Anyone know what this is? - Page 1
Forum section: electronics / beginners

author: mommus
author_rank: Newbie
timestamp: September 23, 2020, 07:20:42 pm
content: My central heating is operated by remote control, and the dongers who fitted the boiler didn't install a cutoff switch, so the remote has obviously gone tits up and we have no way of turning the bloody heating off.The remote turns on ok, but keeps flashing every 30 secs or so and every time it does it resets to midday 1st Jan 2009 (who knows why, it was made in 2013)So I took the remote to bits and it looks like a component has blown or at least corroded to bits, but it has no markings to allow me to order another. I'm not really sure what it is and wondered if anyone here can help. It's surface mounted, with the only contacts on the face of the board, not thru it.My guess was a capacitor of some kind, which might explain why the remote can't remember anything. It's 4.75mm in diameterhttps://ibb.co/PMxx4Zyhttps://ibb.co/bWf73DpThanks in advance for any ideasEdit: couldn't embed the images for some reason

author: ledtester
author_rank: Super Contributor
timestamp: September 23, 2020, 07:34:54 pm
content: My guess is that it is a battery. Just a guess though.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 23, 2020, 07:35:58 pm
content: I would say that's a coin-cell. From the provided diameter that would be a SR416. That remote is a wall mounted remote?That battery is probably used to keep the time while power loss.Before replacement you should clean the mess to prevent further corrosion.

author: mommus
author_rank: Newbie
timestamp: September 23, 2020, 07:44:15 pm
content: ah I seethanks guysIf its an LR41 does that mean it should slip in and out of its contacts? Those three little hot marks look welded (or is that just how they come?)Also, the unit has 4 AAs in it (which I replaced) if that makes any difference

author: Manul
author_rank: Super Contributor
timestamp: September 23, 2020, 07:45:06 pm
content: I think it is more likely a supercapacitor based on leakage color. But thats just a guess. Does your remote have batteries?

author: mommus
author_rank: Newbie
timestamp: September 23, 2020, 07:49:24 pm
content: Quote from: Manul on September 23, 2020, 07:45:06 pmYes - 4 double A 1.5v batteries.I had thought it might be a supercap as they seem to have the same blade-type contacts on the top with the little weld marks.Also, try as I may, I can't get the thing out of the contacts, which yesterday made me thing it might not be a battery.Maybe the inescapable heat is affecting my judgement.

author: Manul
author_rank: Super Contributor
timestamp: September 23, 2020, 07:54:10 pm
content: It is spot welded contacts, both batteries and supercaps may have them. You need to desolder the whole thing from PCB.If your remote also has 4 AA batteries, then this one I would say is 90% supercap and not a battery.

author: Manul
author_rank: Super Contributor
timestamp: September 23, 2020, 08:08:00 pm
content: I would say it is very likely that if you remove that thing and clean PCB from leaked acid it will work just fine without it. It is probably just to keep memory while main batteries are being changed, which is not often I suppose.

author: george.b
author_rank: Frequent Contributor
timestamp: September 23, 2020, 08:08:09 pm
content: Quote from: Manul on September 23, 2020, 07:45:06 pmAgreed.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 23, 2020, 08:10:24 pm
content: Quote from: Manul on September 23, 2020, 07:45:06 pmGood point! As the picture of the remote shows also welding points in the metal strip. I missed them in my first post. It could also be a rechargeable cell. But I don't know if such small cells are available (4.75mm diameter) and the yellowish color don't match with leaking NiCD/NiMH (usually white crystals). So a supercap is a good guess.After de-solder you might measure if there's any voltage at the pins (with the batteries inserted). If you measure any voltage < 2.3V (I think that's the max voltage for single cell supercaps) then it's a good chance that this is supposed to be a supercap.

author: Gyro
author_rank: Super Contributor
timestamp: September 23, 2020, 08:19:09 pm
content: Note that there is a parallel empty footprint next to it. You would tend to parallel capacitors for greater capacity but not battery cells (actually, on second look, it is larger). It will be useful for rework though.

author: Skashkash
author_rank: Regular Contributor
timestamp: September 23, 2020, 08:59:14 pm
content: Kinda looks like a Seiko XH311HG super-cap. I just placed one on a pcb a few weeks ago.You don't usually see them leak like that.

author: george.b
author_rank: Frequent Contributor
timestamp: September 23, 2020, 09:02:58 pm
content: Quote from: Skashkash on September 23, 2020, 08:59:14 pmI've seen similar supercapacitor leakage on an HP Omnibook main board. Can't remember which brand, but same form factor.

author: mommus
author_rank: Newbie
timestamp: September 23, 2020, 09:27:48 pm
content: thanks for all the guidance everyoneI'll try desoldering it first and see if the thing chooches.

author: mommus
author_rank: Newbie
timestamp: September 24, 2020, 09:32:39 am
content: So I got the offending component off, but it seems to have made no difference. I'm at a loss to work out why.I can't see any other obvious signs of nastiness on the board:https://ibb.co/68rPY9rhttps://ibb.co/vDY5jkbSame problem in that the unit turns on and displays correctly, even operates correctly, but stays on for a max of 20 seconds before flashing off and on again, so the clock on the screen always displays 12:00Is there a IC issue that could cause this? Do they ever even go wrong on consumer electronics like this?

author: mommus
author_rank: Newbie
timestamp: September 24, 2020, 09:38:37 am
content: ...so if you put the unit back together, but don't screw it up (with the one screw it has) not only does it work, but it seems to have remembered the correct time and date (despite having removed the mystery component)Which begs the question - what exactly was the mystery component's job?!?

author: mikerj
author_rank: Super Contributor
timestamp: September 24, 2020, 09:54:00 am
content: It looks like the supercap is charged from the output of dc-dc converter. It's possible the converter only runs when the micro comes out of a sleep state, in which case perhaps the supercap is required for normal operation. Can you use a DMM measure the voltage across the supercap pads (at least the remaining ones...) whilst the unit is operating and see if it the malfunction coincides with the voltage dropping?

author: mommus
author_rank: Newbie
timestamp: September 24, 2020, 11:22:15 am
content: I've noticed that despite the correct date and time appearing when I turned it back on, the time has not moved on - it's stuck on the time when I put the batteries back in.So I wonder whether the supercap was something to do with communicating with the boiler to be sent the correct time - ie there's no clock in the remote and it needs to be updated from the controller on the boiler... or something.A less stingy man than myself would just buy a new remote for £100

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 24, 2020, 11:43:24 am
content: Do you have any capacitor (e.g. 10µF or something bigger) at hand? It could be possible that the clock in the µC depends on the cap.The µC seems to have a watch crystal connected (the small metal tube looks like the usual 32kHz crystal).

author: Manul
author_rank: Super Contributor
timestamp: September 24, 2020, 03:02:14 pm
content: Quote from: mommus on September 24, 2020, 09:38:37 amWell, maybe it is your clue. I do not know how it is build so can not comment, but look and think logically. If there is no other difference, just screws, maybe it says, that some solder joint is bad. And if PCB is not micro flexed by a screw, it makes stable contact. I would try to get it working stabely, then try to flex the PCB gently and hopefully reproduce a failure.

author: mommus
author_rank: Newbie
timestamp: September 25, 2020, 04:00:50 pm
content: I think I broke it more trying to fix it.Bought an new one instead.Thanks for the advice all the same everyone.