Smoke machine using resistance wire

Thread Starter

teebee101

Joined Jul 4, 2022
3
Automotive style smoke machine to detect leaks runs on a 12 V system one of the techs used battery charger to run it which burnt it up causing the red light to flash which according to the manufacture is an open circuit, I opened up the system checked the resistance on the existing wire found it was burnt replaced the wire with Nichrome 60 wire, 20 AWG, 0.6592 Ohms/ft, I used 4 ft. at about 2.1k but the red light consistently flashes, checked the diodes, caps, fets and resistors the only thing I did not check was the OP777 op amp and the PIC12F675 Flash 8-Pin 1kb 20MHz Microcontroller . If I turn on the switch and then touch the wire it heats up fine but if the wire is connected and then turn it on, it fails. With 12v supply I get 4.4v at P1, and after turning it on I get 12V. Any help would be appreciated. Also can’t find much info on Q2 (1AL markings)
 

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Thread Starter

teebee101

Joined Jul 4, 2022
3
sorry its 3 ft and here is the data with it powered up and then with Sw1 on, I hope you can understand it, If I turn on the switch with both lights on and then touch the wire it works and heats up, but if the wire is connected and I try to turn it on and fails and the red light blinks, and zero volts at P1.smoke-data-pic.jpg
 

Alec_t

Joined Sep 17, 2013
13,079
If I turn on the switch and then touch the wire it heats up fine
By 'touch the wire' do you mean (a) the wire is already connected between P1 and P2 and you then place a finger on the wire, or (b) the wire was not connected but you temporarily touch it to P1/P2 ?
It's hard to tell from the pic, but are all 3 legs of the 7805 regulator making good solder connections to their pcb pads?
 

Thread Starter

teebee101

Joined Jul 4, 2022
3
I have 4.5 v at P1 without the wire attached as soon as I connect it she fails with blinking red light and 0v at P1, and yes all Solder joints are connected
 

DickCappels

Joined Aug 21, 2008
9,105
When you turn the thing on, do you see a voltage drop across the wire? Either the wire is not connected, the wire has more resistance than you expect, or the circuitry on the board is broken.
 
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