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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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5th Mar 2019, 4:50 am | #41 | |
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Re: General Electrolytic Capacitor Replacement Question
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I like to track the fault down with the aid of the schematic and scope, find the faulty components, then subject them to testing to find out if they are indeed faulty. And when I can (as with electrolytic caps) I cut them open for inspection every time, and dismantle the part if possible or subject it to magnification to try to find out why it failed. It is only then I can convince myself I truly found and corrected the fault and feel that it won't be coming back to surprise me. But like you say, try to understand what went wrong. Bulk blind re-capping actually has no logical basis to it, it could miss the real fault or create others. Though, as I mentioned I do it for all specimens of the same type of electrolytic cap on a vintage pcb where even one has physically leaked, as it is almost certain the others will follow suit in the near future. |
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5th Mar 2019, 1:36 pm | #42 |
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Re: General Electrolytic Capacitor Replacement Question
Yes, first fix faults. Then replace what is likely to become faulty. Leave everything else alone. For most equipment under most circumstances a 'full re-cap' is unnecessary and can be a quick way to stop it from ever working again. Exceptions might be equipment which runs hot (so electrolytics may dry out) or equipment which is rarely used (so electrolytics may have degraded oxide).
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5th Mar 2019, 3:16 pm | #43 |
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Re: General Electrolytic Capacitor Replacement Question
In fairness to our US friends who have an absolute mania for recapping, that's probably the root cause of their mania. To explain, there are lots of very hot, very dry areas in the US - not good for electrolytics and hifi equipment in general. Come to think of it, neither is hot and humid any good for hifi and they have those areas too. Also, they tend to have bigger houses with bigger rooms and are not afraid to play their hifi very loud, with a lot of houses being detached. So again, they're going to get hot and stressed. So in the US, in certain states etc, it may well be a good idea to perform blanket recaps. To me this simply reinforces the horses for courses rule. Take and repair as you find, don't just recap for the sake of it, as more often than not - especially in the UK - it's simply not necessary.
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A digital radio is the latest thing, but a vintage wireless is forever.. |
5th Mar 2019, 6:02 pm | #44 | |
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Re: General Electrolytic Capacitor Replacement Question
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Finding out that a component has failed, replacing it, and hoping things work again usually fixes the fault, but not always. Sometimes a failed part has failed due to something else failing that you haven't picked up on yet. An example is a failed electrolytic cathode bypass capacitor on an output valve - it's failed because the coupling capacitor from the previous stage has gone leaky, the output valve has passed too much current, the resistor it's strapped to has run too hot, so the electrolytic has been overvolted and overheated. You spot it, because it's discoloured and the end cap has perished and cracked. You replace it, the radio sounds better and louder because the cathode is now properly bypassed, but it's still not 'right.' The original fault remains, but you now are homing in on the problem area. Soon you find the real culprit, you replace 'that cap,' maybe the output valve too. You remember it for the future, and the next radio you fix you can do in a fraction of the time it takes to re-cap the whole thing. You've learned about fault propagation too! So when you start work designing valve radios, you specify a better-quality component in this position, costing a few pence more, having learned that failure of this component can propagate the fault through several other components. It's like knocking down a row of dominoes. |
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5th Mar 2019, 7:15 pm | #45 | |
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Re: General Electrolytic Capacitor Replacement Question
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Ahah, I'm going to start using that here, Hugo!
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6th Mar 2019, 6:53 pm | #46 |
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Re: General Electrolytic Capacitor Replacement Question
Just as a data point, I recently restored a Radford SPA.50 amplifier dating from the early 1970s. Nothing is known of its history other than that it clearly had a hard life and experienced some less than sympathetic "repairs".
Each of the four electrolytic capacitors on the channel boards was checked with the Chinese component tester. The small ones (6.4uF 25V) were fine but all the others all exhibited much less than their stated capacitance and one was open-circuit. The main reservoir capacitor, nominally 3300uF 100V, was down to about 900uF Both the 100uFs between the collectors of the output transistors (made by 'Ai-Elko' in Germany) measured about 30uF and also exhibited about 12-15K of resistance. For some reason the output capacitors (2500uF 64V) were both fine. Apart from the Ai-Elkos I don't know who made Radford's capacitors but they're blue and the font looks slightly like that Philips used on the 108-series in the 1980s. |
7th Mar 2019, 12:19 pm | #47 |
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Re: General Electrolytic Capacitor Replacement Question
Al Elko means aluminium electrolytic capacitor.
I think 6.4uF was a typical value made by Philips, so that's probably the manufacturer of the small ones. In some other sets from the late 1970's, the small ones actually dry out first. |
7th Mar 2019, 1:41 pm | #48 |
Pentode
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Re: General Electrolytic Capacitor Replacement Question
Interesting -- the reverse seems to have happened in this case. Photos of two of the capacitors attached in case anyone can identify the manufacturer.
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7th Mar 2019, 2:08 pm | #49 |
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Re: General Electrolytic Capacitor Replacement Question
The lower one (golden tape) is Siemens manufacture.
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7th Mar 2019, 2:18 pm | #50 |
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Re: General Electrolytic Capacitor Replacement Question
The upper one could be Philips, but it looks somewhat off. Is there any other text on it?
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7th Mar 2019, 2:31 pm | #51 |
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Re: General Electrolytic Capacitor Replacement Question
The lower capacitor looks to me like a Frako. These can be prone to failure, sometimes going s/c.
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7th Mar 2019, 3:23 pm | #52 |
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Re: General Electrolytic Capacitor Replacement Question
The lower one has the stylized S for Siemens logo. So definitely Siemens. Even small Frako electrolytics tend to have their name in full on the can.
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7th Mar 2019, 4:04 pm | #53 |
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Re: General Electrolytic Capacitor Replacement Question
Yes the lower one is definitely a Siemens.
The logo is actually an intersecting S and H - the full title of the company historically being "Siemens und Halske" - seed https://www.cryptomuseum.com/manuf/siemens/index.htm |
7th Mar 2019, 5:31 pm | #54 | |
Pentode
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Re: General Electrolytic Capacitor Replacement Question
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Incidentally the reservoir capacitor was a Plessey type. So it seems that in this particular amplifier the capacitors from three different makers all exhibited the same loss of capacity. |
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10th Mar 2019, 2:41 pm | #55 |
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Re: General Electrolytic Capacitor Replacement Question
001 would correspond to the Philips 2222 001 xxxxx series of capacitors. I think those are indeed miniature type electrolytics, so I'd confirm it's a Philips. Also, this marking would date it after roughly 1965.
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10th Mar 2019, 3:50 pm | #56 | |
Pentode
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Re: General Electrolytic Capacitor Replacement Question
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It'll be interesting to see what condition the (numerous) electrolytics in the contemporary control unit are in when the time comes. For now I'd settle for working out how to get the main reservoir capacitor out without disassembling the entire chassis. Messrs Radford seem to have started with this and erected everything else round it... |
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22nd Mar 2019, 2:33 pm | #57 |
Diode
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Re: General Electrolytic Capacitor Replacement Question
Personally, I just undertake the mechanical repairs of my own kit, and leave the electronic repairs to my technician. He is also from the “if it ain’t broke...” school and none of the repairs he’s undertaken for me on our TEAC amp, tuner and R2R’s have involved a full recap. The amp was a great case in point. It had a mains buzz through the speakers at zero volume which was driving me nuts. He went through the process of going through the unit to diagnose the issue, but despite replacing numerous caps which were not within spec, the buzz remained, albeit at a much reduced level. Now this was now driving him nuts! During discussions, I asked if it could be the transformer and when testing that theory, he bypassed two large Nippon Chemi-Con 50v 3300uf caps, which were originally tested and found to be absolutely fine, yet in so doing, the buzz disappeared, so bingo! So despite them testing as being fine, they were doing something strange and naturally, they were replaced. Had he not gone through a diagnostic process and undertaken a blanket recap, he wouldn’t have been able to pin-point the problem I’d engaged him to fix. Conversely, if I was in his position of selling items which need a guarantee, I also completely understand NorfolkDave’s cautionary approach by looking to future-proof said items with a preventative full recap; as a potential purchaser, I’d certainly be very happy hearing that’d been done.
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