Reverse Engineering 15 yr old electronics

[Tony Duell]

> 
> Thanks to all who responded, it is real food for thought.  To sum up, my 
> project is to extract wiring diagrams from 2 boards.  The first has about 
> 25 TTL ICs and about a dozen op amps, lots of resistors and capacitors, 
> etc.  On the first board only the IC's are numbered, the resistors and 
> capacitors and diodes are not.  The second board only has a few components 
> but all the parts are numbered, which is good. However, the second board 
> has a large A/D convertor from 1985 that I know nothing about, it has no 
> markings but I think it is an Analog Solutions model.
> 
> I will proceed by following some of the wisdom from the group:
> 
> 1. If I can, put sticky labels on the IC's with diagrams of the functions, 
> some of the IC's are, e.g., quad and gates, number the IC's and the gates 

I don't think that's essential. Maybe it's because I can remember most of 
the common TTL (and other) ICs and their pinouts, and only have to look 
up the more obscure ones, but anyway. Much more important is the abiliity 
to uniquely identify each IC (and other major components) on the board, 
giving each one a U1, U2, U3... number. You may need to add labels to do 
that.

> individually.  Is it possible to print on some kind of Avery sticky 
> paper?  Will I be able to see that small?
> 
> 2. Label all resistors and capacitors, R1 C1 ....

Not so important. I never, for example draw out decoupling capacitors 
unless there are very good reasons for doing so (e.g. it's a single 
capacitor on a derrived power line, output of a potential divider)

> 
> 3. Label all connectors also, J1 pin 2 ....

If you draw out connectors, be cosistent as to how you do it. For 
example, I always draw edge connectors looking into the socket. Drawing 2 
mating connectors as mirror images drives me mad!.

For complete units, I often put arrows on the connectors showing the 
orientation -- pointing, say, to the back and left of the machine. All 
such references refer to the unit in the normal operating position 
(again, be consistent about this).

> 
> 4. Oh, almost forgot, get data sheets on all the IC's.
> 
> 5. Use a large sheet of paper for drawing.

Actually, I find it better to stick to A4 (or equivalent) paper and not 
try to pack too much on a page. It makes copying/scanning a lot easier, 
it also makes the schematic easier to follow since it's divided up into 
functional blocks. Of course this means you have to think a lot when 
drawing it out in the first place (which is no bad thing!)

> 
> 6. Continuity tester is a must.

Yes.

I have been known to make copies of IC pinouts or connector pinouts (e.g. 
the ISA slot pinout if I'm working on PC stuff) and pin them up over the 
bench where I'm working. And have at least 4 databooks open at once. You 
don't waht to have to keep on stopping to look stuff up :-)

-tony