Elka Synthex PSU; help w/ schems and measurements

[rjd2]

hey folks, so i am trying to get the PSU on this synthex up and running. it currently has the +12v and -12v rails working, the +2.5v, +5v and +6.8v rails are down. 2.5v and 5v rails both read +1.5v.

attached is a screen cap of the PSU. if it's not readable, here is a link to the full schems, PSU on page 3:

http://www.sendspace.com/file/lf9j65

here's what the approximate voltages look like, per pin, on the UA723 voltage regulator:
1: 6v (should be 0v): NC
2: 6v: CURR LIM
3: 4v: CURR SENS
4: 4v: IN-
5: 4v: IN+
6: 7v: REF
7: 0v: Vcc-
8: 5v (should be 0v): NC
9: 4v : Vz
10: 4v (should be 7v): Output
11: 22v : Vc
12: 22v : Vcc+
13: 5v (should be 8v): Freq Comp
14: 3v : NC

where i have the notes "should be x", it's because i have readings off a properly working synthex. in addition, i have V readings from the 1458, and many points of the PSU board; let me know if those would be helpful.

the output 1 of the 1458 opamp is also reading +12V when it should be 0V, but it looks like the input is fed by the +5V of the UA723, so i'm going to work to get the UA723 working, and then assess from there.

any ideas what might be bad? these readings are off of newly installed UA723 and 1458 opamp; i'm not quite sure where to go from here. thanks, rj

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[Mongo1]

I don't have an answer, but I have some suggestions.

First, I suspect that the 723 is trying to work, since the output pin is the same as the +In. To verify that, you could try tweaking the trim pot, and see of the output voltage tracks it. I'd bet that it will.

If that's the case it may be that one of the other components has changed value. The power transistors are certainly the top of the list of things to change, but you might also want to take a look at that 1.5 ohm resistor. Some times those big boys will overheat and change values - that in turn could provide bad data to the regulator, which will then shove out a bad output.

Frankly that regulator configuration is giving me a headache. I'm having a hard time figuring out what they wanted to do there. The good thing is that there aren't a lot of components involved, so you can certainly fix it given enough patience...

Gary

PS - I never did manage to see the full view of the schematic. That file sharing thing is a pain in the butt.

[rjd2]

thanks mych, mongo.

fyi, here is another link to view or pull down the schems, these should be a higher resolution and much easier to look at:

http://manuals.fdiskc.com/flat/Elka%20Synthex%20Schematic.pdf

so i sourced what i think is a problem-the bridge rectifier is only putting out 1.5V. i've got a 12A version on order, the original was a 10A that is hard to find.

but i've got another question, and frankly it might help to hear your thoughts on the PSU schems: capacitors 1 and 2 are listed as 1000uf, but the actual values in the machine were 10,000uf. what gives? what do you think i should be going with?

[Mongo1]