Help resurrect my Xerox Alto

Tony Duell ard at p850ug1.demon.co.uk
Tue Sep 21 15:59:45 CDT 2010


> The Alto monitor timing is pretty unique. The display is portrait, 606 

Is 'pretty unique' like 'slightly pregnant' ? :-)


> x 808 with
> the high frequency scan from top to bottom.  Overheating and 
> horizontal deflection
> failures are very common in Alto monitors. The most common cause of 
> failure is that> 
> the horizontal width coil overheats and unsolders itself from the PC 
> board. Because the
> horizontal scan occurs across the narrower dimension of the tube, a 

THis doesn't make sense to me. In the first part you're saying that th 
high frequency scna in the vertical one -- that is that it's like a 
normal monitor turned on its side. And they you talk about a width coil 
which to me would always be associated with the fsster scan (horizontal 
in anromal monitor), and yoy then say that it's the horizotnal scan on 
the shorter tube axis (OK, I get that, it's a portait monitor) here too. 

Can you tell me if the scan lines are horizontal or verticla here?

FWIW, the PEEQ portrait monbitors have horizontal scan lines alont the 
shorter acixe of the screen. 

> lot of power is 
> dissipated in the width coil. It also burns up the paper tube it is 
> wound on, making
> it impossible to adjust the width. I ended up rewinding a bunch of 
> them recently using 
> new coil forms and heavier wire.
> 
> Horizonal and vertical drive are hardwired in the display hardware. 
> You won't get a
> raster until the display microcode is loaded and running, though, and 
> you have a long 
> way to go before you're that far.

Do you get syncpulses from the start? If so, at least things like the HV 
should be coming up[ in the monitor (check this...)

If you are as insane as I am, you might make a little board with a clcok 
oscillator and timing chain on it (TTL, FPGA, whatever you are 
comfortable with) to genrate the sync pulses and some kind of fixed video 
(corsshatch, checkerboard, etc)(. Then use that to test the monitor.

-tony



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