General electrical question, figured this might be the best place to post...

[savage1987]

Whilst not strictly Commodore related (at all), I need help on a small interference issue. I am using an 'aftermarket' (I guess you could call it that) power cord on a laptop as the original one was destroyed by my dogs.. and now I get major interference when it's plugged in. Anything I can do about this? Speakers constantly whine, muted or not, headphones and external stereo gear do the same. Also ruins reception on certain TV channels on the household TV. I bought this off ebay under the impression it was designed to suit these laptops, should I be complaining? No chance of getting money back I imagine as it was sourced from Hong Kong. Couldn't find an original cord at the time.

So yeah, what do I do about this?? I have no idea.
Sam

 

[bezz]

i would be guessing but i would say it would be increased electromagnetic interference caused by the dodgy stepdown transformer on your power supply. You could try a powerboard with EMI mains filtration on it, however I don't know how much difference it will make. Jackson make them, can be found at your local dickies.

 

[savage1987]

hmm. Might be worth a go..
I know it's the power supply because when I unplug it the audio interference stops immediately, and with the old one I never had this problem.

 

[bezz]

having an emi filtered powerboard wont do anything for your audio interference unfortunately, but its possible it could stop the interference on your tv.

honestly tho man if i was you id be looking for another power cable.

 

[kopper69]

Just to check a few things. On the power supply does it say that it is rated for 240V 50Hz. It will probably say something like 90-250V 35-60Hz. Just to make sure that 240V is within range. Also, quick test. With the power supply connected and turned on, but NOT plugged into the laptop - does it still interfere with the tv etc? When you purchased the power supply, what made you think that it was for your laptop? Did the seller say or you just matched the voltage? What is the current output of the power supply?

 

[savage1987]

Test 1: Input 100-240V 50-60Hz
Test 2: No audio or TV interference with the power cord on but unplugged from laptop.

Seller had Toshiba Satellite (with my laptop model) listed as one of the supported laptops for the power cord.

Output: DC 19V 3.42A


Sound OK?
Sam

 

[bezz]

yep that all sounds ok, you wouldn't get any real noticable interference on your tv/audio with no load on the transformer, as all that would be running through it would be a bit of residual current attributing to losses on the transformer itself. Once connected the laptop however, much more current travels through, resulting in said interference increasing significantly. Apart from the powerboard I mentioned above (which will only help with interference on other devices, not your laptop itself), I don't think there's really much you can do. Look at getting your money back for it if you can, or maybe pressuring them to send you a replacement?

 

[kopper69]

Im no expert in noise, its a tricky field, but lets try a few things. Thanks for doing those above tests too.

OK. Its cheap and easy so give this a go. Get some cooking foil and wrap around the power supply, heck if you have enough wrap some around the wire between the laptop and power supply too. The idea is to create a Faraday cage Faraday cage - Wikipedia, the free encyclopedia that shields this noise. I would be surprised if it worked, not a solution if it did, but we could work something out.

The other thing I wanted to ask was - out of the power supply you have the cable going to the laptop. Does this have a cable ferrite?

(This is an cable ferrite

).

These are based on a similar principle. Did your old power supply (if you can remember) have a cable ferrite? You can purchase clip on ferrites

.

Jaycar sell them for about $10, few different types. Just go to jaycars website and search 'ferrite'. Again, may or may not help. Plenty of info on the net about them, good page here:

Filtering Out Interference Signals with Cable Ferrites

Does the mains cord going into the power supply have 2 pins or 3 pins on the mains plug that plugs into the wall? Im going to guess that it has 3 prongs, which means it is using the earth. If this is the case, let me know. This is probably a very likely cause of your noise, with the problem fixed by simply using a travel adaptor that looses the earth pin. Can be dangerous, but we can discuss this if you do have a 3 prong mains cable.

 

[bezz]

OK. Its cheap and easy so give this a go. Get some cooking foil and wrap around the power supply, heck if you have enough wrap some around the wire between the laptop and power supply too. The idea is to create a Faraday cage Faraday cage - Wikipedia, the free encyclopedia that shields this noise. I would be surprised if it worked, not a solution if it did, but we could work something out.

haha nice, sort of the bush mechanics solution hey! be interested to see if it works :thumbsup:

 

[savage1987]

The old one had a ferrite, the new one does too. I will test out that foil trick a little later.

Thanks so much for your help guys, I have no clue about this stuff. We were only just starting electronics in University when I chose a different path

Power supply has an earth pin, the old one didn't.

Sam