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Tips for testing a 520 STm?

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  • 304 posts
  • Location:Minden, NV

Posted Sun Apr 21, 2019 5:46 PM

I may have an opportunity to get a 520 STm and I'm pretty excited for it!


I found some disk images in MSA format of TOS 1.00 and will try making a disk after this post. Were later versions released on disk?


Anything interesting to look for when running something like sysinfo.prg?


What else should I look for when examining the machine?



#2 Fletch OFFLINE  



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  • Location:Pennsylvania

Posted Mon Apr 22, 2019 1:13 PM

The 520STm likely already has TOS in ROM.  




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  • Location:Minden, NV

Posted Tue Apr 23, 2019 1:03 AM

Yes, I discovered this after my post during my Google search for TOS images. :)

I still can’t figure out if there are other disk-bootable versions of TOS that can be loaded to override the TOS ROMs.

Also, can the ROM based TOS be upgraded to a later version?

#4 ParanoidLittleMan ONLINE  



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Posted Tue Apr 23, 2019 2:12 AM

Here is SW what makes bootable TOS loader floppy.  http://atari.8bitchip.info/tosload.htm


ROM based TOS can be upgraded, of course. For STs it is 1.04 . 6 chips . I can program and send it for you. 2.06 works on STs too, but it needs some + HW beside ROM chips, so not that simple upgrade. And is not really good for gaming, for instance.


What to test in 30+ years old computer ? Power supply in first place. Electrolyte capacitors need replacement, if it is not done already.




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  • Location:Minden, NV

Posted Tue Apr 30, 2019 6:17 PM

I visited the seller and decided to purchase the STm. The machine cost $40. Some issues :


First ...


I took my SF314 external drive with some disks I formatted/created on my STe with TOS 1.06. None of the disks could be read by the SF314 by the STm. A quick Google search says TOS 1.00 used a slightly incompatible format. Is this true? Supposedly my disks were not 720kB but <null>. Yes, <null>. All the property fields were blank. I also couldn't format the disks. The machine would crash, quickly flash three bombs, and reboot. Does the older STm not like the newer SF314 drives?


Second ...


When switching between low and medium resolutions the machine would sometimes reboot itself after flashing two or three bombs. Most times it would work just fine.


Third ...


Upon initial power-on, I see 3 to 5 "stuck" pixels in red in the upper left corner. Sometimes pixel #4 from (0,0) flickers. I think something may be wrong with the RAM. Once the desktop appears all stuck pixels disappear.


Otherwise, the computer is very clean, really small, and super cute. :) I really want to see if I can make it stable. Something tells me it is possible. In the next day or two I will open the case and look inside. If everything looks clean then I think I would ...


1) Check all chips in sockets, re-seat as necessary.

2) Replace capacitors.

3) Check memory.

4) Upgrade TOS from 1.00 to 1.04.



#6 ParanoidLittleMan ONLINE  



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Posted Wed May 1, 2019 1:11 AM

"A quick Google search says TOS 1.00 used a slightly incompatible format." - That's typical - partial info. Incompatible with what ? Incompatible with DOS, Windows. I mean, Atari made some stupid mistakes in SW and HW design, but that later TOS versions using incompatible floppy format with TOS 1.00 - no . Actually, at 1.04 there is proper start byte on floppy, so it is DOS compatible. But there are many floppy formatter programs for Atari ST than what is in Desktop/TOS .

What you can try is to format floppy with that some 33 years old machine - probably will fail there. If it passes try Save Desktop, and will it read it back properly - restart.

If it works, then there is likely head disalign with other floppy drive(s) in other Atari(s) .

If works not, what is to expect should clean drive. Check it's power ...




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Posted Wed May 1, 2019 8:32 AM

Long post with many pictures. Get ready and hang on! :grin:  :grin:


I spent last night opening up the STm and testing it. On the outside the machine is generally very clean and in good condition. I don't see any cracks, dings, or damage. Some of the keys are yellowed and some are not. Under proper light it almost looks like a checkerboard. I think someone may have swapped keys in and out.


The top of the motherboard is generally clean as well. I see a few jumper wires coming out of RF shield boxes. None of the chips popped out of their sockets but I did press down gently to re-seat them. Almost all of them "clicked" into the socket by a small distance. The bottom of the motherboard is a completely different story. Very messy with lots of dirty rework. I know Atari performed official rework on finished products to fix bugs and to complete circuits but this looks sloppy. I see flux on many pins and globs of glue. Is this normal? I can't imagine Atari authorized this work. The rework in my STe machines is very clean compared to this. Maybe I got a "Monday Morning" computer and the technician was recovering from a strong hangover? Underneath the RF shield is not better. :( :(


I powered up the motherboard without a keyboard and floppy using monochrome cable. It fired up almost instantly and I saw desktop minus icons. No funny pixel glitches or bombs. Hooray!! :D


I powered down and added mouse. Also good result! LIke before but now I have an arrow to move! :D


Next I try add my external floppy drive. This was surprising. I had a hard time inserting the cable. In order to do I had to support the connector from behind with left hand and push the cable in with my right hand. It went in but with difficulty. Maybe the connector is dirty? I powered on the motherboard and now I see icons. Floppies were unreadable. Power down, remove cable, reinsert cable, power up. Now I can read floppies! Hooray again! :grin: I may have been battling two issues : poorly seated cable and dirty connector. I can format and write to disks on my SF314 + STm and my STe can read them. Likewise, the STe can write to these disks and STm can read them back. So, maybe no major incompatibility issues exists here.


Finally I add keyboard. Now behavior becomes strange. Pressing certain keys would cause the computer to hang, usually keys in upper left corner. I think the keyboard may be shorting power lines and causing glitches. Perhaps the keyboard is flexing? I need to investigate more.


I ran SYSINFO and played a demo. Everything looks OK so far. I also ran YAART for more than one hour and no errors appeared.



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#8 Zogging Hell OFFLINE  

Zogging Hell


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Posted Thu May 2, 2019 4:15 AM

Perhaps there is some spillage in the keyboard, sounds like it will be worth stripping it down and giving it a good clean, it might also be worth resetting the IKBD chip on the keyboard itself (I recall the STm and original ST have a different keyboard from the later STs - different connector anyway, so you will probably need to fix this)




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Posted Thu May 2, 2019 12:56 PM

Keyboard - yes, the keyboard is a bit dirty and dusty. It definitely needs a cleaning and examination. That will be my next task. Oh, and the connector is very different from later ST keyboard. It's wider with more contacts.


Just wanted to post another quick picture here. It's a close-up of the color output from the STm. I wanted to highlight two features. The display shows a lot of "jail bars". I think that is what they are called. They are dark vertical lines that cover the screen in a repetitive pattern. They are present in low and medium resolution. It could be the VCANDO converter creating the lines based on mismatched input levels and reflections in the cable. I also noticed the screen is significantly darker compared to similar STe output with the same converter.

(Don't mind the strange moire pattern on the right hand side of the image. I think that is my phone's camera going a little nuts.)

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#10 JamesWD OFFLINE  


    Space Invader

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Posted Sat May 4, 2019 8:23 AM

Keep us all posted on progress please, always good to know the various fixes.

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