1200XL RESET problems

[ACML]

More data on a second unit with same positive results.  Recently acquired a beat up 1200XL that had the glossy motherboard with the non-clipped heat sink on the corner mount.  This seems to be an indicator of units with the cold start reset problem.  The easy way to tell if your 1200XL has the reset problem is to type the 10 ? "hello world" program in BASIC.  Hit the reset button a dozen times (some quick, some hold RESET down a whole "one Mississippi").  The correct response is a warm reset.  That means the program stays in memory.  If you get the longer pause and the fart sound, the machine is cold starting and you have lost the program in memory.  Another way to tell is run the Defender cartridge on demo and it will intermittently crash usually before it gets to 700,000 points. It has the be the hardware cartridge version, not an XEX file.  The solution is simple.

 

1)  Replace the 74LS14 with a 74AC14 IC chip

2)  Replace capacitor C7 (47 uF) with a 15 uF 35v electrolytic capacitor.  Remember polarity matters when you re-install it!

 

The results on the second unit with a reset problem were cured following steps 1 & 2.  Also, I can run the Defender cartridge demo and it no longer locks up.  I'm 2 for 2 so far.  I think if a third chance comes along and it too works, I think we can say this is a good solution with high confidence.

 

[ACML]

I now have a third unit.  It too had the intermittent cold start when a warm start was correct.  I swapped out the 74LS14 with a 74AC14 and swapped C7 (47 uF) with a 15 uF capacitor.  It cured the cold start issue and each press of the RESET key in BASIC returned a warm start and the program remained in memory.  What was different this time is that it did not cure the Defender random lock-up like it did on the previous two units. So I am:

 

3 for 3 fixing the cold start RESET issue

2 for 3 also having the Defender cartridge lock-up fixed

 

I do believe the 74AC14 and C7 swap did fix the Defender cartridge issue on the first two units.  The data I acquired during exhaustive testing is compelling.  Not sure why it didn't also fix the third.  Regardless, the swap definitively fixes the cold start issue.

 

Thanks bob1200XL 

[_The Doctor__]

For the third 1200XL Have you done the cartridge port grounding mod? also consider CPU swap.

[ACML]

28 minutes ago, _The Doctor__ said:

For the third 1200XL Have you done the cartridge port grounding mod? also consider CPU swap.

The copper grounding strap is present, but I'm not familiar with the cart port grounding mod.  I did swap out the SALLY, GTIA and ANTIC, but no change.

 

[_The Doctor__]

non mexico cpu's I hope

[ACML]

1 minute ago, _The Doctor__ said:

non mexico cpu's I hope

Don't think so.  What manufacturer code is that?

 

[mimo]

28 minutes ago, ACML said:

Don't think so.  What manufacturer code is that?

 

The ones that have died on me have all been Rockwell Mexico.

Mainly on xegs 

[_The Doctor__]

Spurious noise and ground bounce may be an issue because you can fix the 1200XL cart port a little by adding a 22 gauge wire from pin 8 of the MMU and/or pin 1 of the CPU as they are both grounds to pin B of the cart connector which is also ground. The ground path from the CPU or MMU is about 18 inches or more in a 1200XL and this puts a lot of noise on the cart connector. Also make sure to use rev 11 OS or some of the better hacks or even the 800xl os in if you don't mind losin the rainbow fuji. Rev 10 is an issue maker in and of itself.

Rockwell Mexico, any of the cpus that have mexico printed on them have been a pain.

I really wish all of the 1200XL fixes were put into a @bob1200xl compendium for all to read (since he is synonymous with fixed 1200XL) ... we all forget these nuggets and are lucky to recall something about them.

Possible even think we licked the congo bongo issue somewhere along the line... (blob on pcb shit 'kart') but can't quite pull it all together - it may have come down to the cart signal fix like in the 800, some of us used to have a switch that swapped RAS/PHI in and out to use certain carts because certain carts would work with phi on left cart and others wouldn't.

Edited January 29, 2023 by _The Doctor__

[ACML]

On 1/29/2023 at 11:17 AM, _The Doctor__ said:

Spurious noise and ground bounce may be an issue because you can fix the 1200XL cart port a little by adding a 22 gauge wire from pin 8 of the MMU and/or pin 1 of the CPU as they are both grounds to pin B of the cart connector which is also ground.

You sure it's pin 8 on the MMU as it's a 20 pin IC (2x10)?  Also, what orientation is pin B on the cartridge port?  Depends on your frame of reference.  

[ACML]

On 1/29/2023 at 9:28 AM, _The Doctor__ said:

For the third 1200XL Have you done the cartridge port grounding mod? also consider CPU swap.

What is the cartridge port grounding mod?

 

[hueyjones70]

Does it make any difference if the 1200XL has been modified by giving it an 800XL ROM and internal BASIC?

[ACML]

The CPU in the third unit is a Synertek.  

 

[ACML]

3 hours ago, hueyjones70 said:

Does it make any difference if the 1200XL has been modified by giving it an 800XL ROM and internal BASIC?

I believe the production shipped Rev 10 OS for the 1200XL would contribute to the issue since it does not have the longer pause coded in the OS like Rev 11 or the 600/8000XL OS does. Also, even Omniview 256 is baselined on OSb so it too would have an issue.  Remember, not all 1200XLs have this issue, just certain ones for what ever reason have an issue with the voltage on the 74LS14 reaching a threshold too fast.  As bob1200XL explains, the 74AC14 has a higher voltage threshold and takes longer to get there which ensures the warm start, but an unintended consequence is a long "One Mississippi" delay at RESET.  That's where replacing C7 (47uF) with a 15uF capacitor brings the delay back to near normal (i.e. 1/3 second).

 

No, the 800XL OS in a 1200XL should not have a warm start issue as the longer delay is coded into the OS which allows 74LS14 to work as intended.  I guess Atari knew it back then and fixed it in Rev 11.

 

 

Edited March 29, 2023 by ACML

[+mytek]

10 hours ago, ACML said:

but an unintended consequence is a long "One Mississippi" delay at RESET.

I wish my daily driver PC booted up that fast

 

EDIT: Bottom line, adding one second more delay on boot isn't going to be a deal breaker. In fact other than helping a 1200XL to not have start-up issues, it's also beneficial for peripherals like FujiNet in order to allow them to fully initialize. In fact on the 576NUC+ the TKII aspect intentionally lengthens the power-up reset for this very reason.

[ACML]

Going back to the way back machine, I remember in 1984 two brothers showing up to our Atari User Group ("Pirate") meeting in Mira Mesa, CA (San Diego County).  They were the only ones to have the 1200XL and it was still new and kind of novel back then.  I remember them bragging that their 1200XLs had a real cold start RESET, unlike the 400 and 800's we all had.  After thinking about it, what they had was the RESET problem.  Atari didn't design it that way, it was not supposed to cold start.  They and we thought it was deliberately designed that way.  Don't remember if the translator disk was out back then, but we dogged them that their 1200XLs were Edsels because of the OS incompatibility issues that killed sales.  The C64 selling for much less was probably the nail in the coffin for the 1200XL that could not be manufactured and be completive with the C64.  The 600XL and 800XL would attempt that.  The XE systems were cheap toy quality machines that I'm sure was Atari's continued attempt to cost reduce the machines to compete with C64s eventually selling for $199.

 

[ACML]

UPDATE:  When this thread started, I was able to modify two 1200XLs by replacing the 74LS14 and C7 with a 74AC14 and 15uF cap and the random Defender Demo stability issue seemed to be resolved.  Since then, I've had the chance to modify several more 1200XLs and yes, changing those two components will greatly improve if not fully eliminate the RESET issue, but it does nothing to cure the random Defender Demo stability issue (just coincidence on the those first two units).  To fix that, you need to swap CPUs (6502C SALLY) until you find one that tolerates the Defender cartridge.  If the RESET issue is not completely eliminated, but improved, swapping CPUs to one that makes it 100% reliable also works.  The 1200XL can have weird quirks depending on the particular CPU or DRAM type/brand installed.  These are not things (random lock up, cold starts) you will likely find with a quick function check, but it requires more rigorous testing.  You might not notice the issues under normal use, but eventually, given enough time, they will show up.