Help identify a Zener?

[tester272001]

Re: Help identify a Zener?

After measuring some voltages, I found: The 8 pin LM2903 has pins: 1=5v 2=4.8V 3=3.3V 4=0 5=2.24V, 6=0V, 7=1.68V and 8=5.6V - when I scoped the the IC and the Transistor driving the IR LED it had no pulses, the Base was 160mv, Collector is 880mv and emitter is 140mv. I think is not being driven by the IC with enough and no 38K frequency pulse. D106 looks good. I guess the IC got fried. I think my next step is to replace the LM2903. I will try the REMOTE trick (Redwire) to see if the receiver lights up!

[stj]

Re: Help identify a Zener?

did you check the transmitter output by looking at it with a phone camera yet?
most people forget that simple trick.

[tester272001]

Re: Help identify a Zener?

I did! the LED WORKs but is a a little DIM. I think its not being driven enough or the LED is nearing end of life.

[tester272001]

Re: Help identify a Zener?

Here is my schematic for older very similar 14LG472, yours is 14LG479. Same basic circuit as the other. The diode is not a zener but is a 1N4002 in series with power to the board.
Very hard to kill a 1N4002 there, it must have been a -ve spike that hopefully found no path to arc.

Redwire, Do you also have the Receiver schematic? I think yours is closer to my circuit. I'd like to compare if you do have it. Thanks!

[redwire]

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.

[tester272001]

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, I will get the value for D3 but I think is a normal diode. I scoped the emitter board LM2903 and there are no pulses on pin 1 or pin 7 . so i will replace that next.

[tester272001]

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.

D1 and D3 are marked LT 1N4002

[redwire]

Re: Help identify a Zener?

In these 14LG372 receiver pictures, I see the two glass diodes the same look and part number as the transmitter 052 critter you have. I think 1N4002 is what I've seen everywhere else. As long as the IR module does not get more than 5.5V (6.2V power) which would kill it.

The 14LG472 seems to impose the receiver's pulses on the bus, while the 14LG372 looks a strange design having a big capacitor across it.

I think the garage door opener outputs a low current-loop at around 6V max. so the MCU can see the pulses from the receiver yet power the IR transmitter.
One manufacturer has the patent for everything on the two-wire bus, so transmitter, receiver, pushbutton door/lights - all in parallel.

[tester272001]

Re: Help identify a Zener?

Emitter now looking better! I replace the LM2903M with LM2903D and have pulses and I can see the IR LED flickers more in my phone camera. SO i think that was the primary casue of failure and of course the shorted DIODE. Now on to the Receiver board! thanks everyone for your nput and suggestions!

[tester272001]

Re: Help identify a Zener?

Confirmed the emitter is working fine now. One question Redwire on the RECEIVER boards, the transistor that is fed by the IR receiver is a 2B on my board is that the same as BC849? The SMD cross reference I found says that but that does not match some of the schematics I have seen. I see some are PNP and some are NPN.

[redwire]

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.

[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.

[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?

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.

[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?

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.

[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.

[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?

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?

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.