Liftmaste/ Chamberlain PD612EV Problems

[timmy tyler]

Hi All:

I am hoping someone can help this 60 year old frustrated geezer. I am having issues with a new Liftmaster/Chamberlain PD612EV 1/2HP opener that I offered to help install for a friend. This was a replacement opener for a older failed Craftsman unit. Torsion spring is mildy un-balanced, and the door wants to be in the down position. The down force from the un-balanced spring is very low, and the door does not "slam" closed by itself. The new opener (purchased Feb 2015 from Home Depot) has all electronic (microprocessor controlled) limit settings and automatically adjusting force sensing. 1 week after install (and operating normally) the opener went nuts and started ignoring the previously programmed limit settings. It also quit measuring force because the trolley would hit the mechanical stops at both extremes and would not back up or stop the motor until the motors thermal breaker opened! Excess cable tension placed on the idler pulley near the header caused it to crack at the center of it's hub. The trolley rail was under such extreme tension that it bowed severely to one side. I had a time just getting the chain off the sprocket because of the extreme tension at the sprocket itself The chain side tension was slack, but the tension on the cable side of the sprocket was way, way beyond normal.

Called the manufacturer and the Chamberlain support person felt that the logic board had failed. This was a very dangerous failure mode to say the least since the motor would not reverse. We have since received and replaced the logic board and installed a new idler pulley. Per customer support, removed chain off sprocket & re-installed chain with door down and resting on concrete with trolley dis-engaged. Tensioned chain to 1/4" above rail per all instructions per manual and customer support.

Limits programmed flawlessly with new board. Door stops perfectly BEFORE reaching both mechanical stop limits....just as it should. Here is the NEW problem which I can't quite wrap my head around (nor can customer support). After cycling the door up down a couple of times, the chain becomes slack again (door closed position) and the tension on the cable side of the sprocket goes back up to very tight. What is happening here? Re-adjusting the chain tension again to correct the chain slack is not the answer. Doing that eventually causes the trolley rail to bow due to the steel cable tension increasing way beyond normal, while the chain side of the sprocket gets more slack.

I know there is a good reason for this happening and Sir Isaac Newton would have the answer certainly. I have a basic knowledge of physics but I can't see big the picture here so I am kindly asking for some advice if anyone has seen a similar situation before. Customer support is now sending out a new free chain at their advice, but I honestly don't see how that is the answer. I have never seen one fail, short of stretching over a normal working life span. Can anyone shed any light on this what's going on here?

[TJR]

That's a great opener, good product from Chamberlain that I see little to no problems with.
In the prefect world with everything adjusted and assembled correct, when the door is closed with the opener you will have a little slack in the chain and a little tighter cable as the door is lightly forced into the floor. You can pull the emergency release to disconnect the opener and the chain will be as per the manual.

[timmy tyler]

Thanks for your reply TJR. I could not get customer support to tell me how much slack in the chain is considered normal after cycling the door. The chain is drooping about 2-3 inches below the rail after. I am pretty sure that is too much and I am going to try to remove some of that by another re-adjustment as the manual suggests.....then cycling again.

My own opener (an older but similar Craftsman with mechanical limits) does not have near the slack in the chain as this new unit. The manual does mention that the chain will slacken some after initial tensioning, but I guess I was a bit alarmed at just how much slack I was seeing.

The whole incident with the failure of the logic board kind of through me into a tailspin. If you work with these things then you may have seen a bowed rail along with a chain "locked" onto a sprocket. Quite a dangerous situation for the unsuspecting person. I too have read the reviews on this opener, and as you suggest they are almost all very good. I did find one other report of a failure like this one. Everything is so dependent on the microprocessor now and my first thought was that this being a new design (electronic limits & force sense) that the manufacturer might have had a bad run of chips or a design flaw....which isn't unheard of in the electronics world.

I stepped back from the situation, had a cold beer, read your comment, and calmly reflected. I think I am probably OK now. I will re-tension one more time, cycle it, and it should be OK. As a side note, I just viewed a number of You tube videos of these chain driven openers, and it was a eye opener for me just how much slack in the chain many of them had and still were operating without the chain drifting off the sprocket. One of the videos was narrated by a professional in the business, and he did not seem concerned at all by all that droop! It would be nice if the manufacturer would be a little more clear on this subject. There is only one brief line in the manual about this chain slackening after initial adjustment, and it's mentioned pretty much as an afterthought.

Thanks again!