Defender

[DanP]

Symptom: No blue
on screen.

Action: Found transistor missing (Q1, Q2, or Q3 can’t
remember which).

Fix: Replaced missing transistor.

 

[DanP]

Symptom: Stuck in Rug test

Action: Romident all the ROMs, found bad ROM.

Fix: Replaced and all OK.

 

[DanP]

Symptom: Stuck in Rug test

Action: Replaced IDE ribbon cable (just used an old IDE cable from a hard drive)

Fix: Replace IDE cable

 

[DanP]

Symptom: Screen blank, all 4 LEDs lit. No Q clock at 6809. Problem first appeared after a reset.

Fix: Outputs of 74LS107 flip-flop at 7R not oscillating despite ok inputs. Replacing the IC fixed the problem.

 

[DanP]

Symptom: Blank bands across screen.

Fix: Open track between pin4 of 6M and pin 4 of 6N (on CPU board). Repairing the track fixed the problem.

 

[DanP]

Symptom: Blank screen. H/V sync present but no colours.

Fix: Both outputs of 74LS20 @ 3S (CPU board) stuck low. Replacing IC fixed the problem.

 

[DanP]

Symptom: Rug pattern incorrect. Instead of being a random pattern, it is a very uniform horizontal line pattern. Keeps repeating.

Fix: Bad output on pin 5 of 7474@6E (CPU board). Replacing the IC solved the problem.

 

[DanP]

Symptom: Blank screen. All 4 LED's on ROM board are illuminated and stay illuminated.

Fix: Faulty 7474 @ 6D on CPU board. Replacing the IC fixed the problem.

 

[DanP]

Symptom: Vertical colour bands across screen.

Fix: No output from 74LS74 @ 6E. Replacing the IC fixed the problem.

 

[DanP]

Symptom: Different crap on screen each time the boards were powered up. From blank screen to white lines/dots.

Fix: No output from pins 2 and 4 of 7404 @ IC19 on ROM board. Replacing the IC fixed the problem.

 

[DanP]

Symptom: Rug test pattern wrong colour. When text should appear the screen goes blank.

Fix: Bad output on 74165 @ 5J (CPU board). Replacing the IC fixed the problem.

 

[DanP]

Symptom: Each time the the boards were powered up it would get to a different part of the self test. Sometimes you would simply get garbage.

Fix: Poor solder joints on the connector that the ROM board plugs into on the CPU board. Re-flowing the solder joints cured the problem.

 

[DanP]

Symptom: Rug test incorrect. Instead of the rug being one complete screen it looks like it was broken into blocks/slabs. Instead of single line scrolling down the rug (refresh type idea) the block/slab scrolls down the screen. LED's and 4 illuminated on the ROM board.

Fix: No output from 74LS153 @ 3F (next to video decode 3 ROM on CPU board). Replacing the IC cured the problem.

 

[DanP]

Symptom: Rug test pattern wrong colour. When text should appear the screen goes blank.

Fix: Pin 12 of 74LS257 @ 2J stuck high. Replacing the IC cured the problem.

 

[DanP]

Symptom: No sound. Speaker "pop" at switch on is present.

Fix: Faulty 6808 @ IC9 on sound board. Replacing the IC fixed the problem.

 

[DanP]

Symptom: No sound. Speaker "pop" at switch on is present.

Fix: All data pins on 6808 were floating. Problem traced back to a faulty 6810 @ IC11 on sound board. Replacing the IC fixed the problem.

 

[DanP]

Symptom: Complete blank screen. All 4 LED's on ROM board stay constant illuminated.

Fix: The reset was constantly low. If it was manually over-ridden then the game would play as normal. The problem was traced to R2 going high resistance. It should be 22K but was reading 41K. Replacing the resistor fixed the problem.

 

[DanP]

Symptom: After self test the game gives "INITIAL TESTS OK" message. First message after that should be "01 0000 COIN". The message I got was "01 ???? COIN".

Fix: Faulty CMOS RAM @ 1I on CPU board. Replacing the IC fixed the problem.

 

[DanP]

Symptom: Game would do the rug test then come up with some yellow vertical lines every inch or so and then reset to the rug test.

Fix: Pin 14 of RAM @ 1M was not making contact with the socket. The leg was corroded. Replacing the RAM and the socket cured the problem.

 

[DanP]

Symptom: When the sound board was plugged in the game failed to boot. It was noticed that the +12V output was only reading +5.5V.

Fix: The sound EPROM was inserted the wrong way round.