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Moe

Atari 520 STfm - Freezes

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Hi everyone,

 

So I bought an Atari 520 STfm as "un-test" from an estate sale locally, and I'm having a few issues I hope some of you might be able to help with.

 

When I finally got it home I gave it a light cleaning and dusting and then powered it on.  When started the 520 STfm did boot into TOS, but it took 30-45 seconds.  Once in TOS I could move the mouse around the screen, but it moved very slow and sluggishly (Note:  I have used this exact mouse on my Atari 520ST and it moves very smoothly) .  I then put a disk in the drive an attempted to read it.  As soon as I tried to access the disk the computer froze/hung.  I also tried booting the computer with a disk in the drive.  When I did this the computer NEVER responded.  The disk never loaded and it never loaded TOS.  I waited almost 10 minutes and the disk did not spin up.

 

So I did some research and found out about the issues with the internal power supplies caps, so I opened up and case and measured the 5V and 12V lines coming off the PSU.  The 5V was ~5.002V and the 12V was ~11.56V.  I figured that the this was the cause of my issues. I ordered a set of replaces caps from Console5 (https://console5.com/store/atari-1040-computer-power-supply-cap-kit-mitsumi-68-4242a-1040stf.html)

 

While I waited for the new caps to arrive my Gotek (FlashFloppy ) drive arrived.  Since the Gotek drive only uses the 5V line I figured I'd give it a try while I wait for the caps to arrive.  I installed the Gotek in the drive and I got similar results.  If I had a memory stick in the drive and a image selected the computer would not boot at all (I left it for almost 10 minutes).  If I don't have a memory stick in the drive the computer will boot into TOS (still takes 30-45 sec).  I then inserted the memory stick into the drive and open "Floppy Disk A" in TOS and it opened a window showing the selected .prg file.  If I then try to open the .prg file the computer freezes.

 

Last Thursday my order from Console5 arrived and I replaced the caps this evening.  The PSU is now putting out ~5.006V and ~11.76V (I was expecting this to be closer to 12V) with the new caps.  When I test the computer with the Gotek drive I get the EXTACT same results.  On the Gotek drive I have single jumper set on S0, and I have pin 1 on the IDE cable going to pin 1 on the Gotek.

 

Any ideas what might be wrong, or what I am doing wrong?

 

 

Thanks

Moe

 

 

 

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Try reseating the chips. Pull them out carefully and put them back in.

 

I wish you could run a memory tester like YAART. Maybe you have bad memory that is causing the CPU to hang.

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I did push the socketed chips down, but I didn't pull them and completely re-seat them.  I'll try this tomorrow.

 

You "think" it might be memory issues?

 

Moe

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I tried re-seated the socketed chips, but I'm getting similar results.

 

When I was re-seating the chips I took a few pictures of the board.  It looks like my 520STfm has a 1040ST board with only 512k dram installed. I guess Atari just used whatever parts they had available at the time ...

 

If we thought it might be a dram issue I'd remove the existing 16 dram chips, socket the board and install some new 41256.  If I did this could I just add 16 more dram chips into the existing spots and get a full 1MB of ram?

 

I do find it odd that when I do boot into TOS that the mouse is really slow and sluggish. The same mouse on my 520 ST moves fast and smooth ...

 

 

 

Any ideas?

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Forgot to add the pictures ...

IMG_20210405_122444.jpg

IMG_20210405_122426.jpg

IMG_20210405_122505.jpg

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17 hours ago, Moe said:

The 5V was ~5.002V and the 12V was ~11.56V

Wouldn't worry about those voltages, they are fine usually 5V +/- 5% and 12 also +/- 5%

 

image.thumb.png.d535cb50c08aa4fa8905db665786dd19.png

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2 minutes ago, TGB1718 said:

Wouldn't worry about those voltages, they are fine usually 5V +/- 5% and 12 also +/- 5%

 

image.thumb.png.d535cb50c08aa4fa8905db665786dd19.png

Thanks. That removes one possible source of my issues.  Now only n - 1 remaining, where n is a real number greater then 1 and less then 

 

😉

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Since I can't run any software from the Gotek drive or original floppy drive it's hard to run any test/diagnostic software on the 520.

 

What's the chances of a diagnostic cartridge running?  I could by one from exxos.

 

https://www.exxoshost.co.uk/atari/store2/#0165

 

Thoughts?

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12 minutes ago, Moe said:

What's the chances of a diagnostic cartridge running? 

Really high it will run fine. But I don't think it will show much though. You already know that floppy isn't working. So maybe pull up resistors on the 8 data lines on the DMA or WD1772 could help.

 

Otherwise check WD1772, DMA and a 74LS06 that is part of the floppy circuit. Ribbon cable for the floppy of course. Check continuity on each leg with schematics. You should clean the legs on the chips with IPA or deoxit in the sockets when you reseat them.

 

Schematics here.

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1 hour ago, snarkdluG said:

Really high it will run fine. But I don't think it will show much though. You already know that floppy isn't working. So maybe pull up resistors on the 8 data lines on the DMA or WD1772 could help.

 

Otherwise check WD1772, DMA and a 74LS06 that is part of the floppy circuit. Ribbon cable for the floppy of course. Check continuity on each leg with schematics. You should clean the legs on the chips with IPA or deoxit in the sockets when you reseat them.

 

Schematics here.

Ok, all good ideas.  I'll start working on these recommendations.

 

Thanks!

 

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Could it be you just have a bad keyboard with a faulty interface or bad cable connection to the motherboard?

 

You said your computer freezes at the desktop. What if you ran some sort of demo that auto-booted from a floppy disk image? Would the demo freeze midway through loading?

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21 hours ago, Moe said:

I tried re-seated the socketed chips, but I'm getting similar results.

 

When I was re-seating the chips I took a few pictures of the board.  It looks like my 520STfm has a 1040ST board with only 512k dram installed. I guess Atari just used whatever parts they had available at the time ...

 

If we thought it might be a dram issue I'd remove the existing 16 dram chips, socket the board and install some new 41256.  If I did this could I just add 16 more dram chips into the existing spots and get a full 1MB of ram?

 

I do find it odd that when I do boot into TOS that the mouse is really slow and sluggish. The same mouse on my 520 ST moves fast and smooth ...

 

 

 

Any ideas?

RAM expansion is easy when there is space for chips, so yes adding 16 chips, and 3 resistors - just look some schematic of 1040 and will see which go to second bank.

That mouse issue indicates problem with some line, most likely. Should check and by need resolder 9-pin connector for it - soldering often cracks because lot of attaching, detaching. How about keyboard click ? It should happen after shorter key holding down, and then repeat frequently.

If that's not case need to check IKBD chip, keyboard connector to mainboard ...

If Desktop appears after some delay (caused by not working floppy/circuit/cable) is it stable, no crash (bombs), reset by self ?

If it is stable, RAM is most likely OK, so better check other things for start. And if possible should check power voltages with oscilloscope.

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Thanks for the feedback and info everyone.  Please keep it coming!

 

Life has gotten in the way of retro, and I haven't had a chance to test any of your recommendation yet.

 

Hopefully I'll find some free time this weekend and test a few things out.  I'll keep you posted!

 

Cheers

Moe

 

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On 4/6/2021 at 3:39 AM, ParanoidLittleMan said:

RAM expansion is easy when there is space for chips, so yes adding 16 chips, and 3 resistors - just look some schematic of 1040 and will see which go to second bank.

That mouse issue indicates problem with some line, most likely. Should check and by need resolder 9-pin connector for it - soldering often cracks because lot of attaching, detaching. How about keyboard click ? It should happen after shorter key holding down, and then repeat frequently.

If that's not case need to check IKBD chip, keyboard connector to mainboard ...

If Desktop appears after some delay (caused by not working floppy/circuit/cable) is it stable, no crash (bombs), reset by self ?

If it is stable, RAM is most likely OK, so better check other things for start. And if possible should check power voltages with oscilloscope.

Thanks for the RAM info @ParanoidLittleMan.

 

- I did resolder the two 9-pin connectors on the bottom of the keyboard.  They looked good under a magnifying glass , but I resoldered them anyways. 

- Yes the keyboard clicks.  When I use the keyboard to move the cursor around the click repeats frequently

- When I get the computer to boot into TOS it is stable for at least 60 minutes ( this is as long as I tested it).  No crashes, no bombs (more on Bombs shortly)

- I currently only have a digital multi-meter.  No scope or logic probe 😞

 

On the topic of Bombs and resets:

As stated before, if I attempt to boot the computer with a disk in the drive or an image selected in the Gotek the computer never really starts up or responds.  The screen remains white and nothing appears.  I have waited or 10 minutes before to see if it would respond, no luck.

 

With the system in this frozen state if I hit the reset button most of the time (~80%) the computer just freezes again, no change.  HOWEVER, about 20 % of the time I do get some bombs.  I normally get 11 bombs but one time I did get 2 bombs.  I've know that 2 bombs are a "Bus error" and 11 bombs is a "Line 1111 Emulator".  But I don't really know what these mean in the context of my issues.  Any ideas?

 

 

I still need to go through the schematics and check continuity on each leg, as recommended by @snarkdluG. However without more knowledge and tools I don't know what else to try.  I might by the diagnostic cartridge and see if that can tell me anything.

 

Any other ideas or recommendations?

 

 

Thanks again for all your help!

 

 

Moe

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Bombs are more for programmers, users - indicate that CPU reached specific bad code, or attempt to access invalid memory loc. (that would be bus error for instance).  If they appear randomly, even if no program is started that's just  unreliable work.

Well, best what can do in this case is to replace components - and may start with those quad socketed chips - Glue, MMU ... Yes, I know, don't have replacement chips, but ... That's practically only way - in theory could deduct some things with logic analyzer but that's very slow and complicated - in time spent with it could earn money to buy couple working Ataris.

My worse repair was, and it was when machines were under 10 years age - when 1 74LSXXX chip worked unreliable - they cause problems very rare, and I replaced before going to it almost all larger chips, RAM ...  Just an extreme example.

And  since it is not really stable even without floppy, it can be RAM. No diagnostic cartridge - get 16 RAM chips - you anyway plan to expand it. That will be plenty of soldering, but must not to replace all them at once.

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I ordered a diagnostic cart.  Not sure that will help, but it can be useful to have around, even if it doesn't help.

 

A question about replacing boards.  There is a place in the US that sell tested, untested 1040 STf, and they now also sell Tested 1040STf motherboard only.  Looking at the price of the tested motherboard and comparing it to Glue and MMU prices, there almost the same.

 

My question is, will a 1040STf motherboard fit in my 520STfm case WITHOUT cutting or modding the case?  I know I'll loss the TV modulator, but ok with that.

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10 hours ago, ParanoidLittleMan said:

...

Well, best what can do in this case is to replace components - and may start with those quad socketed chips - Glue, MMU ... Yes, I know, don't have replacement chips, but ... That's practically only way - in theory could deduct some things with logic analyzer but that's very slow and complicated - in time spent with it could earn money to buy couple working Ataris.

 

I just realized, I have a working 520 ST packed away.  I could try swapping the Glue and MMU chips from the 520ST into the 520STfm.  That might help narrow down, or identify the problem.   

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6 hours ago, Moe said:

My question is, will a 1040STf motherboard fit in my 520STfm case WITHOUT cutting or modding the case?  I know I'll loss the TV modulator, but ok with that.

Yes.

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Just now, snarkdluG said:

Yes.

Thanks 👍

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On 4/12/2021 at 1:39 PM, Moe said:

I just realized, I have a working 520 ST packed away.  I could try swapping the Glue and MMU chips from the 520ST into the 520STfm.  That might help narrow down, or identify the problem.   

I swapped out the Glue and MMU chips; I continued to have the same issue with the 520STfm.  That removes two possibilities. 

 

 

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I received the diagnostic cart (https://www.exxoshost.co.uk/atari/store2/#0165)  this week and test the 520STfm tonight.

 

When I run the the YAART ST RAM testing program I don't receive any errors.  I ran 10 passes.

 

When I "try" and run the GenBench 6.0 program I receive an error.  The message is "ERROR - not enough memory".  When this happens the mouse can still be moved around the screen, but the mouse icon remains the bee, and I can not interact with anything.

 

Does anyone know what this "might" mean?  (other than the obvious answer of "you don't have enough memory"  😃 ) 

 

Thanks for any information you might have.

 

 

Moe

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It's not real error - if GemBench started, you should have enough memory - it will even not start if there is no enough RAM.

That's just unreliable work of machine - can be CPU, slow RAM error not detected by diagnostic SW, any of chips ...

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5 hours ago, ParanoidLittleMan said:

It's not real error - if GemBench started, you should have enough memory - it will even not start if there is no enough RAM.

That's just unreliable work of machine - can be CPU, slow RAM error not detected by diagnostic SW, any of chips ...

OK, thanks.  I was also guessing it was just a "symptom of the real problem".  I guess I'll have to find someone (preferably in Canada because of shipping costs) that can ship the board off to, to get fixed. 

 

Good thing I ordered a TESTED replacement 1040 STf board from the The Brewing Academy (https://thebrewingacademy.com/), which arrived yesterday ;-)

 

 

Moe

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