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Reverse Engineering Techniques and Project

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I've been following the EEVblog videos and forums for some time now and, before I make my first post, I just wanna say many thanks to all of those who have contributed to this rich collection of information.

I have this little black box (literally, see pictures) with 7 wires coming out of it.  I thought that I could learn quite a bit by opening it up, tracing out the PCB (see attached schematic), trying to figure out what it is, and then reverse engineering it such that I can make my own.   This may seem pointless to some, but for me it's a good learning experience. 

I think this is a 24V power supply with a relay that can be turned on and off via a signal line.  I'll be curious to see what more experienced folks here think.  when I hook it up to AC 120V I get 24V on the output red and black wires. 

I have several questions:

1.  What tips do you have for someone doing a reverse engineering project like this?
2.  Are there specific techniques used for determining what some of these surface mount chips are?
3.  What do you think Q1 and Q2 are?
4.  What electrical measurement should I make to determine what Q1 and Q2 are?

I believe that in order to get the resistor measurements, I will need to de-solder them from the board before I measure them.  Luckily the caps are labeled so figuring them out is simple.  I'm assuming the transformer puts out under 50 V on the secondaries (the caps are rated for 50 V) and I will be able to use a 1N4001 diode bridge configuration (these diodes are rated for 50 V reverse bias).  I'm pretty confident Q3 is a LM317L, as I used the label to ID the part and the data sheet corresponds with how the this is being used on the board.  My basic difficulty is determining what Q1 and Q2 are.  Transistors possibly?  I have no idea what I would buy from Digikey to mimic these.  Any ideas?


Here as an electrician Q usually means (high power) relay.
Don't know if it will help you ...

Here is an attempt to make the schematic upright.

Thanks for the response Spikee.  Q1 and Q2 are chips on the PCB that are too small to be relays.


"Q#" on a pcb ususlly denotes a transistor. Although the type of transistor is anyones guess. Are there any numbers on the transistors?


There are dip sized relays

even smd ones at digikey :O


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