1200XL diagnosis help?

[+DrVenkman]

Here's the situation: I have a 1200XL that I haven't so much as looked at for at least 10 years. I turned it on a couple weeks ago long enough to figure out it has problems then left it until today. After investigation, here's what I've found:

 

1. Without a cart, it boots very, very slowly (like 5+ seconds) to a blank blue screen, no rainbow Atari screen, no self-test on Help either.

2. With BASIC, it boots the ROM but sounds very odd, almost muffled. It also does this very slowly, 6 - 10 seconds to the READY prompt. A simple 3 line "Hello world" program to print 10 times takes several seconds to run, with pauses after printing every line or two.

3. Some carts boot but have distorted graphics (DONKEY KONG looks okay but Mario is about twice as wide as he should be. MS. PACMAN is a completely distorted mess. MISSILE COMMAND boots up after a very long delay but the text at the top of the screen is messed up. ATARIWRITER never gets past the splash title screen to the menu. Et cetera.

4. The box does not recognize a working floppy drive connected to the SIO port and will not boot from disk.

 

So, what chips should I start looking to replace? The screen issues make me think GTIA or ANTIC but inability to boot from a floppy? Slow-running BASIC? Weird muffled sound? Heck the boot screen never appears so ... could it be the OS ROMS?

Suggestions welcome. I have spare chips in the form of other machines for everything but the ROMS.

Edited July 27, 2014 by DrVenkman

[+bob1200xl]

If it doesn't drop into the diagnostic, the CPU, ROM and memory are probably OK. I would go with ANTIC and/or GTIA. ANTIC would be my first choice.

 

If the system spends a lot of time in POR (Power On Reset), the timing capacitor may be bad. C7 - vert=very bottom of the PCB horiz= between POKEY and 6520

 

Sounds like you're running a whole lot of -HALT cycles.

 

Bob

[+DrVenkman]

If it doesn't drop into the diagnostic, the CPU, ROM and memory are probably OK. I would go with ANTIC and/or GTIA. ANTIC would be my first choice.

 

If the system spends a lot of time in POR (Power On Reset), the timing capacitor may be bad. C7 - vert=very bottom of the PCB horiz= between POKEY and 6520

 

Sounds like you're running a whole lot of -HALT cycles.

 

Bob

 

Thanks for that info, Bob. I really appreciate it. I will pull an ANTIC out of a spare system in a couple days and see what happens.

[Willsy]

I'd look to change out as many capacitors as you can. They're certainly due for a change after ~30 years!

[+DrVenkman]

I'd look to change out as many capacitors as you can. They're certainly due for a change after ~30 years!

 

I've got 8 other working A8's with original caps. I'm not gonna go replacing anything I don't have to. Besides, I haven't soldered anything since I was a teenager in the 80's and don't even currently have a soldering iron.

 

Anyway, later today I plan to disassemble a spare 600XL that I know to be working and swap out ANTICs. If that doesn't work, I'll swap GTIA chips as well. Then and only then will I try to borrow soldering supplies from someone and start trying real surgery.

[Rybags]

I'd suspect Antic, MMU, CPU. Got doubts GTIA is at fault and if it was it's doubtful it'd cause slow program execution.

The fat Mario is likely the program bugging out due to whatever problem it is.

[+DrVenkman]

So, update:

 

Replacing ANTIC with one from a 600XL gets it to boot to the rainbow ATARI screen but pressing Help does not run the self-tests. Several cartridges I tried seemed to load okay but I didn't play any of them. However, the machine still won't boot from floppy, and sound seems ... off. I don't know how else to describe it. Keyclicks don't quite sound right in BASIC and AtariWriter.

 

While I've got things torn to hell and back, any other suggestions?

[+bob1200xl]

Sounds like Bad POKEY...

 

Bob

[+DrVenkman]

More updates -

I tried replacing the POKEY, 6520, GTIA and even the CPU ... all have the same results. It boots to the splash screen but won't run self-tests. Carts load okay but sound is just not quite right. BASIC and ATARIWRITER will boot to as normal. Trying to boot with a working disk drive, however, gives a short, angry-sounding buzz and that's it. No activity light on the drive to indicate it was polled or anything.

 

I don't have a spare 1200XL MMU or I'd try that, but in the meantime I'm kind of at a loss for now. Well, I do but it's in my other (working) 1200XL. Thank you all for your suggestions.

Edited July 29, 2014 by DrVenkman

[DocRotCod]

I've got the 1200XL MMU i'll send your way if you need it. I'm converting mine to standard XL

 

Have you tried a different power supply?

Edited July 29, 2014 by DocRotCod

[+DrVenkman]

I've got the 1200XL MMU i'll send your way if you need it. I'm converting mine to standard XL

 

Have you tried a different power supply?

 

Thans for that offer, I'll let you know after I've had time to ponder a bit.

 

I did not try another power supply, though I guess will if I decide to attack this again tomorrow, just to check the possibility off the list. The one I'm using is the one my other 1200XL runs on fine - and is running on at this very moment in fact. When I checked it with a multimeter a couple weeks ago it was good.

 

Anyway, a little more background here - I have two 1200XLs. One looks great. A little 409 on the outside, a some canned air and isopropyl alcohol to wipe down the inside and it's ready to party. Only a few small scuffs on the aluminum keys and that's it. The other one looks like crap - filthy outside and in, the clear plastic strip over the LEDs is cracked and the last 1/2 inch or so is missing on the left side. One of the rubber feet isn't missing, it looks like it's been chewed off!

 

When I did a quick check a few weeks ago, they both powered on but the only thing I noticed off-hand was the expected keyboard problems. As luck would have it, after I fixed the keyboard, the pretty one wouldn't boot without the other problems noted in my first post. So as a medium-term solution, I tore the "ugly one" down to check under the RF shield and, despite the ugly exterior and seriously grimy/dusty/nasty interior, the PCB under the shield looks great. So I cleaned up that motherboard and swapped it into the pretty case and I'm golden - mostly. Sometime during its long, mistreated life, some joker didn't seem to realize that the joystick ports are angled and tried to shove something into each of them. The result was a couple bent pins. I was able to straighten all the pins in Port 1 and it works great. However, Pin #1 broke off completely in Port 2 while I was trying to fix it. But despite that, that board boots up, runs all my carts fine, recognizes the SIO port and boots off floppy just like it should.

 

So, my PLAN for today was to get the board that was originally in the "pretty one" - which has two intact joystick ports! - working by swapping out whatever chip was the problem, and then put it back into its own case, so I wouldn't have to hassle with that jacked up controller port on the ugly one yet. I don't even own a soldering iron these days so I lack the tools to replace the jack on that board. I figure I'll get around that at some point, at which time I will tackle restoration and de-yellowing the case, trying to find or make a new clear plastic strip, polish the aluminum, et cetera.

 

So that's where I stand today. One machine working, in a pretty case, but with a non-usable second joystick port. The second machine, in the ugly case with a keyboard I haven't yet fixed, that won't boot without those problems, but with two good joystick ports. Ah, the joys of keeping old computers alive ...

[+bob1200xl]

Do the keys work? You should be able to run self-tests even if the sound and SIO are trash.

 

That nasty SIO sound is something like a framing error or some such. Means you have a bad device on the SIO chain or bad h/w. Does it do the normal polling sounds if nothing is plugged into the SIO? Remember, SIO is not powered in a 1200XL. If you have a P:R Connection or some other SIO powered device, it will fail.

 

Bob

[+DrVenkman]

Do the keys work? You should be able to run self-tests even if the sound and SIO are trash.

 

That nasty SIO sound is something like a framing error or some such. Means you have a bad device on the SIO chain or bad h/w. Does it do the normal polling sounds if nothing is plugged into the SIO? Remember, SIO is not powered in a 1200XL. If you have a P:R Connection or some other SIO powered device, it will fail.

 

Bob

 

The keys are hit-and-miss on that one - I haven't done the keyboard repair yet. But without a cartridge inserted, it does recognize the HELP key, because the splash screen rainbow stops cycling when you press it, but then nothing else happens. With BASIC inserted and nothing on the SIO bus, you can hear the normal little "purr" sound. It's only when I plug in my drive chain (two 1050's) that I get the protesting squawk sound, without any activity light on either drive. As it happens, I do have an P:R: Connection, but it's currently put away in a drawer.

[+bob1200xl]

Plug in an ASM/ED cart - power on - type BUG to enter the de-bugger - type L5000 to see what is in $5000 should be all $00 - type C D301<$7F to enable the diagnostic code - type L5000 again should be code in $5000 - type G5000 should drop into Self-Test.

 

Leave SIO unplugged...

 

Bob

[+DrVenkman]

Plug in an ASM/ED cart - power on - type BUG to enter the de-bugger - type L5000 to see what is in $5000 should be all $00 - type C D301<$7F to enable the diagnostic code - type L5000 again should be code in $5000 - type G5000 should drop into Self-Test.

 

Leave SIO unplugged...

 

Bob

 

Heh. I guess I need to do the keyboard repair on that one first thing tomorrow then. As soon as I've done that, gotten it all put back together and run the suggested test, I'll let you know the results!

[ACML]

However, Pin #1 broke off completely in Port 2 while I was trying to fix it.

 

Possible fix for this worked for me. I had a SIO pin break off trying to straighten. I pulled the pin through the back of the connector leaving a hole with the missing pin. Bought a steel sewing needle, same thickness, ran it through the hole, soldered it to the inside connector to PCB and trimmed the excess. Looks OEM from the outside and works perfectly.

[+DrVenkman]

Possible fix for this worked for me. I had a SIO pin break off trying to straighten. I pulled the pin through the back of the connector leaving a hole with the missing pin. Bought a steel sewing needle, same thickness, ran it through the hole, soldered it to the inside connector to PCB and trimmed the excess. Looks OEM from the outside and works perfectly.

 

Good suggestion, thanks. I might give that a try; it's less overall work than desoldering the entire connector and installing a new one. On the other hand, there's still that little catch that I don't currently have a soldering iron.

[+DrVenkman]

Plug in an ASM/ED cart - power on - type BUG to enter the de-bugger - type L5000 to see what is in $5000 should be all $00 - type C D301<$7F to enable the diagnostic code - type L5000 again should be code in $5000 - type G5000 should drop into Self-Test.

 

Leave SIO unplugged...

 

Bob

Okay, got the keyboard fixed. Tried this in the ASM/ED cart but when I type "C D301<$7F" the cart gets hissy and just says, "WHAT?"

 

Clearly I need help with the syntax.

[Rybags]

Leave the $ out - you only need that for hex inside programs.

[+DrVenkman]

Thanks for that. Okay, did that. Nothing happens. After entering the C command in the debugger there's still no code in 5000 and so there is nothing to run.

[+DrVenkman]

Okay well thank you all for your continued help - I think I'm about to put a nail into this!

 

So earlier today I did Bob's infamous 1200XL keyboard repair. That went great. After that I couldn't get the Self Test to run to save my life, even with his suggest ASM/ED hack.

 

Be that as it may, I opened up the RF shield again today and dug into my donor 600XL. I had already salvaged the ANTIC from it, as it was definitely bad (confirmed by the fact that it does not work in the 600XL). So today I decided to swap the POKEY (because of the weird, muffled sound I had reported earlier as well as the 6520 because of the SIO problems. I also removed and re-seated both ROMS - I had done this all a couple days ago but I didn't change them all at the same. And perhaps it is all just a coincidence, but I did one more thing today - I removed and re-seated all the RAM chips.

 

After all of that, for some miraculous reason, it now boots normally, I can access the System Tests from the keyboard normally, and all seems to be well.

 

So in closing, I'm gonna put this newly-functional board into my "pretty" case, complete with its TWO working controller ports, then swap the previously-functional 1200XL board with the busted jack back into the "ugly" case for future restoration/repair. The one good thing that came out of all this from my perspective is that I learned that both these boards have 28 pin ROM sockets, so if I get the urge to install something like the APE WARP OS 32-in-1, it'll just be a matter of a few wires and moving a couple jumpers.