BA23 common component failures?

On Nov 24, 2013, at 19:55 , Cory Smelosky <b4 at gewt.net> wrote: The white glorp might be hot melt glue, or it might be some leaked innards of something. The yellowish block to the right of the glorp appears to be one of those ^#%!$$#% metallized-paper dielectric EMI filtering caps that I mentioned. The TRS-80 Model 12 power supply of mine which blew out one of those caps was also made by Astec. I would replace it with a class "X" safety-rated EMI filtering cap with the same voltage and capacitance ratings, but NOT a metallized paper type. Identical Rifa caps (actually Kemet-Evox-Rifa due to acquisitions) are still available from Digi-Key, but I would NOT use those blasted things. I theorize that the failure mechanism is that after a few decades, the plastic cap shell cracks, allowing moisture to get it. That gets absorbed by the paper dielectric, and eventually the dielectric breaks down under power. Polypropylene film dielectric is supposed to have very low moisture absorption, so I figure they should last longer, even after their seals degrade. Notice the cracking of the plastic on that cap in your picture. If it hasn't already blown, it will. The one right above where it says "C102"? That looks like another one of those &#%!*&$* metallized-paper dielectric EMI caps which has blown its top. If you can't find a schematic diagram to get its ratings, then maybe somebody else here with a BA23 can try to read the markings off that cap in their supply. I found that safety-rated EMI caps other than the (#&%*^$ Rifa ones have different lead spacings. At least in my Model 12 supply, there were extra holes to allow caps with different lead spacings to be substituted, and the Panasonic caps I bought dropped right in. Their lead spacings weren't quite right for the Rifa caps in my Model 4 supply (also made by Astec). Pick out caps with long wire leads instead of short pins in case the lead spacing isn't the same as any of the holes on your PCB. If you can get the numbers off the top and sides of those caps, then I can help you pick out some replacement parts if you don't know how to. I did this just last week for a couple of my TRS-80 systems, and I expect I'll be doing the same thing again once I get started on my PDP-11/44 project soon. I recommend replacing every one of those metallized-paper caps that you encounter, whether it's already blown or not. -- Mark J. Blair, NF6X <nf6x at nf6x.net> http://www.nf6x.net/