Defeated by a Commodore 1950 Monitor

[Mark J. Blair]

> On Dec 1, 2014, at 16:30 , Zane Healy <healyzh at aracnet.com> wrote:
> 
> Are you just driving it off the built in VGA, or do you have a VGA card in it?

Just the built-in VGA. As I understand it, plain old 31 kHz monitors will work with the flicker-fixer turned on, right?

> On Dec 1, 2014, at 16:42 , Geoff Oltmans <oltmansg at gmail.com> wrote:
> Well, if you do replace it with another CRT monitor, don't toss the 1950! Monitors that sync that low are few and far between, and although the Commodore monitor ain't the best, it is a brand match and will work with the A3000 as well as the A1200 and A4000 in all unflicker-fixed modes.

Yeah, I'd love to use the brand-matched monitor even though it's not the greatest monitor. Maybe another parts-donor will come along, and I can build a working monitor out of the pair?

> An oscilloscope would go a long way to helping with the repair.

It sure would, if I knew what any of the pins on the chip were supposed to be doing! It's just a 20-pin DIP with no explanation of what the chip's function is in the circuit, other than what I can infer from circuit topology.

I really don't enjoy working on monitors like this one, or else I might poke around some more... lots of pointy high-voltage stuff, and very poor circuit accessibility without reducing it to a pile of loose boards and a tangle of cables next to a naked CRT rocking on the bench. Pretty much the whole thing needs to be taken to pieces to get to the solder side of the main board. Grr!

If I could identify and procure that IC, and perhaps a few others in the vertical drive circuit, I'd happily tear it all apart, swap the chips, and cross my fingers. Hmm, maybe I should expend some more effort to try to find out if the OEM is still around (said to be a company called AOC, in Milpitas, CA), and whether anybody there might be able to identify the IC in question? I think it's a long shot, but maybe I'll get lucky.

-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/