Exidy Targ & Spectar
Color Adapter Board Troubleshooting

exidy targ and spectar color adapter pcb

Differences between Targ & Spectar Color Adapter Boards
The Video PCB used for Targ and Spectar are the same exact board with additional modifications made to the Spectar board to change a few colors (jumpers at 4A & 4C) and some have been changed to add composite blanking (wire patch on bottom of board from pin 2 of J1 at 1B to pin 7 of 74LS151 at 5C, trace cut between pin 7 & 8 at 5C [photo]).

Targ color adapter boards can be used with a Spectar PCB, but the colors will be wrong- most noticeably the maze walls will be yellow instead of green.

Spectar color adapter boards that have the wire patch to add composite blanking will not display blue when used with Targ PCBs, since Targ boards don't send anything to this output and this lack of signal affects the blue output of the 74LS151 at 5C.

Spectar color adapter boards that don't have this patch when hooked up to a Targ PCB display Spectar colors- the maze walls will be green instead of yellow.

Summary of how the board works:
The Spectar manual contains an excellent description of each of the game's PCBs. Here's a summary of my understanding of how the color adapter board functions:

1. The video signals enter the PCB from the motherboard via a 14-pin DIP ribbon cable to the socket at 1B.
2. The hex value of the character to be displayed is divided into 4 equal segments in the 74LS74 at 1A. Each of these segments has its own priority code and color determined by jumpers at 4A (Red), 4B (Green), 4C (Blue).
3. The decoder 74LS139 at 2A merges the composite video signal with the output from 1A.
4. The 74LS148 prioritizes which element is to be displayed at that screen position: Moving Object 1, Moving Object 2, or the character from character RAM.
5. The 3 74LS151 color multiplexers at 5A, 5B, 5C output each separate RGB color from the color jumpers based on the priority code.
6. The color info goes to the 74LS86 at 6A that allows for output video to be negative true if a jumper at 2C is cut.
7. The sync info goes to the 74LS86 at 1C that allows for sync video to be negative true if a jumper at 2C is cut.
8. Final video is output to the monitor from the 74LS174 at 6B.

Color is determined by jumpers at 4A (Red), 4B (Green), 4C (Blue). Unconnected jumpers add color (the white squares below):

Targ					Spectar
Jumper Line	Red	Green	Blue	Resulting Color	Jumper Line	Red	Green	Blue	Resulting Color
0 - Background	-	-		Blue	0 - Background	-	-		Blue
1 - Character RAM ($00 - $3F)		-	-	Red	1 - Character RAM ($00 - $3F)		-	-	Red
2 - Character RAM ($40 - $7F)	-			Light Blue	2 - Character RAM ($40 - $7F)			-	Yellow
3 - Character RAM ($80 - $BF)			-	Yellow	3 - Character RAM ($80 - $BF)	-		-	Green
4 - Character RAM ($C0 - $FF)	-			Light Blue	4 - Character RAM ($C0 - $FF)			-	Yellow
5 - ?	-			Light Blue	5 - ?	-			Light Blue
6 - Moving Object 2 (Player's Missile)				White	6 - Moving Object 2 (Player's Missile)				White
7 - Moving Object 1 (Player's Ship)	-		-	Green	7 - Moving Object 1 (Player's Ship)			-	Yellow

Using the Targ Test Roms
The Targ Test ROM's video tests send known signals to the color adapter board which can be used to much more easily isolate problems.

LOGIC PROBE TESTS:

Targ Test ROM Screen 1:	Targ Test ROM Screen 2:	Targ Test ROM Screen 3:
74LS74 (1A) pin 5 = Low pin 9 = Low 74LS139 (2A) pin 4 = Pulsing pins 5,6,7 = High 74LS148 (2B) pins 6,7 = High pin 9 = Pulsing 74LS151 Red (5A) pin 5 = Pulsing Green (5B) pin 5 = Low Blue (5C) pin 5 = Pulsing 74LS86 (6A) pin 3 = Pulsing pin 6 = Low pin 8 = Pulsing 74LS174 (6B) pin 2 = Pulsing pin 5 = Low pin 7 = Pulsing	74LS74 (1A) pin 5 = Low pin 9 = High 74LS139 (2A) pin 5 = Pulsing pins 4,6,7 = High 74LS148 (2B) pins 6,9 = High pin 7 = Pulsing 74LS151 Red (5A) pin 5 = Low Green (5B) pin 5 = Pulsing Blue (5C) pin 5 = High 74LS86 (6A) pin 3 = Low pin 6 = Pulsing pin 8 = Low 74LS174 (6B) pin 2 = Low pin 5 = Pulsing pin 7 = Low	74LS74 (1A) pin 5 = High pin 9 = Low 74LS139 (2A) pin 6 = Pulsing pins 4,5,7 = High 74LS148 (2B) pins 6 = High pin 7,9 = Pulsing 74LS151 Red (5A) pin 5 = Pulsing Green (5B) pin 5 = Pulsing Blue (5C) pin 5 = Pulsing 74LS86 (6A) pin 3 = Pulsing pin 6 = Pulsing pin 8 = Pulsing 74LS174 (6B) pin 2 = Pulsing pin 5 = Pulsing pin 7 = Pulsing
Targ Test ROM Screen 4:	Targ Test ROM Screen 5: (Character Set Test)	Targ Test ROM Screen 6: (Background Test)
74LS74 (1A) pin 5 = High pin 9 = High 74LS139 (2A) pin 7 = Pulsing pins 4,5,6 = High 74LS148 (2B) pins 7,9 = High pin 6 = Pulsing 74LS151 Red (5A) pin 5 = Low Green (5B) pin 5 = Pulse Blue (5C) pin 5 = High 74LS86 (6A) pin 3 = Low pin 6 = Pulsing pin 8 = High 74LS174 (6B) pin 2 = Low pin 5 = Pulsing pin 7 = High		74LS74 (1A) pin 5 = Low pin 9 = Low 74LS139 (2A) pins 4,5,6, 7 = High 74LS148 (2B) pins 6,7,9 = High 74LS151 Red (5A) pin 5 = Low Green (5B) pin 5 = Low Blue (5C) pin 5 = High 74LS86 (6A) pin 3 = Low pin 6 = Low pin 8 = High 74LS174 (6B) pin 2 = Low pin 5 = Low pin 7 = High

Targ & Spectar Color Adapter PCB Repair Log:

Spectar Color Adapter PCB: Board not displaying the green playfield.

Cycling through the video tests in the Spectar Test ROM showed that Screen 3 displayed nothing except the blue background. With Screen 3 displayed I ran though the tests with a logic probe. I found that the inputs to the 74LS148 at 2B were correct but the all the outputs were HIGH. Pin 7 should be pulsing.

The 74LS148 was bad and replacing it fixed the board.

Targ Color Adapter PCB: Colors not displayed properly

After cycling through the video tests in the Targ Test ROM, I tracked the problem to a bad output on pin 3 of the 74LS86 at 6A. After examining the bottom of the board, I discovered that pins 3 & 4 were pressed together and shorted. Bending the pins apart fixed the board.

Targ Color Adapter PCB: Magenta Background. Everything on screen has red component turned on.

Using video test screen #1 in the Targ Test ROM, I tracked the problem to a dead output on pin 5 of the 74LS151 at 5A. This in turn was causing:

74LS86 (6A) pin 3 to be HIGH when it should be PULSING
74LS174 (6B) pin 2 to be HIGH when it should be PULSING

Piggybacking a known good 74LS151 over the one at 5A fixed the symptom.

Targ Color Adapter PCB: Blue Background Black

After bringing up video test screen #5 (Background only) on the Targ Test ROM, I tracked the problem to a short between pin 4 and pin 12 of the 74LS151 at 5C under a socket that had been added to the board.

This was causing input pin 12 to be LOW when it should be HIGH (causing the black background). Another short also caused input pin 7 to be LOW rather than HIGH and the output pin 6 to be HIGH when it should be LOW.

Replacing the socket and cleaning up the traces fixed the problem.

Targ Sync Jumper

Targ Color Adapter PCB: Sync not correct

The jumper for sync video to be negative true at 2C is was not cut. Cutting it fixed the sync issue for my monitor.

Another monitor brand might require a positive true input and this jumper to be intact.

Targ Color Adapter PCB: Issues using monitors requiring composite sync

A visitor to the Outerworld Arcade web site discussed with me a problem with their Targ where the blue background was black and other game colors were incorrect.

They were using a newer replacement monitor that required composite sync. The Targ Color Adapter PCB outputs horizontal and vertical sync separately and they had combined these outputs into one "composite" sync input for the new monitor.

The Color Adapter PCB's monitor output does have a composite marking, but I'm unsure if it's active.

I was told the problem was remedied only by using an older monitor that had inputs for horizontal and vertical sync.

At this time I'm not sure if it's possible to properly hook a Targ Color Adapter PCB to newer monitors. If you have any info let me know!

Exidy Targ & Spectar Color Adapter Board Troubleshooting

Exidy Targ & Spectar
Color Adapter Board Troubleshooting