car remote draing battery 20uA - Page 1
Forum section: electronics / repair

author: boo9
author_rank: Contributor
timestamp: August 26, 2014, 05:31:55 pm
content: I have put week or so new battery and it stopped working, no LED after press, works after putting new battery in.I checked and the remote is using 20uA when not pressed.With battery removed, I have 15K resistance on battery terminals.C1 (upper right corner) shows aroud 20K resistance.Is C1 kaput ?What should be the value for C1 ? 90nF ?

author: wraper
author_rank: Unknown
timestamp: August 26, 2014, 06:26:00 pm
content: Is that battery CR2032? Considering 220 mA/h capacity, with 20uA current it will last more than 400 days. Even if it have 10x lower capacity, it would last much longer than a week.

author: SeanB
author_rank: Super Contributor
timestamp: August 26, 2014, 06:35:48 pm
content: I would go for any value from 1uF to 47uF ceramic 16/ 25V capacitor there, whatever you have in that size or with that spacing that will physically fit in the space. Scrub the board with IPA and dry thoroughly as well, to get rid of the fluc residues. Check the switches are not leaking as well. The higher value cap will help prolong battery life as it will better decouple the supply as the battery ages.It likely is the capacitor leaking, and as many of these remotes use a CR2016 to save thickness they often do not have much spare capacity to begin with. A CR2032 works better, but might be too thick.

author: boo9
author_rank: Contributor
timestamp: August 26, 2014, 07:01:32 pm
content: CR2032 it is.54uA (micro) shows now. with my $5 meterThe reason I suspect C1 leak because couple weeks ago I had garage door remote with a leaking cap but then the LED was lit up slighly all the time, the cap at the bottom, I replaced it with 90nF and problem (LED lit) went away. Should I be replacing the 90nF with something larger ?

author: SeanB
author_rank: Super Contributor
timestamp: August 26, 2014, 07:31:05 pm
content: 100n, 220n or 470n that will fit, with a 50v rating will work there. it is there for bypassing, not anything else, and in this application the exact value is not critical. I have added 10uF 25V tantalums in some to get better battery life, they work till the battery gets totally flat and no longer has an open circuit voltage above 5V.

author: boo9
author_rank: Contributor
timestamp: August 26, 2014, 08:03:08 pm
content: > I have added 10uF 25V tantalums in some to get better battery life,these would be THT not SMD, would they not ?and why higher caps would prolong battery life ? Me thinks that if the circuit needs x Watt to function then no tricks will make it work with x/2 energy.

author: tautech
author_rank: Super Contributor
timestamp: August 26, 2014, 08:42:46 pm
content: I have recently fixed one that was doing similar.All components tested OK.This remote had never been right and owner was using the spare one.Found a "solder paste ball" of solder stuck to the overlay that was causing the current drain.It was tucked very close to a device and easily missed but should have been found with post manufacturing testing, no doubt there was none.Good magnification and a scalpel blade fixed it.

author: wagon
author_rank: Frequent Contributor
timestamp: August 27, 2014, 11:14:04 am
content: Remote controls get a fair bit of abuse and contaminants can build up on the pcb. As was mentioned, clean the device with IPA.

author: boo9
author_rank: Contributor
timestamp: August 27, 2014, 02:02:10 pm
content: No change after Cleaning with IPA.Door garage remote I fixed with transformer soldering iron, can I use transformer soldering iron on that C1 cap or wait till the proper ESD safe soldering iron arrives ?

author: David Hess
author_rank: Super Contributor
timestamp: August 27, 2014, 03:23:57 pm
content: Quote from: boo9 on August 26, 2014, 08:03:08 pmHigher voltage capacitors generally have lower leakage when used at low voltages.

author: wagon
author_rank: Frequent Contributor
timestamp: August 27, 2014, 08:49:31 pm
content: Quote from: boo9 on August 27, 2014, 02:02:10 pmJust change the cap with what you've got.

author: boo9
author_rank: Contributor
timestamp: August 28, 2014, 04:18:36 pm
content: I lifted the cap and with the cap removed I still have 20K on battery terminals. Cap measures open on 2000k range. Looks like cap is OK.As far as I know tHis remote is not only for car door but is has immobilizer inside, may be 20uA is normal for idle immobilizer circuit ?Anybody sees the immobilizer ciruciut on the pictures ?

author: SeanB
author_rank: Super Contributor
timestamp: August 28, 2014, 04:45:25 pm
content: Clean the board and then apply flux and resolder the MCU pins, then clean again with IPA and try to get the last of the flux out from under the MCU. That likely will cure the problem of the flux residue being slightly conductive.

author: jlmoon
author_rank: Unknown
timestamp: August 28, 2014, 04:49:17 pm
content: Quote from: boo9 on August 27, 2014, 02:02:10 pmIf you don't have a return path to Vdd for that battery powered remote, there is a very slim chance (like nill) you can ESD that device. I suspect the parts employed on that remote are not your typical ESD sensitive LSI parts anyway. Just remove the battery and solder until your hearts content!

author: boo9
author_rank: Contributor
timestamp: August 28, 2014, 04:53:18 pm
content: > MCUwhich one is the MCU ? marked IC1 or SAW1 ?should I lift the MCU then resolder o just reflow the joints ?> Clean the boardany suggestions how to clean the board properly ? I have flooded the board profusely with the IPA and brushed with toothbrush several times already.

author: David Hess
author_rank: Super Contributor
timestamp: August 28, 2014, 05:38:03 pm
content: Water with a little bit of dish soap will be better than IPA by itself.

author: SeanB
author_rank: Super Contributor
timestamp: August 28, 2014, 05:45:37 pm
content: IC1, you can remove it, clean it top and bottom along with the board and then resolder it. As well check the small transistor and the SAW resonator for flux residue. Dry the board thoroughly after scrubbing with the IPA, I use the top of a CRt Tv for ones at work, or just place it on a surface and aim a 12V PC fan at it for a hour or two.