A1200 crackley audio...?

[darksun9210]

me again
my A1200 is generating crackly audio when i have an ATX PSU plugged into the power port, its like the volume is maxed out and distoring...
running of the normal A1200 PSU, the audio is fine, correct volume etc.

the ATX power is hooked up via a D-Box A1200 ATX to AT adapter, then the AT power lines goto the Amiga power socket as follows
the red +5V to +5v,
the blue -12V to -12v,
the yellow +12V to +12v,
the black GND to GND,
and just incase, shield to GND,
but this hasn't made any difference.

no floppy is plugged in, no accellerator is plugged in, just a basic A1200 (rev 1D4), with 3.1 roms, and a 4Gb CF card on the IDE port with some games on it for testing...

anyone got any ideas? is there a line i'm missing? the PSU earth is attatched to the bottom case shielding...

 :-?

[Daedalus]

Are you sure that the -12V is connected and working properly? This is the type of thing that happens when the -12V line isn't working properly.

[rkauer]

 Check the PSU with a multimeter with the machine turn on.

 If everything ok (all voltages in the correct range), swap the capacitors near the RCA audio jacks.

[xeron]

Sounds like a -12V problem.

[CLS2086]

Dying caps or ground problem (socket/plug) or -12v bad.

[AmiJIm]

hi there,
once i made a good in my opinion DIY atx psu hack.
And i was having this kind of problem.
But ,by mistake i connected the ground line to -5v.
I followed the color guide on a scheme found on the net,but my compaq atx psu used their custom color wires for each voltage line.
Once i connected the GND line on the GND line of the psu,all was OK.
No harm was done to the amiga.
only crawly sound and a low whispering while moving the mouse around.

http://www.alexnavigation.com/amiga/DSC01161.JPG
http://www.alexnavigation.com/amiga/DSC01162.JPG
http://www.alexnavigation.com/amiga/DSC01163.JPG
http://www.alexnavigation.com/amiga/DSC01164.JPG

ps:i will upload a video with sound if wanted.
it was a nice update over standard amiga psu.

[darksun9210]

cool thanks guys, i was a little suspect about the -12V connection. i'll see if i can re-jig it after i find and check it all with amy multimeter.  :-)

--edit--
argh! whats going on? i'm getting -3.95V on the -12V...

[AmiJIm]

on some psus,voltages does not go along with the colors....
check each wire with a polumeter and find the -12v you need , and rewire that nano psu.

[darksun9210]

its no good, i can't find a -12V on the nano/Pico PSU.
i'm talking to the miniITX guys who i got it from to see if they can come up with anything, and they'll ask the guy that builds these PicoPSU's whats going on... i just have to test everything to make sure we don't miss any thing as i quote, "the guy that builds these things will usually only give one sentence answers" :-D .

so i'd better make that one sentence count... ;-)

if i plug a normal ATX psu into the D-box ATX to AT adapter, i get a -11.85V and a clean sounding audio - just can't fit a normal sized ATX PSU into the A1200 case... so the problem seems to be the PicoPSU not supplying a good -12V... i just need to put all my proof together to present my case... lol... sounds official...  :lol:

anyway, the saga continues... or it would have done if i hadn't have gotten bored on sunday and built a PC into a shoebox so it doesn't look so "PC" like... hey it was raining outside! :crazy: