My garage door opener (Chamberlain Liftmaster pro 3280/3280-267) has been working fine up until I had my house and garage door painted (yeah I know that sounds odd).
Before the house was painted I could open the door from about 60 feet away with the 373LM remote, and about 100 feet with my Subaru homelink.
Now I have trouble getting the homelink to work at all, and the 373LM will sometimes work about 40 to 50 feet, and sometimes I have to get about 25 feet from the opener.
What I have tried:
new batteries in remotes.
running coax to an antenna outside the garage.
checking the openers circuit board for cold solder joints. re-soldering some even though they looked fine.
extending the antenna on the unit to a full wave length. removing the outside antenna I had installed earlier.
checked for interference on 315mhz (there is none) I have an SDR radio so I can look at a large chunk of the spectrum. nothing transmits within 1mhz of 315mhz (or really at all near me).
Replaced my LED bulbs with incandescent.
re-calibrating my remote. it was off frequency by 500khz. same for my wife's (hers is having similar issues).
purchased a Chamberlain 953EV-P2 which is supposed to work up to 1500 feet (it seems to work no better than the old remote). it is off frequency by 10khz (which is within spec).
I do not want to use a phone app to control the door as that is clunky.
One morning I had an appointment and took my portable SDR with me. I seem to be chasing multiple issues. while monitoring the SDR when I pulled out of the garage I tried to close the door with my subaru homelink which would not work I found that the homelink signal was very strong, distorted, and wandering all over the spectrum.
my old 373LM remote seemed to be dead (no signal on SDR).
the new remote worked fine to close the door.
After that I decided to do more checking for interference on 315mhz.
I didn't really see anything until I turned the gain and amplification all the way up on my SDR. the background noise level (per my sdr with all amplification off) is -85dbfs.
You can just make out a slight "throbbing" of about 1hz in the background noise that turns in to a hump from 308mhz to 327mhz when amplification is turned all the way up. I highly doubt this is causing a problem as it isn't even measurable normally. though I am intrigued as to what it might be. there is a military base 12 miles away, though I can't really pickup any radio activity from my house from there.
on another day I left the house to visit someone and had trouble closing the door and had to resort to using my alarm app. when I came home 7 hours later I was able to open the door from a reasonable distance with the newest remote.
I reprogrammed my homelink and had a lot of trouble getting it to accept the signal.
Drove home one day and could not get the door to open with any of the remotes at all. had to open with my app. I do not like using the apps because it way more involved than just pressing a button.
I found that what I thought was as dead battery in my 373LM was a cold solder joint on the main chip on the circuit board. The signal on the 373lm is all over the place but mostly within spec though sometimes will wander off by as much as 500khz. just to see if it would help I replaced the 4.7uf electrolytic with a new on which made no difference.
Pulled the main board in the opener this morning, found 3 electrolytic capacitors with high ESR. several that tested fine but I replaced anyways. there was one loose trace to one of the capacitors, don't know if I broke it or it was always like that.
Checked the cap on the power supply, it had a low ESR (which is good) I left it in since I did not have a replacement of that voltage. Resoldered anything that look suspicious under my video microscope.
I removed the original antenna and added a short coax lead going to a BNC connector so I can easily experiment with different antennas. yes there is strain relief. Antenna is half wave.
tested range and there seems to be a slight increase but I will have to test from the car at a later date.
Here are some things I found while working on this:
The older remotes use a tuning capacitor to align the signal. not 100% sure about this but it appears that they may tune the wide button at 315.5mhz instead of right on 315mhz as the Chamberlain FCC paperwork indicated. The FCC papers say that it is supposed to be 315mhz +/- .1% or 315khz FCC tolerance is .25%. if you want to find the paperwork google the FCC id and fcc the ID is on the back of the remotes. it's a somewhat technical read.
so the 3 buttons seem to be on slightly different frequencies. at least that is what it looks like on the spectrum from my SDR. If the wide button is on 315mhz then the other 2 will be at a slightly lower frequency separated by 100 or 200khz. This is true for the 953EV-P2, though this unit seems to be self tuning as there is no adjustments. all the remotes I tried have a signal that wanders, though the opener does not seem to care.
on my board there was a space on the circuit board for attaching a coax connector. I did not have one that was of the design but it is nice to know.
I have had a chance to test the remotes since working on the main board in the opener.
I was still having problems with the handheld remotes but my homelink in my car was back to normal after the opener re-learned it. it could open the door from about 50 feet away (which is about what it did before. Sometimes (before all this) it would work from 75 to 100 feet away in certain instances.
however mine and my wife's 373LM and my 953EV-P2 would still not work unless they were less than 20 feet from the opener (with the door closed).
I re-learned all the handheld remotes (before going somewhere) and coming back to the house my 373LM worked from about 50 feet away. I had not tested the other ones yet.
I suspect that with the failing capacitors and maybe something else I am not aware of it is possible that the memory on the opener got corrupted.
upon testing all the remote everything seems to be back to normal. so it appears it was multiple issues:
bad capacitors on opener PCB.
possibly corrupt memory in opener.
possible cold solder joints in 1 or more remotes and PCB of opener.
Don't try to calibrate the remotes. without proper equipment you can put them way off frequency or they will not transmit at all. a tiny microscopic movement of the adjustment will put the signal WAY off. Do not make any adjustments to the tuning slug on the opener PCB (metal can with hole in the top).
I was still not getting the range I wanted so I added an antenna connected by coax to the opener, the antenna was 36" long and put between the 2 garage doors. now I can open the door with my car homelink from the neighbors house in front of their garage.
