unknown part

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lfg
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unknown part

Post by lfg » Wed Aug 14, 2002 7:51 pm

I have a burned chamberlain garage opener logic board. The part which is D12 (diode) is burned and can not read the part. It looks more like a small red cap., the silk screen shows no anode or cathode placement. Company has no parts #'s only new boards. This part is in-between the hot and neutral wires, which is then fed to a transformer.
The guy burned this out be shorting the wires with power on at the breaker panel. Go figure?
Any help? Never have seen this part before.

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Edd
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Re: unknown part

Post by Edd » Wed Aug 14, 2002 11:08 pm

LFG:
Just a stab at this. If this should be across the AC power which is also wired into the units primary of its power transformer. I somehow want to suspect it to be a MOV surge protector. But U wud also have a line fuse between it and the hot line for protection, if it really clamps down . Can't see any correlation on the diode
marking of the bds silk screening. These units usually have a gloss red- slick epoxy type cladding of the units. As compared to the matte reddish/orange of round disc ceramic caps. A median size is~ 3/4 in dia, a few smaller and some just under an inch: in accordance to their joule ratings. I'm assuming the device to probably to have been good, anyhow. Also, I'm assuming its leads are either vaporized off
or spot welded to Dudes 3 in pocket screwdriver...........no make that 2 in.<p>Another thought was that if this was a common unit used by a builder in your neighborhood, of homes that he build, there would be others, that U might get a concerned/friendly neighbor permit U to get info from his unit as to data from the component, as to any manufacturer ID/logo or value numbers on the device.These units have their avalanche threshold voltage specs on the side.<p>73's de Edd<p>[email protected] (Interstellar~~~~Warp~~~~~Speed)
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keymaker
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Re: unknown part

Post by keymaker » Thu Aug 15, 2002 1:31 am

If they have new boards available, Have your wife, or any female call them and ask them to identify it for you.<p> And you would hope they'd have a schematic,,, Right??

russlk
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Re: unknown part

Post by russlk » Thu Aug 15, 2002 11:38 am

Since the part is across the line, it is most likely a surge protector. But, it would not be damaged by shorting any wires that I can think of. Did he perhaps connect to 220 VAC instead of 110? If so, there is more trouble than the blown protector.

lfg
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Re: unknown part

Post by lfg » Thu Aug 15, 2002 2:46 pm

All 3 of you gave great answers, I will check them all out. It now does sound like an avalanch diode, but the side that blew had the markings. also, if someone in the hood has a chanberlain opener that would be easy to check too. And last, they should be able to read the darn part from a new board. If they wouldn't then they really need the $78 bucks I guess.<p>Thanks a lot. Go Packers!

lfg
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Re: unknown part

Post by lfg » Thu Aug 15, 2002 2:51 pm

And EDD, it is glossy red, and about 3/8 " dia.<p>Could be the part you mentioned.
Also, it is possible he shorted it to 220v too. Who knows. The guy never works with the power off. One of these days.

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jollyrgr
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Re: unknown part

Post by jollyrgr » Thu Aug 15, 2002 3:22 pm

If it is a device that looks like a ceramic disk capacitor, it is an MOV. If it looks like a diode and is directly across the AC line, I would think it would be a device know as a TRANSORB or Transient Voltage Suppressor. MOVs can be found at Radio Shack or even "liberated" from a power strip. A transorb is not as popular but can be found for under a buck at Mouser. Go here for an example:<p>http://www.mouser.com/index.cfm?handler ... tid=586450
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Donald S. Lambert
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Re: unknown part

Post by Donald S. Lambert » Fri Aug 16, 2002 7:39 am

I am not an electronics guru, I barely am able to spell electronics if you gt the picture. BUT from my understanding of MOV's it isn't necessary to be in the circuit for the circuit to operate. So if it doesn't work with it out of the circuit there is much more damage than just that blown component.<p>I had a garage door opener fail, not electronic but mechanical. The plastic gear teeth on the motor got worn off and the motor would merrily spin with no action. My suggestion is to bite the bullet and buy a new garage door opener unless it is a special setup in which case a new board would be in order. HTH Greybie

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Edd
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Re: unknown part

Post by Edd » Fri Aug 16, 2002 1:43 pm

LFG:
Sure sounds like you have yourself a MOV ; they are more "forgiving" to a longer duration spike/overvoltage than the transzorb, which I
find more frequently designed in, downline, at lower voltages. I had interpreted the screwdriver being probed across this devices leads WITH the AC power still on the system.......Right ? And the units
operation/continuity wud still not be affected with this protective MOV being OUT of the circuit..but if this is the proper scenario as to what happened.... one does need to check the foil path on the PCB bottom where there is probably a portion of it in that AC path now
vaporized away !
As sophisticated as these unit's receiver decoding circuitry seems to get, seems like they still tend to design in a mechanical relay for
the GDO drive activation element. Your currently malfunctioning PCB shud also be precluding the use of your manual wall switch,so U're probably lifting the door a lot manually now...hi hi .Shud you get the AC power path complete to the pwr xformer and reconnect up, U might then check for secondary AC voltage on it.Then you could check the manual remoted pushbutton to ascertain if it then wud activate the unit, since it merely activates the PWR relay driver transistor . This wud let you know that there is no problem in Ur GDO motor/ drive train/limit switches. And even if that doesn't work, that
relay, which activates that mechanism, has 4 connections: 2 small connections to its drive coil, and two larger power connections that
switches the GDO motor on..till the limit switch latches it into its cycle.
A jumper clip across that relay's power terms
.....momentarily .....shud start a door cycle and at least answer the question fielded forth by Greybie as to the functionality of your GDO's basic electro/mechanics.
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lfg
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Re: unknown part

Post by lfg » Fri Aug 16, 2002 5:23 pm

Edd, I forgot to mention that 2 traces, hot and neutral were burned up to the MOV. It looks like it protected the input to the transformer. Go figure.<p>Thanks for all of your help too.<p>Baseball strike????

lfg
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Re: unknown part

Post by lfg » Fri Aug 16, 2002 5:27 pm

Greybie, there were 2 traces that were gone up to the MOV. Otherwise the board should work. The transformer seemed to be OK. Wouldn't know for sure until I repair them, and give the board back to the guy that blew it out. He is 200 miles away in the Northwoods of Wisconsin, where they work on live circuits. My goodness.<p>Thanks.
Larry

Dean Huster
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Re: unknown part

Post by Dean Huster » Fri Aug 16, 2002 7:23 pm

I have seen very few designs incorporating MOVs that are correct. All implementations are supposed to have fusing in series with the source and the MOV as the device reacts as a dead short. Without a weak link, board traces can go up in smoke, especially with a high-energy overload. As mentioned, with the MOV out of the circuit and the traces repaired, the circuit should work OK if nothing else is defective.<p>We had a lightning strike take out our Sears/Chamberlain garage door opener. It was repairable, but schematics are available only if someone's reverse-engineered one.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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