Garage door opener

How old is the unit? I have a couple schematics - but - I think they're for "much" older units. On the other side of the coin - nothing like "customer service" - but then again "job security"........ take your pick!

Age and model number of the opener? Sears has sold a variety of them over time...

I have employed a garage opener for a wireless job as a 14 bit transmitter/receiver set. I have used google to find docs and application notes on the parr/serial/parr. chips on the boards. Also a scope can tell you much about the operation of the unit. In the end I used a serial/parr. shift register to decode the serial stream from the receiver. As it received a total of 42 bits, I used a comparator on about 15 of the steady state bits, to test for integrity of the data. If you have a pic of the transmitter unit,(post on a.b.s.electr, or you might delouse my email adress,figures in the first part,after @ no double letters) I might see if I recognise it, it had a rather stange shape.Also indicate what you want to do to(with) it.

This opener is probably in the neighborhood of fifteen years old.

This opener is about 15 years old. The number on the printed circuit board is 14PC366B. Will have to get out the ladder again to get the Craftsman model number. I'll get back with you.

I've found that 70% of the people who say "It's proprietary" simply don't know.

Chamberlain has some real technicians who can sometimes be reached if you ask a specific enough question, and I was once able to speak to one by getting technical enough about a safety defect. But I doubt they'll give you a schematic, and instead you'll have to trace out the pins from the processor (probably Zilog or Microchip) to the relays. Most of the failures tend to be from cracked solder joints (motor vibration), a bad motor capacitor, leaky electrolytic capacitors, burnt relay contacts (if you can't find new relays that fit, try substituting the overhead lamp relay for one of the motor relays), or shorted relay driver transistors and the diodes meant to protect them from relay coil back EMF. Usually the back EMF won't damage the processor or control circuitry. If your Sears/Chamberlain is like the one I bought in the early 1990s and has 2 circuit boards, I wouldn't be surprised if the pins that connect them together (like square wire wrap pins) have corroded. If your door will open but not close, check for the wires being broken right where they enter the optical receiver and sender boxes. Also, just becuase the indicator light for them shines steadily doesn't mean they're aligned well enough.

I'd check the remote circuit anyway since there's a trace from it with a logic signal to indicate when the remote has been activated. If it blips when you press the button, very likely the power circuitry is OK.

"Silver Surfer" wrote in news:MJmdnRisCIJtNoDYnZ2dnUVZ snipped-for-privacy@comcast.com:

Quite often the problem is dirty contacts on the relay. Cleaning them with light emery paper usually has worked for me...

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You've given me some good ideas on things to check. Thanks for your interest in my problem.

Some observations:

The 110V incandescent bulb stays lit all the time. The board uses three Omron 24V relays to do its thing. One of them is an open type, and its contacts are in good shape. On the bench I can't hear any relays operate when shorting the up/down button terminals. I don't see any suspicious looking solder joints. Don't see any burned up or darkened components. Don't see any cracked or melted circuit board traces. This opener has no optical safety sensors. There is a 16-pin integrated circuit on the board made by TI. Cannot find the number anywhere on the Web. Called TI. They could not identify it either and concluded that it was an ASIC.

More questions:

What effect on the circuitry does the optical speed sensor on the motor shaft have? Does its output need faked with the main board on the bench for troubleshooting? How do the up and down force limiters work?

The revolution counter board (optical speed sensor) is a timing circuit. The pulses are sent from the counter board to the main logic board at a uniform rate. So when the door meets an obstruction the motor slows down, which changes the timing of the pulses & this tells the opener to stop if the door while opening or stop & reverse while closing.

So the force limiters set how much the motor has to slow down before the opener will react to the change in the timing.

If the counter board is bad or not hooked up the opener will run for exactly 4" in & then stop or stop & reverse back for 4". So for bench testing the relays should still pull in even though the counter board isn't connected.

There is 3 relays on the board, one is for open, one is for close, & the third is for the light. As soon as the opener is plugged in the light should come on & then time out & shut off. If it stays on all the time it sounds like the light relay contacts have fused together. If the open & close relays won't pull in, then either the coils in the relays are bad, or they are getting power. Check for incoming power to the relays & trace backwards if they aren't getting power.

DoorDoc

You've given me a wealth of knowledge on this subject. I am grateful. Heading for the bench . . .

Mr. Doordoc,

The light relay contacts are not welded. The relay simply picks up as soon as power is applied and stays picked up from that point.

The up and down relays will operate if I momentarily fake a signal to the base of the transistors that drive them.

Shorting the up/down switch terminals makes nothing happen whatsoever.

Just how exotic is that proprietary IC on this board, the 16-pin one? There is another proprietary chip that has only 8 pins. Not sure of its function.

I'm thinking that the IC is bad or else a critical input it needs is not present. What do you think?