[Coco] Coco monitors 1084s-xx ?

[mike delyea]

None of them will work.  You need to wire in a 74ls02 to change the
horiz/vert signal.  I have done this myself because nobody seemed to know
how at the time.  I spent a lot of time tracking down pinouts for Amiga
monitors and the signals on each wire.  I posted instructions and a wiring
diagram on coco3.com but who knows if its still there.  Searched and found.

I picked up an old Amiga 1080 monitor for next to nothing and

wanted to use it for my coco because I had heard it was a good

display for the 80 column mode. The first difficulty I ran into

interfacing the 1080 and the coco was the lack of an available

pinout for the 1080's RGB connector. Further research eventually

yielded the information that the 1084 pinout was the same as the

1080. After finding the correct pinout (at pinouts.ru) and making

a couple false starts I eventually found the correct information I

needed to make this combination work. One of the mistakes I made

was getting the HSYNC (horizontal sync) and VSYNC (vertical sync)

signals going to the monitor correctly. At first I assumed (for

various reasons) that I needed to invert the HSYNC and VSYNC so I

made up a little circuit using a 74ls04 hex inverter chip. This

didn't work and was completely off the mark as I later found out

(these chips are maybe 50 cents each so it wasn't a big deal

moneywise). Then as I was glancing through an old Rainbow I came

across the information I needed in Marty Goodman's column. The

chip I actually needed was a 74ls02 NOR gate to combine the HSYNC

and VSYNC into one CSYNC (composite sync). So I made up another

little circuit using a 74ls02 and 14 pin socket, an LED, a switch

and an external 5 volt power supply. I had originally intended to

grab 5 volts from the coco internally but I just wanted to get this

thing working and it was easier to use the external power supply.

If you want to try this yourself be warned - this only works if you

have a 1080 (or 1084) with the 9-pin D-type RGB connector, not the

round 6-pin DIN type connector. If your monitor has the DIN

connector you lucked out - you won't have to add any circuitry at

all.

Parts list:

14 pin 74ls02 NOR gate (dual input)
14 pin socket
LED
Switch (I used a double pole single throw slider I had laying

around)
5 volt power supply (I used 5volts 200 mA)
1k ohm resistor (I didn't need it and you won't either if you get

the right LED)
A small project board to attach everything to

Note: For your power supply you need 5 volts and keep the milliamps

below 400. Also, you might have to test the lines for positive and

negative if you bought the power supply at a surplus store (like I

did). If you don't know which line is positive and which is

negative it won't work and you might let the magic smoke out. You

can use a mulitmeter to find out which is which.

The Cable

For the actual cable I cobbled together a 10 pin header with ribbon

cable attached (from an old motherboard serial port connector), a 9

pin D type connector with ribbon cable attached (again from another

old serial port), and a length of Ethernet cable. Special care

must be taken when connecting the D end. The wires are not

sequential with the pins! Pin 1 is wire 1, pin 2 is wire 3, pin 3

is wire 5, pin 4 is wire 7 and so on.

The Pinouts

Coco (looking at the bottom with the back of the coco facing away

from you)

2 4 6 8 10
1 3 5 7 9

1 ground
2 ground
3 Red
4 Green
5 Blue
6 No pin
7 Sound
8 HSYNC
9 VSYNC
10 Not used

Amiga 1080 RGB D-type (looking at the back of the monitor)

1 2 3 4 5
6 7 8 9

1 ground
2 ground
3 Red
4 Green
5 Blue
6 Not used
7 CSYNC
8 Not used
9 Not used

Note: Pins 6, 8 and 9 are used with other computers, just not the

coco.

Cable Assembly:

I started at the coco end, attaching pins 1, 2, 3, 4, 5, 8 and 9 to

the Ethernet cable. The Ethernet cable is conveniently

colour-coded so make a note of what wire goes to what colour (eg.

pin 1 to blue, pin 2 to blue/white etc.). At the Amiga end I

attached the corresponding wires to pins 1, 2, 3, 4 and 5 (making

sure I followed the wiring scheme I noted earlier wherein pin 1 is

wire 1 and pin 2 is wire 3 and so on). When you've finished this,

check the connections for continuity using a mulitmeter.

The Circuit Board:

switch
----- + ------./ .-----w-----|O|----------------------|
| 5v | resistor LED ______ |
----- 1-| 7 |-14----
neg 2-| 4 |-13
| 3-| L |-12
| 4-| S |-11
| 5-| 0 |-10------------|
| 6-| 2 |-9-------| |
|----------------------------------- 7-| |-8--| | |
------- | | |
| | |
>From coco pin 8 ------------| | |
>From coco pin 9 -----------------| |
To Amiga pin 7 -----------------------|

Connect +5 to the switch and run it to the LED. Make sure you have

the LED oriented correctly or it won't work - usually the long wire

is positive. Also, unless you have an LED with a built in resistor

(mine does) you should put a resistor in front of the LED (a 1k ohm

resistor will do in a pinch). Connect the negative end of the LED

to pin 14 of the 74ls02 and attach pin 7 to the negative side of

the power supply. Attach wire 8 from the coco to pin 8 of the

74ls02 and wire 9 from the coco to pin 9 (easy eh!). Now attach

the wire from pin 7 of the Amiga's RGB to pin 10 of the 74ls02.

When you turn the switch on the LED should light. If it doesn't

light up then check your connections (and didn't I warn you about

the resistor?).

My circuit board looks a bit messy right now so I'm going to redo

it and pack it into a little project box I picked up for $2.00. I
think I'll even add a jack for the power supply.




On Fri, Mar 28, 2014 at 10:14 PM, William Haywood <
firstsecondary at verizon.net> wrote:

>  Does any one know which 1084S-xx monitors will work with the coco3?
> Without combining the Horz -Vert Sync?
>
>
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