1902 analog RGB
bs...@freenet.edmonton.ab.ca
accept analog RGB signals, ya caught me in a good mood. It didn't hurt
that I just happened to be in that same issue, looking at another article.
BTW, the text is a verbatim copy.
Have Fun!
later...
Bruce (bs...@freenet.edmonton.ab.ca)
---* Censure, not censor! *---
start of article ----------------------------------------------------------
from: Transactor: The Magazine for Commodore Programmers
November 1987: Volume 8, Issue 3, page 72
Adding Analog RGB Capability to the 1902 Monitor
Larry Phillips
Vancouver, BC
------------------------------------------------------------------
...analog RGB mode was present only on very early 1902 monitors...
------------------------------------------------------------------
When I first purchased my Amiga, I thought that I would be able to use a 1902
for the monitor, as it has a switch position for RGB analog. This feeling
was reinforced by the fact that the Amiga's 1080 monitor looked identical to
the 1902 in terms of the case, controls, and switches. Alas, it was not to
be, for in Commodore's infinite wisdom, and probably at the insistence of the
marketing types, the analog RGB mode was present only on very early 1902
monitors. Later versions had some components missing that crippled the
analog RGB circuitry. This article describes how to add the components
necessary. This modification will work on the 1902 only,
and NOT on the 1902A.
Note: If you do not feel comfortable working inside your monitor, this
modification is not for you! If this is the case, either find someone who
has the experience and knowledge necessary or take this article and your 1902
to a qualified service technician. Read this disclaimer until you realize
that I will not be held responsible [and neither will I! (bs)] for any damage
you may do to yourself or your monitor.
If you find the components already in place, yet the monitor will not allow
analog RGB, it is possible that some traces have been cut on the board near
the RGB switch. If so, you are on your own, but simply reconnecting them
should be sufficient to get it working.
Now to the modification itself. Figure 1 is the complete parts list, and all
components are both commonly available and low cost. Figure 2 shows the
layout of the board and the approximate location of the parts to add. All
parts to be added are clearly marked with silk screen on the 1902 main
board. Step by step, here we go:
1. Remove the back cover
- 6 screws
2. Remove shield on bottom of main board
- unsolder and twist tabs
3. Remove metal mounting plates holding input jacks and small boards.
- 3 screws through main board
- 1 screw holding the two plates together
- 1 screw holding RCA jack block
- 2 posts holding RGB connector
4. Remove metal shield from component side of board.
- twist tabs
5. Locate and suck the solder from the holes for the components to be added.
- R7267/8/9 in area 1, near IC7201
- R7270/1/2 in area 3
- D7218/19/20 in area 3
- C7202/3/4 in area 3
- C7219/20 in area 2
- JM123/4/5 in area 3
6. Solder in components, paying particular attention to the polarity of the
electrolytic capacitors and diodes. Capacitors are marked on the board's
silk screening with a 'dot' near the negative lead. Diodes are shown
with a picture just like the schematic representation.
* NOTE: The board is single sided, and the bonding is not the best on the
traces, so use caution and low heat so you won't damage the traces.
7. Replace the top shield and metal mounting plates.
8. Test your work at this time by placing the switch in the third position
(to the right as seen from the rear of the monitor, facing the switch)
and hooking the Amiga to the monitor through a standard Amiga RGB cable.
9. If all is well, replace the bottom shield and resolder the tabs.
10. Some 1902 monitors had a smaller hole through which the RGB switch
protruded, allowing it to be used in only 2 positions (positive and
negative RGBI). If this is the case, cut the slot in the case to allow
the switch to be placed in the newly acquired RGB analog position.
11. Replace the cover. Enjoy!
Figure 1: Parts List
Resistors Capacitors Diodes Jumpers
R7267 150 ohms C7202 330 uf - 10V D7218 1N4148 JM123 wire
R7268 150 ohms C7203 330 uf - 10V D7219 1N4148 JM124 wire
R7269 150 ohms C7204 330 uf - 10V D7220 1N4148 JM125 wire
R7270 820 ohms C7219 .01 uf
R7271 820 ohms C7220 47 uf - 10V
R7272 820 ohms
Figure 2: As viewed from bottom of board
/------------------------------------------------
| | AC | | RGB Switch |
| | CONN | \------------/
| \------/
| /--------\
| | IC7203 | 11111111111111
| \--------/
| /--------\
| 222 | IC7201 |
| 3333333333333333333333 222 \--------/
| 3333333333333333333333
| 3333333333333333333333
| 3333333333333333333333
|
| /--------\
| | IC7202 |
| \--------/
end of article ---------------------------------------------------------