[solved] SG-1100 dead with pulsing LED
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My SG-1100 died today with no network and no output on the serial console. It would either:
- Have all leds off
- Pulse one led with very short pulses
I suspected a power supply in hick up mode, but the external supply was OK and could supply 2A without any problems.
It turned out to be DZ3 that had failed shorted spontaneously and that it forces the external power supply in hick up mode. It looks like the it could be an On semi 1SMA13CAT3G transient protection diode, so I removed it and it now starts up again.
If you have the same symptoms it could be worth measuring the resistance over DZ3, in my case it was about 1Ω and a normal value would be over 10 kΩ.
Next time I order components I'll order a replacement. 1SMA13CAT3G seems to be an obsolete part, but I will try to replace it with Littelfuse SMAJ13CA.
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Nice save. It does imply there might have been a surge at some point. You might consider replacing the PSU to be safe if there is no chance it was ever connected to another PSU with the wrong voltage.
Steve
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My SG-1100 has died and shows the same symptoms as @csa described. Someone has offered me an equivalent part: SS14 DO-214AC Schottky Diode 1A 40V (1N5819 SMA DO214). However, I don't know enough about electronics. Can this diode be used as a replace instead of either the 1SMA13CAT3G or SMAJ13CA?
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@mentisdominus
SS14 can unfortunately not be used to replace DZ3.Schottky diodes like SS14 are designed to conduct current in one direction already at a low voltage whereas TVS diodes like SMAJ13CA are designed to only conduct current when a high voltage is present across it (a voltage that is so high that it should never be seen during normal conditions).
I have been running my SG-1100 without DZ3 fitted for some time, but this leaves the device unprotected against defective or wrong power supplies as stephenw10 points out.
