Power off death noise

[john1979]

My A1200 is running on an A500 PSU. It used to crash and hang randomly using the A1200 PSU but has been stable since changing. However now it makes some strange noises when I turn the power off.

I've attached an MP3 amplified by 14db. Is it okay for these kind of thing to come from the audio circuitry after power off?

(Had to zip it because EAB does not allow MP3 attachments)

[Amiga1992]

I don't think so. Capacitor problem maybe?
Or perhaps your Amiga has decided to experiment in noise music

[john1979]

I just tried another PSU and the sound doesnt happen.

Is it as simple as the PSU needs a recap?

[Amiga1992]

Or throwing it away.

[john1979]

I'd be loathe to do that since it's the more sought after A500 PSU and powers my setup without a sweat.

I'll try to get it recapped then see if it helps or not.

Still wondering if it's "safe" in it's current state, I'd like to carry on using it for the time being.

[Amiga1992]

Well it's gonna ruin your setup unless you change it for a proper one. I don't think fixing a PSU like that is worth it. I don't think it even has to be "recapped", there may be a bigger problem with it.

[lesta_smsc]

Good point - for little gain, you might be risking power surge or something to blow other hardware on your Amiga.

If you've spent a lot on it, it would be worth spending that little bit extra for a proper PSU.

Recapping is good - but only if you have a standard setup and not something as power hungry ... there's a reason why the cap failed (if it did) ...

[bdb]

Doesn't mean much if the power supply is working, but ANY change from its status quo MIGHT mean imminent failure. If this is coming from your audio circuitry, and not heard at the level of the power supply itself, then it is a shielding issue and have the shielding repaired.

If it is heard out of the power supply itself, then Repair, Replace, or Substitute a newer power supply; these are all options. Or put it under a static load and give it a burn-in period to see what happens.

[john1979]

Originally Posted by bdb

If this is coming from your audio circuitry, and not heard at the level of the power supply itself, then it is a shielding issue and have the shielding repaired.

Yes it's coming from the audio out of the A1200 a few seconds after the power has been switched off at the brick. My other PSU, an official A1200 doesn't cause this noise, but it is not powerful enough to use instead of the A500 brick.

What do you mean by shielding issue? Shielding on the PSU or the shielding in the A1200?

[lesta_smsc]

It's likely to be intereference due to the increased current/power which is interfering with the audio due to the radio waves it generates.

Shielding might be required.

[bdb]

If you can live with noise, the do nothing; if you removed the tin shields from your A1200, replace them. If not, and you want to decrease the noise, get some thin tin (galvanized steel), cut a box out of it to go around the PSU, and attach it a ground. Or turn off the sound before the power

What is happening is the electrical interference from the capacitors discharging is being transmitted in a radio frequency range (FCC HATES THIS) and being picked up by the sensative audio circuits. if you've seen the "FCC approval" information on a device label about, "In the case of..., move the device further away..." If your neighbors have a short-wave radio and bitch ever time you turn off your Amy, then the FCC will be required to do something like send you a warning letter [actually I don't know if they do anything but chase down Pirate Radio channels for movies like "Pump Up the Volume"].

[john1979]

Thanks bdb. This forum is awesome, as ever

I did a quick multimeter test of the PSU, the 12V line is reading high at 14.4V, but I assumed that is because it is not under any load?

[prowler]

Originally Posted by john1979

I did a quick multimeter test of the PSU, the 12V line is reading high at 14.4V, but I assumed that is because it is not under any load?

Never measure the DC voltages on the power rails of a Commodore Amiga PSU under open circuit conditions; the readings will be meaningless.

Connect it to your Amiga and measure the voltages from behind the PSU socket with the Amiga's top cover removed. Be very careful not to short the connections with the multimeter probes.

[cosmicfrog]

just got say what an ace sound that is,I really like it

cosmic sideways though sound thingy

[bdb]

I played it back on AmiAmp and it took me back in time to when I repaired my Grandmother's 1938 Philco AM/2-band shortwave radio that she and my father had listened to the news on in World War II. That beast still works, although it needs a large antenna for shortwave and they drove the speakers with household 120Volt AC current modulated to deliver sound; you want to talk about 60Hz hum!

[Muzer]

Mine does this, except it sounds even more like a creaky door (the second noise).