Defender Repair Log

The game was 100% dead upon arrival.  Upon close inspection the LED lights for the +12vdc and -5vdc on the power board were out which indicated zero output.  I cleaned the very dirty fuse holder but that didn't solve the problem.  I also repaired many cracked solder joints on the board but the LED's remained out.  Both voltage regulator LM723's were checked with a logic probe and it was confirmed that heir outputs were dead.  As indicated by the red arrows in the picture, both voltage regulators were replaced and the +12vdc and -5vdc were now present!

With the power supply board up and running the game still did nothing.  I discovered the bank of 4116 RAM on the main CPU board was missing the +12vdc. The power board and harness were checked and found to be good.  After an extensive search a 0.1uf capacitor at C22 was found to be dead shorted to ground.  The capacitor, indicated by the red arrow, was replaced and the bank of 4116 RAM was now buzzing along.

The game still was not booting and the interconnect cable from the ROM board was dropping out multiple signals including the PSO signal.  A replacement cable repair kit is available so I ordered one and installed it.  There are many pins and solder pads to deal with during this repair so I recommend if you attempt sure to have patience as you go.  The first picture shows the old brittle cable removed and the 1000 solder pads (Mom told me a million times never to exagerate!) cleaned up.  The second picture shows the new cable soldered in and ready to go!

At this point everything seemed to be working but I still had a blank sceen and no sound to indicate that the game was at least playing blind.  On to the WG4600 monitor.  There were the typical cracked solder joints everywhere but even after the picture.  It turns out my 'black adjust' pot was bad and once replaced I finally had a picture!  The game was booting up but going straight to the bookkeeping screen.  As it turns out, the original battery holder was corroded so it was replaced with a lithium ion battery kit.  The pictures show the original crusty battery holder and the new clean lithium ion battery holder.

With the battery kit installed I was able to play the game but there was no sound.  The game was found to have a bad 6808 CPU on the sound board. Once that was replaced - I FINALLY HAD DEFENDER RUNNING!  I was never so happy to finally see the screen shown in the picture to the left.  After a long series of tough repairs...this game is still just as TOUGH to play as I remember!