Yet another FDD on the bench - Atari 1050

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rubber_jonnie
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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Fri Nov 19, 2021 11:09 pm

stephen_usher wrote:
Fri Nov 19, 2021 6:45 pm
Well, without /CS not much is going to happen. :-)
Quite, and no continuity between U12 pin 6, where the signal comes from and pin 3 of the 279X FDC.

So, I've bodge wired it and guess what, we have a working power up sequence!!

Power on and the drive spins, the track 0 check happens and the drive stops spinning.

I've also replaced the switch that activates the drive when you insert a disk as the original had very high resistance, which also helped.

However, I think I need to shorten my bodge wire as scoping it , it seems quite noisy, and the startup does occasionally fail.

Otherwise it's great progress I think, but I will need to wait until the shorted component replacement arrives before I can actually properly test, as it forms part of the SIO circuitry, so no data flow without it.

:girldance: :girldance: :girldance:
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...

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Re: Yet another FDD on the bench - Atari 1050

Post by stephen_usher » Sat Nov 20, 2021 8:26 am

:dualthumbup:

To paraphrase Dune, "The data must flow." ;-)
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Sat Nov 20, 2021 9:17 am

stephen_usher wrote:
Sat Nov 20, 2021 8:26 am
:dualthumbup:

To paraphrase Dune, "The data must flow." ;-)
Indeed it must! 😁
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...

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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Sun Nov 21, 2021 3:50 pm

Despite feeling crappy after my booster Jab, I wanted to do something to keep me occupied and not thinking about it too much.

So I went back to the 1050, intent on shortening the bodge wire as it seemed to have a bit of noise on it causing the drive to sometimes fail to initialise.

Since I'd replaced U16, a 74LS04 and U12, a 74LS00, I figured it couldn't hurt to drop them back in for a quick test.

I changed out U12 first, the 74LS00, and the one I'd had to bodge wire to the FDC chip select from. No different with the old chip in. Sometimes worked, sometimes not.

So I dropped in the original 74LS04 into the U16 socket, and lo and behold it worked. I tried a second new 74LS04 and the same result, sometimes it worked, sometimes it didn't and scoping pin 9, which feeds U12, with the brand new chips, the signal is super weak and only occasionally works.

Incidentally, the new SN74LS00 worked just fine with the old 74LS04.

The only difference I can see between the new and old chips is that the old is a 74LS04, the new ones are SN74LS04. I can't find if SN makes a difference (I know HC does), bot for now I've reverted to the original as it works every power on.

Time to test if it works with a real machine.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...

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Re: Yet another FDD on the bench - Atari 1050

Post by stephen_usher » Sun Nov 21, 2021 3:56 pm

The SN prefix is merely TI's designation.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Sun Nov 21, 2021 5:53 pm

stephen_usher wrote:
Sun Nov 21, 2021 3:56 pm
The SN prefix is merely TI's designation.
Weird then, I shall have to test them with my TL866, see if they are marginal/bad.

I have however, managed to get to a conclusion this afternoon!!

I had been told the 2793 FDC could be replaced with a 2797, but it seems not.

Once I dropped the 2793 from my known good drive into the problem drive, it worked, so reading, writing, everything, so all I need is a replacement 2793, or at least compare it with the 2797 and see just what the differences are and if there is a way round it.

So basically if I'd been able to find the missing CS signal to begin with, I may never have snapped the original 2793 in two :(

I have my suspicions that the original 2793 was dead anyway, but what can you do?

At least I know it can be repaired with the correct part.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...

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Re: Yet another FDD on the bench - Atari 1050

Post by stephen_usher » Sun Nov 21, 2021 6:33 pm

:dualthumbup:

Good to hear that you're now only one chip away from from a fully operational machine.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

User avatar
rubber_jonnie
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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Sun Nov 21, 2021 6:52 pm

stephen_usher wrote:
Sun Nov 21, 2021 6:33 pm
:dualthumbup:

Good to hear that you're now only one chip away from from a fully operational machine.
Me too as I have a bunch of disks I'd like to backup. The working drive is back together now and I've reinstalled its Happy mod, and it's all looking great.

Just got to get that one chip now!!
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...

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rubber_jonnie
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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Sun Nov 21, 2021 7:09 pm

Hmm, interesting @stephen_usher .

I just found this post on AA: https://atariage.com/forums/topic/28262 ... isk-drive/ that specifically states a 2797 is fine, BUT needs adjustment.

It then goes into how you can do this, so I think that's my next stop as there is no 2793 data sheet to compare to the 2797, just a global sheet covering 279X as I may have mentioned before.

This process should be quick to do and may well give me a result, since the drive does appear to be initialising correctly.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...

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rubber_jonnie
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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Mon Nov 22, 2021 9:47 pm

Ok, so a little more diagnosis today.

I followed the AA post and set up the faulty drive to see if I could make it work with the 2797. All the measurements were as suggested after a little tweaking, but it still won't work with the 2797, and will work with the 2793 from my working drive.

I decided against trying to make the 2797 work in the good drive as I didn't want to tweak pots that were already known good and were locked in place.

I'm beginning to think the replacement 2797 has a fault :(

So, I had a trawl of eBay and have managed to find what is supposedly a NOS 2793, but I'll have to wait for it to come from the Netherlands.

Fingers crossed it'll work this time!

So good news, the final (Hopefully!!) part is on the way, I've learned a lot more on 1050 troubleshooting and learned a few more features of my oscilloscope.

:girldance: :girldance: :girldance:
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...

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