Something the electrically minded may enjoy and related to cars because people sometimes actually use their garage to park cars… I believe people enjoyed some of my prior postings related to these kind of repairs so here goes-
Symptom- opener stopped working, just clicks once and no motion at all. Lights do not illuminate. Diagnostic LED flashing 5 times.
Background- User manual states 5 flashes is miscellaneous fault. If power cycle does not fix, then replace control board. Preliminary research shows same basic control board used for many different brands of opener.
Diagnosis- Removed control board. Visual inspection reveals one SMT SOT323 package device has back blown off. Reverse engineer entire circuit. Affected component is an NPN driver transistor for the light relay. There are three of the same circuits; one for light, one for motor up and one for motor down relays. Blown component is dragging down power supply for board.
Interesting detail- controller is PIC variant. Has custom part number but likely due to mask ROM programming. All other details match commercially available PIC controller.
Repair- Replace all three SMT transistors with general purpose 3904 NPN transistors (2x Ic rating). Opener now functions but will not close door due to error with safety reversing sensors.
This is where it gets more interesting. How do the sensors work?
I know they are infrared but is it more complicated than an emitter and detector?
Here’s a pic of the inside of the receiver module-
Here is the reverse engineered circuit-
The receiver IC is actually a small module designed to receive modulated data over infrared. It is not being used in that way however.
To provide an extra measure of safety in the design, a pulse of a specific frequency and duration is generated when the receiver detects the IR energy from the emitter.
D1 isolates the two sides of the circuit. As U1 output transistor conducts when it sees the IR, it causes Q2 to produce an output pulse that drives Q1 and crowbars the input voltage. This also turns on the LED to indicate the receiver is aligned with the emitter. Pulse train is low ~0.5ms and repeats at ~6ms rate.
The control board micro looks for the right pulse frequency from the safety sensors to ensure nothing is in the path of the closing door.
Q1 was damaged and not doing its job. Once replaced, it began working properly again.
If you decide to work on your own, be aware that you need a current limited supply. The control board has a 2W 200 ohm resistor feeding the sensors to limit the current when Q1 turns on. If not, you’ll burn it up in short order.
All of these failed transistors have connections to the supply side and most likely were damaged during some transient event- like a lightning storm. Strangely enough, I have three openers in close proximity and only one was fatally damaged.
Price for new control board and sensors- $110+
Actual cost of failed components- ~$0.25
Things learned- Pricele$$