v4.2 BROKEN PCB - the fix?


 
J

JohnBerry

New member
Hi all,
I have been interested in putting together a HM for a while now, but I have been hesitant because a lot about this process is new to me. I saw that Bryan offered some the v4.2 BROKEN PCB. The ability to get a do-over, gave me enough confidence to give it a try. So, here I am at square one. I found the 4.2 Assembly album, another breakthrough at my level :)

Anyway, I am trying to follow Bryan's instructions on how to either cut the blue or cut the trace entirely.

I have a good 4.2 board, so I can test where I am not supposed to have continuity. I gave the scrapping a whirl, but I still get continuity. The instructions seem to be conflicting. One picture says to "Cut the trace entirely (both pad and via side) and run a wire to Q5". Yet the text on the product page says "Option 2: Cut the trace before the pad, and before it goes into the via (2 cuts) and run a wire to the lower pin of Q2 (just follow the trace)."

1. Does Q5 exist? I think that was a typo for Q2. Is there a way to test continuity on a good board?
2. TL;DR > Has anyone fixed one of these? A picture is worth a thousand words and it has taken me half that many to get to this point...
3. I still get continuity after the scrapping in this pic. Have I gone too far or not far enough? I would like to use this purple board instead of the green as it is a little easier to read.

This is the best focus I could get from my phone...
HM%20Broken%20PCB.jpg



TIA!
John
 
It looks like you've only scraped off the solder mask, as the shiny copper is still quite evident in the picture. You need to cut/scrape carefully through the copper until you get to the main PCB substrate. A sharp knife and slow, controlled movements are key.
 
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It looks like you scraped the purple resist (paint like substance) off the top of the copper..... What you need to do is take a razor and cut straight down through where the inner trace touches the larger flooded area.... When you are done they should be electrically isolated from each other.
In this picture you can clearly see where the trace touches the flooded area (which is a big ground plane), cut them appart...
I didn't read all about the flaws on the board so I cant say this is all you need to do, but thats how to conquer this part of it at least.
 
Thanks Ralph! I continued to gouge in that same place to get through copper and I lost continuity! With all the work that lies ahead, I feel like I had better ask, does this look good?

HM%20Broken%20PCB%202.jpg
 
Looks really blurry! LOL
All you really had to do was cut one line with the razor pressed straight down into the board.... I can't see clearly enough to say for sure but if there is a space between the inner trace and the outer ground plane and there is no continuity as described in Bryans instructions then yah, you should be good to go....
 
I tried one line and it didn't work. I either didn't press hard enough or didn't extend the line long enough. Not knowing how deep I could cut, I went with scraping. I used my third hand magnifying glass to improve the pic...
 
IDK, looks to me like the copper is still connected there, in the picture below inside the box??? CUT with a razor blade straight down where I put the line on the right picture, press hard to gouge into the board a tiny bit and cut the trace...
Graphic1.jpg
 
For posterity, Q5 is where the bit you're cutting leads to


The two options are
-- Prevent the ground pour from touching the trace, by cutting like you have
-- The the affected area out entirely and replace the trace with a wire that goes where the pink does (except take it all the way to the resistor).
 
Honestly, I just did two of these. Rather than trying to get that tiny bit of mask cut, I just cut the trace and ran a jumper wire from the resistor to Q5. It was quick and easy. A dab of hot glue to secure the wire and in business!
 
As long as you CUT rather than scrape, cleaning up the shorted trace should be a no brainer, should take about 10 seconds...
 
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