Atari 1200xl Repair and Fujinet Funkiness

[WildBill777]

Hey guys,

 

I've been working on fixing up my Atari 1200xl.  Diagnosed it to a bad CPU and possible ANTIC.  I ordered both chips from myatari on ebay.  After a back and forth, I got the chips in.  Popped in the new CPU and voila, my Atari 1200xl was back up and running.  Not so fast....

 

While it was working great with the Pole Position cartridge, after a few more boots and hooking up the Fujinet, I started to get some weird graphic artifacts and the Fujinet would lock up on connecting to WiFi.  So, I go and replace the ANTIC chip.  Success!  I am able to boot into Fujinet and actually load some files.  Not so fast....

 

After booting into some games, watched a demo, I started to get this funkiness.  When finished with the current program, I would power off the Atari 1200xl, power it back on, and just a black screen.  Nothing, no Fujinet boot.  Power cycle a few more times, still nothing.  Removed the Fujinet.  Power cycle, still black screen.  Pop in the Pole Position cartridge, and bam, back up and running.  So I go back and insert the Fujinet, it powers up fine.  So.. let's load up some SALT or tests.  They work and all tests are passed.  Power cycle to go back to Fujinet and Not so fast.. black screen again.  If I remove the Fujinet, pop in Pole Position it comes back.

 

What could it possibly be at this point?  Is there a delay-line reset chip I need to look at?  

Suggestions what to tackle next?

 

Oh, and I'm going to have to do the mylar fix on the keyboard too.

 

 

[Sugarland]

Have you checked voltages on your PSU? How do your capacitors look? Are they leaking or bulging?  Have you tried swapping all of your RAM chips to see if that improves things?

[_The Doctor__]

you may need to give time for chips to draw down give a good 8 or 11 count

[damosan]

I'd run a memory test in a loop for a bit.  This gives the machine time to warm up as you're looking for hot chips.  I had a 130XE that had ram issues in the high bank.  Running Star Raiders was ok - loading stuff that required more than 64k would introduce weirdness - screen artifacts, locks, etc.

 

I wrote a cc65 program to scan the bank - as time progressed it identified more and more bad bits.  Some would lock high...some low.  I had the memory replaced and everything was good.

 

 

[WildBill777]

6 hours ago, _The Doctor__ said:

you may need to give time for chips to draw down give a good 8 or 11 count

Yeah, I did wait a good 10 to 30 count before powering back up.

[WildBill777]

7 hours ago, Sugarland said:

Have you checked voltages on your PSU? How do your capacitors look? Are they leaking or bulging?  Have you tried swapping all of your RAM chips to see if that improves things?

Oh yes, all of this was checked before getting to the CPU and ANTIC. I used a logic probe to look at all the address and data lines.  Found out that A7 was held high or low (cant remember now) instead of pulsing.  I also pulled and reseated all ram.  And pulled all ram and tested externally on an arduino tester.

 

 

[WildBill777]

39 minutes ago, damosan said:

I'd run a memory test in a loop for a bit.  This gives the machine time to warm up as you're looking for hot chips.  I had a 130XE that had ram issues in the high bank.  Running Star Raiders was ok - loading stuff that required more than 64k would introduce weirdness - screen artifacts, locks, etc.

 

I wrote a cc65 program to scan the bank - as time progressed it identified more and more bad bits.  Some would lock high...some low.  I had the memory replaced and everything was good.

 

 

I did let it run through a memory test twice and even checked the memory out of the system with a ram checker I built.  

 

I'll let it run some more memory checks for a good while to see if it is a heat problem.

 

I also have a UAV upgrade I want to do on this one but would like to see a stable system before upgrading.

[+bob1200xl]

C7 is in the RESET circuit. It causes funny things when you boot. It's just to the right of the k/b connector. Watch the polarity.

 

U14, the MMU, may be bad.

 

Try C7, first. I can send you an MMU.

 

Bob