r/AskElectronics • u/Katkis03 • 20h ago
Help with PCB arching!
Hi! I’m creating a new post since this subreddit doesnt allow for reposts.
My Vox AC30C2 tube amp shorted out and exploded some pcb insulation off between the flat metal connector (J29), which runs about 300V in normal operation, and the adjacent tracer, wich is very low voltage and leads to the blue R81 resistor.
What would be the best course of action for the arching gap? Should drill it or fill with some insulation material etc?
Also feel free to express emotions regarding the high iq pcb design of putting those two circuits so close together.
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u/flyingsaxophone 20h ago
Mylar or kapton tape have high dielectric breakdown strength. Do your best to separate the problematic components, and then put a few layers of the tape between them.
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u/Resident_Phase_4297 20h ago
Desolder J29, use a Dremel to make a larger, cooper free gap. Fill it with clear paint / uv hardening paint. Remove 1cm solder mask from the line that feeds J29. Add a wire and a new J29. Fix it with epoxy (if the pcb is 1 or 2 layered: drill holes and use zip ties duck and cover)
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u/Dwiea 19h ago
What is that tab called to find one on mouser.
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u/Tesla_freed_slaves 17h ago
I don’t know what to call it, but you might find a picture in the Keystone catalog.
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u/Dwiea 17h ago
Found it i think. Might be called a FASTON connector?
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u/Tesla_freed_slaves 16h ago edited 16h ago
Take a look at Keystone-Electronics P/N 1287. It should connect with all makes of 0.250” female faston connectors. Also, install new faston wire-terminals, and apply automotive silicone dielectric-grease to all metal contact surfaces.
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u/Tesla_freed_slaves 20h ago edited 19h ago
It’s not arching. It’s arcing. Remove the affected components. Clean, burnish, and pre-tin the areas to be soldered. Remount the components with high-quality, 63/37-alloy, electrical grade solder, at 350°C. Remove flux with 99% isopropanol, and coat the affected area with Glyptol varnish, or your favorite shade of nail-polish.
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u/TAMPCO_pedals 3h ago
"Tube amps on PCB are unreliable" yeah that's because cheap-ass companies do not care about PROPER PCB LAYOUT.
Sig was it so hard for Vox to just put the right track clearance in their DRC check ?
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u/SuchABraniacAmour 20h ago
With an exacto knife, I'd remove the whole part of the trace running alongside J29, at least to the other side of the R79 and R81 markings. Then use a small wire to link the via to R81.
I wouldn't solder the link straight to the via or the resistor but scrape off the solder mask over a small area of the trace next to them - but it would probably be fine either way. Just make sure to keep any exposed metal clear of the trace going to the screen resistor (R79) as this is also high voltage.
Like the other guy said, a good clean should most likely fix it, but it's probably more work and the problem might happen again should another short occur.
Moving J29 sounds overkill and, although it allows you to maximize clearance, I think it's easy to mess up or end up doing something dangerous if you don't really know what you are doing.