Now someone's pinched my capacitors!

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roobarb!
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Now someone's pinched my capacitors!

Post by roobarb! »

Another Beeb procurement has landed me with an Astec Components PSU which appears to be missing its C1 and C2 capacitors entirely. The PSU works, but I assume nothing downstream is having a quiet ride...

IMG_0458 2.jpeg
IMG_0459.jpeg

This isn't "a thing", is it - someone's been in here and just whizzed them off without replacing them?
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gslug
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Re: Now someone's pinched my capacitors!

Post by gslug »

It should work just fine without them, though will probably be injecting all kinds of nasty harmonics back into the mains. They aren't to filter the incoming mains, but rather to reduce the electrical noise the PSU produces.
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Papalapa
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Re: Now someone's pinched my capacitors!

Post by Papalapa »

I have a similar Astec PSU in my Apple IIe and most probably these capacitors are a paper RIFA ones. In mi case as were damaged i replaced them by a new ones but until they come the PSU worked without these capacitors without problems.

Image

As they only filter the AC entering into the PSU are not critical components.
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tricky
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Re: Now someone's pinched my capacitors!

Post by tricky »

I'm surprised that they went to the trouble to remove them and not replace them, unless they have been missing for a loooong time ;)
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JasonStonier
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Re: Now someone's pinched my capacitors!

Post by JasonStonier »

Those caps are about suppressing the mains noise, rather than protecting the downstream equipment. In the old days of CRT televisions, you'd have really noticed the RF hum from that PSU as distortion on the screen - some of us who are old enough might have had the experience of a car with a dodgy ignition coil causing TV distortion as it drove past. If you can find a radio which can tune MW or LW you might be able to pick up the hum now - if I could be bothered to reboot my knowledge of RF and antennas I could probably work out the region for you to tune to...but I can't...:wink:

So, it'll work, but it's causing harmonic ripple and a lot of RF noise which you probably don't want.
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Re: Now someone's pinched my capacitors!

Post by Coeus »

JasonStonier wrote:
Wed Oct 28, 2020 12:59 pm
So, it'll work, but it's causing harmonic ripple and a lot of RF noise which you probably don't want.
I think it's temping to think that the problem no longer exists now much radio transmission (including TV, WiFi etc) is digital and we don't directly see noise in the received signal. Remember, though, that for many purposes the distance over which we can receieve a signal may be more to do with noise than signal strength.

Have you ever noticed that you can hear ordinary conversion a surprising distance away when in a very quiet place or at night whereas it doesn't seem possible to do the same in a busy place during the day? It's not because the signal has dropped below the threshold of hearing but because the noise floor is much higher during the day - noise from cars and factories and other conversations etc.

Obviously receivers filter the incoming signal to pick the frequencies they are interested in but interference sources may be broadband, i.e. emitting a large range of frequencies.
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Re: Now someone's pinched my capacitors!

Post by JasonStonier »

You're quite right and 'white noise' is by definition broadband, which is what you get from an unfiltered transformer...so whether the thing works or not, you want to suppress the noise as much as possible.
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Re: Now someone's pinched my capacitors!

Post by roobarb! »

gslug wrote:
Wed Oct 28, 2020 2:22 am
They aren't to filter the incoming mains, but rather to reduce the electrical noise the PSU produces.
Well, there’s my assumption out of the water! Thank you, I didn’t realise that was their job. I’ve only ever seen them described as filter capacitors and didn’t even consider that noise going “the other way”.

Think I still have a couple around here, I’ll get them replaced.
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Re: Now someone's pinched my capacitors!

Post by Bobbi »

For what it's worth, an experienced hardware repair person from the Apple II world advised me they just remove those filtering caps and don't replace them.

You are correct - they filter nasty harmonics from the SMPS from getting back onto the mains lines and affecting other devices. I think this was more of a concern in the days of analogue TV. Radio hams may be mad at you if you don't replace the caps ;)
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Re: Now someone's pinched my capacitors!

Post by JasonStonier »

There are certain frequencies of white noise that give me visual effects in real life (true story) - I have audio/visual synesthesia, so normal audio can cause visual effects for me. It's not as cool a super power as it sounds, and I'm not saying I can see WiFi but I'm not not saying that either (if anyone from Marvel is reading this).

So...it's not just radio hams you might be annoying :wink:
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Re: Now someone's pinched my capacitors!

Post by danielj »

Bobbi wrote:
Wed Oct 28, 2020 4:58 pm
For what it's worth, an experienced hardware repair person from the Apple II world advised me they just remove those filtering caps and don't replace them.

You are correct - they filter nasty harmonics from the SMPS from getting back onto the mains lines and affecting other devices. I think this was more of a concern in the days of analogue TV. Radio hams may be mad at you if you don't replace the caps ;)
In truth, I suspect most people wouldn't notice with the state of NTSC reception *runs for cover*
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Re: Now someone's pinched my capacitors!

Post by Bobbi »

Never Twice the Same Colo(u)r
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1024MAK
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Re: Now someone's pinched my capacitors!

Post by 1024MAK »

roobarb! wrote:
Wed Oct 28, 2020 4:31 pm
gslug wrote:
Wed Oct 28, 2020 2:22 am
They aren't to filter the incoming mains, but rather to reduce the electrical noise the PSU produces.
Well, there’s my assumption out of the water! Thank you, I didn’t realise that was their job. I’ve only ever seen them described as filter capacitors and didn’t even consider that noise going “the other way”.
The actually filter out high frequencies in both directions. Both into the PSU and to reduce the noise produced by the PSU that will be transmitted back into, through and radiated out of the mains wiring.

If you live near a radio ham, they will not be best pleased to have extra crap filling part of the air waves. Especially if any of your mains wiring happens to be the right length to match a harmonic frequency from the PSU oscillator...

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Re: Now someone's pinched my capacitors!

Post by 1024MAK »

Coeus wrote:
Wed Oct 28, 2020 2:20 pm
JasonStonier wrote:
Wed Oct 28, 2020 12:59 pm
So, it'll work, but it's causing harmonic ripple and a lot of RF noise which you probably don't want.
I think it's temping to think that the problem no longer exists now much radio transmission (including TV, WiFi etc) is digital and we don't directly see noise in the received signal. Remember, though, that for many purposes the distance over which we can receieve a signal may be more to do with noise than signal strength.

Have you ever noticed that you can hear ordinary conversion a surprising distance away when in a very quiet place or at night whereas it doesn't seem possible to do the same in a busy place during the day? It's not because the signal has dropped below the threshold of hearing but because the noise floor is much higher during the day - noise from cars and factories and other conversations etc.
Also known as signal to noise ratio...

If there is too much noise, the radio receiver will not be able to detect the wanted signal. This still happens with digital transmission, the difference is that the error correction systems hide the problem from us humans. Until it gets so bad that the sound/visuals/data stream cuts out completely (also known as the knife edge effect).

DAB does this when you are driving in an area where coverage comes from a single transmitter and hills or large buildings get in the way.

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Re: Now someone's pinched my capacitors!

Post by guesser »

You also don't want to be the person on the news websites and all the papers when "Old computer causes broadband outages in village for 18 months" :D

(though I'd hope anyone repairing their own power supplies would be technical enough to figure it out sooner than that themselves) :lol:
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Re: Now someone's pinched my capacitors!

Post by 1024MAK »

That reminds me, civil aircraft, air traffic control, airfield/airport tower, and the military aircraft all still use analogue radio. And you really, really don’t want OFCOM investigating if they complain about interference causing them trouble...

There are also still plenty of people using AM (LW, MW) and FM/VHF radios (there are now more FM/VHF transmitters than in the past, even if many “local” stations have been bought out by larger operators). I once asked OFCOM to investigate when I suffered from co-channel interference caused by a new FM radio transmitter that was operating on a frequency very close to the frequency of my favourite radio station.

Cheap (read rubbish) switch mode power supplies (SMPSU) from China and elsewhere, have been known to cause various interference issues, primarily due to very poor design. Such as not bothering with any interference suppression components (to keep the cost low).

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Re: Now someone's pinched my capacitors!

Post by Marvin »

Bobbi wrote:
Wed Oct 28, 2020 4:58 pm
For what it's worth, an experienced hardware repair person from the Apple II world advised me they just remove those filtering caps and don't replace them.

You are correct - they filter nasty harmonics from the SMPS from getting back onto the mains lines and affecting other devices. I think this was more of a concern in the days of analogue TV. Radio hams may be mad at you if you don't replace the caps ;)
Sounds like the "experienced hardware repair person from the Apple II world" shouldn't be allowed to touch anything electrical/electronic ever again with that sort of attitude... I wonder if that was official policy or just him being lazy ?
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Re: Now someone's pinched my capacitors!

Post by Bobbi »

Definitely not official policy.
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Re: Now someone's pinched my capacitors!

Post by danielj »

Marvin wrote:
Thu Oct 29, 2020 11:01 am
Sounds like the "experienced hardware repair person from the Apple II world" shouldn't be allowed to touch anything electrical/electronic ever again with that sort of attitude... I wonder if that was official policy or just him being lazy ?
It's pretty rife as an opinion expressed in the Apple II group on facebook, but there are certainly enough people who pull that kind of RF generating activity up ;) :D

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Re: Now someone's pinched my capacitors!

Post by roobarb! »

1024MAK wrote:
Wed Oct 28, 2020 7:39 pm
roobarb! wrote:
Wed Oct 28, 2020 4:31 pm
gslug wrote:
Wed Oct 28, 2020 2:22 am
They aren't to filter the incoming mains, but rather to reduce the electrical noise the PSU produces.
Well, there’s my assumption out of the water! Thank you, I didn’t realise that was their job. I’ve only ever seen them described as filter capacitors and didn’t even consider that noise going “the other way”.
The actually filter out high frequencies in both directions. Both into the PSU and to reduce the noise produced by the PSU that will be transmitted back into, through and radiated out of the mains wiring.
Ah, so forwards and backwards, but not side to side or back in time? :lol:

I'm convinced I have spare capacitors somewhere in this mess. It'll get done.
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Re: Now someone's pinched my capacitors!

Post by JasonStonier »

roobarb! wrote:
Fri Oct 30, 2020 12:34 am
Ah, so forwards and backwards, but not side to side or back in time? :lol:
:lol:

Now listen carefully...I want you to pull on the thing...that's near the other thing...

I do love an obscure Simpsons quote.
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