Buzzing sound Amiga 1200

[Gravedigger]

Hello, I have a strange problem...

I have an amiga 1200 plugged into a scart "Hydra" power strip with an RGB scart cable purchased on amigastore 6 years ago.
When I plug it in, a big hum is heard in my speakers even though the amiga is turned off!
On the other hand, the noise stops if I turn on the Amiga 1200...

I also noticed that it causes video interference on my other devices connected to my scart Hydra power strip.

 

[miggygossip]

If the Scart cable audio rca plugs are not connected to the Amiga audio out rca then it may hum and cause interference. It also may depend on how well your Amiga PSU is grounded.

 

[Gravedigger]

If the Scart cable audio rca plugs are not connected to the Amiga audio out rca then it may hum and cause interference. It also may depend on how well your Amiga PSU is grounded.

The buzzing is a little less loud when I unplug the RCAs behind the amiga but is still present.

As I said, the buzzing occurs while the Amiga (and therefore the PSU) is not powered.

 

[miggygossip]

The grounding of the Amiga via the PSU is always connected so it may depend on what type of PSU you have. Sounds like you have a ground-loop situation. I had a similar event with my TRS-80 model 1 and speaker setup. I bought a cheap filter and made some adjustments and it was a lot better, but still there at max volume.
It could also be an improperly shielded scart cable. I'm not sure what the scart cable from amigastore is like, there are several scart cable variations around. The Retro Computer Shack scart cables from the UK are reported as among the best shielded, resistors etc.

 

[Gravedigger]

I have the original power supply. For the RGB cable, I took the cheapest at €14.
Do you think that by purchasing a better quality cable the problem will be solved?
or buy a new power supply?

 

[miggymad]

Screened cable is always best to use for anything like video cables.

You can try adding clip-on ferrite beads (also known as a ferrite block, ferrite core, ferrite ring, EMI filter, or ferrite choke) to both ends of the scart cable to help cut down on the line noise.

Failing that, see if @a.mi.goun can help you with a properly screened Amiga to Scart cable. His cables are top-notch!

<edit>

Check also the power supply for the "Hydra" and see if it is that which is introducing the line noise. As the noise is present when the Amiga is switched off, it could be the culprit.

 

[Gravedigger]

Screened cable is always best to use for anything like video cables.

You can try adding clip-on ferrite beads (also known as a ferrite block, ferrite core, ferrite ring, EMI filter, or ferrite choke) to both ends of the scart cable to help cut down on the line noise.

Failing that, see if @a.mi.goun can help you with a properly screened Amiga to Scart cable. His cables are top-notch!

<edit>

Check also the power block and see if it is that which is introducing the line noise. As the noise is present when the Amiga is switched off, it could be the culprit.

To check the power supply, I unplug it from the amiga to see if it's coming from there?

 

[miggymad]

Unplug the power supply from the Amiga and see if the noise disappears. Then do likewise to the power supply to the "Hydra".

I would look more towards to the "Hydra" being the problem here. I have never experienced Amiga power supply line noise on my Amiga's but not saying it doesn't occur.

 

[Gravedigger]

Ok, I'll try that this afternoon. I'll come back to you then.
Thank you both for your help.

 

[imqqmi]

I have a similar issue with my ReAmiga 1200 hooked up to my plasma TV, though the noise is in the video itself. The horizontal lines are wavy by about 1 pixel, like a sine wave over 10 vertical pixels. The picture is also way too bright. I've added 3 blocks of ferrite clip on beads and looped the video cable twice through them. It did make the sine wave stationary to a degree but other than that no changes. Ferrite beads filter high frequency noise of 100MHz and up. Hooking up an old DVD player to the same scart port on the TV yields a stable and clear picture. Maybe I should try a power outlet strip without earth ground, as the DVD player has no earth ground.

I used an old A500 PSU as well as the one from icomp (new one with the cartridge housing). It did clean up some other switching noise but not the waviness. I'll have to inspect further what causes it. On my 1084 CRT the picture is without distortion and isn't washed out so it must be an interaction between the TV psu and the Amiga or some ground loop issues. I suspect it's due to shield ground is connected to power ground causing ground loops and interference. I'll also see what the difference in signal level is between DVD player and Amiga and try to adjust the levels to match the DVD player.

 

[Gravedigger]

I tested the psu just now and as soon as I unplugged it from the amiga the buzzing disappeared!

 

[Buzzfuzz]

Original PSU's are very bad! I wouldn't use those anymore, goes for Amiga's as well as C64 and everything else!
Plenty of shops who offer better PSU's, or do an ATX conversion.

A-Power - HQ Power Supply for Amiga 500/500+/600/1200 - AMIGAstore.eu

HQ Power Supply for Amiga 500/500+/600/1200. This power supply offers a 120% of additional power with respect the last power supply manufactured by Commodore

amigastore.eu

Has your 1200 been recapped ?

 

[Gravedigger]

Original PSU's are very bad! I wouldn't use those anymore, goes for Amiga's as well as C64 and everything else!
Plenty of shops who offer better PSU's, or do an ATX conversion.

A-Power - HQ Power Supply for Amiga 500/500+/600/1200 - AMIGAstore.eu

HQ Power Supply for Amiga 500/500+/600/1200. This power supply offers a 120% of additional power with respect the last power supply manufactured by Commodore

amigastore.eu

Do you have a PSU model to recommend to me? yes, the amiga is completely recaped

 

[miggymad]

Let's make certain it is the Amiga PSU at fault by plugging it directly into the wall socket and firing up the A1200. If the buzzing is present then there's your problem and it's a good indication that a replacement should be purchased.

Also, now would be an excellent time to have the A1200 mainboard recapped if it has not already been done.