28 Feb
2013
28 Feb
'13
1:58 p.m.
------------------------------
On Thu, Feb 28, 2013 11:59 AM PST Tony Duell wrote:
Bulb/s?
BUT this will not coverrt scan rates. You end up with a
composite signal
with an 18kHz horizotnal scan frequency if you start with an MDA singal.
Some monuitors can be tweked ot handle that, many cannot. Of those that
can, they might not like it too much,m you are stressing the horizotnal
ouptu transisotr and flyback transoformer a bit.
Are said xsistors readily replaceable with one that can handle a wider range? What
ultimately happens if you push a flyback too far? Burnt winding?
Have you
tried beeping? I think rom BASIC supports beeping or some
The cassette mtoor control commands (is that MOTOR ON and MOTOR OFF?) are
suitable too. When I had a floppy disk controller problem on mt
PC/XT, I put the board
on an extender, booted to ROM BASIC and used port acccess commanedst to
fiddle eith the control registers on the FDC board. A bit of work with a
logic probe and I found the faulty IC.
The only logic probe I ever owned, still own I think, was only good to 1mhz I think.
Probably suitable for what you mentioned, but not everything on a pc obviously. Address
and data is pulsed at what frequency?
1 Mar
1 Mar
3:18 p.m.
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On Thu, Feb 28, 2013 11:59 AM PST Tony Duell wrote:
Not really. Horizotnal output trnasistos are run under very unusual
conditions (HV pulses on the collector, etc) and quite often, even
equiveletns that look OK on paper will not work in practice. Finding a
mnore robust replacemetn is almost impossible unless you know rather a
lot about the actual output stage.
Even replacing the transistor with the same type for normal use is not
always trivial. it may have been specially selected. Sometimes that means
it gets a house number, which at least number. Sometiems it has just the
notmal nymber, but not all fo that type work.
BUT this will not coverrt scan rates. You end up
with a composite signal
with an 18kHz horizotnal scan frequency if you start with an MDA singal.
Some monuitors can be tweked ot handle that, many cannot. Of those that
can, they might not like it too much,m you are stressing the horizotnal
ouptu transisotr and flyback transoformer a bit.
Are said xsistors readily replaceable with one that can handle a
wider range? What ultimately happens if you push a flyback too far? Burnt winding?
What normanlyl happens is insualtion breakdown. The insualtion burns off,
and the turns short together. it is rare fo the copepr wire to melt.
Of course shorted turns totally ruin the transoformer.
Becuae of hte high votlages involved, these transformers are 'potted' in
a suitable compount. Often vacuum impregnated to make sure that potting
compound gets eveywhere and imporves the insualtion. Repairing a flyback
transformer or makign a replacemtn is not easy, it's something I must
look into one day...
-tony
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