Amplifone Design... Wonders me

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

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Tue Mar 9 12:05:22 2004