If you don't have phase 2 clock on pin 1 of U29 with a pulse then the problem is even more rudimentary with phase 2 clock and U29 might be an innocent here. Lack of phase 2 clock would be a bad U18, a 74LS08 AND chip. I do strongly suggest it be replaced with 74HCT08 AND chip for the better/stronger clock signal shape that this chip will provide over the LS version. HCT08 even when it's not a problem is the rule in my house.
OR the lack of phase 2 clock could be a bad ANTIC U7. Short list. I see where your swapping to a 5200 should have ruled this one out entirely.
Further, pins 6 and 8 of U30 need to be showing some logic state changes in order for ram to work as well.
U29 is not solely responsible for no ram situation which is what you have when all data lines are high on the 800XL.
(I'm curious if anyone has seen a utility that uses something different).
Bob Puff's US+ OS and the Black Box both can use 'something different' IIRC. It appeared to be something I had not seen before either, but done so long ago at this point I have no further useful thing to say about unusual skews found in the wild.
Had I equipment that could actually explore the area just a little, I might have paid a bit more attention to what I found. As it was just a side note that the BB will change your skew if you do it wrong and the code for US+ has yet a different set of skew tables.
Quick comment, perhaps could lead on to something else. All D lines from D0 to D7 are High instead of Pulse...accross the boad U4, U5, Pokey, etc..... Is this significant? Or could it be a symptom/confirm from bad U5 ROM, U29 or U30.? Assuming antic,gtia, cpu worked fine on a atari 5200 test. Ram is all new ics, mutiplexer are new as well.
R23-30 on the 800XL pull the data lines high so it's not unusual to see that unless you were expecting data.
How can a machine function if it's not using data? It can't.
Without a working U29 you have no ram or even stack for the CPU. The CPU is likely stuck doing something internal forevermore?
Best is probably the only one that stocks it, so outside of killing other Atari for it there is the below circuit that is supposed to be the equivalent. I got this from across the pond from a site where they don't speak english.
And I didn't save the url for it either so you could find it today. At any rate it is using one 74LS14 Hex Inverter with Schmitt Trigger Inputs plus a handful of discrete parts such as resistors and capacitors to generate time delayed signals that purportedly work as well as the stock U29. I've never built it so I've never tested it to see if it does work. I can see that it does have potential too or I never would have saved it.
From what I know they actually make RBG, luminance, and sync first then marry it all into color phase encoding. Those signals being GTIA's LUM0-3 respectively, perhaps. Just a suspicion mind you - no facts can be proven by me anyway. Somebody with moar better setup might be able to smell around in there though.
I've seen a lot of TV circuits that take RGB with sync and run it thru the 'double down' resistor network scheme as in R47-50 to do the TV signal generation with. Each resistor in that network is half the value of what the previous one is for a precise reason you see. What people can't fathom is that within the following transistor's gain function, FM modulation occurs with the color phase signal and the results are the perfect marriage made for TV use. Again can't prove it by me, to twist a phrase.
Not a high priority issues that I will ever defend either. You can think what you want over there just as I'm going to do over here. rant/OFF