My garage alarm siren was sounding a bit quiet and the tone was weird, like mixed with another tone.
Powered up it draws about 14V 300mA with a spike to ~1A briefly during the low pitch yelp, seems normal.
Teardown reveals only two electrolytic capacitors inside, so I replaced them. 100uF 25V for the warble ramp, and 47uF 16V for decoupling.
The old ones tested OK sort of? - 100uF reads 68uF (-32%) ESR 0.80Ω, and 47uF reads 41uF ESR 0.87Ω as well so it was a bit confusing if the caps were to blame.
The tone caps are green film caps I left alone. Newer versions of this siren are more SMT but the same 6-transistor circuit I think.
I checked drive voltage from the alarm control board and it's good.
Afterwards, the siren is loud and not making the strange whimpy tones.
I did a schematic for the siren as well, it seems to use a SCR out of 2 transistors for the ramp i.e. cap charges pitch goes up, SCR fires and discharges and it repeats. The main tone osc and VCO is a two transistor multivibrator.
If this doesn't fix it, I will go nuts. The alarm board I made using an ESP8266 and TIP110 to drive the siren. I hauled it onto the bench and could not find anything wrong with the siren output.
It usually goes off around 3-4AM when hobos and thugs are trying break-ins in the back alley, so I am half awake wondering what happened.
Last time it went off I thought it was a cheezy not loud car alarm until I checked the datalog and it had gone off.
I made a few touch/ vibration sensors and have one now that detects the garage door handle being mangled, so it chirps and warns before they trash the door. If the door gets pushed open or motion it goes off hard.
Powered up it draws about 14V 300mA with a spike to ~1A briefly during the low pitch yelp, seems normal.
Teardown reveals only two electrolytic capacitors inside, so I replaced them. 100uF 25V for the warble ramp, and 47uF 16V for decoupling.
The old ones tested OK sort of? - 100uF reads 68uF (-32%) ESR 0.80Ω, and 47uF reads 41uF ESR 0.87Ω as well so it was a bit confusing if the caps were to blame.
The tone caps are green film caps I left alone. Newer versions of this siren are more SMT but the same 6-transistor circuit I think.
I checked drive voltage from the alarm control board and it's good.
Afterwards, the siren is loud and not making the strange whimpy tones.
I did a schematic for the siren as well, it seems to use a SCR out of 2 transistors for the ramp i.e. cap charges pitch goes up, SCR fires and discharges and it repeats. The main tone osc and VCO is a two transistor multivibrator.
If this doesn't fix it, I will go nuts. The alarm board I made using an ESP8266 and TIP110 to drive the siren. I hauled it onto the bench and could not find anything wrong with the siren output.
It usually goes off around 3-4AM when hobos and thugs are trying break-ins in the back alley, so I am half awake wondering what happened.
Last time it went off I thought it was a cheezy not loud car alarm until I checked the datalog and it had gone off.
I made a few touch/ vibration sensors and have one now that detects the garage door handle being mangled, so it chirps and warns before they trash the door. If the door gets pushed open or motion it goes off hard.
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