Text 270, 120 rader
Skriven 2005-02-27 12:06:09 av Roy J. Tellason (1:270/615.0)
    Kommentar till text 268 av MIKE ROSS (1:167/133.0)
Ärende: Fan Of True Multitasking
================================
MIKE ROSS wrote in a message to Roy J. Tellason:

 MR> "Roy J. Tellason" bravely wrote to "MIKE ROSS" (26 Feb 05 
 MR> 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_!

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

Even still it goes into a lot of aspects of how those things are designed and
what the tradeoffs are during the manufacturing process.

 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.

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

That's another part for which there seems to exist no standards whatsoever as
far as I can see.

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

 MR> Schematics can be a help for specific part numbers and stuff but if
 MR> you understand general principles then the key parts will look
 MR> familiar. There tends to be a set of problems areas which are
 MR> typical and only require tracing back from the broken part.

Sure,  but I don't like tracing boards anyhow.  It's just *much* nicer when you
have a board layout diagram and a schematic at hand.

 MR> However, the more obscure faults require much more digging. It used
 MR> to be the easy problems that made it worthwhile working on these.
 MR> As you know repairing electronics isn't profitable anymore unless
 MR> it is high end stuff. I just do it for myself and friends but it's
 MR> mainly a hobby. 

Yeah.  I rather liked that monitor,  though -- it was one of the sharper ones
I've used that I can recall.

 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...

 MR> Sorry, I just assumed you had a scope ready but from your
 MR> description of available space it isn't likely to be on hand just
 MR> now? 

It's sitting in the bottom drawer of my toolbox,  which has stuff in front of
it,  and there's *no* place to set it up here.  I suppose I could get there
with some effort...

 MR> You could test the LV supply independantly using an ohmmeter by 
 MR> checking out the semis and use an ESR meter on the electros.

ESR is another thing I've been looking at making a tester for,  snagged some
stuff off the 'net but as little as I do in terms of repair work it hardly
seems to be worth my while.

 MR> You might take some voltage measurements if you put a small load 
 MR> on the supply line that is sensed for feedback. What were the 
 MR> sypmtoms when the monitor died? Just died powering up or just one 
 MR> line across the screen, what?

It was sitting here on,  and when I grabbed the mouse and went to click on
something it just went black -- no power light,  nothing.  Which is why my
tracing started at the power plug and found fuse, thermister,  etc. OK so far.

 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...

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

One of those weird tradeoffs.  I have a P233 in a box in the other room I got
off a guy which has no HD in it,  this being a P-I.  (Socket 7).  I'm thinking
about using it to replace the old Compaq that's currently the old windoze
machine here.  I'm not looking forward to it because that box is all SCSI,  and
the new one won't be,  and 98 upgrades can be a real PITA.  Much different with
linux,  where I've just taken drives from one box and put them in another and
it just deals with it with relatively little hassle.

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