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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 29th Apr 2020, 2:10 pm   #1
Malcolm T
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Default Power supply QRM shielding

I have a very nasty qrm coming from my psu inside the computer . Does anyone have any suggestions as to how to tackle this please . I have not had it apart yet so dont know if there are some critical filtering components missing !.

Thank you.
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Old 29th Apr 2020, 4:41 pm   #2
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Default Re: Power supply QRM shielding

I think you are right about missing filter components, all too prevalent today. A portable radio waved around the mains cable will find out.
 
Old 29th Apr 2020, 5:22 pm   #3
Andrew2
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Default Re: Power supply QRM shielding

I found our previous PC was putting a lot of noise onto the mains lead and it was radiating all over the house.
So I made a short flylead which plugged into the PC's IEC socket and was fitted with a filtered IEC socket, see picture. This socket was mounted in a small plastic box for safety. Once fitted, peace & quiet reigned again!
The filtered socket came from Surplectronics. https://www.surplectronics.com/ It's listed under capacitors.
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Old 29th Apr 2020, 6:14 pm   #4
Malcolm T
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Default Re: Power supply QRM shielding

Thanks for replies. Looks like i,m going to have the lid off and take a look see first then maybe even roll my own filter , its very noisy its unreal on the s meter.
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Old 29th Apr 2020, 6:39 pm   #5
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Default Re: Power supply QRM shielding

You'll probably find a nice virgin area on the PCB ready for X and Y capacitors, and a pair of links where a common mode choke ought to have been. Probably was on the one sent for testing. Fitting these ought to be a start. Adding a big ferrite on the output wires might help as well. 1 per connector.

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Old 29th Apr 2020, 8:39 pm   #6
Malcolm T
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Default Re: Power supply QRM shielding

Yep, that's got me curious now as to missing stuff!!!. We shall see.
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