Reverse engineering - PCB to Schematic

barnsleyboy

In the continuing saga trying to get my Bass 12 working properly, I need the correct schematic. The only ones available are the Bass 12 and the Lead 12, which are hand drawn and look like they have been scanned using an old 1970's school Banda machine (you'll need to be of a certain age to know what they are)!

So far I have imported jpegs of the board (both top & bottom) into powerpoint, then traced over the PCB and superimposed the component symbols on this. Unfortunately there are limitations doing it this way. If I want to move any of the components around, the connecting node points don't move. Enter this rather stupendous piece of software:

https://www.kicad.org/

I stumbled across this and it seems that this might be the answer. My current thinking is to add all the components, then when I start connecting them together I'll delete the pathway off my powerpoint so that I can keep track of what is connected where. Hopefully this will give me a circuit that is all joined up so I can move things around to come up with a more accurate schematic. As a starter for 10 I may lay the components out in the same approximate positions as the Lead 12 schematic, start connecting them and see where it goes from there. If I can reverse engineer the schematic, at least I'll have a solid foundation to move forward. At the moment I'm stumbling around in the dark, although the help and advise that I have got from you guys and in particular @icbm, has been a maglite illuminating the way!

SteveRobinson

I can't help sorry but I used to love the smell of the solvent used in a Banda machine. Ours was replaced with a Gestetner which was never the same, except maybe that pink correction fluid which was heavenly.

Funkfingers

SteveRobinson said:

Gestetner 

Those were terrible. 

A journey I used to make took me right past Gestetner House on the Euston Road. It seemed appropriate to me that some of the company sign letters were missing - just like Sunshine Desserts in The Fall And Rise Of Reginald Perrin.*

Back on topic, I think that I have the Bass 12 schematic diagram in a book about the history of Marshall.

* You'll need to be of a certain age to get the Reggie Perrin reference.

barnsleyboy

SteveRobinson said:

I used to love the smell of the solvent used in a Banda machine.

Yep - that was the best bit about junior school, then in senior school it was tip-ex, and sniffing that opened up a whole different can of worms for the more unruly faction in the school!!

Funkfingers said:

Back on topic, I think that I have the Bass 12 schematic diagram in a book about the history of Marshall.

A scan of the actual schematic would really help!

Funkfingers said:

Sunshine Desserts in The Fall And Rise Of Reginald Perrin.*

An absolute comedy classic! Whenever I threaten to do a Reggie Perrin off Cromer beach, less and less people know what I'm talking about!

Funkfingers

barnsleyboy said:

Funkfingers said:

I think that I have the Bass 12 schematic diagram in a book about the history of Marshall.

A scan of the actual schematic would really help!

My mistake. The book has diagrams for the 5205 Lead 12, the Keyboard 12 and the later Lead 12 with Reverb. 

Another diagram illustrates 30w solid state amps for lead, for keyboard and for bass. It might be possible to extrapolate the information you need from these two diagrams.

barnsleyboy

Ah, no worries mate. I've already got those. I'll continue with my quest using Kicad. Post-scipt to my earlier post, unfortunately the links don't stay connected to the component leads when you move them, but it is still a rather impressive piece of software.

CasperCaster

I just recently found KiCAD as well, through Digi-Key. I haven't had much time using it yet but it does seem to have potential. Digi-Key also have a piece of software called Scheme-it which also has its uses. 

normula1

Before I had access to tools like Visio I used the built in MS Paint I created a series of shapes and just pasted them in

poopot

Try this:

https://bancika.github.io/diy-layout-creator/

Kittyfrisk

SteveRobinson said:

I can't help sorry but I used to love the smell of the solvent used in a Banda machine. Ours was replaced with a Gestetner which was never the same, except maybe that pink correction fluid which was heavenly.

I'm no help either, but Banda fluid was Isopropanol & Methanol mix (later with added yummy trichlorofluoromethane). I was the BandaMan, when I was duplicating bazillions of sheets for science classes 
Out Principal Technician used to nick cans of it to top up his car.
Stripped the paint off where it dripped on the outside & he eventually burned a hole in his pistons. Oh how we laughed...  

barnsleyboy

poopot said:

Try this:

https://bancika.github.io/diy-layout-creator/

Oooh! that looks interesting! I'll be checking that out tonight. Ta very much