Tips for creating schematic of circuit (for troubleshooting) - Page 1
Forum section: electronics / projects

author: staze
author_rank: Frequent Contributor
timestamp: June 23, 2014, 07:13:29 pm
content: All,Curious if anyone has any tips for creating schematics from a circuit (that doesn't have one publicly available) for troubleshooting?Reason I ask, I have the Remote Control Unit from a garage door opener that, for some reason, isn't working. The relay isn't tripping, but can be tripped manually by applying a voltage to the coil (so, it's good).Anyway, thought this would be a good exercise in drawing out a schematic for the purpose of troubleshooting. Or, should I just not bother and just troubleshoot up the line?Wish schematics were available for everything.... =)

author: MickM
author_rank: Regular Contributor
timestamp: June 23, 2014, 10:19:28 pm
content: Hi;Take the pcb's and scan them both sides with a flatbed scanner..Then reverse the foil side and print it out.Draw on it in say red, the components.Scan that, to save it as you will need new copies.Then its just a matter of datasheets and coffee.Mick M

author: staze
author_rank: Frequent Contributor
timestamp: June 23, 2014, 10:20:46 pm
content: Quote from: MickM on June 23, 2014, 10:19:28 pmnot bad. I would assume use some type of schematics software, since erasing and redrawing sections would get kinda old... =P

author: What_NZ
author_rank: Regular Contributor
timestamp: June 23, 2014, 10:57:58 pm
content: Quote from: MickM on June 23, 2014, 10:19:28 pmPrinting the PCB's onto transparency film and holding them together can make following tracks easier. Adjust the contrast to get the tracks to stand out and not the board.

author: SirNick
author_rank: Frequent Contributor
timestamp: June 24, 2014, 08:42:25 pm
content: You're basically looking for an OCR-like solution for PCBs then? Yeah, never heard of such a thing. Reverse-engineering a PCB to schematics is pretty much a manual endeavor. For something simple (like a modest remote control), it's anywhere from a few minutes to a few hours of work.Just be glad you don't work at One Hung Low, reverse-engineering smartphones and such. That's the very definition of 'tedious'.

author: staze
author_rank: Frequent Contributor
timestamp: June 24, 2014, 08:47:00 pm
content: Quote from: SirNick on June 24, 2014, 08:42:25 pmGod, that would be awesome, but no. I meant just software for schematic diagramming rather that drawing it by hand (since that would quickly turn into a rats nest).Oddly, this is all a bit academic since the circuit works. It just didn't like one remote... go figure.

author: tautech
author_rank: Super Contributor
timestamp: June 24, 2014, 09:02:27 pm
content: Quote from: staze on June 24, 2014, 08:47:00 pmVisio can do that.

author: jlmoon
author_rank: Unknown
timestamp: June 24, 2014, 09:48:06 pm
content: Quote from: SirNick on June 24, 2014, 08:42:25 pmEspecially when it comes to multilayer boards.

author: SirNick
author_rank: Frequent Contributor
timestamp: June 24, 2014, 10:52:25 pm
content: Quote from: staze on June 24, 2014, 08:47:00 pmOK, so are you looking for recommendations for schematic software, or something like an auto-router for schematics?If you mean to draw the schematic yourself, but are just hoping to use something more purpose-built than Paint or Visio, check out ExpressPCB. They're a board house that gives away (proprietary) software. It comes with ExpressSCH, which is a decent and easy-to-use schematics capture tool.The PCB tool is also super easy to use, but saves in a native format that is only useful for making PCBs through their house. Schematics are schematics though. The PCB tool can still be useful if you're a beginner looking to learn how to design your own boards, without drowning in the complexity of the bigger CAD packages. Robot Room's Copper Connection will read ExpressPCB files and export them to Gerber if you ever need to. (Although it's nearly as simple as ExpressPCB, so you might just skip the middle man instead.)

author: staze
author_rank: Frequent Contributor
timestamp: June 24, 2014, 10:54:26 pm
content: Cool. I'll have to figure out something... =)

author: liquibyte
author_rank: Frequent Contributor
timestamp: June 24, 2014, 11:19:10 pm
content: Mount a camera/phone in a static place. Mark place for board. Place board and take pic from top. Flip upside down and take pic from bottom. Open both pics in GIMP and copy one pic to new layer in other pic. Choose a layer, Layer>Transform>Flip Horizontally. Adjust one layers transparency to suit to see through to the other layer.I've done this many times trying to troubleshoot boards and it works well but you need to make sure the camera and boards are in the same place so that you don't have to adjust the layer sizes to make them line up.

author: amyk
author_rank: Super Contributor
timestamp: June 25, 2014, 12:16:58 pm
content: Quote from: jlmoon on June 24, 2014, 09:48:06 pmThe professional RE services depopulate the board after noting where the components are, then use an automatic flying-probe scanner to recover the netlist.

author: richfiles
author_rank: Regular Contributor
timestamp: June 27, 2014, 04:30:43 am
content: I've successfully managed to map the schematic of a TI-85 calculator main board, back the the 1990s, using a multimeter and a lot of patience. I think your project might not be too bad. I can't say how the radio circuits would be. I'm less familiar with the nuances of those bits. I've always been a logic guy, myself. Truth is, troubleshooting up the line is probably the most logical thing to do. Are you having issues with a radio based remote unit not being detected, or any action, including the wired buttons? Do you have multiple remotes, or just one? Never forget the ever obvious... Is my battery good/in the right way questions... We are ALL guilty of missing the obvious on occasion.A few things to consider, might be if the relay is simply the last stage, to actually activate the final drive stage, you should look into the emergency stop photo detector. if it's misaligned or non functional, it might prevent the unit from operating. Most garage door openers will toggle the light to "announce" that it detected an obstruction though.If you do want to continue mapping out the schematic, even if only as an exercise, I'm certain that it's possible, even if it does seem daunting...I have a rather daunting schematic reverse engineering task myself... Not sure if I'll ever get around to it. I DO want to do it, for the sake of preservation though.I have a 1965 SCM (Smith Corona Marchant) Cogito 240SR calculator that desperately needs servicing. The machine has a fault in the calculating logic, which unfortunately consists of 6 large PC boards that consist of almost NOTHING BUT resistors, diodes, and transistors. No chips at all! There are 4 smaller PC boards that appear to be associated with the CRT display, and a small pair of PC boards that are related to the magnetostrictive delay line memory. All those boards, and they're wired together with plug in cables... No socketed back plane. WHY can't things be simple!Fortunately, if it's any consolation... the boards appear to have all the components very nicely laid out in a grid. No clue about the traces beneath.I don't doubt Icouldmap it out, given enough time and unfathomable levels of patience to do it. It's that it only uses about 3 or 4 major part types to perform logic! Even AFTER mapping out the schematic, I'd have to actually figure out and organize what diodes and resistors are grouped together, and what logic function they perform! I have no idea if there is any way to test the boards live either... They are not situated in a means that appears to make that simple. Hybrid modules are also troublesome... They are like chips with no datasheets. Joy.At least it is still an amazing piece of history, and quite the sight to look at, even if it is not functioning at 100% anymore.I was considering using a program like Eagle to try to create an approximation of each of the PCBs, and see if it can generate the schematic off of that. Not sure if the process can go in reverse. I suppose, another option would be laying out all the part symbols exactly as they lay on each of the PC boards and then making connections based on the actual PC board layout might work too. Once the nets are made, I imagine you can play around with arranging them in a more logical arrangement. Just start with a part, move it, and then move the parts the net connects to before or after it or beside it based on where the part connects. Eventually, recognizable logic gates and structures would be spotted, and could be further arranged logically....Oh dear... I have my work cut out for me.Sorry... that message was huge... felt like it was taking over your post. Trimmed it to just the relevant bits and made a separate post for my own stuff.Separate post for my Cogito 240SR:https://www.eevblog.com/forum/projects/scm-cogito-240sr-calculator-(1965)-schematic-mapping-repairs/

author: vk6zgo
author_rank: Super Contributor
timestamp: June 27, 2014, 05:28:00 am
content: Quote from: staze on June 23, 2014, 07:13:29 pmDo you have any test equipment?Some of those things work at 27MHz--- if so,you should be able to see any RF coming out of it,using a 'scope with a loop on its input.There is probably a crystal there somewhere,so you should be able to see if that is oscillating.What does happen with these things is that the external buttons stop making good mechanical contact with the small PCB mounted switches.Have you tried pushing them directly?Even comparing the good one side by side with the faulty one may not only find your fault,but make it easier to draw a schematic,as you can look at opposite sides of the two boards.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 27, 2014, 07:10:26 am
content: Even if you only make minimum wage flipping burgers, it isn't worth the time to repair those things when total replacements (transmitters and receiver) are so remarkably inexpensive. And certainly not worth the time to trace out the schematic, IMHO. Unless you need practice drawing schematic. Or you are restoring some valuable antique garage door opener (is there such a thing?) If you want practice reading schematics and troubleshooting, there are plenty of things to practice on where you can download the original schematic in a few seconds from the interweb.

author: miguelvp
author_rank: Super Contributor
timestamp: June 27, 2014, 07:17:57 am
content: Quote from: Richard Crowley on June 27, 2014, 07:10:26 amI actually started to reply to mention "Then again you can go to Home Depot and get another one" but cancelled because.. I don't know, I guess I should have post it, it doesn't sound like a mean response even if I thought at the time it was mean.

author: MickM
author_rank: Regular Contributor
timestamp: June 27, 2014, 08:23:54 am
content: "not bad. I would assume use some type of schematics software, since erasing and redrawing sections would get kinda old... =P"No redrawing, just re-printing.I use gimp to make it B/W and adjust the threshold, then print it out and color between the lines.I use different colored hi-liters.Once you have the major signals figured out, then use eagle to draw the schematic.Change the eagle part numbers to match the silkscreen, if any.If not, then number them on a printout from top left to bottom right, and use those.This will give you the signal names and whether it it is an input or output.Also this lets you see what pins you missed.I don't try to make the schematic legible at this point.I just try to make sure most of the pins are connected to something.You can move and spin the parts later.Then just refine and repeat.Mick M