OT: Help understanding trimpots in a power supply

[Gil]

Hi all !

Need some help please. The following schematics is of a synth power supply. I recapped it and then trying to adjust for precise voltages, I also tweaked the two trimpots in the picture (both marked red). I then realized that they do not make any change in the values of the main voltagr rails (-15v,+5v,+13.2v). I would like to get them back to their "correct" position by have no calibration procedure I can find anywhere.

I thouhgt maybe some of you will be able to understand what they're doing and how they should be set... Just worrying that I will get my precisous analog machine defected... Thanks

[PRR]

I'm not sure what R109 and R110 should do. They are not regulating voltage, but controlling oscillator operation.

R109 and R110 are at LINE VOLTAGE!!!
Touching them while on could be lethal.
I suggest you power-off, let bleed (5 minutes), and set them where they were or in the center.

R116 is the master voltage adjuster.

You have cut off the master voltage reference. A104 seems to supply -15V. I can not tell if it is trimmable.

R116 R119 and R122 ratio the -15V against the +5V onto Q105 Q106 which drive Q104 and the magic opto-coupler A101. The other end of A101 gimmicks the line-powered oscillator. This tends to hold the +5V rail at the right voltage. Trim R116 for pretty-near +5V.

If A104 is an untrimmed 7915, then this supply is NOT critical. Whatever precision this synth has is out in the analog circuits, not the power supply. (That's normal: only a few small circuits need point-oh-oh precision, and that's easier with some local trim or reference than by making the WHOLE supply precision.)

If the "+5V" is 4.9V to 5.1V, it will be fine.

Check the other outputs for "about" the right voltage. The +12V is not regulated nor adjustable except indirectly by setting the +5V with R116. The +13.2V is trimmed with R134.

[Gil]

Thanks very much, unfortunately I haven't marked the original position of these trimpots so there's no way I can return them back there.
I currently put them in center. Here's the complete schematics, can this put anything into a clearer picture ?

http://f1.grp.yahoofs.com/v1/cHAsTd6dwy3rBo3y7Z45dKY4svyHvtgge721q5XILZX7HNOi4fnz7CsOuKENs9qwFjaw2nbxKyHupnlU_Iu0HSNn_lA/Technical/EmulatorIIPSUSchematic.pdf

[PRR]

"The document you requested could not be found."

The f1.grp.yahoofs.com servers don't share well.

Is it working? (It needs a load.) Do the pots I pointed-to trim the voltage?

[Gil]

http://www.fileden.com/files/2009/5/8/2434738//EmulatorIIPSUSchematic.pdf

I only see four trimpots on the circuit board. Two of them trim the +5v/+13.2/-15v rails and I managed to get accurate reading.
This while R110 and R109 are centered. Moving them doesn't affect the values of the +5v/+13.2/-15v rails.

How would you suggest positioning them two ?

As for the +12v rail, I get about +16v here instead, and it is not adjustable... Should I worry ?

Thanks for your help !

[Gil]

Hi, only bumping.. Thanks