9 May
2021
9 May
'21
2:16 p.m.
Working on restoring my very first computer, an Apple II+. Got it mostly
working with just a couple of issues identified at the moment. Some of
the keys on the keyboard don't register but I can work on that. The real
question I have is about the video, it constantly rolls and no amount of
playing with the vertical hold on any monitor I try will completely stop
it. I can get it close but it will slowly roll one way or the other at
best. Tried several different monitors and it is the same on each. Also
tried my old Apple IIe and it seems fine on all the monitors so trying
to decide what might be the issue with the II+. Any ideas or areas to
look?
Thanks.
David Williams
www.trailingedge.com
9 May
9 May
2:53 p.m.
On 2021-May-09, at 2:16 PM, David Williams via cctalk wrote:
Working on restoring my very first computer, an Apple
II+. Got it mostly working with just a couple of issues identified at the moment. Some of
the keys on the keyboard don't register but I can work on that. The real question I
have is about the video, it constantly rolls and no amount of playing with the vertical
hold on any monitor I try will completely stop it. I can get it close but it will slowly
roll one way or the other at best. Tried several different monitors and it is the same on
each. Also tried my old Apple IIe and it seems fine on all the monitors so trying to
decide what might be the issue with the II+. Any ideas or areas to look?
It sounds like the vertical sync pulse may be missing, or 'weak', in the composite
video output signal.
You 'get it close' with the V-Hold as your adjusting effort brings the monitor
frame rate (V frequency) to match the frame rate the Apple II is generating.
Pull out the schematic and look at how V sync is generated. Probably easiest to start at
the video output and work backwards, to where the combined V&H sync are added to the
pixel video to form the final composite signal, then back to where V sync & H sync are
combined, and so on.
10 May
10 May
12:27 p.m.
On 2021-05-09 16:53, Brent Hilpert via cctalk wrote:
It sounds like the vertical sync pulse may be missing,
or 'weak', in
the composite video output signal.
You 'get it close' with the V-Hold as your adjusting effort brings the
monitor frame rate (V frequency) to match the frame rate the Apple II
is generating.
Pull out the schematic and look at how V sync is generated. Probably
easiest to start at the video output and work backwards, to where the
combined V&H sync are added to the pixel video to form the final
composite signal, then back to where V sync & H sync are combined, and
so on.
Someone suggested bad ram and as I tried to boot DOS 3.3 it would drop
into the monitor and display some memory. Since it loads into high mem I
pulled the language card and the top 16K of ram leaving me 32K in the
system. Now it turns on and the vertical sync is fine but have other
issues. Namely it wouldn't give me a beep and prompt, just the standard
screen of @ and ? which is normal for boot up but wouldn't respond
otherwise. So pulled the next bank of ram and it would boot and give me
a prompt but was still randomly failing in various ways.
So I am guessing some bad ram is possible cause of the sync issue at
least, though there appears to still be other issues with the board
somewhere else. As the sync made it hard to follow stuff on the screen I
wanted that fixed first. I need to work on the keyboard next as having a
bunch of keys not responding makes it difficult to find issues. For
example the "3" doesn't work so can't get into BASIC from the monitor
even. At least I feel like I'm making progress.
David Williams
www.trailingedge.com
1327
days inactive
1328
days old
2 comments
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bhilpert＠shaw.ca -
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