Old equipment recapping (mostly Heathkit) - Page 1
Forum section: electronics / repair

author: JNSurma
author_rank: Newbie
timestamp: December 17, 2024, 10:25:37 pm
content: I'm trying to get more in to electronics and have purchased a bunch of old equipment to repair/use in my lab. Being new to troubleshooting I was looking for any info on what moder replacements for components to use. X caps Y caps, resistor wattage to use, electrolytic/thin film/whateverelse to replace with, etc. I have no idea. I know I'm in over my head, but was looking for advice or any good places to learn. Does it matter what capacitor you use as long as the capacitance and voltage match more or less? 1/4, 1/2, 1 watt resistors? I want to learn, just don't know where to start. Knowing enough to be dangerous is fun until it gets dangerous 😅

author: DaJMasta
author_rank: Super Contributor
timestamp: December 17, 2024, 10:53:26 pm
content: The short answer is: don't blanket recap unless it's really old or you actually see a lot of evidence of dead ones. The replacement should be as close a match as possible to the originally, generally speaking.Recapping is a brute-force tactic that is pretty costly with both money and time, and I would only resort to using it if you've had multiple capacitor failures in the same unit or if it was in particularly bad condition when starting. Some capacitors can be larger than the used value, and many modern equivalents will be physically smaller for the same value, but many capacitors are sized for their purpose and too much deviation from that can degrade or prevent operation. Resistors should be at least as high a rating of the original, but higher power rating isn't a bad thing, generally, if they still physically fit. Higher voltage rated capacitors are generally fine to replace lower voltage provided their capacitance is the same, but as with most of these rules it's a guideline and not the case 100% of the time. If the components in question are old and show signs of significant wear (bulging caps, leaky caps, charred resistors, etc.) replacing without testing is fine, and if you determine the problem is in a certain area and you suspect a capacitor or something it's not that you shouldn't replace it, it's that going in and just swapping every electrolytic and tantalum out as soon as you get it is expensive, time consuming, and more likely to do damage than fix it, especially when inexperienced, because of random desoldering, soldering, or component placement errors.The one notable exception with capacitors is Rifa branded mains input filter capacitors, as there are a good number (generally in more modern gear than Heathkits) that go bad with time and which can make a stinky mess on failure because of their construction and because they are directly exposed to the mains voltage. If you find a capacitor like that in a design, changing it proactively is a reasonable course of action, but waiting for an eventual failure isn't all that likely to cause fire or other damage, just a mess.

author: JNSurma
author_rank: Newbie
timestamp: December 17, 2024, 11:48:32 pm
content: Thanks for the reply. Yes, I've seen Dave's Rifa maddeness issues 😅. I've had a few physically leaky I've replaced with modern electrolytics. Is there a certain type I should be using in certain areas? I bought a recap kit for a CT-1 that had all yellow axials (you're right, after checking them I probably didn't have to?) Is there something special with those compared to regular aluminum caps? Or do they just look cool 😎 🤔? So many different choices, does it really matter?

author: vk6zgo
author_rank: Super Contributor
timestamp: December 17, 2024, 11:49:08 pm
content: There are "traps for young players"!Back in the early/mid 1990s, I had occasion to repair a number of "Electrohome"black & white TV picture monitors.Most of the faults were relatively easy, including the one I'm going to describe.The monitor had collapsed vertical scans, the classic cause of which was failure of a power supply, of around +150v derived from an overwind on the horizontal output transformer.The line rate voltage from the winding was half wave rectified, then filtered with a single non-polarised (NPB) electrolytic cap.There was a bit of extra circuitry hanging off this circuit which apparently demanded an NPB cap (which was not remarked as anything special, either on the cap, the schematic, or elsewhere).Being pre-Internet, I looked up the "X-On" catalogue, & sure enough, "front & centre" was what looked like a suitable type of non polarised electrolytic.They were much smaller than the clunky EHome one, but they tended to use clunky parts, anyway, so marvelling at the advances in Technology which had delivered such a size reduction, I ordered some.On arrival, I fitted one, & up came the monitor with normal height----for all of 10 seconds, then the picture collapsed & the magic smoke emanated from the cap.It turned out the "clunky" cap was a low ESR non polarised electro.Such was unobtainium, so the monitor returned to service with a "Christmas tree" of Mylar greencapsUgly?-------Yes,Functional?-----Oh, Yeah!PS:- Such supplies had another "sting in the tail".The silicon rectifiers look like a "bog-standard" package, so it is tempting to replace faulty ones with 1N4007's or the like, which also give up their magic smoke, as the rectifiersmustbe fast recovery types.

author: JNSurma
author_rank: Newbie
timestamp: December 18, 2024, 04:43:58 am
content: So that begs the question from the young player 🤔 😅. How did you know Mylar caps would work? ESR rating? Every "all about capacitors" article I find only goes over the basics or goes right over my head 🤪. I'm sure if I bash my head against it enough I'll figure it out, but I'm running out of asprin 🤣