Help identify a Zener?

[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?

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.

[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!

[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?

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

[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.

[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?

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!

[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.

[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?

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!

[tester272001]

Re: Help identify a Zener?

In your PCB, there are no zener diodes at all. All are regular diodes. If any of them were actually zeners, the behavior would be weird.

However in your PCB, physically where the label "D104" stands on top of (not the actual component that it's currently pointing to), you can see two holes to either side, where there's no component there. Those two holes probably used to be for D107 but is not labeled as such anymore. That position used to be a zener diode - 6 volts according to the schematic. You can put a 6 or 6.2V zener diode there if you wish, but make sure you get the polarity right.

The D107 in later models was MOVED to the Main board and is called D10. it is a 6.2V Zener. That was blown on the logic board. Replaced that and a few SOT23 transistors and that board is FINE

[redwire]

Re: Help identify a Zener?

Try a TV remote pointed at the receiver, sometimes the pulse pattern will fool them for a bit.

[tester272001]

Re: Help identify a Zener?

Until I get the emitter pulsing the 38K frequency I won't know for certain. I suspect the receiver may have gotten zapped as well. I did not detect any pulsing on the U1 device when I put the output on a scope. I thought that maybe the emitter was not strong enough to make the receiver pulse.

[redwire]

Re: Help identify a Zener?

The emitter does not care so much about it's operating voltage, the IC is good to 36V. The receiver module is a 5V part though so a zener there would be needed.

Since these (emitter, detector, light switch) are all on the same two-wire (sorta constant current) bus, I have to wonder if the receiver survived the lightning surge.

[eccerr0r]

Re: Help identify a Zener?

In your PCB, there are no zener diodes at all. All are regular diodes. If any of them were actually zeners, the behavior would be weird.

However in your PCB, physically where the label "D104" stands on top of (not the actual component that it's currently pointing to), you can see two holes to either side, where there's no component there. Those two holes probably used to be for D107 but is not labeled as such anymore. That position used to be a zener diode - 6 volts according to the schematic. You can put a 6 or 6.2V zener diode there if you wish, but make sure you get the polarity right.

[tester272001]

Re: Help identify a Zener?

Yes the D106 in the schematic I posted has 2 resistors with +5.3V off them and 4.3K Ohm resistor feeds D106. It also does not depict as ZENER (as it does for D107) - so is my diode a 1n4001 or a 5V zener ? Even the schematic Red posted does not show as Zener.

[stj]

Re: Help identify a Zener?

the only schematic I found was darn close but older for sure. Doe snot identify actual part VALUES for some components.

but it shows the zener voltages.

[tester272001]

Re: Help identify a Zener?

Ecc, Glad to help ! And Red thanks for the schematic. When I saw the red and black casing on the diode it definitely reminded me of a Zener. The silkscreen does not show it as one! When I did a diode test is shows good. So next I will hunt down my IR LED and give it a try!

[redwire]

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.