Atari TT internal/external floppy issues

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saulot
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Atari TT internal/external floppy issues

Post by saulot »

Hello, anone has an issues with not workin internal/external floppy drive on tt? I turned on mine after long while and it refuses to work with any floppy drive (external sf314(which works with other st's), internal sony mfp). Changing psu's doesn't help (same situation with old at psu and new pico psu (with proper adapter)).
Led isn't blinking and it refuses to turn motor on which is weird. Anyone had similar issues? I've checked it with diagnostic cartridge and on start i've got red screen and wait states off, mcu msb (7) never set, fail at cycle 0xffffffff. All floppy test fail red screen at start.
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saulot
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Re: Atari TT internal/external floppy issues

Post by saulot »

doublepost sorry
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Arne
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Re: Atari TT internal/external floppy issues

Post by Arne »

saulot wrote:I've checked it with diagnostic cartridge and on start i've got red screen and wait states off, mcu msb (7) never set, fail at cycle 0xffffffff.
That's normal. I think (!) the diag software looks for RAM on an additional VME test-board.
If the FDD-LED is not blinking (checking for floppy media change) then the PSG or a 26LS31 (in my TT schematics) could be the source of that error. I suggest to check the D0SEL, D1SEL and S0SEL lines coming from the PSG with a scope.
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saulot
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Re: Atari TT internal/external floppy issues

Post by saulot »

[img]unfortunately i don't have one. Led is blinking, but only once at start, but motor doesn't spin and system reports that disc is damaged. Toggling 7th dip switch on mb didn't help too (i've read somewhere that it togles between hd/dd). Ym2149 was replaced once on this mb many years ago and mfp (not by me). In general everything else works fine.
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Arne
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Re: Atari TT internal/external floppy issues

Post by Arne »

Then I suggest to check the MO (Motor On) signal coming from FDC (pin 20), that runs to an inverter (7406 U405 pin 11) and exits it on pin 10 the same IC. Check the PCB tracks with a multimeter first when TT is powered off. With a FDD attached there needs to be a resistance of ~10KOhm between pin 10 (7406) and +5V. Have you checked the Shugart-bus cable to FDD?
Then set to voltmeter to check the levels. MO is active-high on the FDC's side and active-low on the Shugart bus. Active signal lasts for a couple of seconds so you should be able to catch it with a multimeter.
saulot wrote:In general everything else works fine.
ACSI devices, too? ACSI shares the /INT with FDD before it reaches the MFP. INTRQ form pin 28 FDC runs to pin 9 U306 (74LS02).
Check TT schematics.
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Re: Atari TT internal/external floppy issues

Post by FelR »

I had issues on my MSTE with the internal and external floppy drives. The fix was to replace the CPU with a low power version from Exxo's store.
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