Commodore 1902A Monitor CAN be modified for ANALOG RGB (Philips/Magnavox)
Anonymous
1902A to accept ANALOG RGB instead of DIGITAL RGB.
It's well known that the 1902 (non "A") model, the one with rounded
face and corners instead of square either directly supports Analog by
hacking the case to expose the 3rd position of the RGB switch, or that
and adding a handful of components missing on some boards.
Though I searched Google/Usenet high and low, not finding anything
[other than for the original 1902], it IS possible to modify the 1902A
series (and presumably its cousins in the Magnavox line) to accept
analog RGB for use by either an Amiga computer or arcade game boards!
The procedure:
0a) I take NO responsibility if you do not know what you are doing and
proceede to shock, maim and/or kill yourself, or any equipment you may
choose to attach to this modification.
0b) I have tested this out to ensure it is safe to connect to these
points are they ARE isolated, they are not part of a "HOT" chassis.
It's totally safe to touch these points and connect them, if done
correctly.
1) Open your 1902A. Remove the 2 screws recessed at the top back, and
2 on the bottom back, slide the cover off partway.
2) Disconnect the speaker from the connector inside, finish removing
the cover.
3) Desolder the back edge of the shield ground. Be careful--use a hot
enough iron (more than 35 watts) and don't tug, you may end up ripping
off some of the ground traces like I did.
4) Bend the shield back.
5) Locate on the top of the board the vertical riser card. This card
has a couple 74LS04 chips on it and a load of resistors. This is the
digital to analog converter board.
6) Towards the back of the monitor where the card attaches, there is a
pin labeled +5V. Locate the pin on top, then find it on the bottom
side.
7) Using a sharp knife, scrape OFF the trace just before it connects
to the pin on the card going thru the main board. We want to depower
the card, we no longer need it for analog. Test that there is no
continuity with an ohmmeter. We cannot have any voltage running into
that pin.
8) Looking on the top again, towards the front of the monitor the card
connects with 3 pins labeled R, G, B. They are NOT the set of 4 pins
labeled RGBI that were closer to the back and the +5 pin you just cut
the trace on.
9) Locate the front 3 connectors and solder RED/GREEN/BLUE wires to
these 3 points on the bottom. This is the RGB Analog out from the
converter card that we have just disabled. This is where you will feed
in your own analog RGB
10) Locate the left 8-PIN din connector on the left back edge.
11) Locate pin 6. It is down and to the left of pin 1, and down and to
the right of pin 4. Solder a BLACK wire here. This is VIDEO GROUND.
12) On the same connector, locate pin 8. It's the lowest pin in the
group. Follow the trace down til it ends. Solder a YELLOW wire here.
This is VERTICAL SYNC.
13) One the same connector, locate pin 7. It's down and to the left of
5 and directly left of 2. Follow the trace down til it ends. Solder a
BROWN wire here. This is HORIZONTAL SYNC.
14) Wrap the wires up and lead them out from under the metal shield.
15) Resolder the metal shield on the bottom.
16) Run the wires out the back around the power cord and up.
17) Reconnect the speaker in the back case and reattach the case with
4 screws after aligning the board when closing it up.
You are now done with the modification. If you used the wire colors I
suggested above, your wire connections are as follows:
RED/GREEN/BLUE: Analog RGB signal wires
BLACK: Video Ground
YELLOW: Vertical Sync
BROWN: Horizontal Sync.
Note: If connecting to something like an arcade game board that only
outputs composite sync, you can simply tie together the brown and
yellow wires and attach to the composite sync lead. Nothing special
(usually) needs to be done.
Also note: You may need to place a hex inverter (7404) inline with the
sync (and/or video) signals if your video source doesn't have the same
positive/negative signals as the monitor expects. Diagram here:
1 - U - 8
2 - x - 9
3 - x - 10
4 - x - 11
5 - x - 12
6 - x - 13
7 - x - 14
Pin 1: Sync from video source
Pin 2: Sync out to monitor
Pin 7: Ground
Pin 8: VCC (+5 volts DC)
Use pin pairs 3/4, 5/6, 9/10, 11/12, 13/14 if you need to invert any
other lines such as RGB. The odd # is the input, the even # is the
output.
Final Note: You may find that your signal is very strong and you have
to turn down the brightness and contrast and still not get an exact
picture. I am working on solving this problem yet. It may be as easy
as adjusting the DRIVE or CUTOFF or SCREEN controls.
The original daughter board seemed to output 1.0 volts on the analog
outs, so that may be the range it's expecting.
If I find a web site to host, modification pictures are available to
help with your efforts.
Enjoy!
PS: If anyone has ideas on how to reduce the brightness on it (which
control SHOULD be adjusted), please let me know. I have mine connected
to an Arkanoid board, and you can only barely see the 3d effect on
some (e.g. gold) blocks, others look solid. They should all have 3d
edges, but are being driven so high they can't be seen.
Josh McCormick
Wow! Lots of information. (Although I generally am more trusting of
electronics advice that is not anonymous posted.)
I noticed THIS ebay auction...
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2032389135
It is a Commodore 128 with a 1902A monitor. It says it has a rare video
out cable for running RGB on the 1902A monitor.
Could this be even simpler than
Anonymous
Sorry bout the anonymous part. I'm tired of spam mail filling up my
normal email addresses and only use this one address to post to usenet
(that already receives on average, 60-80 spam messages a day (1/2 a
meg worth daily, sadly).
Re: That auction.
What they're referring to is that it's including the "hard to find"
RGBI DIN cable to connect the C-128 to the 8 pin RGBI DIN connector on
the back of the monitor. As I was researching google before I posted
looking for the solution before I tried it myself, I found a few posts
saying that people always find the monitor, but no DIN cables. Most
probably think it's yet another 1541 serial drive cable and throw it
in a box with them or out because it doesn't work with their drives :(
So, no, by default, there is no way the 1902A series is analog. The
128 puts out digital RGB, and they're simply referring to the fact
that it's hard to find the RGBI cable with the monitor.
Josh McCormick <jmc...@yahoo.com> wrote in message news:<3D0E9326...@yahoo.com>...
> Wow! Lots of information. (Although I generally am more trusting of
> electronics advice that is not anonymous posted.)
>
> I noticed THIS ebay auction...
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2032389135
>
> It is a Commodore 128 with a 1902A monitor. It says it has a rare video
> out cable for running RGB on the 1902A monitor.
>
> Could this be even simpler than
[cut]
- remove !@#$&change$tos William R. Walsh
> So, no, by default, there is no way the 1902A series is analog. The
> 128 puts out digital RGB, and they're simply referring to the fact
> that it's hard to find the RGBI cable with the monitor.
I've got a friend with a Commodore 128, but I haven't looked at in much
detail to know what the video output options are or even the specifics on
the monitor....but surely it also has analog RGB output?
When my friend's TV set broke down and was in the shop, he used the monitor
from his 128 with a VCR for a dandy TV replacement--and it worked great with
no changes to the monitor whatsoever.
William
Kate Slaminko
"William R. Walsh" wrote:
He was using the composite audio/video. There's no analog RGB on a 1902A,
though I have one with an analog/digital switch. There's a sticker stating that
the analog setting is inoperable, which I've verified. They probably used a
back casing and chassis from a 1080 or 1084, which are physically identical
models that *did* have analog input and had overlapping manufacturing periods
with the 1902A.
-Ron
J. Robertson
<!@#$wwalsh@mch$i.com - remove !@#$ & change $ to S> wrote:
>I've got a friend with a Commodore 128, but I haven't looked at in much
>detail to know what the video output options are or even the specifics on
>the monitor....but surely it also has analog RGB output?
The 40 column mode is analog but the 80 column is digital output.
Jason
--
E-mail #1: jkr[at]westol.com
E-mail #2: jk...@juno.com
(Use E-mail #1 for a quicker response.)
Web site : http://www.westol.com/~jkr/
--
Mike Leavitt
He may have an A1080 or 1084. The 1080, at least has a switch to
change it from RGB to composite, and I used my 1080 as a spare TV with
my spare VCR, until my old PS2 VGA monitor died, and I needed it back
on my spare A3000. I know, SPARE me the details, and I will. :-)
--
Mike Leavitt ac...@lafn.org + team Amiga +
Anonymous
NTSC - Connect using RF (Channel 3/4), Composite, Separate (Y/C,
Luma/Chroma)
The Commdore 128 supports:
Digital RGB - 80 column, native C128 mode only
NTSC - 40 colum 128 or C64 mode, through RF to TV, Composite (thru
Video In on VCR/TV) or Separate (now known as "S-video" but that also
implies a specific connector the 128 didn't have).
So, no, the C128 does NOT output Analog RGB. The Amiga series does.
Your friend connected the Analog NTSC output through a color composite
RCA cable to the line in of a VCR, and not thru a 9-pin RGBI
connector.
"William R. Walsh" <!@#$wwalsh@mch$i.com - remove !@#$ & change $ to S> wrote in message news:<JaQP8.72779$R61....@rwcrnsc52.ops.asp.att.net>...
Overdoc
Anonymous schrieb in Nachricht ...
>Yes, it *IS* possible to convert a Philips/Magnavox made Commodore
>1902A to accept ANALOG RGB instead of DIGITAL RGB.
>
Cool !
That reminds me of my 1901 monitor, which normally has only RGBI and
chroma/luma inputs.
But when you open the case you can see some solder points on the board which
look exactly like if they were made for a scart connector. Only problem is
that they are in the wrong direction, so that the scart would point into the
inside of the monitor and not to it's back :(
So I soldered the scart there with the help of 2 flat cables and now the
1901 works perfectly with RGB also ! So I can use my Amiga with this
monitor, too :)
Also in my opinion it has an even better picture than other monitors I know,
like 1084, CM8802, CM8833,...
But I think this monitor was only sold in Europe. Some models also have
'Thompson' written on their back instead of 'Commodore 1901' because the
1901's tubes where made by Thmpson.
Reini
Michael A. Terrell
>
> RGB - Digital (RGBI) and Analog (RGBA) flavors
> NTSC - Connect using RF (Channel 3/4), Composite, Separate (Y/C,
> Luma/Chroma)
>
> The Commdore 128 supports:
> Digital RGB - 80 column, native C128 mode only
> NTSC - 40 colum 128 or C64 mode, through RF to TV, Composite (thru
> Video In on VCR/TV) or Separate (now known as "S-video" but that also
> implies a specific connector the 128 didn't have).
The C128, and C128D DO use S-video output in 40 column mode. The 40
column mode is the standard C64 output, and any C64 with an 8 pin DIN
connector had S-Video output. Its available on the 8 pin DIN plug that
has the audio output on the back of the computer. (I should know, I've
owned and repaired these units for over 15 years.)
If you need it, I can look up the pinouts for you.
Anonymous
The 128 supports 80 column Digital RGBI, and 40 column NTSC via RF,
Composite or Separate.
What I meant by the statement: "or Separate (now known as "S-video"
but that also implies a specific connector that the 128 didn't have)"
was that while the 128 DOES output Separate (Y/C), it does so through
a different connector than what we now refer to as a "S-video"
connector.
You are correct, the 128 has a 8 pin DIN connector that has the
separate video on it, that with standard C= supplied cabling becomes 2
separate RCA plugs that then plug into 2 ports on most Commodore
monitors. It however doesn't present the "separate" video through the
interface of a "S-video" 4 pin min-DIN connector which is what we are
currently used to seeing on consumer video equipment like SVHS vcr's
and DVD players.
Sorry if I was unclear with the end comment :)
"Michael A. Terrell" <ter...@mfi.net> wrote in message news:<3D1564A2...@mfi.net>...
Anonymous
very easily.
I simply hacked apart some old VCR circuit boards that had some
variable resistors on them. (You should be able to measure them
in-circuit just by taking an Ohmmeter set to 20K or 200K and testing
the two ends (not center) of each pot). Look for any between 2 KOhm
and 5KOhms.
I found a set of 3 identical ones that tested at 4.4 Kilo-Ohms across
their ends. You MIGHT be able to get by with a 2.2 KOhm, but it might
not allow enough adjustment depending on your configuration. Using
larger ones is okay, but it's VERY hard to adjust just right if the
range is too large.
Simply place the 3 pots in the middle of the Red, Green and Blue lines
from the arcade game board to the monitor. (Pot wiring for dummies:
Wire one end to the center post, and wire the other to one of the two
side leads.)
There is no need to place one in the Sync line. Once connected, boot
up your favorite board in Test mode. (I used Arkanoid which presents a
crosshatch with a 4 level RGB+Gray gradient blocks).
Adjusting color: (Using Arkanoid's test pattern, may be similar on
other boards)
1) Set the monitor's Brightness and Contrast in the center indent.
2) Turn the brightness all the way down (counter clockwise)
3) The top two levels of squares should have disappeared. If not,
adjust each R, G, B pot just until the matching colored square on the
second row disappears (do this in a darkened room)
4) Turn back up the brightness so that the top row barely appears.
5) Adjust the RGB pots so that the level of brightness of each sqare
is the same---barely visible. You should NOT have to turn very much at
all.
6) Turn the brightness back to center. Examine the screen. Should have
25%, 50%, 75% and 100% brightness blocks evenly shown with no
oversaturation at the 100% level.
Reboot the board into game mode and check to ensure it looks good.
Arkanoid is a great board to use as it both has the test screen, but
also, the multi colored blocks and grey border in demo mode help spot
errors in color adjusting. One problem may be if the gold blocks look
green (reduce your green). If you did the setup on the test pattern
screen correctly, everything should look "Perfect" (and better than
ANY arcade monitor probably ever looked)
My settings ended up between 1.55 and 1.85 KiloOhms for each gun.
Yours will vary based upon how "in tune" your 1902A monitor was to
begin with, as well as your particular arcade game board you use.
-- Enjoy.
Josh McCormick <jmc...@yahoo.com> wrote in message news:<3D0E9326...@yahoo.com>...