simple circuit reverse engineering

Thank you again jremington for your post,
but if all you have to say are derogatory comments I would suggest that you dont waste your time on that.

Regards

There is nothing "derogatory" about being a novice. Everyone has to start somewhere!

I still think your comments are not adding anything to this forum, and not offering any help..., just wasting space and time.

Get a box of colored pencils.

With a regular lead pencil, draw a box on a sheet of paper for each and every component on the board. Label the boxes with the id of each component it represents.

Pick one box and with a colored pencil draw all the connections from that component to every other component. Lay that color aside.

Pick another color and begin to draw the connections for another box.

When all done, draw a proper schematic using standard symbols. All connections needed for the schematic should be apparent from your colored pencil drawing. Where multiple colored lines connect components, you know only a single board trace connects them all.

Paul

Thank you Paul,
that is what i did to obtain the drawings I posted... but i still do not know if the gray/brown parts are capacitors or what... and what A7p is, I was hoping for some help in identifying those parts.

cloxart:
Thank you Paul,
that is what i did to obtain the drawings I posted... but i still do not know if the gray/brown parts are capacitors or what... and what A7p is, I was hoping for some help in identifying those parts.

Did you try your ohmmeter?

Paul

yes

Paul_KD7HB:
Did you try your ohmmeter?

Paul

Yes, and the black ones looks indeed resistors (marked 1002 and reading indeed 10Kohms) the gray parts all read as no conduction but one, which reads 22Kohms so I take that's a resistor, which would make sense as it is the one connected to the non inverting input of the op amp. still struggling with the A7p... 3 pins so at first look i thought it was a transistor, but only TWO pins of it are connected.

I can only make sense of the circuit if I assume that A7p is a diode. I indeed sketched up the circuit in a simulator and it is working if I apply 12V to yellow and 5V on red, GND on green and I take black as output.
in that way I can get an output on the black wire depending on the voltage (0~20mV) I apply on on the feedback pin of the laser diode. Still no clue about the red/white wire. (the original equipment is connected through a shielded cable, and the red/white is connected to the outer mesh of the cable, but NOT to ground)

A7p - on the bottom of the page

http://radioskot.ru/forum/9-449-27

Thanks Ted! so it IS a diode! :slight_smile:

single
http://etronics.free.fr/dossiers/analog/analog10/images/image28.gif

Thanks Ted, that really helps

More problems ?

Oh yes! lol
still dont know what the red/white wire is for, for instance.
in the simulator i put a generic op amp (the only choice I have) but the AD706 in my circuit is a DUAL op amp so I guess it must be powered with a dual voltage.... and not as I did

dual = 2 op amp in one package

opps, sorry I meant BIPOLAR
http://www.analog.com/media/en/technical-documentation/data-sheets/AD706.pdf

Op amp can work in two modes or single mode of power supply.
google - dual supply op amp circuit and single supply

here is the schematics i was able to make

post # 1 top drawing, which wire is red and which white ?