Re: Amplifone Design... Wonders me

Have you tried running direct, heavy ground wires
(to the relevant tracks on the pcb's themselves)
between the AR/II ground, the game board ground and
the monitor ground?
I cured a lot of wobble that way on mine.

That would also explain why you can't filter out
the ps section with good caps, the isolated lab supply
may have temporarily got rid of the relatively poor ground
connection causing ground offset ripple from deflection current draw.

Cheers,

Marc

----- Original Message -----
From: mypearl
To: vectorlist@vectorlist.org
Sent: Wednesday, March 10, 2004 9:31 AM
Subject: Re: VECTOR: Amplifone Design... Wonders me

I have been testing that...

I had the degaussing coil plugged out (on AC supply) and it didn't make any difference. In fact, I had all AC equipment (fluoriscent
lamp, AC fan) unplugged at some point and it did not make any difference.

My concern now is why the amplifone deflection board is so sensitive to power supply ripple...

I have never seen any home stereo amp with regulation. They have very good ripple rejection though... I don't suppose those are
voltage feedback amplifiers makes a difference for PSRRR ?

Mendel
----- Original Message -----
From: Rodger Boots
To: vectorlist@vectorlist.org
Sent: Tuesday, March 09, 2004 9:39 PM
Subject: Re: VECTOR: Amplifone Design... Wonders me

I'm going to say your problem isn't ripple, it's more likely to be the degauss circuit never turning off. By supplying DC instead
of AC you basically stopped the degauss coil from putting out an AC field.

Try it on AC with the degauss coil unplugged and see what you get.

mypearl wrote:

Hello Group,

I've been posting before about my Star Wars with amplifone that is giving me a wobbling image.

After a lot of testing and replacing old components on the amplifone deflection board, I found that If I connect my regular lab
power supply to the amplifone's + and - 30V rails, the wobbling goes away and the picture is rock-steady! I just connected the +
and - 30 VDC to the AC power input on the Deflection board.

This means the Amplifone (or mine) isn't very good in rejecting power supply ripple.

The ripple on the supply rails is about 200 mV AC RMS, what doesn't seem to be extraordinary considering the currents involved.

I understood from someone that the biasing transistors Q3 and Q13 are extremely of influence when it comes to power supply ripple,
but that section seems fine and I've replaced both the 3904 and the MPSU57, as well as the 914 diodes (by 1N4148's) on both
channels. I also installed 10.000 MFD capicators with low ESR specs for the main filter caps.

I cannot believe the image on every Amplifone should be wobbling somewhat. Can anybody confirm that it should be very stable?

What for Atari's sake could cause the deflection board to be so sensitive to power supply ripple?

Being very curious!

Mendel Pearl

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Received on Tue Mar 9 18:22:01 2004