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I have a couple defender boards both with similar video issues. I am focused on one I have that has new Dual swipes on all the boards and 4164 mod. The issue I am getting stumped on is the clock and video signals.
One is using 4116's as I left it and I started my focal point on the clock generating circuit because with 3 different scopes I got similar scrambled reading on the one with 4164 mod it jumps around badly and when I clamp my digital analyzer on 7P I believe which is the 74ls107 which divides the 12Mhz to 6 the scrambled screen goes dead but I was able to get samples on the DA screen to reveal that the frequencies are not stable at all. I am now carefully going over that whole clock circuit with a fine tooth comb and looking for loose ends or grounds because that is almost what it seems is happening.
Things that have been verified:
Ribbon cable replaced with new one and ohm tested.
Voltages all good.. getting 4.9-5.01 on TTL Buss.
Seems try and boot all LEDs Go out but stuck in rug(video scrambled)
For most part all probe checks out when a reset is a applied.
Issues found:
When probing clock generator 7404/74ls107 (video has more interference)
Video goes dead when Using the Digital Analyzer coupler on the 74ls107
O-scope shows blurry clock signals.

Any suggestions,ideas or replies welcome.
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