23 Jun
1997
23 Jun
'97
2:26 p.m.
The 5V
regulator seems to be a switching one, which is what I'd have
expected.
Huh? That would make sense because the linear regulator in T220 case
is limited to 1.5amp which it requires measly 3.6amp on that 5v
lines. Yes, is that suprising? After all, a switching
supply is nothing magical.
You still need to transform the AC output into DC and regulate it. Of
course you can always perform some regulation on an SMPS by varying the
drive waveforms on the primary side.
Hmmm...I fix PC powers and modern SMPS for
the computer all the time
to save $. Around here in canada costs above $60cdn for a new
200watt PSU.
Talking of bad design (I was earlier...) I've seen some _crazy_ SMPS's in
my time. In a Zenith monitor there's a supply that combines the
reliability of a switcher with the efficiency of a linear. It rectifies
the mains, feeds it to a free-running chopper (no regulation applied
here), shoves that into a little transformer, rectifies the output and
feeds it (about 18V DC) into a linear regulator that uses the power-on LED
as the reference. It's the only monitor that _requires_ a green power-on
LED. When my blew up (chopper failed, etc), I replaced the entire mess
with a little torroidal transformer. It was cheaper than a new chopper
transistor and a lot simpler.
Ewwww.... that is bit overkill to design that! But closed loop switchers is very efficient and compact but that
transformer is
certainly larger than the orignals.
Actually, the 50Hz 30VA transformer was no larger than the original
bits...
Are you talking about this beige tiny 12" green
or amber monitor with
That's the one.
angular back? In this, chopper trans pops and kills
one resistor.
Well, I had shorted turns in the chopper transformer (tested on a homebrew
'ring tester'). It didn't seem worth rewinding.
They are usually either TTL or composite.
I have a working zenith Eazy PC with hd in it. Slow and buggy. :)
I still have mine on a much-hacked PC/AT
Then there are the Boschert 2-stage supplies that
are used in Sanders
printers and PERQ 1's (and probably elsewhere). A shorted chopper in one
of those (which is a very common failure mode) will blow up 2 more
expensive power transistors and then take out a number of small
transistors, the chopper control IC (a good old 723), a few passives and a
couple of PCB tracks. I had to sort out such a mess once - I can provide
the full story if anyone's interested.
Hmmm... you could email me privately
with this account of yours. :) By the way, where I could buy this real techref and
how much?
Soooo, I could fix up it with addons to XT standards.
I got mine from IBM about 2 months ago. I'll try and find the part
number/form number to order it if you like.
Jason D.
--
-tony
ard12(a)eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill