14 Jun
2016
14 Jun
'16
9:02 a.m.
I am in possession of two Magnavox (North American Philips) CM8562
monitors. Out of the box they handle composite and digital RGBI (CGA)
input. What I'd like to do is get one to handle analog RGB (like arcade
boards, Amiga, Atari ST, and Apple IIGS put out). I wouldn't think this was
possible, but I seem to have a certain memory that I saw mention of doing
just that *somewhere* on the web a few years ago, even though I can't find
that mention now.
According to the rather unwieldy chart at
http://gona.mactar.hu/Commodore/monitor/Commodore_monitors_by_model_number.…
, the service manual and schematic for the Commodore-branded 1084 and
1084S-P is "also good for Magnavox ... CM8562". I assume this means the
monitors are basically the same underneath. Both of those Commodore
monitors support analog RGB. However, when I look at the service manuals
provided for those, they specifically state in several places that parts of
the manual referring to analog RGB do not apply to the CM8562.
Also, according to
http://www.retrocomputing.net/parts/commodore/1084S-P1/docs/1084p/readme.txt
, there are two chassis designations, which both confusingly include the
string "CM8562": CM8505/CM8562/CM8705/CM8762, 8CM505/8CM515/8CM542/8CM643
on the one hand; and 8CM542/CM8562/CM8762 on the other. The latter is noted
as only accepting digital RGBI.
Physically, both monitors I have have an 8-pin DIN input for the digital
RGBI, and a circular area with the legend "lin RGB" underneath. One one
monitor, that circular area is perforated; on the other one, it's just a
circle but with no indication that it can be easily knocked out. I have not
yet opened either one.
So... does anyone know if these monitors can in fact be made to accept
analog RGB? Or have a way I could tell after opening them up? And, of
course, I'd like instructions on just how to do it, if it is possible.
--
Eric Christopherson
14 Jun
14 Jun
9:25 a.m.
I am in possession of two Magnavox (North American
Philips) CM8562
monitors. Out of the box they handle composite and digital RGBI (CGA)
input. What I'd like to do is get one to handle analog RGB (like arcade
boards, Amiga, Atari ST, and Apple IIGS put out). I wouldn't think this was
possible, but I seem to have a certain memory that I saw mention of doing
My guess is that it is possible. The CRT is an analogue device. There must
be circuitry in the monitor that accepts the 4 digital signals and turns them
into 3 analogue signals to feed to the video amplifiers. So you should be
able to feed in a suitable analogue signal after said conversion stage.
Last time I was inside a similar Philips monitor, the main PCB was designed
for all possible versions, but only the necessary components were fitted. If
you can get the service manual for the version you want (with analogue
inputs) compare the PCB layout with the version you have to find out what is
missing.
When I had to do something like this, the hardest part was finding the
right switches and connectors that would fit on the PCB and line up
with the holes in the case.
-tony
4:09 p.m.
On Tue, Jun 14, 2016, tony duell wrote:
Thanks to both of you. This might give me a goal to work toward while
learning electronics.
Is the 15kHz RGB signal fundamentally the same as the VGA signal, except
at a lower horizontal frequency? If not, how do they differ?
--
Eric Christopherson
I am in
possession of two Magnavox (North American Philips) CM8562
monitors. Out of the box they handle composite and digital RGBI (CGA)
input. What I'd like to do is get one to handle analog RGB (like arcade
boards, Amiga, Atari ST, and Apple IIGS put out). I wouldn't think this was
possible, but I seem to have a certain memory that I saw mention of doing
My guess is that it is possible. The CRT is an analogue device. There must
be circuitry in the monitor that accepts the 4 digital signals and turns them
into 3 analogue signals to feed to the video amplifiers. So you should be
able to feed in a suitable analogue signal after said conversion stage.
Last time I was inside a similar Philips monitor, the main PCB was designed
for all possible versions, but only the necessary components were fitted. If
you can get the service manual for the version you want (with analogue
inputs) compare the PCB layout with the version you have to find out what is
missing.
When I had to do something like this, the hardest part was finding the
right switches and connectors that would fit on the PCB and line up
with the holes in the case.
15 Jun
15 Jun
6:13 a.m.
Is the 15kHz RGB signal fundamentally the same as the
VGA signal, except
at a lower horizontal frequency? If not, how do they differ?
Basically, yes. 3 separate analogue video signals, one for each primary
colour.
The drifference might be the sync signals. VGA has two, basically think
of them as one to start a new scan line (horizontal sync), the other
to start a new field (vertical sync). Often analogue RGB as a combined
(or composite) sync, which is normally the logical XOR of the 2
separate sync signals. Since they are of very different frequencies, they
can be separated again in the monitor.
There is also 'sync on green'. In this one the sync signals are combined
with the green video signal to make something similar to a monchrome
composite video signal. With separate red and blue signals.
-tony
14 Jun
14 Jun
9:34 a.m.
On 15/06/2016 01:32, Eric Christopherson wrote:
I am in possession of two Magnavox (North American
Philips) CM8562
monitors. Out of the box they handle composite and digital RGBI (CGA)
input. What I'd like to do is get one to handle analog RGB (like
arcade boards, Amiga, Atari ST, and Apple IIGS put out). I wouldn't
think this was possible, but I seem to have a certain memory that I
saw mention of doing just that *somewhere* on the web a few years
ago, even though I can't find that mention now.
...
So... does anyone know if these monitors can in fact be made to
accept analog RGB? Or have a way I could tell after opening them up?
And, of course, I'd like instructions on just how to do it, if it is
possible.
The schematic details the TTL interface stepping down the 5V levels to
0.7V analog levels, which get sent through three capacitors, C217, C218,
and C219 (all schematics) to a CRT driver IC (IC502). If you were to
correctly terminate and buffer your analog RGB levels first, you'd only
need to feed those signals into the driver IC. The sync signals for
analog RGB are usually at TTL levels anyway, so they can go to the
normal inputs.
Alexis.
3112
days inactive
3113
days old
4 comments
3 participants
participants (3)
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ard＠p850ug1.demon.co.uk -
echristopherson＠gmail.com -
thrashbarg＠kaput.homeunix.org