Attempting to fix a garage door remote

Discussion in 'General Electronics Chat' started by veritas, Oct 26, 2008.

  1. veritas

    Thread Starter Active Member

    Feb 7, 2008
    I have two remotes for a Genie model 880 (ancient) garage door opener. The thing looks like it's from about 1970. Neither one of the remotes work reliably for opening the garage door, but both will work if I try a couple times, and I have only been able to get the door to close once with either of them (I just moved in a couple months ago, and before today I had only tried the remotes a couple times before today).

    I opened one of them up, hoping to find a dead battery or a loose button connection, only to find both of them fully functional. I did, however, notice that there appeared to be a resistor(?) missing on the PCB. I opened up the other remote, and found the same open connection, plus another resistor missing (R5)! I've been trying to debug the circuit with my cheapo DMM, but I don't have any other lab equipment handy on the weekend.

    Is anyone familiar with these types of garage door openers? I drew up a schematic of the PCB. R6 is the missing resistor, and R5 is missing on the second remote.
  2. veritas

    Thread Starter Active Member

    Feb 7, 2008
    BTW, I measured the voltages while holding the open/close button.

    *edit* I measured voltages of the pins of the IC to the battery's ground:
    pins 1-6 and 8: 9.22 V
    pin 7: 0V
    pin 9: 0V
    pin 10 (battery +): 9.3V
    pin 11: gnd
    pin 12: 4.55V
    pin 13: 6.27V
    pin 14: 6.14V
    pin 15: 4.78V
    pin 16: 9.3V

    Pins 1-8 are the dip switches for the remote code. I have no idea what the IC does though, and I can't find a datasheet online.
    The IC says for remote 1 says: 179 2628 049 ESSEX
    For remote 2: 7927BP 19039A ALLIANCE
    Last edited: Oct 27, 2008
  3. Wendy


    Mar 24, 2008
    I can't speak with authority towards you're design, but I did an analysis on a Stanley from the same era many orbits ago. The transistor is a simple RF oscillator, transmitter, keyed on by a 1 from the chip, which biases the transistor base. With no bias (a zero) the oscillator is disabled. This sets up the pulses.

    The actual modulation scheme is 10 of 16 bits are encoded either 25% or 75% duty cycles, a 0 or a 1 respectively. The remaining 6 bits are dead, used to set up the framing. I suspect they both use the same chippie, but can't prove it.

    The transmit freq was 301Mhz, with is major out of favor because it conflicts with military. I remember hearing about a SAC base whose transmitters drove a lot of local residents nuts, wanna guess who had to change? I believe they worked with the folks to get the problems resolved amicably, since (I think) the garage doors were using the channel before SAC was.
  4. veritas

    Thread Starter Active Member

    Feb 7, 2008
    Interesting, I will have to take one of my PCB's into a proper lab sometime and see what they're spitting out. I have still had zero luck finding anything else out about the IC or transistor elsewhere on the internet, but I will have to see if your descriptions are similar to what I end up finding.

    I fear I will not have any way to identify either what the problem is or what resistor/component I should insert in the open socket without a significant amount of time with an oscilliscope. Luckily, I'm still a student for another couple months (and after that I won't have access to the garage door anyway :) )

    I did end up finding a sticker on the back of the second remote, which I failed to look at last night. The remote is a Genie Model AT-79, and it says the frequency is "325"; I'm assuming MHz.
  5. floomdoggle

    Senior Member

    Sep 1, 2008
    Hi! I,m just a handyman, but I have found that if the remote works at all, the problem is usually in the receiver. Particularly the antenna.
  6. veritas

    Thread Starter Active Member

    Feb 7, 2008
    Thanks for the suggestion. That thought had crossed my mind; I I'll have to look into it.
  7. pups91360

    New Member

    Nov 28, 2008
    Veritas, I am wondering if you solved your problem. I also have this old Genie system and use 3 remotes. They are the same 325mhz units using the same parts you sketched. One of my remotes recently quit and I also am searching for a replacement part or remote. Have you had any luck?