Practices for Analyzing and Modifying Consumer Electronics

[Jubilee]

Hey y'all! First time posting here. I asked this over on stack exchange, but I'm a little worried it's too subjective, so I thought I'd try joining a few EE communities and asking around. Copy pasting below:


I'm an Engineering student in my junior year and felt it would be good practice to analyze and modify consumer electronics, particularly with the goal of programmatically controlling sound/light as I also have some interest in music.

I picked a simple children's toy (https://www.walmart.com/ip/Fisher-Price-Laugh-Learn-Sis-s-Remote-Baby-Toddler-Learning-Toy-with-Music-Lights/46239158) to start with and removed the circuit board. When trying to draw a representative diagram, I ran into some issues with being unable to characterize certain portions of the circuit (picture included here: https://i.sstatic.net/E4845PBZ.jpg)

My primary concern is this: There are multiple areas where several components have their connections somewhat obscured by, or possibly interconnecting with, a larger grid. I've indicated one of these with an orange arrow. For example, C7 seems like it links to the negative terminal with a single trace surrounded by many smaller traces, but it also looks as though it connects to C3. So...

  1. Is there any more practical method of determining where connections lie other than removing each component? I expect because of the capacitors involved it would be difficult to just test for continuity, although there are many exposed points on the board that seem to be for that purpose.
  2. Is there a convenient method to do any analysis on the microprocessor? I have read about some methods for removing resin blobs with fuming nitric acid, but those seemed to be in a context where the chip was fully removed.
  3. Are there symbols or marks here I am missing that would indicate where an obscured connection is going?
  4.  Besides a multimeter, soldering iron, and microscope, are there any other tools that are necessary or beneficial for this kind of task?

Any advice would be appreciated. Thank you for your time


End copy paste. Since we're not on Stack Exchange and this is a little more discussion oriented, I would also love to hear about your experiences with analyzing and modifying electronics, and if there's any general best practices you might recommend. Pleased to meet y'all and thanks again!

[tggzzz]

Since we're not on Stack Exchange and this is a little more discussion oriented, I would also love to hear about your experiences with analyzing and modifying electronics, and if there's any general best practices you might recommend.

Welcome to the forum.

That is a very perceptive comment about the difference between here and stackexchange. IMNSHO stack exchange is useful for "which button do I press to zaptangle the squirdilflopp" and similar boring questions.

You are beginning to realise that there are several levels at which circuits can be analysed and modified. The appropriate techniques, if any, will depend on the level. Examples:

• complete subsystem, black box. Here you observe the signals going in and out, compare those with the instruction manual, and match all that with your mental model of what is happening internally. !modification is changing the controls defined in the manual, and/or adding circuits to change the input output signals to match your purposes
• transparent box hardware. Here you have the schematics and can probe or modify signals on the board. PCB traces can be cut when helpful.
• transparent box software. Here you have the source code for the software, can change and compile it, and download it into the hardware.
• beyond that it becomes progressively more difficult, time consuming, and requires specialised equipment. Reverse engineering hardware and software is not for the fainthearted! You need to consider how much your time is worth.

A very different but related topic is repairing something broken to get it to work again. In these cases you need to understand generic failure mechanisms and how to spot them. A detailed understanding of the device internals is not required. Examples: aged electrolytic capacitors with high ESR, dirty connectors and switch contacts, inputs damaged by overvoltage, outputs damaged by short circuits.

Have fun, safely. (Fuming nitric acid is not safe!)

[44kgk1lkf6u]

The entire mesh is the ground pour.  One learns that the entire visible layer is a single layer.  That board does not have very large capacitors.  So they should not cause a problem.  The threshold where a multimeter starts beeping is on the order of 100 Ω.  A ceramic capacitor like featured in the picture tends to be at most on the order of 10 μF.  That gives a time constant of 1 ms.

I would not try to study the microprocessor.  In a high volume product like this, the microprocessor may well be programmed by OTP memory or even mask.  If I need to change its behavior only a little, I may try to connect something to trick it into behaving as if a button is pressed.

The mesh tells it is likely a ground plane.  And like they have said on Stack Exchange, the connections are all visible.

More experience is likely the most useful.  Someone used to looking at circuit boards like this can tell what things do simply by looking at the picture.  As for tools.  An LCR meter in for measuring the capacitors.  An oscilloscope in case you need to figure out what the blob of resin does.  Probes sharp enough to pierce conformal coating for boards that have it.  Wire brush or wool for finding connections on large boards.

I wish my coworkers were all like you.  Some of us lack what you are learning as you do this.

[golden_labels]

Hey y'all! First time posting here.

Welcome to EEVblog forum.

I’ll answer each question separately below, but two general points:

• Knowing common circuits. It helps analysis a lot, if you can quickly spot familiar patterns. Virtually everything, in particular consumer goods, contains no unique, “rocket science” designs. That also makes you quickly realize that some connections would make no sense at all.
• Comparing with datasheets. Most circuits built around chips are literal copies of what is in chip’s datasheet. Where not, it usually remains very similar. Looking at diagrams in the datasheet also makes you aware, what connections make no sense.

1. Is there any more practical method of determining where connections lie other than removing each component? I expect because of the capacitors involved it would be difficult to just test for continuity, although there are many exposed points on the board that seem to be for that purpose.

A capacitor conducts for only a short moment. After that it is equivalent to no connection.

2. Is there a convenient method to do any analysis on the microprocessor? I have read about some methods for removing resin blobs with fuming nitric acid, but those seemed to be in a context where the chip was fully removed.

The keyword for what you mention is “decapping.” But this isn’t really of much value, unless you go truly deep into reverse-engineering. At least assuming you mean an actual microprocessor and not just any chip. Even 1980s microprocessors were already very complicated. Nowadays they’re beyond human comprehension and you end up using image analysis to scan microcode, or finding a way to extract EEPROM/flash data. And another year trying to wrap your head around that, risking being sued for IP violations. Again, I stress: for proper microprocessors. You may have much more luck with smaller chips, but decapping is generally a process requiring quite expensive gear (also for your own safety), and some knowledge. To get some feel, see IC die photos at Zeptobars or Ken Shirriff’s series on 8086 CPU (e.g. this about address bus, which already presents only an extract of his conclusions).

Are there symbols or marks here I am missing that would indicate where an obscured connection is going?

Other than the mark for chip’s pin 1, usually no. However anything, that lets you understand the entire circuit, is of value.

4.  Besides a multimeter, soldering iron, and microscope, are there any other tools that are necessary or beneficial for this kind of task?

A microscope will not be needed: a good magnifying glass is usually more than enough. Even more so: a way to take good photos, so you could use your favourite graphics program to mark traces. Nowadays even a decent smartphone has a camera good enough, but you must find a way to have good light and a stable support.

I asked this over on stack exchange, but I'm a little worried it's too subjective, so I thought I'd try joining a few EE communities and asking around. Copy pasting below:

SO is a different kind of a place. It’s a content aggregation business. Here Dave offers a forum for the community, or at least I believe so. Also note that the forum offers attachments. Better to include images that way.

[RJSV]

   {duplicate}

[RJSV]

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[inse]

A couple of years ago I read an article, possibly on Hackaday, about Circuit Bending - creating strange behaviour or sounds by shorting ‘random‘ traces on electronic devices.
Maybe that search term will return interesting resources.

[RJSV]

Hello ?
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