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Consultant Recommendation Request
thermistor-guy:
--- Quote from: Poe on February 25, 2021, 09:39:50 pm ---...
It's possible that the Chinese CM and/or the designer could have been asked to make changes that we never documented.
Although the new CM might also have build issues. This is what we need someone to help us determine.
...
--- End quote ---
Yes, I've seen this in practice, although some time ago.
In one case, the PCB files at the CM didn't match the schematic and PCB files at the design house. The designer made
some "last-minute" changes shortly before he left the company. It was a 5-person start-up, so forget about version control.
It wasn't just connectivity (tracks), there were also problems with PCB hole sizes for through-hole components.
Another case: a problem with PCB footprints. The PCB footprint for a high pin count, fine-pitch component was slightly off
- the pitch was too small. The CM could sometimes make the component connect to the pads, just barely, with careful manual touch-up,
but not always. The CM informed the client company there was a problem, but somehow the message didn't sink in. You could just detect
the pin pitch discrepancy with the naked eye. Several revisions of the PCB went through the CM, with the same bad footprint.
Until one day, a particularly handsome and dashing engineer (ahem), new to the company, took it upon himself
to audit the board's PCB library, and clean up all the problems in one go. Rumor has it that he particularly enjoyed standing over
some snooty PCB layout specialists, demanding that they justify every dimension of every footprint ... NOW.
Auditing the design and build files you have, against what the old CM was supplying you, is a good place to start.
Tomorokoshi:
Can you add a little more about this:
--- Quote from: Poe on February 25, 2021, 09:39:50 pm ---...
Now the design company is gone and the Chinese CM is not cooperating.
We tried to build a batch of boards with a different CM, but they're all failing with the same symptom.
It's possible that the Chinese CM and/or the designer could have been asked to make changes that we never documented.
Although the new CM might also have build issues. This is what we need someone to help us determine.
...
--- End quote ---
1. What was the relationship between the original design company and the original Chinese CM? Was the original Chinese CM subcontracted through the original design company? What made them become "not cooperating"? Is the problem one of not building the boards, not providing build documentation, not providing design files, etc.? Is there a translation problem? Do you have a representative in China?
2. Did the original Chinese CM order or manufacture the blank PCBs? Is the new CM using a different supplier? Note that sometimes either a CM or the PCB manufacturer will analyze the PCB Gerber files and determine that some dimension is not right, add some feature for the carrier pallets, etc. That means the actual delivered PCB may have some variation that isn't in your design files. Additionally, the PCB layer stackup thicknesses may not be the same. Check if those are specified on the PCB print.
3. Who managed the relationship with the original designer?
4. Whatever consulting or engineering route you go, make sure they get examples of the older functional boards. Allow enough that a couple can be modified to compare sub-circuits between the two builds.
Ice-Tea:
Sending out a failed board is good, sending out a failed board together with a working board from back when "things were fine" is probably even better ;)
Poe:
Blueskull - Unfortunately all I have is a multimeter and a soldering iron from the early 80s. I'll see if I can check some of that though. Thank you.
Thermistor-guy - I've experienced a scary number of big companies dependent on suppliers to handle their documentation control. It's crazy.
Tomorokoshi - There was no relationship that I'm aware of between the company contracted to design and the original CM selected to build. The new CM is using a different bare PCB supplier since we have no record of the original CM's bare PCB supplier. Our files appear to match the original CM's boards, but we can only do simple visual inspections. We have a stackup which defines an impedance for each layer and thickness, but we can't tell if the new CM followed it.
AndyC_772:
This really doesn't sound like a difficult problem; there's a hundred reasons why a new batch of boards from a new supplier may not work, and very few of them are as obscure or difficult to track down as passives that vary slightly between manufacturers.
Start with the basics. Look up all the ICs on the board, check their data sheets and see if any of them contain non-volatile memory. If they do, swap them between a working board and a non working one.
Check the supply rails. Check the clocks. Are they all ticking? If not, does something need programming? Some crystal oscillators come with factory programmed PLLs; do you have any of these, and are they programmed as they should be?
Test and see if anything on the board is working.
Check connectivity between the ports and the devices they connect to; it could just be a poor quality connector, or one which superficially resembles the correct type but has a different pin-out. (I've seen this, especially Ethernet).
Plenty of components come in subtly different variants - different speed grades, or versions with/without features enabled. Do the markings on the parts on the new boards match those on the working ones?
Are any parts held in reset? What normally causes them to come out of reset? Is there one part that wakes up the others?
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