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SEAV LRX 2137 Garage door remote control system repair
My good friend Makis brought this remote control system to me with the complaint that the receiver part of it was not functioning at all.
This photo below is its internal view:
The small white cable you see is used as antenna for its radio receiver. This in turn works just below the UHF IV band of TV broadcasting, around 435MHz.
The radio receiver is the vertically mounted small PCB you see at the right side above and you can see it more detailed below:
In that violet color above, you see the receiver’s adjuster for frequency alignment with the transmitter’s signal.
Well, this was a relatively easy case of repair. First I performed some continuity tests to verify that the primary side of the small power transformer it uses is intact. This was O.K. The fuse test of the motor’s power supply was also intact.
Then I continued with its secondary winding circuitry. Now it’s time for you to see the back side of this PCB, below :
You will easily distinguish the places I worked on it. Anyway the area of interest is better shown below
First of all, there was no contact in one terminal of the full wave cylindrical rectifier with the relevant terminal of the power transformer due to a cut of the PCB foil trace because of electrolytic corrosion. This is the foil trace part starting from the missing pad of the bridge terminal which is bent over the PCB you see above, up to the transformer’s terminal. You can easily realize that the two secondaries of the transformer (the four vertically in line solder joints at the middle of the above photo) are connected in parallel. In the right side of the photo those two solder joints you see are the two terminals of its primary coil.
In order for me to solder the terminal of the bridge at the point of the missing pad and secure a reliable contact of it with the foil trace left, I had to bend it over the (slightly scrapped and tinned) PCB and then solder it. If you notice, with this joint as a reference point, along with the rest three of them, starting from this bent one and counting clockwise, form the four corners of an imaginary rectangular surface. Actually these four joints, being in absolute symmetry to each other, are the solder joints of the rectifier bridge. The original bridge was replaced because just above the solder joint of this bent terminal, its terminal was completely “eaten up” because of the aforesaid corrosion. (What you see above is the terminal of the replacement bridge).
Moreover the color appearance of this part of the PCB foil trace was almost black, revealing in this way its problem. The trace shown on the top left side of the above photo was in the same condition as well.
In order for me to stop the corrosion from any further development, I removed all the components mounted on the top side of this area, namely the defective bridge first and the two filter el-caps and then I cleaned thoroughly the area with cleaner spray. I also removed the power transformer in order to check the extent this corrosion was developed.
I had another surprise with it as well. Its terminal you see above connected to the bent over terminal of the bridge was also “eaten up” from that corrosion. The terminal you see in the picture is of a little bit thinner diameter than all the others, just because this one is a part of wire terminal of a small resistor which I used there by soldering it at the base of the original terminal, after scraping again the resin material at the transformer’s base, around the remainder of that missing terminal. But I was so absorbed with this work (again!) that I forgot to take a relevant picture for you!
Finally by scraping this foil trace as well and applying a fresh coating of tin on it and after having cleaned the bases of the components I had removed and after their reinstallation, the unit became shiny in view and operational in function as it originally was right after its production.
When I powered the unit the little red led showing the programming status was flashing normally, the unit accepted its programming through its transmitter part and a final operational test I performed using two incandescent lamps, one for the “door open” order and one for the “door close” order, was positive too.
Normally I should use a single phase motor with two windings having one common terminal. This is the normal wiring for an a.c motor that can perform clockwise and counterclockwise rotation. The relevant connection is performed through the two relays shown at the components’ side picture of the PCB.
When we need the “open” function, one of them is energized connecting one of the end terminals of the motor with the phase supply, while the middle (or common) terminal remains always connected to the neutral line terminal of the power supply.
When the “close” function is needed, then the second relay is energized connecting the other end terminal of the motor with the phase of the utility. Then the motor spins in the reverse direction.
So I performed this test with two separate 40W incandescent lamps which I use for test purposes, connected in series, and using their common connection as the motor’s common. The rest two ends were representing (along with their relevant lamp) the rotation direction of the (simulated) motor.
Below you can see the front and back views of the tiny transmitter.
I hope you enjoyed this repair case despite the apparently easy to find cause of this failure.
This article was prepared for you by Paris Azis from Athens-Greece. He is 59 years old and has more than 30 years’ experience in electronics repairs, both in consumer and industrial electronics. He started as a hobbyist at the age of 12 years and ended his professional carrier as a senior electronics technician. He has been a specialist in the entire range of consumer electronics repairs (: valve radio and BW TV receivers, transistorized color CRT TV, audio amps, reel and cassette tape recorders, telephone answering and telefax devices, electric irons, MW cooking devices e.t.c) working in his early stages at the official service departments of National-Panasonic first and JVC afterwards, at their premises in Athens.
Then he joined the telecoms industry, working for 20 years as field supporting technician in the sector of DMRs (: Digital Microwave Radio transmission stations), ending his carrier with this subject. Now he is a hobbyist again!
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Note: You can check out his previous repair article below: