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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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23rd Feb 2019, 2:57 am | #21 |
Heptode
Join Date: Jan 2004
Location: Stockport, Greater Manchester, UK.
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Re: General Capacitor Question
In solid-state equipment, I'll pick a couple subjected to the highest ripple current or temperature and test them for ESR and capacitance with the wonderful Cheap Chinese Component Tester.
If good, I leave them all alone. Otherwise, *they* are replaced and half the remainder tested. Again, if good I leave them all alone. If over 10% faulty, I consider relacing all. Similarly, with paper dielectric capacitors in valve equipment, I disconnect one end and test the AVC decoupling and output valve G1 coupling capacitors for leakage with an insulation tester ("Megger"). In the unusual event they are OK, the rest of them can stay; otherwise they go except cathode decoupling capacitors where a megohm leakage is negligible across a few hundred ohms with under 20V. |
23rd Feb 2019, 3:26 am | #22 |
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Re: General Capacitor Question
I've attached a photo of an early Zenith transistor radio. Some electrolytics were on the pcb, others not. They had ceramic bodies. Often they are completely O/C and dried out, especially the ones that filter the AGC circuit. Its worth re-building these capacitors.
Oddly, there is a "classic mistake" in many transistor radios, the AGC capacitor really needs to be a bipolar type. With no signal it usually has a small amount of the correct polarity voltage applied, but with a strong signal it reverses. So in many transistor radios, especially very old ones the AGC filter cap spends most of its life with reverse polarity applied, fails first, and the IF goes unstable. It amazed me that very few manufacturers of transistor radios recognized this and the defect was under everyone's noses for decades and ignored. Some radios had the polarity of the capacitor flipped, so most of the time , on station, the applied voltage polarity was correct. |
28th Feb 2019, 6:40 pm | #23 |
Tetrode
Join Date: Apr 2014
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Re: General Capacitor Question
Thanks for the replies
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1st Mar 2019, 2:10 pm | #24 |
Banned
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Location: Norwich, Norfolk, UK.
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Re: General Capacitor Question
Its a VERY good idea to replace all of the elec caps in anything if its over a certain age . I have this discussion over and over here and I think a lot of the techs in here are old school (no offence to anyone ) and live by the "if it aint broke ..." rule . I , and a few others here , are of a different breed it seems that live by the "if its old prevent it from breaking and keep it that way " rule and I re-cap everything . It gives the sounds a new lease of life and it is future proofs the unit . transistors can get noisy but they are generally only taken out when a cap goes bad . The machines I work with are all 30 - 50 years old so the caps are well past their sell by date so get them out , put new in and then forget about it . Its not expensive , the only skill you need is soldering , I recommend you use a vaccum desoldering gun as apposed to a solder sucker if you can , those things drive me nuts . Other than that just look in the manual , see whats in there and swap them out . Its a very easy process that a tech will charge you the earth for because its time consuming . just get them out . Checking them with an ESR will only tell you what they are like TODAY , who`s to say what they will be like in a week , a month , a year . Just change them and forget them .
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1st Mar 2019, 2:35 pm | #25 | |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,832
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Re: General Capacitor Question
Quote:
I have a large collection of 70s receivers and tuners, all of which have been restored by me and they all work perfectly well having undergone normal electronics fault finding procedures, and it is rare that a faulty cap shows up other than a few PS ones. The difference between doing that - and that itself coupled with the overall restoration process can take days or even weeks - and recapping electrolytics throughout, is massive. Often boards are tucked away in the bowels of units and wired in too, making access to the PCB tracks nigh on impossible unless you perform major disassembly. You say, "Its not expensive , the only skill you need is soldering , I recommend you use a vaccum desoldering gun..". We certainly have to agree to disagree!
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2nd Mar 2019, 11:55 am | #26 |
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Re: General Electrolytic Capacitor Replacement Question
It is interesting to see the disagreements in post 24 & post 25, Also, this is quite a vexed question and it is also troubling people in a parallel universe so to speak. The vintage computing community is pondering it and the remarks here make for interesting reading too:
http://www.vcfed.org/forum/showthrea...the-capacitors It appears though, on balance, bulk re-capping is not a good idea, in most cases, but depending on the circumstance, it may be. So there is no "right answer" to generalize to all cases. |
2nd Mar 2019, 1:04 pm | #27 | |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
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Re: General Electrolytic Capacitor Replacement Question
Quote:
This is a Vintage radio forum, after all. When we can, I feel we should preserve the vintage things. Cheers, GJ
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2nd Mar 2019, 1:06 pm | #28 | ||
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Re: General Capacitor Question
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2nd Mar 2019, 1:52 pm | #29 |
Dekatron
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Location: Cornwall, UK.
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Re: General Electrolytic Capacitor Replacement Question
That's where replace one component then test the machine then replace another component then test the machine etc etc goes out the window.
A bit like the re-cap etc in this receiver I did, testing the receiver between each component change was a bit of a no no, all done in a reasonable amount of time: https://www.vintage-radio.net/forum/...ad.php?t=72777 Lawrence. |
4th Mar 2019, 1:33 am | #30 |
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Join Date: May 2018
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Re: General Electrolytic Capacitor Replacement Question
I dont test between changing caps , its a waste of time , I take a lot more care if there is no marking on the boards but because I do it every day its second nature to me now , yesterday I did a teac 3440 , today I`m doing a Pioneer RT909 for a customer from Italy , he sent me that and a GX-77 to do and a big bag of "fine gold" caps , I personally dont really rate them any higher than a good quality panasonic , but he likes them so they are going in ... (I havent done the ones under the x yet , this is the pic I send him to show him how far I`ve got , those took around and hour and a half to replace , I expect the rest of the machine will take another 2-3 hours )....and yes, I know i missed two ..haha
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4th Mar 2019, 11:52 am | #31 |
Octode
Join Date: Mar 2016
Location: Knutsford, Cheshire, UK.
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Re: General Electrolytic Capacitor Replacement Question
After making various time wasting mistakes over the years, I tend to replace what's likely to be faulty first (caps near sources of heat or that show signs of electrolyte leakage) and take it from there.
Some cap replacement jobs are pointless, some very worthwhile indeed (e.g. changing cheap Chinese caps in SMPS). It always surprises me when people think that caps which are glued to the PCB board [for physical stability] have 'leaked'...!
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4th Mar 2019, 1:09 pm | #32 | |
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Re: General Electrolytic Capacitor Replacement Question
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4th Mar 2019, 1:29 pm | #33 |
Dekatron
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Location: Lynton, N. Devon, UK.
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Re: General Electrolytic Capacitor Replacement Question
I tend to replace wire-ended electrolytics in valve radios I am repairing. Depending where they are (strapped alongside a warm cathode bias resistor!) they can dry out and go low-capacitance, high-ESR, as has been said.
Can-type electrolytics, however, I have had very few problems with. If not used for a long time, they can be leaky (I had two which needed to voltage to be raised slowly, over many hours, but at least one of these had not been used for 20+ years). If the end seal of my cans is OK, and the capacitor works, I leave alone. I have yet to have one spread itself! They are definitely longer-lasting than waxies. However, in a posh, hi-spec piece of kit, if there was a modern drop-in replacement (the BVWS sells several good-quality capacitors), I'd probably go ahead and change it. |
4th Mar 2019, 6:18 pm | #34 | |
Dekatron
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Location: Rugeley, Staffordshire, UK.
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Re: General Capacitor Question
Quote:
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4th Mar 2019, 6:39 pm | #35 |
Dekatron
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Re: General Electrolytic Capacitor Replacement Question
Nicely put, Steve. Every few months or so, I come across a case where someone has started a ‘popcorn ‘ style approach to re-capping, only to find that the amp/ set/ still doesn’t work. It’s sometimes done before establishing what the fault condition/s of the set are and unsurprisingly this leads to frustration and disappointment. If it was all about the output transformer in the first place, fo example ,then bulk recapping is just a waste of money and time ...
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4th Mar 2019, 8:01 pm | #36 |
Octode
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Re: General Electrolytic Capacitor Replacement Question
I think this thread demonstrates that the real answer to the question is "it depends" or "horses for courses"
A major consideration is how much heat the electrolytics have been subject to, since this determines their working life. |
4th Mar 2019, 8:11 pm | #37 |
Dekatron
Join Date: Apr 2011
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Re: General Electrolytic Capacitor Replacement Question
There's no fits all answer, it depends on the equipment, its age, the end game and the amount of nouse the person has to troubleshoot if it happens that things should go wrong.
Lawrence. |
4th Mar 2019, 10:31 pm | #38 |
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Re: General Electrolytic Capacitor Replacement Question
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5th Mar 2019, 12:12 am | #39 |
Heptode
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Re: General Electrolytic Capacitor Replacement Question
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5th Mar 2019, 1:06 am | #40 |
Moderator
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Re: General Electrolytic Capacitor Replacement Question
One drawback of blind shotgun replacement of components is that if it fixes the original problem, you learn nothing about the fault, its diagnosis and its mechanism.
I'm interested in not just getting the thing going, I'm curious about what went wrong. The day-job involves designing things, building prototypes, debugging them and developing improvements. I can't just replace everything, I need to know the underlying mechanisms of problems. The information is much more valuable than the hardware, and I never have the benefit of knowing the damned thing, or one like it ever worked. It's fun! This background comes through into almost everything I do. Shot-gunning done without care is a disaster. Shot-gunning done carefully misses out on the educational aspect. Sometimes it is a valid approach once it's known that there are many parts of the same type and age starting to go off. Sometimes a need for a quick fix may force shot-gun replacements. Above all, as said above, it depends. David
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