[sdiy] MKS70 power supply issue

[ChristianH]

On Thu, 15 Nov 2012 10:52:13 -0600 w.james.meagher at gmail.com wrote:

> Thanks for the suggestions everyone, I'll investigate further when I'm back in town on Monday. 
> 
> What I do know off the top of my head is that the mains in these parts run at 120V, not 117V - I'll test for further particulars when I'm back.
> 
> I agree that it would be nice to know where the +7Vunreg is supposed to be going, but I really can't make it out on my poor copy of the assigner and other schematics. I'll see when I'm back if there's a JX10 service manual out there (that might be clearer than my MKS70 manual), to shed some light on the +7unreg's destination.
> 
> I also recall that there's a diode in that PSU I was eyeing suspiciously (as someone else here...or on AH...has suggested), so I'll also test that one when I'm back to make sure it hasn't failed.


As far as I can see in the JX10 circuit (assuming no big difference to
the MKS), the +7V only goes to the 5V regulator and to the PG800
connector (which most probably has its own 5V regulator).

My guess is that "+7V" isn't to be taken literally, it appears to mean
"something sufficient to drive a 5V regulator". 
If it was something like 15V or more I would start to worry, but as
others have pointed out, if mains voltage is somewhat above nominal
value (e.g. 240 vs. 220V), 10V doesn't look overly suspicious to me.
That's what voltage regulators are for :-)

Christian