Help identify a Zener?

[alwalker]

Re: Help identify a Zener?

I've got the same emitter board 14LG479-2C that is not working. I believe LM2903 is my problem but I found something odd when checking the components on the board. The indicator led, D105 reads 15 ohms and is not lighting. Does anyone know what to replace that with? That is of course not what is causing my IR pulse problem but it does seem odd that this should be bad. Again though--the damage is due to lightning. You can see a slight scorch mark on the board near where the bolt would pass through the board to mount the sensor to the door rail.

[tester272001]

Re: Help identify a Zener?

I had this happen to me twice that lighting struck near my house and twice I had to replace the garage door opener because both times it fried the door sensors and the controller boards on it

And also cable dvd recorder twice also and yard sprinkler controllers

WOW! They say lighning never strikes the same place twice, I guess that is NOT true!

[sam_sam_sam]

Re: Help identify a Zener?

Oh yeah! it destroyed all told: garage sensors, the logic board had 2 fried SOT23 transistors for the relays and one diode across a relay. The Zener 6.2V on the main logic board was shorted. it seems like came in via the sensor and traveled through the A/C mains (flash over lightning?) or it came through the A/C mains and went out the sensors! not sure. I lost Cable modem, router, 2 switches, NAS drive, wireless access point, a small LCD TV and a signal amp in the attic! Oh and I think it did in my 20plus year old A/C compressor (replaced that due to age). When this happended 3 breakers tripped too! I replaced two GFCI recepticles! Whoa! what a list eh?

I had this happen to me twice that lighting struck near my house and twice I had to replace the garage door opener because both times it fried the door sensors and the controller boards on it

And also cable dvd recorder twice also and yard sprinkler controllers

[tester272001]

Re: Help identify a Zener?

Jopat, According to Redwire prior post..."The parts are vanilla switching transistors, anything would work"...I just used parts I had on had or on other unused circuit boards

[jopat]

Re: Help identify a Zener?

14LG472 - I have that schematic.
14LG382 - the schematic you posted but uses lots of parts.
14LG372 - your receiver, I drew a schematic but think you need a zener for D3. Let me know if you get the part numbers for that stuff I can make corrections.

Red Wire, Your schematics were most helpful. I have a question about replacing the NPN BC847 "1H" on a 14LG372-1B Beam Detector Board. DigiKey offers quite a few choices. I could not match up the sizes you listed on your schemo. Could you tell me which DigiKey transistor to get? D3 and The NPN transistor were shorted on my board. I replaced both diodes D1 and D3 with 1N4003. That's what I had lying around. Now to order the little surface mount NPN. Thanks for your help.

[jopat]

Re: Help identify a Zener?

Hello all, I am replying to myself. I just needed to read all of the involved posts to see that Red Wire and others have answered all of my questions on previous pages. I found the exact print I needed. Thank you all for you help.

[jopat]

Re: Help identify a Zener?

Hi Red Wire, I am looking at a 14LG372-1B Detector brd. Did you have a print for that? One of the two diodes (D3) was shorted. I replaced it with a IN4003. From what I can see one of the surface mount components on the rear of the board is shorted too. It has the letters 1H on the three leg device. I am not sure what it is. The Transmit sensor seems to be working. My daughter just bought a house with a 1994 Craftsman opener (139.53636SRT). All wires that go to the opener wall button and both door sensors were cut and removed. The door Detector sensor had both connector male legs completely covered in white paint. I cleaned them off and I am trying resurrect the opener. The motor works fine and I can short the first two opener terminals and open / close the door. I was hoping to get the door sensors working on my bench before I go any farther. Thanks for any help you can provide.

[redwire]

Re: Help identify a Zener?

Chamberlain Liftmaster garage door sensor 14LG372-1B I have not seen you'd have to post some pictures.

The black IR receiver module runs to 5.5V max (plus a diode drop) so the zener needs to be 6.2V max and 5.6V is the next step down, so 1N4734A 5.6V 1W zener is my guess.

[tester272001]

Re: Help identify a Zener?

Welcome to the forums Never! sounds like you will have here and also be a great resource!

[neverthrowaway]

Re: Help identify a Zener?

Hi all,
I'm new to this forum. I've been an electrical engineer in a research lab for over 50 years and am now semi-retired. I have a failed Chamberlain beam detector 14LG372-1A that's bad. I know it's the detector because I have two garage doors with openers and the bad detector doesn't work on either door.
It looks like the diagram Redwire posted of a 14LG372-1B is very close. I think with this information I have a good chance of repairing this thing! I already bought a pair of "universal" units but they are extremely finicky and I can't get them to work reliably, so it's back to repairing the original unit.
As my username suggests I take great pleasure in repairing stuff rather than throwing them out. Two weeks ago I repaired our microwave. Saves a lot of $ but costs time. Another cost (ask my wife) is that we have a lot of old appliances because I keep fixing them instead of throwing them out!
Thanks a lot for your help on this!!!

[tester272001]

Re: Help identify a Zener?

Sure sounds familiar! I have a large deductable so no help there! the a/c compressor was at end of life so they would not offer much and that would be the largest cost! so not worth it in my case. Oh and the I also replaced a 30 foot length of COAX as that went OPEN. nice huh? I never had so many things go bely up all at once! If I could find a decent screw drive opener, I probabaly would have bought that. But the latest and greatest tech is CHAIN or BELT! wtf? I love my screw drive opener and now its working again. I still have to test those sensors but I think is looking pretty good. Oh and the lightning also went through my attic FAN and put a small puncture through the roof directly under the fan! I was able to patch that with some tar and wood...I hope that never happens again! Within the next 5 or so years I will have to replace the roof due to age so...Overall I feel lucky there was no fire.

[redwire]

Re: Help identify a Zener?

That sounds terrible! A lightning ground strike hit near my friend's house, a streamer zapped the cable TV and everything connected to the coax got damaged. TV, cable modem, stereo, DVD player - all got killed. The home insurance company thought he was scamming them, so he took the gear to a TV repair shop and they confirmed the failures/burnt parts were due to that, and he then got everything replaced.

[tester272001]

Re: Help identify a Zener?

Oh yeah! it destroyed all told: garage sensors, the logic board had 2 fried SOT23 transistors for the relays and one diode across a relay. The Zener 6.2V on the main logic board was shorted. it seems like came in via the sensor and traveled through the A/C mains (flash over lightning?) or it came through the A/C mains and went out the sensors! not sure. I lost Cable modem, router, 2 switches, NAS drive, wireless access point, a small LCD TV and a signal amp in the attic! Oh and I think it did in my 20plus year old A/C compressor (replaced that due to age). When this happended 3 breakers tripped too! I replaced two GFCI recepticles! Whoa! what a list eh?

[redwire]

Re: Help identify a Zener?

The waveform looks good, ~160Hz pulses.
Did lightning really damage the garage door sensors? It seems weird as they aren't grounded.

[tester272001]

Re: Help identify a Zener?

here is the waveform from the output of the IR Receiver, PIN 3 OUT. I still have to hook to the actual logic board with the motor and test, but its looking decent. The LED on the logic board when not connected flashes 4 times vs no flashing at all. I might be close to closing this one down. Will report back by tomorrow for sure. BTW for those that may need an LED the datasheet says 950nm is the IR wavelength. I did not have to replace the LED but thought someone might liket to know.

[tester272001]

Re: Help identify a Zener?

Very interesting! I hooked it up to a logic board and that LED lit right up. Interesting. I have likely OVER diagnosed this due to not knowing that little bit about current loop! thanks for that. I will test this hooked to the actual unit next and report back.

[redwire]

Re: Help identify a Zener?

The receiver is powered by a current-loop, so it draws a steady resting current which pulses up when a signal is present. So I would power it with say a 100R-1k resistor in series. A bench supply directly connected I don't think would dip during pulses to light the LED.
I'll fix the schematics and re-post when you finish.

[tester272001]

Re: Help identify a Zener?

I repaired a bad trace and now the receiver is working on the bench. I can see on the scope when I shine the emitter on and off that the puses drop or return with the IR led shining. The indicator LED does not light at all. When I test with my Fluke it does light up. I guess maybe the NPN transistor is defective. Thanks for all your help on the schematic and input! FYI - Of the 2 schematics you posted last the TOP one in the pair is the right one. the bottom image had a possible zener and the unmarked PNP device.

[tester272001]

Re: Help identify a Zener?

The receiver first transistor (connected to module) is PNP, then an NPN in all the receivers I have seen. The parts are vanilla switching transistors, anything would work.
The IR module output should go low with pulses (demodulated 38kHz) at a low frequency 150-200Hz when a beam is present.

I found a trace break on the input to the PNP device. The demodulation makes sense, I am seeing a constant of the 150Hz - when I shine the emitter inthe receiver it does not change but maybe the PNP is demodulating ? Once I repair the trace and retest I will know.

[tester272001]

Re: Help identify a Zener?

Red, thanks for the feedback! Looks like the SMT cross referencshe shows more than one crossref for 2B the MMBT2907 PNP and the BC949B NPN ! now its making sense and your schematic makes sense.