Re: Amplifone +/- 24v regulation

On Mon, 20 Jul 1998 10:11:18 -0400, Joel Rosenzweig <joel-r@an.hp.com> wrote:

>I built the Amplifone current regulation circuit this weekend. It
>achieved mixed results. For the first 7 minutes, the monitor looked
>rock solid, even during the explosion sequence. However, after that,
>the monitor became jittery again regardless of what it was displaying.
>
>I thought that perhaps the transistors and regulators were not cooling
>effectively, but they were cool to the touch. (They were heatsinked.)
>
>Any ideas, Zonn?

Might check the bridge rectifier (the diodes going into the filter caps) and
verify none of them are blown. You also might try adding a couple of new
capacitors in parallel to the main filter caps to see if that helps (maybe the
original caps are starting to dry out.)

It sounded like (from a previous post) you've removed the regulators from the PC
board onto the heatsinks. If this is the case then you will also need some
bypass caps on the inputs and outputs of the regulators.

You'll need 10uf caps from the input pins to ground, and then same thing from
the output pins to ground -- these caps must be located right next to the
regulators themselves, not over on the PCB.

Does it always work for 7 minutes until the monitor heats up? Or was this a one
time deal? If always, get some freeze spray and find out what part changes with
heat. If it was a one time deal, then it sounds like something has fried. If
one of the transistors has opened up, then regulation would be pretty bad and
the screen would be real jittery. Also the 6 ohm resistor would start getting
*real* warm.

Do you have access to an o'scope, and can you look at the regulated voltages
with it to see if they are stable?

-Zonn

<><><><><><><><><><><><><><><><><><><><><><><><><><><><

 ------ ___ Member of A.A.C.S.:
 |---- | ( ) Association for Artistically
    / / ( () ) Challenged Signatures
   / / //\\ // (__)
  / ---/ // \\ //\\ // zonn @ zonn . com
 -------| // \\/
Received on Mon Jul 20 13:32:50 1998