Power Supply calibration - need some help

[gilwe]

I was recapping the power supply in my E-II and mistakenly fiddled with all four trimpots available in the PS circuit, trying to set the correct voltages. I found that only two of them affect the voltage rails (-15v/+15v/+13.2v) but the other two don't affect the voltage at all. I managed to set the accurate above mentioned voltages using them, but have no idea how these other two trimpots (marked as R109 and R110 on the schematics) should be set and am afraid that being set wrongly I will damage the E-II.

Does any of you have any idea what they do and how they should be set, or have an access to the calibration procedure of the E-II ?

Thanks !!

[gilwe]

here's the power supply schematics with these trimpots marked... Thanks

[jimstew37]

I've often wondered about these trimpots, especially the one with the label reading "do not adjust." Why not put in a fixed resistor, then? Anyway, I've seen lots of references to calibrating the power supply in an EIII, so, what about the EII?

Thanks,

Jim

[gilwe]

Mike Pepper from the Synth DIY mailing list has answered me with this, regarding to the same issue.
Can this help some ? Maybe dr.c could kindly help ?

Here's what he wrote:

A few thoughts:

This is a line power switch mode, and the two pots are on the line side of
the high freqency transformer. Be careful, a sort here, or a finger on the
wrong bit is dangerous.

The switchmode gets it's chopping frequency from the Unijunction transistor
Q101, this is used to drive chopper transistor Q103. All this section is
live to the mains! It looks like R109 sets the startup frequency,
independently of the feedback loop. R110, I guess, sets the baseline of the
feedback from the opto in the 5V output, (A101) and the transformer winding
7--8.

You definitely need the manual, and you might need an isolated scope probe
too, or a 1:1 mains isolating transformer.

My advise is to proceed with care, and not to use the Emu until you've
sorted the supply. I'd do my testing with some dummy loads, the Emu is too
precious to risk killing if the supply goes wrong.

There appears to be an over-voltage crowbar circuit, (around A103) in the
12V output. If this goes off, check the mains fuse, and the chopper
transistor.

[gilwe]

OK just for documentation:

Zom from the Emulator II yahoo group has reported these values measured across these two trimpots:
 
R110 : 1.39 (measured at 20k ohm range)

R109 : 42.1 (measured at 200k ohm range)