How do avoid Adrian's C10 replacement short 12V to data line 31?

[djc6]

Adrian's Digital Basement has a recent SE/30 repair series, and he shorted data line 31 to 12V accidentally when replacing capacity C10. The link below goes right to the point in video where he found problem:

Sounds like the leaking electrolyte removed some solder mask over data line 31 which runs near capacitor C10.

I'm about to re-cap my first SE/30. My question is, what checks should I run BEFORE powering my SE/30 board back on after recapping?

I thought maybe I should apply some clear nail polish around C10 preemptively after I remove the old cap. Should I go as far as to check for continuity on various power rails to pins on chips to see if anything is connected where it shouldn't?

I had already planned to triple check the polarity of the replacement caps. And maybe purcahse a loupe to help me see.

 

[DJ68K]

Always check major power lines (+5, +12) to ground as you're recapping sections. I don't know if I'd worry about putting new mask/nailpolish in those areas before you recap them is totally necessary especially if you're not using wide caps where the conductive portion is the full width of the component. If you're using SMD electrolytic caps they have a much smaller "conductive foot" than what's in Adrian's video, same for the tantalum capacitors that I typically use.

Of course, putting some mask around those areas won't hurt, so feel free if this is your first recapping. I've recapped dozens of boards with new SMD caps and so far I haven't had this problem, even with damaged boards that needed trace repair. Of course, now that I say that, I'm sure my next board is going to explode because of this problem.

It doesn't appear to me that the point he toned out on that trace had anything to do with the short he experienced. The edges of the capacitor seem to overlap the multiple rows of traces that run parallel to and just above where he soldered and the edges of his caps overlap those traces. That exposed section to the right wasn't anywhere near where his solder was.

 

[croissantking]

I'm about to re-cap my first SE/30. My question is, what checks should I run BEFORE powering my SE/30 board back on after recapping?

Just check there isn’t continuity between data line 31 and +12V after you recap. Beyond that I wouldn’t worry excessively

I watched Adrian’s video series which was entertaining and excellent, his findings on using the diagnostic mode are a boon to the community too.

Most of us in the community use electrolytics, tantalums, or polymers, which don’t have such wide conductive terminals as the ceramic caps Adrian used. So while he was very unlucky, part of the issue was the unusual component selection. I don’t think anyone here has run into the 12V issue that we know of?

 

[cheesestraws]

Never had a problem with this.

 

[David Cook]

I don’t think anyone here has run into the 12V issue that we know of?

I have recapped a small number of SE/30s (and many other Macs) without incident. I agree with your theory that the size of the terminals of the replacement capacitors is the most likely cause.

Nevertheless, I am grateful for his video, as I have been cavalier about traces underneath. I will just be a little more careful and inspect a little more closely to avoid this disaster.

 

[dv-]

n/m

 

[smrieck511]

I have two happily restored SE/30's but man that video gave me the creeps...now I'm wondering if I should go back and put mask under each of the 12v caps.....someone talk me out of it, please.

Is the risk only at C10? There are several other caps that have 12v, i think?

 

[djc6]

I like this capacitor replacement guide from @Mk.558 because it has a lot of good information together in one page.

http://applefool.com/se30/images/img/2d9cbc05.png

it has a warning "Do not destroy traces near C8 thru C10" without saying why, but I suspect because of this issue Adrian encountered, so I think that whole area by J12 power/analog board connector is important to triple check.

I've been checking continuity from the capacitors I replace to the power rails to see if there is a short or not. The guide shows where the capacitors are supposed to be connected to.

 

[croissantking]

I have two happily restored SE/30's but man that video gave me the creeps...now I'm wondering if I should go back and put mask under each of the 12v caps.....someone talk me out of it, please.

Well, Adrian shorted out the 12V line because he used ceramic caps with a wide conductive footprint. If you used electrolytics or tantalums chances are you’ll be fine.

 

[Unknown_K]

I would think it would be common practice to check for shorts to ground before turning something on.

 

[cheesestraws]

This thread isn't about a short to ground.

 

[Mk.558]

The reason why it says that warning is because there's a bunch of fine traces that run right along the C8 - C10 area, and they're kind of critical. When that image was created, about 11-ish years ago, there was a big rash of people getting a little clumsy with a soldering iron and raking the tip across those 3 traces.

 

[smrieck511]

Put UV mask on the traces under C10 on my SE/30's. No reason not to.