Remote garage door opener - not working

[caphair]

I have two of these and used the working one to do a comparison measurement. Oddly everything seems to be identical in value when measured. I even did a diode mode measurement (+ probe on - battery terminal) of all components and the ic. The values are the same between the two.

Only difference I’ve noticed is as follows:

Working one:
12v on C of NPN transistor
Press button
0v on both B and E

Bad one:
12v on C of NPN
Press button
1.5v on B
1.1v on C

But the transistor measures good and has same values of working one

Any idea on this?

[budm]

What are the Voltage B and E of that RF output Transistor of both units when button is no pressed?
When button is pressed, the Transistor will be fed with high RF frequency so the meter cannot handle to show the readings. We are dealing with high frequency here, so the bad one the IC may not be putting out high frequency drive but just steady state output.
What did you use for circuit ground?

[eccerr0r]

I'm not sure you can measure the voltage on that transistor, it's part of the RF electronics. In any case the readings you gave are suspect, especially when you gave "C" twice on the bad one. Please remeasure and also note when you measure voltage, what is your reference point...

[redwire]

It's hard to tell because the TX transistor operates at VHF and a DMM and long test leads may or may not kill the oscillator at the 315MHz or 433MHz it runs at.
You need an RF probe or SDR or something to see if it's transmitting anything.

What I do is trim the transmitter frequency. There is an adjustment - usually a trimmer capacitor but here it's a slug inside the white tube on the inductor.
Put most of it back together and when far away I adjust for the best range.

This is using Microchip Keeloq like HCS30x series with rolling code. So the remote will need to be "learned" by the garage door opener before anything can happen.

[sam_sam_sam]

This is a rant

I am sick of manufacturers pulling data sheets off line what is this crap!!!

[sam_sam_sam]

Originally Posted by redwire

What I do is trim the transmitter frequency. There is an adjustment - usually a trimmer capacitor but here it's a slug inside the white tube on the inductor.
Put most of it back together and when far away I adjust for the best range.

This works sometimes ———>

I would also recommend that you use plastic tools to this type of adjustment

[R_J]

Is this any help?

[caphair]

Originally Posted by budm

What are the Voltage B and E of that RF output Transistor of both units when button is no pressed?
When button is pressed, the Transistor will be fed with high RF frequency so the meter cannot handle to show the readings. We are dealing with high frequency here, so the bad one the IC may not be putting out high frequency drive but just steady state output.
What did you use for circuit ground?

Both measure 0v when not pressed.

Used battery ground termal when making measurements

[petehall347]

point at a digital camera to see if you see flashes .

[R_J]

Originally Posted by petehall347

point at a digital camera to see if you see flashes .

This is an R.F device not I.R.

[petehall347]

Originally Posted by R_J

This is an R.F device not I.R.

there is a frequency counter device for that job then . seen them used for car key programming to car .

[caphair]

Noticed a mistake in my original post. Can’t edit it so I’ll post here:

Working one:
12v on C of NPN transistor
Press button
0v on both B and E

Bad one:
12v on C of NPN
Press button
1.5v on B
1.1v on E (originally wrote C by mistake)

[redwire]

Maybe measure the voltage drop across the 300R resistor going to MCU power on pin 8. 12V on one side and MCU power on the other. Or measure the current drain on 12V power in.
The MPS918 is pretty tough and not likely to fail, although I'm not sure what happens when a battery is put in backwards on one of these.

On the working one, the transistor reading zero on B, E is not right- it's just off then and doing nothing. The MCU makes 66 bits at 0.1 to 0.4msec/bit pulses when the button is pushed. So a slow multimeter will not catch that.

[caphair]

The way I was able to get readings was to hold the button down. If just pressed normally it was too fast to see anything.

I’m curious what the white tube wrapped in thick wire is. Is that was transmits the signal?

What component is most likely to fail on this? I’m not familiar with the operation of one of these

[petehall347]

all i have seen wrong with similar ones is dead batteries failed switches and bad solder joints . and corrosion .

[R_J]

The white tube with the wire is the coil along with one of the small capacitors that sets the r.f. frequency. I use sdr spectrum analyser software and a cheap usb receiver (RTL2832) to check these now. You could swap the ic or transistor between the two units.

[eccerr0r]

Something still doesn't make sense, i'd expect the voltages on the "working" one to have different voltages on B and E, and neither 0V - unless you can't see it.

Pin 7 appears to be an LED output on the IC that's not connected/used, you should connect an LED there and see if that at least blinks - seems simple enough, connect anode of LED to pin 8 of the IC and cathode to pin 7.

[budm]

It is too high of the frequency for the meter to see the drive Voltage to the Transistor, and probe leads also affect the circuit as well.
He can try using AM radio, it will pick up harmonic of the transmitter, set to the lowest frequency and unused, you should hear pulses when you activate the button, I just verify that with my AM radio (I had to extend the antenna and put the transmitter right next to it) and my garage door opener. I use AM radio a lot as noise detector.

[caphair]

Originally Posted by budm

It is too high of the frequency for the meter to see the drive Voltage to the Transistor, and probe leads also affect the circuit as well.
He can try using AM radio, it will pick up harmonic of the transmitter, set to the lowest frequency and unused, you should hear pulses when you activate the button, I just verify that with my AM radio (I had to extend the antenna and put the transmitter right next to it) and my garage door opener. I use AM radio a lot as noise detector.

Just tried on stations 520-540 and couldn’t hear anything from either one (working and bad)

[CapLeaker]

just swap that rf device out and see if the problem goes with it. Also the transmitter and the receiver need to be paired.