CO 60472 U29 Atari 800XL

[alortegac]

Looking to purchase 1 good U29 IC to try bringing a computer with black screen back to life.

After a thorough check with logic probe and testing main ICs on my 5200 ( I do not have another 800Xl to test with), I have narrow my options to bad ROM, U30 and/or U29 delay.

 

I have a rom and u30 on their way. But I Could not find an U29 anywhere other than Best E.

 

I was hoping someone in this forum will sell me a good U29.

 

Thanks a lot!

Al

[+Nezgar]

That's BASIC Rev B. For troubleshooting, the computer should run fine without it inserted. Only minor issue is the 8K RAM region will still be allocated to nothing unless you hold option on powerup.

[alortegac]

Nazgar, I show U5 CO61598 as OS 8k x 8 ROM Rev B and U4 as CO60302 BASIC 16k x 8 OS ROM.

 

I am looking for a U29 Delay. CO60472.

 

Or maybe I misunderstood your suggestion.

 

Thanks,

Al

Edited September 15, 2018 by alortegac

[Rybags]

There are off-the-shelf delay line equivalents but no idea if a current day one exists that's a plugin or easy adaption for the Atari.

[+Nezgar]

Nazgar, I show U5 CO61598 as OS 8k x 8 ROM Rev B and U4 as CO60302 BASIC 16k x 8 OS ROM.s

D'oh, yes that is indeed delay line.. Embarassing google-fu failure on my part there.

[Roydea6]

Jumper empty socket pin 6 and pin 7

 

http://atariage.com/forums/topic/249405-new-4mb-ram-expansion/?p=3535338

 

Check if it will boot.

[_The Doctor__]

you want basic revision c in all Atari computers... B is for buggy, crashes and trashes...

[alortegac]

I will try jumper on empty socket as suggested.

 

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.

 

Thanks for any feedback.

Edited September 15, 2018 by alortegac

[Rybags]

What does the display do? Most XLs will power up initially reddish brown at least 20% of the time and you'll get a click and change to black within 2 seconds. If that occurs it's a sign that the CPU should be good and that the OS Rom is at least partly working - if there's a hang after that it's probably bad Ram or select logic.

 

A steady non-rolling display means Antic is at least able to send the VSync commands to GTIA. Rolling display can mean a failed Antic.

Edited September 15, 2018 by Rybags

[alortegac]

Hi!

 

I get a brownish/black screen when I turn it on every time and all the time. No signs of any clicks, mode steps/changes, no blinking, no sounds..

I tried the jumper on pin 6-7 empty U29. No change at all.

 

 

Turning a bit the Color control does not make any difference either.

Edited September 15, 2018 by alortegac

[alortegac]

What does the display do? Most XLs will power up initially reddish brown at least 20% of the time and you'll get a click and change to black within 2 seconds. If that occurs it's a sign that the CPU should be good and that the OS Rom is at least partly working - if there's a hang after that it's probably bad Ram or select logic.

 

A steady non-rolling display means Antic is at least able to send the VSync commands to GTIA. Rolling display can mean a failed Antic.

Antic worked fine in a 5200. Appears to be good. Gtia and cpu as well. I understand this is not the best test but all I can do with what I have.

Thanks!

Edited September 15, 2018 by alortegac

[1050]

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.

 

http://www.futurlec.com/74LS/74LS14.shtml

 

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.

[Rybags]

The eventual outcome of a runaway situation is usually execution of an illegal "kill" opcode, so "The CPU is likely stuck doing something
internal forevermore?" is a pretty true description since the internal 6502 PLA Rom tables cause certain instructions to put the CPU into a nonrecoverable idle state https://www.pagetable.com/?p=39

[1050]

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.

[+mytek]

Better still, use a 74F08 .

[alortegac]

If you don't have phase 2 clock on pin 1 of U29with a pulse then the problem is even more rudimentarywith phase 2 clock and U29 might be an innocent here.Lack of phase 2 clock would be a bad U18, a 74LS08 ANDchip. I do strongly suggest it be replaced with 74HCT08AND chip for the better/stronger clock signal shapethat this chip will provide over the LS version. HCT08even 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 ruledthis one out entirely.Further, pins 6 and 8 of U30 need to be showing somelogic state changes in order for ram to work as well.U29 is not solely responsible for no ram situationwhich is what you have when all data lines are highon the 800XL.

Thank you so much for your response.

 

I swapped U18 for a fresh IC I had in my stash. I read all U18 pins again with the probe, they are still all correct. Still no change.

 

As I said before (I think), I have a new ROM U5 and a U30 on the way.

 

Thanks a lot!

Edited September 16, 2018 by alortegac

[1050]

U29.

 

U30 is just the puppet of U29.

[alortegac]

Well, it is not the ROM chip or U30. I just ordered a U29 from Best. I will report back once I receive it.

 

Thanks!!!

[alortegac]

Thank you so much all!! Your support throughout this process has been tremendous!!!

 

Computer with all black screen of death. Is now Alive and well!!!

 

....the last and final suspect was U29. And it was the sole culprit apparently. Why did it fail? I do know. All seems ok now.

 

Thanks so much all!!!

 

Al

[_The Doctor__]

as usual it comes down to delay line or mmu or memory...

 

glad to see it working

 

https://atariage.com/forums/topic/253024-co60472-delay-line/

[alortegac]

Thank a lot! This is the pic. All put back together.

Edited September 21, 2018 by alortegac