Atari 1200XL needs help

[hueyjones70]

I have a 1200XL that doesn't boot. I get an audio click at power on but nothing on the screen. The power light does not come on but there is power through the switch and power at various places on the board. I have another working 1200XL and I used it to check every chip on the MB. All checked out. I guess that leaves resistors, capacitors, and broken traces. Does any one have any advice based on experience.

[+DrVenkman]

I went through this process a year and a half ago with one of my 1200XL’s, so I feel your pain.

 

Even though the screen is dark, if you boot with START pressed, do you get the cassette boot sound? If so, you may have a video issue. If you boot with a drive or drive-emulator device attached to the SIO port, do you get any sounds? Have you tried booting STAR RAIDERS, which ID’s itself to the system as a “diagnostic” cart and thus will sometimes boot when the rest of the OS can’t or won’t.

 

If all the chips on the non-booting machine work in another machine, then there’s the possibility (likelihood?) of either a faulty socket (or three!). Did your swap tests include the OS ROMS and all the support logic as well? On my 1200XL’s, all of those are socketed except the Delay Line chip, which is soldered.

 

My suggestion is to get the Sam’s 800XL Computerfacts PDF from AtariMania and a cheap logic probe and start seeing if all the chips are producing the expected results when you try to boot the troublesome machine. Even though the schematics aren’t quite accurate for the 1200XL, they are illustrative and you can figure out what you need to by comparing the 800XL stuff with the physical traces on the board in front of you.

 

Anyway, if the chips are all good, but you’re not getting the expected activity on each pin, the process is then to basically trace backwards along the circuit until you find the problem. It can be time-consuming but this effort will definitely ID what’s working right and what’s not on the board.

[hueyjones70]

I tried the Star Raiders thing and got nothing. I don't get any kind of reaction on the screen, it is exactly the same as if the monitor is turned off. I had to replace one of the ICs because corrosion had caused two pins to break off. I think I will start checking voltages from the top and bottom of each IC so I can find out if any of the sockets need replacing. Thanks for the input. I read your account of your travails with your two 1200XLs

[_The Doctor__]

corroded pins usually match up with corroded socket swipes/wipes. de-oxit the socket, if they are weak or discolored you end up with issues. might as well check them all with de oxit and a magnifying glass

Edited December 6, 2018 by _The Doctor__

[xrbrevin]

try the easy things first - have you reseated all the chips? check for corrosion / dry joints on the PCB etc

It would be helpful if you can test your chips in another, known working atari

here is the FSM etc:

 

 

1200xl.zip

[_The Doctor__]

he already noted he swapped chips between the two 1200's so it was mentioned the chips worked on the known good 1200...

 

So after socket inspection/ solder joint trace inspection, it might be time to check that last soldered in chip...

 

what kind of cord or method are you using for monitor/tv connection?

Edited December 6, 2018 by _The Doctor__

[xrbrevin]

ah, apologies - i shouldve read it fully...

[+bob1200xl]

You need to try the delay line at some point.

 

Bob

[DavidMil]

I've run across two 1200XL's that had weak connections in the sockets. One was on a RAM socket, and the other was on

one of the ROM sockets. I've also had a delay chip go bad too. You might want to look for 5V DC on all the sockets first

and then follow up with the logic probe. Look for discolored or burned components and also make sure you don't feel any

hot components. One other thing... Are you using the same power supply on both the good and bad computer?

 

DavidMil

[hueyjones70]

Yes to the power supply. I put in a new delay chip because the original was not pocketed and I cut it out, installed a socket and a new chip.

[hueyjones70]

After testing ever IF on the board, I started on the trouble shooting guide. The problem was one of the 5 volt voltage regulators.

[xrbrevin]

this little baby is a direct drop-in replacement for the 7805:

https://www.ebay.com/itm/5W-9V-12V-24V-To-5V-DC-DC-Step-Down-Converter-Module-Replace-TO-220-7805-LM2596/132644227792?hash=item1ee2364ad0:g:3vkAAOSwPGpbD5TT:rk:1:pf:0

they are switching type so they run ultra-cool. i used a pair in one of my 1050s and its fine. just v.unusual to have a cold 1050 that is powered up!!

[hueyjones70]

Auto correct got me again, that should have said "every IC".