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Old 19 November 2012, 10:59   #1
ascp
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Good values for Amiga PSU:s - noise problem.

I had a strange audio/noise problem on 2 of my amigas using an certain PSU. That led me too measure the PSU-output, without load, and with load. With load, i checked the V using the floppyheader pin.

I compared these to another A1200-PSU, which doesn't gave me the noise problems on the same Amigas.
Funny thing is, the "noiseenabling" PSU works fine on another Amiga, so it doesn't seem broken.
So it's just a certain combination of PSU and MB that seems to create noisey/no sound.

Some questions:
On my first PSU, the one with noise problem, the -12v was a bit low off-load. 10,7V - Could this be the causing the audioproblem on the specific Amigas? Also, How can i measure -12v line with load on A600?
On my PSU that works with all Amigas i tested, the +12v line with load was 13.9V. Isn't that a bit too high, or can i continue using it without frying anything.

Thanks for any answers!

Last edited by ascp; 19 November 2012 at 13:34. Reason: Clearified
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Old 19 November 2012, 11:08   #2
roy bates
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the one with a low -12 volts,is that the one causing noise? if so it could be a bad capacitor after the rectifiers.or even bad rectifiers.
EDIT: is it a low humming noise? thats usually a dead giveaway there.its probably not a good idea to connect this one to an amiga untill its fixed.


the one thats reading a bit high on the +12 volts does seem a bit high,did you use a digital meter?

if you want to measure the lines with load you could try using a stop light from a car(try a car spares shop) and just wire it in temperary and take a measure.

Last edited by roy bates; 19 November 2012 at 11:20.
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Old 19 November 2012, 13:27   #3
ascp
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Quote:
Originally Posted by roy bates View Post
the one with a low -12 volts,is that the one causing noise? if so it could be a bad capacitor after the rectifiers.or even bad rectifiers.
EDIT: is it a low humming noise? thats usually a dead giveaway there.its probably not a good idea to connect this one to an amiga untill its fixed.
.
Yes, ( it's causing low/bad sound in the audio of the amiga itself. Not the PSU in itself that sounds bad - it's quiet. But, on my other A600 the same "noisyenabling" PSU gives no noiseenabling/soundproblem. And the A1200 PSU workes fine with all my Amigas - sound's perfect.)

Quote:
Originally Posted by roy bates View Post
the one thats reading a bit high on the +12 volts does seem a bit high,did you use a digital meter?

if you want to measure the lines with load you could try using a stop light from a car(try a car spares shop) and just wire it in temperary and take a measure
Yes, used a digital one. mm, a feels a little to high, i guess the components would be stressed.
This PSU doesn't affect the sound the A600's though. Works fine on both of the Amigas

Last edited by ascp; 19 November 2012 at 13:36.
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Old 19 November 2012, 14:48   #4
roy bates
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yes,im talking about the humming noise comming from the amiga not the power supply.

the -12 volt rail drives the sound on the amiga,thats why im asking.
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Old 19 November 2012, 16:06   #5
ascp
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the -12 volt rail drives the sound on the amiga,thats why im asking.
Ok, Thanks, I might get a new PSU from Amigakit then. Just in case
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Old 21 November 2012, 00:27   #6
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Jonathan,

Just an idea, on the suspect power supply, measure the voltages again but put your meter on AC mode, this may read the ripple voltage of the PSU, if it is very bad. Some DMMs may not read the ripple voltage if the frequency is above 20 KHz.

Your original problem sounds like (pun intended) either the +12V or -12V supply regulation is degrading.

Replacing the PSU is a good idea though.
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