28 Sep
2014
28 Sep
'14
3:19 p.m.
Tony, et al.,
On your Rainbow H7842 PSU pinout you list pin #1 as ACOK H. Do you
know what monitors that signal?
Do you mean what controls that signel, or what htat signal is ued for?
The former is that hit is controleld by the comparatoer E1a (H7842
COntrol Module Sheet 2) whci hcompares a sgian linthe +5V output circuit
wit hteeh reference votlage (Vz). So it essentialyl means that that the
+5V ouput is present and correct.
As for waht it is used for, it drives the reset circuit (first page of
the motherboard diagrams) and thus keeeps the machine reset if the PSU
outptu si not OK.
Is it the AC side OK or the DC output OK? I'm guessing that it
monitors the AC side to ensure that the incoming "mains" voltage is
high enough to not damage the PSU. Is that correct? And nothing
monitors the DC output(s) for correctness?
No, Power OK,does mean does effectively monitor the +5V output.
There does appaer to be an undervoltage shutdown circuit. This is based
roudn E3a (H7842 COtnrol Module Sheet 1). It checks hat VStart is high
enugh (if not, it shuts fown the chopper cotnrol IC). VStart initially
comes from the little linaar 12V supply on sheet 1 of the main PSU
diagram.The main reaso nit would be too low is if the mmains input is too
low.
I have a question about using an automobile's
headlamp for load
testing this PSU. Do I need to use an increasingly rare 6V headlamp
or can I safely use a "relatively modern" 12V incandescent headlamp?
Will the 12V headlamp draw enough to safely load the 5V portion of the
PSU?
It should eb OK. A light bulb is almost a constant current load, It wil
lglow somewhat sdimly on 5V, but nothgin wil lbe damaged (I dont thinmk
the 'bow PSU is damaged by no load anyway).
=====
There is another connector coming out of the PSU that just hangs on a
plastic clip on the superstructure, presumably for another application
that the DECmate II. Since it's probably only one wire, I figured
I've neve seen that. What soer of conenctor, where does it connect in the
PSU?
My next (dumb) question is: "Is the Rainbow PSU a switching PSU?" I
assume that it is based on its size & weight, but would like expert
opinions to verify this.
YEs, it is. The mains rectifier on sheet 1 of my diagrams and the
chopper transsitor on sheet 2 confrm this.
-tony