Fisher 1266-X awakened from the dead!

[ivconic]

[ivconic]

What happened to it?
Here is what happened:



Both LM339 burned, one of them exploded, also one NPN.
That's what you get when you want to bypass stock batteries with outer accumulator...
So common mistake by local detectorists...


Strange enough; mosfet survived!??
Not SVP"##&$$!" one but one with 4 legs, like IRFD... was lazy to catch the label... important is; it is alright.
...
Give me something dead and burned to fix! I am so in a fire now!

[kt315]

DIP-4

[ivconic]

DIP-4

Probably one of those.
I don't mind now, once it is serviced and alright.
Usually I do fix the device and than completely forget about it.
This is probably my XX-th Fisher 12xx on service so far.
It became annoying routine.

[Davor]

That's what you get when you want to bypass stock batteries with outer accumulator...
So common mistake by local detectorists...

A simple circuit with 2 MOSFETs would prevent this problem without any voltage loss. A diode would work too, but with 0.7V loss. Guess all the hobbyist projects should start with a protection circuit. For professional rig manufacturers omitting one is a win-win. They make more money if a rig dies because of tampering.

[ivconic]

A simple circuit with 2 MOSFETs would prevent this problem without any voltage loss. A diode would work too, but with 0.7V loss. Guess all the hobbyist projects should start with a protection circuit. For professional rig manufacturers omitting one is a win-win. They make more money if a rig dies because of tampering.