A couple of months ago I finally figured it out. It was being caused by the fact that the horizontal sync pulse was too long. The oneshot responsible for it was somehow being triggered twice. Looking at the trigger pulse I could only see one real pulse but then just before it was to finish, there was a tiny spur pulse. It looked like a tiny spur pulse on my 100MHz scope, but on a 200MHz scope it was big enough to cause the oneshot to be retriggered. I replaced the chip supplying the trigger pulse, but that did not help. Scoping teh power rails showed the spur pulse there too. Then I remembered that I had used a couple of 74ACT chips where I didn't have 74LS chips. I replaced those ACT chips with LS chips and voila, the problem is gone! They were just switching so hard and fast they were causing a massive glitch throughout the system. The number of bypassing caps and their arrangement on these boards leaves a lot to be desired. Sometimes old tech cannot be ontroduced to new tech without complications.BillO wrote: ↑Thu Jul 23, 2015 4:50 pm A question for anyone that has experience with both the 600B and the 600D.
On my 600D, the first column of video seems to start 3 columns over from where the same first column does on the 600B. Like below:
Is this normal?Code: Select all
600B: D/C/W/M? 600D: D/C/W/M?
Sorry, I should have taken some scope shots and noted all the chips involved .. but sadly didn't