W dniu 26.08.2019 oÂ*17:09, John Robertson pisze:
On 2019/08/26 3:11 a.m., wrote:
Hi Folks

I have a Commax CDV-43k/DRC-4L (Stock Code: PI-1176) intercom that
isn't working anymore. It seems the power supply board in the intercom
(CDV-43K) itself (converting wall power of 220v to 15v) has blown. I
think it might be the transistor (see photos:
https://imgur.com/a/uBCXjwQ). The suppliers say that it is out of
warranty and that I would have to buy a new one.

Here is a link with a few photos of a circuit board that isn't working
anymo
https://imgur.com/a/uBCXjwQ

I have tried searching online, but couldn't find anything that gave me
any indication of the specs of the transistor or what transistor to
try and replace it with. I also tried to search for the schematic, but
couldn't find anything.

If anyone can perhaps help me identify the blown transistor or perhaps
point me in the right direction that would be greatly appreciated.

Let me know if you require any other information from me.

Regards,
Jannie


Actually the PCB silkscreen indicates that this is an IC as it is called
"U2", instead of a "Q" designation - Q for transistor and U for IC is a
common convention. I would then suspect it may be a 15VDC regulator as
this is some sort of switch mode power supply.

John :-#)#


It's likely a TL431, but I wonder how it could have blown so violently
without some external help, as it is connected to the circuit through
relatively high resistances?

Piotr