Strange failure - Amstrad Manufacturing Flaw

[Bryce]

Hi all,
      at the moment I'm repairing a CPC (464 costdown version MC0044D) for @Shaun M. Neary and it's quite an interesting fault which I haven't seen before so I thought I'd share it here. The problem: The CPC works fine, but it was very unreliable at loading things from an M4. Shaun suspected that the contacts to the expansion were possibly worn out, but they actually look quite good. What didn't look good were the tracks going to the expansion pins.
Right before the contacts there is a crack running through almost all of the pins on the underside of the PCB. They're not scratches, because the green solder mask is still intact. They also aren't due to physical stress on the PCB because they aren't straight and they also taper downwards (ie: They are more of a valley than a canyon). That means that they happened during the PCB manufacturing or etching process. This is most obvious on the GND trace, but almost all signal pins are affected. The annoying thing is that they are all connected by a hair thin trace of copper, so they pass both a continuity test and all signals are present when measured with a scope. However, the cracks are limiting the current and dropping the voltage to any expansion and hence the M4 was having problems.
This is the first time I've seen a manufacturing quality problem on a CPC that made it out of the factory.

An easy but time consuming repair. I now need to remove all the solder mask in the area and bridge each crack with a wire or maybe just a blob of solder.

Bryce.

P.s. @Gryzor  Why can't I insert pictures inline anymore??

[Shaun M. Neary]

I don't know about you, @CraigsBar , but that was the LAST thing I expected it to be when we went looking at it a few weeks back!

Nicely done, as always Doktor @Bryce .

[CraigsBar]

I don't know about you, @CraigsBar , but that was the LAST thing I expected it to be when we went looking at it a few weeks back!

Nicely done, as always Doktor @Bryce .

No i would have never seen that! In fact i didnt

Sent from my ONEPLUS 3t using Tapatalk

[rpalmer]

Bryce,

This may be a production issue where they continuity tested only.

As for inline picture issue, maybe the image is the problem as some have suggested this may be the problem in other posts. If not contact the administrator to see what is said.

rpalmer

[rpalmer]

also can you use the pin header holes to insert the Centronics connector to avoid the edge connector issue?

[Shaun M. Neary]

also can you use the pin header holes to insert the Centronics connector to avoid the edge connector issue?

Bryce has given me that option. Given that I've peripherals for a 6128 plus, I've opted for the centronics fitting provided can fit the 464 case without butchering it 

[CraigsBar]

Bryce has given me that option. Given that I've peripherals for a 6128 plus, I've opted for the centronics fitting provided can fit the 464 case without butchering it 

You need to engage in extensive sanding on the case with the centronics fitted

Sent from my ONEPLUS 3t using Tapatalk

[Shaun M. Neary]

You need to engage in extensive sanding on the case with the centronics fitted

Sent from my ONEPLUS 3t using Tapatalk

Eh, I'll pass and stick with the edge connectors then, I think.

[Gryzor]

Cue jokes about it being under warranty etc.


Interesting find. Would it have affected expansions of the era?


As for the images issue, I'll fix it as soon as I find some time to breathe; it was due to a fatal flaw in an update that killed the entire forum. A fix was released, but I haven't had the time to try it just yet.

[Bryce]

Bryce,

This may be a production issue where they continuity tested only.

As for inline picture issue, maybe the image is the problem as some have suggested this may be the problem in other posts. If not contact the administrator to see what is said.

rpalmer

It's extremely unlikely that load tests would be done on those contacts, a simple continuity test only most likely. Load tests are only ever done on things like power supplies.

And yes, a centronics connector would definitely be the best option. Does the case really have to be modified for centronics on the plus? I thought they had gone for a standard case by then? Can't find any comparison pictures on the interwebs.

Bryce.

[Bryce]

I'm leaving this picture here for Shaun to demonstrate that a single padded envelope is not sufficient packaging to send a CPC PCB:

Bryce.

@Gryzor: The inline picture insertion still isn't fixed.

[Shaun M. Neary]

Fuck! 

[gerald]

My contribution 

Second pin from the left is A0 from the ASIC to the DRAM (through a 33 Ohm). The track is missing and only re-appear once under the solder mask.
Oddly enough the GX4000 was working before exhibiting symptoms of dead RAM.

[Bryce]

Has a capacitor nearby leaked? Or is the board generally in a corroded condition.

Bryce.

[gerald]

No capacitor nearby (except one ceramic), but a lot of soldering flux as on all GX and Plus.