Defender CT. Help stop the madness.

vintagegamer

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I got this Defender CT in December, as many of you know already. When powered up, it would either start the rug pattern and freeze, or just show frozen lines. It would not give the initial Williams sound or go any further.

I switched out the RAM with an extra set that I had lying around, unhooked and rehooked the connectors and (unbelievably) it came to life. It would play, but would reset during games. I decided to take the advice of the crew here and rebuild the original PS. I did and it seemed to work but then suddenly stopped working. I sent the PS to Dokert, found out I'd done substandard work (specifically I replaced the wrong transistor with the one that came in the BR kit), and he reworked it as needed. He sent the board back to me and I put it in the machine.

Now, on power up, the 3 LEDs are lit on the PS, I have nothing happening on the screen (except for some bars displayed, SOMETIMES), and the game won't boot. The 4 lights are lit on the ROM board. I ordered 4116 RAM from Bob Roberts and installed them, and it made no difference. I checked the voltages on the 4 corners of the RAM chips, and they are +5, 11.7-8, -5, and 0 as they should be.

Please let me know what I need to look at or check next. I am so bummed out.
 
Aw man. Anyone? Anyone at all? I actually have some time to tinker with this thing now and of course don't have any other suggestions coming in :(

I checked the power input voltages and they are all correct as well. I just looked up the big chip at location 2I to see if maybe that chip is bad and if it's a Z80 or Z80A, but unfortunately it's a 6809E which I don't have an extra of here at the house.

I tried removing and reseating the ROMs with no change.
 
Most common issues with Defender boards are addressing issues which cause the watchdog circuit to pulse and clock issues. Those are not easy to find and fix without a lot of work with a logic probe.

ken
 
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