How to find the voltage of a broken zener diode

Thread Starter

laban93

Joined Jan 4, 2017
2
Hi!
I'm currently trying to repair some broken smoke-detectors.
They have 2 circuitboards inside, one detection board and one voltage and signal regulating board.
They operate at a 12V input, but by a mistake the where connected to 24V
The detection board needs a 9V input from the regulating board, and works when hooked up to my powersupply.
On the regulating board i found a zener diode that was broken, but i don't know it's clamping voltage.
Is there another way to find a suitable replacement zener?
I'm not an experienced reverse-engineerer as you probably can tell...
The 12V supply gos straight trough the diode to power the regulating board.
It was soldered over CR120170103_182352.jpg 20170103_182400.jpg 20170103_182409.jpg 20170103_182419.jpg 20170103_182503.jpg
 

#12

Joined Nov 30, 2010
18,223
There might be other clues, like capacitors rated at 6 volts or an IC that is designed for 5 volts or the coil voltage on that relay.
See if you can read the chip number and look it up.
 

Thread Starter

laban93

Joined Jan 4, 2017
2
It's a 12V relay used for signaling the control panel, and the numbering is F4148 on the zener. The caps are rated 10V.:)
 

Alec_t

Joined Sep 17, 2013
13,155
Are you sure it's a zener? A 1N4148 is a common silicon signal diode (which could be used as a catching diode across a 12V relay coil) but Google hasn't heard of a F4148.
 

WBahn

Joined Mar 31, 2012
27,433
That you say the 12 C goes "straight through" the diode to power the regulating board would indicate that it is NOT a zener, but rather a rectifier diode. That agrees with what the others have found looking up the part numbers. Though it appears likely you are reading the 'F' correctly since it clearly isn't a surface mount part. It possible, of course, that this particular manufacture is using a prefix that contains an 'F' followed by the industry standard designation for the 1N4148 diode.
 
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