monitor tweaking

Tony Duell ard at p850ug1.demon.co.uk
Tue Nov 29 03:00:30 CST 2005


> 
> to what extent is it advisable to use a say ~350 line
> monitor with a 400 line video output? Granted, I
> probably shouldn't try this with the original IBM mono
> display (reported to explode if you plug it into a CGA
> card), but this was a more or less common practice
> back when. Assuming you get a legible image, after
> adjusting the horizontal sweep, is there any risk to
> the equipment or operator when doing this?

I can see no obvious risk to the _operator_. The EHT will not rise that 
much, if at all, so the X-ray emissions won't be any worse. The CRT is 
not going to implode. The thing should not catch fire (assuming it was 
safely designed in the first place).

As regards danger to the monitor. The problem is not the change in number 
of lines, it's the change in horizontal scan frequency. You can get more 
lines for essentially the same horizontal scan rate by lowering the 
vertical frequncy (an example of this is that UK 625 line TV and US 525 
line TV have very similar horizontal rates, the difference is in the 
vertical rate (50 Hz or 60Hz)). In general tweaking the vertical rate is 
'safe' and will do no damage to anything.

Tweaking the horizontal rate may be OK. Certainly small changes will do 
no harm. In some cases even larger changes are OK (the original TRS-80 
model 1 monitor -- the one based on the RCA TV chassis -- can be made to 
lock to MDA rates, and seems not to mind). If the monitor seems happy 
(stable picture, correct size, etc) then I would give it a go.

-tony



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