reverse engineering schematics

[SleeplessDad]

Hi Everyone

I service instruments used by Chemists. The OEMs have not provided schematics for about 10 years now and they obsolete instruments in about 5 years. I am having trouble servicing the relatively newer instruments and in a few more years I will be really screwed.

Does anyone have advice on how to go about reverse engineering schematics. I have been searching for x-ray imagining services but have not had much luck

Thanks in advance-Patrick

 

[chemelec]

Hi Everyone

I service instruments used by Chemists. The OEMs have not provided schematics for about 10 years now and they obsolete instruments in about 5 years. I am having trouble servicing the relatively newer instruments and in a few more years I will be really screwed.

Does anyone have advice on how to go about reverse engineering schematics. I have been searching for x-ray imagining services but have not had much luck

Thanks in advance-Patrick

Welcome to the NEW World.
Unfortunately, Even if you can Reverse Engineer these products, It probably won't help you much, because of the Many Microprocessors and Custom IC's, being used in them.

We now live in a Fast Changing, Disposable and Throw away world.
Manufacturers GREED!

Maybe Time to consider a New Profession, Before it becomes Really Impossible to do your present job.

 

[Leftyretro]

Yes, this has been going on for decades. As a field engineer for a minicomputer manufacture in the 70s, we generally repaired circuit boards in the field down to the component level. Then gradually the components and modules changed with ever more dense and custom components that service became a board swapping thing by the mid to late 80s, totally dependent on getting replacements from the factory. I loved the challenge back then of troubleshooting using scopes and soldering irons, but times change, tech changes and the same job is much different now, and I suspects it pays less in real dollars then it did back then.

 

[Nigel Goodwin]

Hi Everyone

I service instruments used by Chemists. The OEMs have not provided schematics for about 10 years now and they obsolete instruments in about 5 years. I am having trouble servicing the relatively newer instruments and in a few more years I will be really screwed.

Does anyone have advice on how to go about reverse engineering schematics. I have been searching for x-ray imagining services but have not had much luck

As suggested, you're probably going to struggle anyway, because of custom spares - but, ensure you obtain schematics as soon as the products are released, don't wait until you can't get them any more.

Drawing out schematics of anything complicated, and using multilayer boards, is next to impossible. Even drawing out a simple audio amplifer circuit accurately takes a few hours.

 

[SleeplessDad]

Thanks to everyone for their posts.

It looks like the response is a universal "bad idea don't" but I can't let this go. I may start a new thread regarding how long people actually spend on repairs. I don't have any friends or family that service boards, I have no point of reference.

Our comrades repairing VCRs for a living are in a bad spot. What could you possibly charge for a $50 VCR. However the "throw away" society has not yet overtaken my business model. Can you really throw away a 50K instrument, of course not but if the manufacturer will not sell you a new circuit board and they try to sell you a prettier version of the same thing, well you better hope that someone can fix the board.

It is still feasible for me to spend 40-80 hours on a single board. Do these responses still apply to me, in this case?

If they do not, does anyone have some suggestions about how to go about reverse engineering a board?

Thanks again to Nigel, Leftyretro and Chemelec

 

[blueroomelectronics]

Start by posting a clear photo. A glimpse at the chips used will offer insight on its difficulty.

 

[tonigau]

Something that works for me with simple boards is to take well aligned photos or scans (depending on the height of components).

I scale the 2 photos as objects in Corel draw & set them to lock.
Then trace over the tracks, .then add the pads
Any tracks that are the same Copper are grouped to aid netlist creation.
Flip the tracing to the component side & add in the parts.
In corel draw the parts are objects so only need to draw them once & then past... its actually quite fast.
Now the circuit can be analysed much easier than turning over the board to look at the other side & making mistakes trying to visualise & remember the previous side.
Should be able to do the same with a PCB cad program if it can import a photo could import a photo, one could trace this with tracks, place pads & components then generate a netlist to import into schematic capture.


example tracing XV TCI.gif...


I once had to reverse engineer some generator plugin control cards to the extent of using 2 PCB's to mimic the mechanics of the connectors that were no longer manufactured. Total cost including spares was about 3K$ but at the end of the day the small village had reliable power again.

tonig.au

 

[MrAl]

Hi there,

I've done something like this in the past. I use two ideas...

One is to scan the bottom of the board with a regular scanner.
The second is to shine a flashlight on one side of the board while
looking on the other, but this only helps when the board is translucent.

It does take hours though. A little driver board i did once just to understand
it (not really because i wanted to service it) took about two or three hours.

Taking a scan of the top where the components are helps a little, and then look
at the board and fill in the top traces manually in a good paint program. Still
not easy though.

What i dont know is how you are going to get replacement parts if some of the
devices are in house numbered or in house programmed. You'd have to have
a cross reference and/or a list of the program, as well as a programmer for
whatever chip is required.

 

[SleeplessDad]

Thanks Tonigau and MrAl

I am am an experienced GIMP and Inkscape user(open source alternatives to Photoshop and Illustator) these techniques would likely work well for me, thanks.

I have posted a photo of a board I am trying to repair:
**broken link removed**
It is about 4.5K U.S.
I tried my best but the chips are hard to read. The CPU chip is a:
MC68332GCFC20

The main feature of the detector that this board is part of is the two analog signals that come from an optical bench. The signals are compared, one as sample, one as reference. There are lots of op-amps on the board.

Any feedback as to where other service people would rank this board in terms of difficulty would be really appreciated.

Thanks-Patrick

 

[tonigau]

With regard to repairing this board, without a diagram or circuit operation description I would rank reasonably difficult to very difficult, but then it depends on other factors as well...

How much is known about its operation & the nature of the fault.
What external influence is likely to cause a failure.
How accessible is the board when connected to equipment.
....

I repair control & I/O boards for railway signalling & the faults are very predictable most of the time due to the similar external influences & other similar environmental influences.

There is always the basics to check for: Contacts, IC socket pins, crystal oscillators, data & address lines, hot IC's, transistors, power rails, supply current, visual.
& dont forget the good old resistance/ diode drop check & good board / bad board compare.
You can always trace out part of the circuit if this area is suspected.

4 common causes of failure are:
1. Component end of life,
2. Assembly weaknesses (eg: solder joins)
3. I/O - Damage from driving shorts or over voltage applied inputs.
4. Connectors(including IC sockets) contamination, corrosion, weak contact springs.


-----------------------------

As far as reverse engineering this board It would take considerable resources, & there could be stubling blocks as previously mentioned.
U3 Looks like a flash ROM however there may be some code in MCU & might be locked, Xilinx FPGA might be locked to disable reading - . there could be a jtag (in circuit programming) connector on the board.


You would need to evaluate feasability before starting :
Code accessible
Parts available
SMD parts often difficult to ID (diodes, Transistors, Caps. (although most caps will be decoupling)

Then there is many hours of tracing out the circuit, this board is reasonably complex, some tracks under components, vias look solder masked (hard to beep)
You will likely get errors in Rev. 0 proto type.

Another approach to reverse engineering is to replicate the functionality of the board but this requires indepth knowledge & understanding of all aspects of operation & any safety operating requirements.

Have you tried contacting someone in technical at the manufacturer, I have had success this way in getting tecnical data.

It might be better to focus resources on repair if the down time can be tolerated.

Tonig.au

 

[SleeplessDad]

Hey Tonig.au

Thank you for your great post. That was packed with so much useful information, I really appreciate it.

I just wanted to mention that the reverse engineering is for circuit analysis only and it is okay to have the equipment down for a while and I wanted to mention that the manufacturer hates me very much. They hate anyone who dares to service their equipment

Thanks once again, there is lots of useful information to digest here.

All the best-Patrick

 

[Mikebits]

SleeplessDad. If you can reverse Eng that circuit board, I think there will be many companies wanting to hire you.

 

[Mikebits]

Out of curiosity, was the circuit board for some sort of spectrograph gizmo thingie?

Maybe you could make a service contract agreement with the OEM's. Perhaps you can form some sort of mutualistic symbiotic relationship. The scratch my back your back sort of thing. If you have the client base I would think you and the OEM's might talk some sort of a deal.

Just a thought... Then again what do I know

 

[SleeplessDad]

Hi Mikebits
Yes it is from something similar, I'll send you all the details offline-Patrick

 

[blueroomelectronics]

SleeplessDad. If you can reverse Eng that circuit board, I think there will be many companies wanting to hire you.

It's a major task, infinite time and patience. PLUS it appears to be a multilayer PCB which means near impossible. IMO it would be far cheaper to buy a dozen spares at $4500 unless your time and effort are worth nothing.

 

[Snaz]

where i used to work, sounds very much like this. to me it was outdated but you did learn alot by doing it. it was a very small shop, and we took anything industrila like motors, heater controls, timers, power supplies, etc. and we never had schematics and the only complaints were, it dont work. so literally you had to sit there and draw it out to determine what kind of power it used, how much, and sometimes they would send in just the board and you never knew what you were even working on. i worked there 6 weeks and i realized i was in wayyy over my head.

taking a board and drawing a schematic of it to me, was the hardest thing i ever tried to do. the other 2 techs i worked with, both had worked here doing this for about 25 yrs a piece. it was like walking thru the backyard to them. my first electronics place i worked was called tyco. we did RF stuff and it was easy. the mobiles and portables were DC and you had schematics and they would tell us at orientation for new hires, that component level replacement is out, when in doubt, change the board out.

this last place they actually made you do component level replacement. we didnt have spare boards and often times you had to order your parts. 2 yrs of college did NOTHING to prepare me for this and i dont know that it could. alot of the stuff i have learned i think could only have been learned by experience. once i figured out how to hook something up, it would usually take me 4-5 hrs to test, trouble shoot and as long as we had parts replace whatever was wrong. curve tracers are your friend though. i used them to help me locate the path of the circuit. i am glad i no longer have to do that though as it was mentally tough some days. we didnt have any time limits on how long you had to fix something. and there are some days it would take me all day to figure out what was wrong with something. say something had like 10 IC's, and you had to use 10 signal gen's to input signals, that took time to set up and then you had to get the pin outs of those IC's to see if they were any good. that also took google time there lol.

if you do try and map out the schematic, best of luck, and what i learned is use pencil, coz you will make mistakes along the way, and at first try to figure out where everything is eventually going. is there anything going off the board? is there any inputs from connectors on the board? stuff like that.

 

[SleeplessDad]

Thanks Snaz

That was a big help. I have actually been looking into a Huntron tracker or rigging up my own with the schematics people have graciously provided.

It is great to learn from your experience-Patrick