Apple IIc - use of NTSC machine min 240v / 50hz-land, have screen issues

2 replies [Last post]
Offline
Joined: May 2 2010
Posts: 23

Hi

So I have my nice Apple iic, bought in canada - 110v, 60hz printed on the psu and monitor. But I'm now in the UK.

I'm running it via my trusty stepdown transformer, which outputs 110v but naturally still at 50hz.

The iic seems to run perfectly, but the iic monitor - and i have a spare that does exactly the same - displays fine, all readable but is displayed with a rather neat constant and regular 'wobble', which I assume is the 60hz circuitry having a bit of an issue coping with 50hz.

my questions are, please:

a are there any internal adjustments possible on the iic monitor that may help hide this screen wobble?

b are there any mods anyone's aware of that can get rid of this?

cheers in advance for any help or advice!

Iain

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
speedyG's picture
Online
Joined: Nov 16 2011
Posts: 1286
Re: Apple IIc - use of NTSC machine min 240v / 50hz-land, ...

Hello iainjh,
there is a mistake in thought.....
the timing is generated in the computer and not in the monitor.....
allthough both are from U.S. so both are calibrated to NTSC...
of course the signal is basically by using the terms PAL or NTSC locked to the definitions of TV-Sets...
but the timing dependent from 50 Hz or from 60 Hz is still locked to the timing from the 14 Mhz-signal that
is issued from the crystal and the following dividers within the mainboard and ... of course... the video-signals
like color, color kill and other signals that are used to generate the video-output
....
so what you see as effect on the monitor is the effect generated in the computer by a slight shift of the video-signals...
Allthough there is no real circuitplan specially for the IIc Monitor availiable ... i asume that monitor to be very similar internal to the regular Apple FBAS Monitor so i guess that the circuitplan of that monitor will be nearly identic to the one
availiable at :
http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Peripherals/Monitors/Apple%20Monitor%20II/Schematics/Apple%20Monitor%20II%20-%20Schematics%20050-5020-A.pdf
and if you view that plan there is close to the right side of the internal signaldrivingchip TDA1180P in the lower bottom of the circuitplan and left from that chip is a variable trimming-resistor R406 that is defined as H-HOLD ( = Horizontal Hold )which is resposible for catching the horizontal sync signal as part from the entire videosignal..... that might solve your problem...

BUT PAY ATTENTION ! OPENING THE MONITOR - SPECIALLY IF THE MONITOR IS NOT DISCONNECTED FROM POWER-SOURCE AND LEFT IN RUNNING MODE - THERE ARE LETHAL VOLTAGES INSIDE OF THE MONITOR UP TO 2000 VOLT ! THIS CAN KILL A PERSON IF TOUCHED BY MISTAKE ! THE DEFLECTOR ISSUES VOLTAGE UP TO 13,8 kV ( that is 13800 Volt ! )

__________________

In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

Offline
Joined: May 2 2010
Posts: 23
Re: Apple IIc - use of NTSC machine min 240v / 50hz-land, ...

ahh..of course.

I had a few troubles with my 50hz monitors when I was running them on 60hz USA mains last year.. I made a slight leap of thought didnt I Smile

thank you for that!

One thing I will do, later in the summer is to dismantle the case for the screen and the iic to retrobrite them so I will discharge the tube v carefully. My dad was an electronics engineer and though its terrifies me mildly now I did last discharge a screen when I was about 8! fat lot of use that is now Ive forgotten much of it but I will be v careful and take all precautions.

thanks again and for the circuit diagrams.

I'll update you once I'm done.

thanks!! Smile iain