Help needed with basic A/C IR remote

I’ve been doing a lot of learning with troubleshooting Nintendo Switch (all models) and as much as I’ve learned, I still haven’t learned enough to successfully diagnose this ultra-basic remote control I have that only works at exactly 3V. I have no idea why either. I found the data sheet for the main IC and it says it can run between 1.8V-3.6V.

The remote only works at exactly 3V - if I drop it any lower, using my bench power supply, to say, 2.9V then the remote will not flash the display and turn off.

SMD chip: HB8514F ( 8-Bit Micro-Controller with 116 dots LCD driver and IAP function)

I’ve done the following so far:

  • replaced the E1 capacitor as it did not read the proper value (16V, 42uF)
  • verified the Y1 crystal is reading properly - it is
  • removed and tested all SMD resistors and capacitors
  • replaced all 0 ohm resistors with jumper wire

There were two 0805 white smds, with no resistance, no capacitance, and no continuity - so my best guess is that these are blown smd fuses. Doesn’t make sense though, since they’re marked as what would normally be a capacitor since they were located at C2 and C3.

J2 was empty from the start.

Could the problem be missing capacitors for the C2 and C3 spots on the legs of the crystal oscillator? Would that cause a problem with lower voltage?

Adafruit says this crystal oscillator doesn’t normally need capacitors, but there was something there originally which is why I’m wondering if this is the missing piece.

I measured the voltage going through C2 and C3 and it’s:
C2: 0.945V
C3: 1.403V

I have a lot of spare SMD caps to choose from - but I have no idea what would be appropriate to use here.

To save anyone a wild goose chase, the IC is actually HB8513F

datasheet HB8513F_HBG(浩博高)(HBG(浩博高)) 中文资料_价格_PDF手册-iCEasy商城

Datasheet calls for 20pF for these in their application circuit, though this remote controller use case could be a fair bit different to that provided in the datasheets typical application circuit (strange IC for them to opt for…)

You sure your meter is capable of reading these values?

Was there a particular reason for doing this? were the original ones open?

It’s possible, if the crystal is for the CPU and it’s not operating properly then maybe it’s causing issues downstream.

What about the voltage at the IR diode? could be faulty or maybe an old diode not getting a high enough voltage to operate as a result or could be it’s just not being supplied a high enough voltage, maybe for other reasons

Alright - first of all - thank you. I’ve been learning so much from you in the other post I didn’t think you’d be coming to my rescue here too!

That’s the same datasheet I was looking at prior to posting and I didn’t see anything about 20pF anywhere. If you don’t mind my asking, where did you find this info in the sheet so I can know what I missed. I even searched for “20” and “pF” and didn’t find anything relevant.

Desperation and having run out of ideas. I got this air conditioner w/remote and was told the remote never worked reliably. I figured it’d be a good learning experience and opened it up a little while back and am just now getting back to it.

Well, no, not even close. I now know why I couldn’t read them at all though in any setting, so that’s helpful…and another lesson learned.

I’m not sure how to tell if it’s faulty other than using it normally. With 3V in the remote the IR diode blasts across the room normally from what I can tell.

I should add that the behavior is identical to how it was before I removed C2 & C3 - which is partially why I suspected they were bad. I was removing the resistors and capacitors to test them off of the board and put the regular capacitors back. The ones I couldn’t get a read on I thought were bad and left off.

If you scroll to the bottom, page 26 , you’ll find the “Application Circuit” with an example schematic

I mean it might be able to but some lower end meters might not be able to or they might auto range (if applicable) it in a stange way that it appears the value is virtually nothing

You can supply voltage to the remote via the battery terminals and then measure the voltage at the IR LED , you can then use your phone camera over the IR LED while pushing a button on the remote to see if it’s illuminating, adjust the voltage on your supply down in increments. The potential issue here though, is if they’re using a comlpex/fast protocol your meter may not pick up the voltage even if your meter has peak mode. So maybe just easier to remove the LED, set a current limit of 20mA (you’ll have to double check this though for what typica max current is on an IR led of the size you’ve got) and a voltage 3V (again, double check this prior as I forget for IR diodes) then adjustr supply voltage down and see at what point the IR LED stops illuminating on your phone screen , if for example it cuts out below 3V then that may be the potential issue (assuming the board is driving the LED at battery voltage ordinarily) and you’d assume you might have a weak LED diode maybe.

It might well be the case they were bad, though it’d be rare for ceramic caps to fail open essentially and for both to do so.

Can you take a photo of he otherside of the board too?

also, you also have the very real possibility the issue lies at the receiver end (air conditioner), which it’s far more common for IR receivers to wear out than the transmitters but we’ll see what your results lead to.

a scope would be handy here,though not essential :slight_smile:

btw my thinking in the previous post is, if the IR LED (transmitter) is worn out, and now requires 3V to even illumintate (assuming it’s being driven at battery voltage) as seen on your phone cam, then, the moment battery voltage drops below this it cuts out (assuming 3.XV coin cell?) in which case it wouldn’t work for long. In which case you could look at getting a new IR LED which operates at a lower voltage and works over an increased range of the battery life cycle

Happy Friday. Here are my findings.

Also, to clarify, the experienced issue with the remote is not inconsistency in commands being received by the unit, but that the remote completely turns off a second or two after powering the remote on. If the voltage is anything less than exactly 3.0V (just confirmed at 2.99V the issue is still present), the remote turns off 1 second after turning on. At 3.0V though, the remote will stay on and function normally.

I removed the LED to test with and it was nice and bright from 1.2V to 3V @ 20mA so I think the LED is good. For fun, I tried to power on the remote with the LED removed and the behavior was the same.

The other side of the board is pretty bare, but here it is:

Here’s what the front looks like with the casing:

2x AAA batteries

Thank you so much. Don’t know how I missed that but I see I couldn’t search it because it’s a non-OCR image.

Absolutely, and you :+1:

Ah I see now, this IC makes a lot more sense for an IR remote with the display in your image

hmm, instead of going directly on the battery terminals have you tried powering the IC directly on it’s VIN pin incase there is external issues, you could even discoonect the display too, shouldn’t affect anything and you should still be able to see the IR LED on your phone cam for verification.

Given there is no obvious shorts or opens, outside of that, the only thing which could be wrong would be the IC itself that I can think of.

Yeah seems fine

Whats the current draw when connected up to the battery terminals on your bench supply? might indicate excessive draw because of failed chip, should be virtually nothing, definately less than a few mA

and just to clarify, screen goes off below 3V right? and the IR/buttons don’t work also right? just wanna rule out the display. they also, when they age degrade in contrast over time and require a higher voltage to compensate so just ruling out

Sure seems like it might be the IC at this point. Without the display I don’t get any IR flashes at 2.99V but at 3.0V I do.

Whatever it is, it’s small enough that it doesn’t register on my power supply.

Yes, that’s correct. Whole remote is unresponsive below 3V.

yeah IC best guess unfortunately, not sure if there is a pin compatiable IC these days… even then you’d need the rom…

Maybe a workaround is in order to boost the supplied VIN so it lasts for the battery duration :thinking: leave it with me and I’ll come back to you for a botch job to do this with basic components (unless you’ve got regs on hand?)

I love botch jobs. hahaha. I was just thinking and even started writing out, "what if I added an extra battery or used a higher volt battery pack instead and bucked it down to 3V?

:+1:

Something like this would work

Just set the output to the upper IC max and it will maintain it. This particular one may be a touch bulky because of the variable resistor but just set it, measure it, the remove it and swap it out for fixed resistors and it should fit in the case no worries, or try and find an smd variant.

All you’ll have to do is cut the trace for the battery in betwwen it and the IC Vin and add this :slight_smile: workarond should be achieved

There are other ways to deal with this using simpler components but when all is said and done this is simpler and likely more efficient

Looks like a great solution to this problem. Thanks for working through it all with me! Can’t tell you how much I appreciate your patient guidance.

no worries :+1:

There should be smaller modules availiable as you require basically zero current, if you can find a smaller alt module lemme know and I’ll take a look

Check this out. It’s super small and has a fixed output of 3.3V. I’m thinking if I used something like this I could just fit it in the remote shell and use regular AAA batteries.

pololu . com/product/2563

or this one, cheap and easy on eBay:
ebay . com/itm/295942859305

both would be fine, though the efficiancy is quite low for both, though, you may compensate for this given their input voltage go lower (make more use of your batteries)

First one might be better as graph suggests efficiency is better the higher the input voltage is, so you might net closer to 90% with two AAA