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Member Since 24 May 2007
OFFLINE Last Active Yesterday, 6:19 PM

Posts I've Made

In Topic: CO 60472 U29 Atari 800XL

Mon Sep 17, 2018 12:13 AM


U30 is just the puppet of U29.

In Topic: CO 60472 U29 Atari 800XL

Sun Sep 16, 2018 9:47 AM

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.

In Topic: The Atari 810 Revision B ROM has finally been found & dumped!

Sun Sep 16, 2018 4:33 AM

(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.

In Topic: CO 60472 U29 Atari 800XL

Sun Sep 16, 2018 3:55 AM

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

Attached File  delaylin.gif   3KB   2 downloads

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


Only thing wrong with your swap it method is the lack
of a full complement of ammo to work with. It is the
fastest way to find a faulty IC that there is. And
almost anybody can do it.

In Topic: RGB availablity inside the original 8-bit motherboards?

Tue Sep 11, 2018 1:26 AM

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