of MS Natural 4000s (one bought used from eBay) that are each approximately a decade old. I had to take them apart once to clean the key membrane, but they've been fine since. (Just looking at one of them now in front of me... it could really use a good vacuuming.)

All that work to avoid purchasing a $5 keyboard? People are cheap about the weirdest things.

Some people are tinkerers, and I for one enjoy reading through some in-depth physical bug chasing like this. I certainly don't have the patience (let alone the expertise or equipment) to do it myself, but I'll sure as hell read about it.

My dad is an old school EE and this post really reminds me of him.

It doesn't matter that he lives comfortably and could much more easily replace the hardware. He enjoys the process of taking something broken and making it useful again.

I liken it to spending hours configuring and modifying open source software when a paid option exists, if you have the expertise and/or interest. And doing that with hardware has the added benefit of reducing waste, which is something I admire.

I do these sorts of things. I don't do it to save money (sometimes, the repair is more expensive than the replacement cost). I do it to avoid sending stuff to the landfill as much as possible.

Show me where can I buy a mechanical keyboard with Cherry switches for $5

People with too much free time or not too many interest outside tech.

I guess if you value your time far less than money you can save a couple bucks on cheap keyboards? I guess they now have a cherry brown based keyboard and can experience the different between that and awful membrane boards. Personally I think a little extra money is worth it for a keyboard that lasts years instead of dumping a membrane board in the landfill like OP apparently does.

OP got the membrane board from a dumpster, it was already headed for the landfill. Not sure how that deserves any shame?

It's not shame, but IMO if you value your time very little than sure dumpster diving can pay off.

If you know how to value time you don't say stuff like this: the point of time is to live life meaningfully by your own standards (which may or may not align with society's standard)

Our brains all generate relatively the same amount of happy/sad chemicals, so it turns out the satisfaction of winning a nobel peace prize and the satisfaction this person feels fixing their dumpster dived keyboard can only be so different in magnitude.

It's not like doing universally meaningful things unlocks some kind of super-happiness, so there's no reason to shy away from "unmeaningful" things if they bring you joy.

I assumed the point was that your comment "dumping a membrane board in the landfill like OP apparently does" was a misrepresentation, as the author was doing the exact opposite of dumping the keyboard in the landfill!

Whether this represents a good or bad use of one's time, who can say. Some things, people do because they enjoy them, even if the activity doesn't make complete economic sense.

OK, you are right. I was focused in on "that’s a decade of $20 keyboards lasting a year each." BUT they didn't actually do that, which is good.

I've been moderately happy with Tecware Phantom series keyboards. Per-key RGB, socketed switches, etc for $40-$50 USD.

I'll never go back to membrane keyboards.

They are totally worth it. The cost is almost secondary to me, it's an excellent typing experience and it reduces reparative stress injury.

I have a rosewill that is made from cherry brown switches and apparently the minimum electronics to make it work reliably unlike the low end one OP wound up with. Probably cost me $80 six years ago but it works the same as it was new, and I expect to get a decade out of it no problem.

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