Viewing underside of PCBs - UK Vintage Radio Repair and Restoration Discussion Forum

RogerWalker · 15th May 2009, 2:30 pm

Manufacturers often provide diagrams indicating the location of components on a circuit board; often with a ghost trace of the copper circuit underneath superimposed. Rarely do they provide a [much more useful] view of the copper circuit with component locations superimposed - a view of the underside. On a tightly packed PCB this makes it very difficult to apply one's soldering iron to the right pad when removing components.

In the past, I have had some success producing a reversed image by printing the component location diagram on thin paper, putting it in a scanner or copier upside down and getting an inverted image of the PCB through the paper. Depending on the clarity and darkness of the original, a fairly bleary inverted image was usually obtainable.

Recently, faced with a Philips scope to repair and having to remove a number of components for checking, I chanced upon a facility within Adobe Acrobat [in which I was viewing the .pdf manual file] to 'flip' the diagram horizontally or vertically - which produced a crystal clear view of the print side with components superimposed. The file has to be 'unlocked' to do this and I don't think the facility exists in the freebie Adobe Reader program. However anyone with basic computing skills and a scanner ought to be able to achieve the same result using Photo shop or similar image-editing software. Unfortunately, the flipping process also produces a mirror image of component references and values, but I just ink in the references/values of any components needing removal.

Apologies if this is common knowledge and has been reported before - it was such a Eureka moment that I wanted to pass it on!

Regards
Roger Walker

richrussell · 15th May 2009, 4:08 pm

A bright light placed behind the PCB (supported in a frame/blocks/vice/croc clips etc) can make locating which track a component goes to on the other side a lot easier too.

Nickthedentist · 15th May 2009, 4:37 pm

I sometimes scan the track side of a PCB that I want to reverse-engineer.

Then, I print out a mirror image (with the free Irfanview, choose image and horizontal flip).

This can by placed next to the board, tracks-down, and makes it nice and easy to see what's connected to what.

Nick.

Tom_I · 18th May 2009, 1:10 pm

A couple of times now, for this sort of thing, I have photographed both sides of a board, adjusted both shots to exactly the same size, inverted one of them, then printed one on paper, and one on an OHP transparency. You can then do a direct overlay of one on to the other. I have to say that it's better in theory than in practice, but it does work.

One thing I use all the time, which really does work, is a keychain sized laser pointer. Shone at one side of a board, it lets you identify the exact point from the other side.

Tom

RogerWalker · 18th May 2009, 11:03 pm

Thanks Tom - I have always been a bit queasy about pointing any kind of laser at my eyes - even with something as opaque as a pcb in between - but I can see it is a brilliant way of identifying what one is looking at. I will invest in a pointer and try it out.

Best

Roger

15th May 2009, 2:30 pm	#1
RogerWalker Hexode Join Date: Sep 2005 Location: Powys, Mid-Wales, UK. Posts: 289	Viewing underside of PCBs Manufacturers often provide diagrams indicating the location of components on a circuit board; often with a ghost trace of the copper circuit underneath superimposed. Rarely do they provide a [much more useful] view of the copper circuit with component locations superimposed - a view of the underside. On a tightly packed PCB this makes it very difficult to apply one's soldering iron to the right pad when removing components. In the past, I have had some success producing a reversed image by printing the component location diagram on thin paper, putting it in a scanner or copier upside down and getting an inverted image of the PCB through the paper. Depending on the clarity and darkness of the original, a fairly bleary inverted image was usually obtainable. Recently, faced with a Philips scope to repair and having to remove a number of components for checking, I chanced upon a facility within Adobe Acrobat [in which I was viewing the .pdf manual file] to 'flip' the diagram horizontally or vertically - which produced a crystal clear view of the print side with components superimposed. The file has to be 'unlocked' to do this and I don't think the facility exists in the freebie Adobe Reader program. However anyone with basic computing skills and a scanner ought to be able to achieve the same result using Photo shop or similar image-editing software. Unfortunately, the flipping process also produces a mirror image of component references and values, but I just ink in the references/values of any components needing removal. Apologies if this is common knowledge and has been reported before - it was such a Eureka moment that I wanted to pass it on! Regards Roger Walker

15th May 2009, 4:08 pm	#2
richrussell Heptode Join Date: Jul 2008 Location: Selby, North Yorkshire, UK. Posts: 979	Re: Viewing underside of PCBs A bright light placed behind the PCB (supported in a frame/blocks/vice/croc clips etc) can make locating which track a component goes to on the other side a lot easier too.

15th May 2009, 4:37 pm	#3
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,846	Re: Viewing underside of PCBs I sometimes scan the track side of a PCB that I want to reverse-engineer. Then, I print out a mirror image (with the free Irfanview, choose image and horizontal flip). This can by placed next to the board, tracks-down, and makes it nice and easy to see what's connected to what. Nick.

18th May 2009, 1:10 pm	#4
Tom_I Heptode Join Date: Jul 2006 Location: North Herts. UK. Posts: 549	Re: Viewing underside of PCBs A couple of times now, for this sort of thing, I have photographed both sides of a board, adjusted both shots to exactly the same size, inverted one of them, then printed one on paper, and one on an OHP transparency. You can then do a direct overlay of one on to the other. I have to say that it's better in theory than in practice, but it does work. One thing I use all the time, which really does work, is a keychain sized laser pointer. Shone at one side of a board, it lets you identify the exact point from the other side. Tom

18th May 2009, 11:03 pm	#5
RogerWalker Hexode Join Date: Sep 2005 Location: Powys, Mid-Wales, UK. Posts: 289	Re: Viewing underside of PCBs Thanks Tom - I have always been a bit queasy about pointing any kind of laser at my eyes - even with something as opaque as a pcb in between - but I can see it is a brilliant way of identifying what one is looking at. I will invest in a pointer and try it out. Best Roger