EEVblog 1415 - Reverse Engineering the DP10007 Differential Probe

Reverse engineering the Micsig DP10007 high voltage differential probe.
Turning the PCB into a schematic.

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[pnjunction]

I think the dual n/p channel transistor arrangement is actually an h-bridge for switching the _latching_ relay. Cool videos! Love that stuff!

[somo]

The relay is AGQ210A03 which is 1 coil latching, so relay keeps position without power. Therefore you need bipolar driver to reverse voltage for switching.

[richardrudek]

I just use GIMP. Add layers (one reversed, of course), set the alpha channels, then toggle the visibility of the top layer as needed (eyeball icon on the layers toolbox). You can even set a shortcut key to toggle the visibility of the *current* layer. Not perfect, but better than printing stuff out...

[somo]

The PCB capacitor is for matching the positive and negative input(impedance). If the capacity matches you don't use them. The input with the lower capacity will get additional PCB capacitor for best match. High voltage capacitor have higher tolerance, so you might need this matching mechanism.

[benhoffman]

Just a comment on getting good images for reverse engineering. About 15 years ago I was doing a first article inspection for a power supply I had designed after I received it from the factory. I figured out that instead of sitting in the lab at a microscope to inspect solder joints and looking for flipped/rotated components, I could just scan both sides of the board on our copier (at high resolution), and then I could inspect the board at my desk by zooming in and viewing the scanned image. A big advantage of "taking a picture" with a flatbed scanner is that every part of the board is seen as if you are looking at it from directly above (which of course is how the image is captured by the scanner). Scanning an assembly would give you the same advantages when trying to reverse engineer a design, and it would also enable the images of both sides to be at the exact same scale.

[pixiepaws]

There is an auto-zero function. If you press and hold both x10 and x100 buttons at the same time, it zeroes the offset. So the microcontroller is doing a bit more than overvoltage detection.

[Ziferten]

"TI 98 OPMI" is an OPA2171 dual CMOS opamp.

[_hackwell]

hi the reason of the 2 6604 fets is that the AGQ210 is a latching relay single coil so I guess they're here to invert the voltage across the coli to make if change state

[TheDefpom]

Another trick for reverse engineering is to put the board on a light panel to shine light through it as it makes it a lot easier to see the tracks, I use one of my flat studio lights, on its back and just lay the board on top.

[DuroLabs]

How about starting a series about Reverse Engineering. ?
I would like to see videos like this :D

[c]

Dave, AGQ210A03 is a 3V single coil latching relay (relay is set and reset with different direction coil current). To drive a latching relay two complementary mosfets are required configured as a H-bridge, so the 6604 is a N- and P-mosfet pair. Latching relays are often used in battery powered applications .

[caggius]

This brought back a lot of memories. Back in the early 80's I did all of my own board layouts (for logic card test equipment) using the forward version of this - i.e. acetate projector copies of top, bottom and 2 internal power layers in different colours sheets then using foil pens to add the connections - great fun. Passed the roughs to the CAD team who would tidy them up and send me back proofs - back to the photocopier with colour acetates and check everything out before having them sent out for etching.

[kiq]

We have several (15 maybe ?) of these probes. We do have a few that developed a DC offset that can not be calibrated out by pressing and holding the 50X and 500X buttons. This video might help us to fix those ! Thank you Dave ! 😁😀
Yes, I'm you're uncle ! (bob)

I bet that the extra circuitry has to do with the microcontroller's role in adjusting the offset when you short the input probe and hold the two buttons down for a few seconds. A/D input, being slow-ish, would also make sense for that role. Read the offset and inject another offset to counter it.
That is what I would probably do anyway

[luiurco]

I think the feedback from output is for automatic zero adjust voltage and over-voltage detection.

[listerdave]

@3:55 I use an ancient Paintshop Pro to do just that for reverse engineering PCBs. I start layers for the front and back of the PCB, then I add layers for front and back traces, which I trace manually, often in different colours depending on the function, for instance data lines, power lines, control lines etc and another layer for labels, mostly the componenet numbers.
I find it very useful but I have always wanted to make something more dedicated and have worked on and off on a custom application to do it in a more streamlined way though haven;t progressed much. In the meantime Paintshop Pro is proving quite helpful. I guess Photoshop could also be used but I found it very cumbersome for this sort of thing.

[shakaibsafvi]

I usually take off all components after taking multiple hi res pix of the fully assembled PCB... and then put the PCB without the components in a flat bed scanner and scan both sides. Simple !

[ppdan]

18:58 It's a latching relay so you need to be able to reverse the polarity on the coil.
Edit : wrote this while watching and saw that it was already mentioned ;)

[imqqmi]

I still have a flatbed scanner and use it to scan PCBs for reverse engineering/repair etc. All you need to do is rotate and align them, no lens distortion. Components shouldn't be too high or you do get some distortion, so mostly good with smd boards or bottom side. Scanned images also have a set DPI so you can do 1:1 printouts if that's needed and you can measure distance in software without having to convert number of pixels to measuring units. There's also panorama/stitching software like Hugin (open source/free) that can align images automatically based on a few points you give it. Or deep stacker software that can do the same if you don't want to do it manually. Hugin can also remove perspective and lens distortions.
I use Photoshop for alignment and Illustrator for annotations because it's vector based and is easy to scale/edit/change. But Gimp and Inkscape can do the same job, just a matter of preference and availability. I usually also change the colours between top and bottom layer for easier tracing out of vias etc. using the transparency slider to switch back and forth or using the layers panel eye on/off button.

[ninetailscosmicfox]

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[Stelios.Posantzis]

5:17 The proposed tool could easily do that too, i.e. align the two board faces, magnify, de-magnify, stretch, skew and remove lens distortion and shading as necessary all in one go.