Text 268, 86 rader
Skriven 2005-02-26 10:41:06 av MIKE ROSS (1:167/133.0)
    Kommentar till text 267 av Roy J. Tellason (1:270/615.0)
Ärende: Fan Of True Multitasking
================================
"Roy J. Tellason" bravely wrote to "MIKE ROSS" (26 Feb 05  04:06:01)
 --- on the heady topic of "Fan Of True Multitasking"

 RJT> MIKE ROSS wrote in a message to Roy J. Tellason:

 RJT> I downloaded a book a while back that I had originally thought to be
 RJT> about "designing analog circuits".  Well,  it was,  but they were
 RJT> talking about designing analog _chips_!

You're right, I'd imagine analog small signal IC's are quite different
from high power output transistors. I think the closest one might come
to these high voltage types is open collector drivers for alphanumeric
fluorescent displays. These IC drivers are rated at a couple hundred
volts. Those are the coolest plasma light and always fascinated me.


 RJT> Some of them also have built-in damper diodes.

 RJT> I never did get it clear why some had it and some didn't.  I thought
 RJT> pretty much took power off the flyback these days,  it seems to be a
 RJT> pretty common approach to stuff any more.

Take for example the power supply only outputs say +130Vdc regulated
but perhaps the horizontal section requires +300 volts or more. One
could add an extra winding to the flyback or add an external damper.
I guess it depends if there already exists a suitable flyback or a new
one needs to be made.


 RJT> Though it's been quite some
 RJT> time now since I really sat down and studied schematics for that stuff
 RJT> -- I don't work on tv and haven't for years,  and I have no schematics
 RJT> for monitors that are all that recent,  though I may be getting a hold
 RJT> of some.

Schematics can be a help for specific part numbers and stuff but if
you understand general principles then the key parts will look
familiar. There tends to be a set of problems areas which are typical
and only require tracing back from the broken part. However, the more
obscure faults require much more digging. It used to be the easy
problems that made it worthwhile working on these. As you know
repairing electronics isn't profitable anymore unless it is high end
stuff. I just do it for myself and friends but it's mainly a hobby.


 MR> Sometimes a powerline spike can fry the HOT or short out the
 MR> regulator. You can probe the circuit without the HOT by tack
 MR> soldering a rectifier and parallel resistance to simulate the B-E
 MR> junction. The drive should have clean edges, going positive to 0.7
 MR> volts and negative ~2 volts.

 RJT> There's a thought.  I just hope it isn't one of those setups that
 RJT> kicks it once to get it started and then relies on the HOT to keep
 RJT> things going after that.  I guess it depends on where the H oscillator
 RJT> gets its power from.  Though there _is_ a pretty hefty power FET in
 RJT> there for the LV supply...

Sorry, I just assumed you had a scope ready but from your description
of available space it isn't likely to be on hand just now? You could
test the LV supply independantly using an ohmmeter by checking out the
semis and use an ESR meter on the electros. You might take some
voltage measurements if you put a small load on the supply line that
is sensed for feedback. What were the sypmtoms when the monitor died?
Just died powering up or just one line across the screen, what?


 RJT> Right now my available work space is taken up by a MB and monitor and
 RJT> a couple of drives,  I was testing ram sticks (and did find one bad
 RJT> one),  and just last night tested out one 10G HD that I'm probably
 RJT> going to add to my setup,  I just need to decide what else I'm going
 RJT> to test and go from there,  maybe get that monitor back there
 RJT> shortly...

I rescued a PIImmx 233MHz pc without a HD in the trash a while back
and finally got around to putting one in. I ran some tests and SI gave
a result of 1,119 which made sense but then I tried some integer
benchmarks and it turns out to be about 20% slower than this mail
machine with a P120. But this machine only has an SI of 254. I tried
some trig and the PIImmx was about 3 times faster though. The PIImmx
is obviously faster yet how come the integer math is slower?

 Mike

... That was a fascinating period of time for electronics
--- Blue Wave/DOS v2.30
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