Yet another FDD on the bench - Atari 1050

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rubber_jonnie
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Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Fri Oct 22, 2021 3:42 pm

So as part of my FDD investigations today, I've been looking at not only the Seltron for my Apple, but also a 2nd Atari 1050 I acquired just prior to moving house, that was never tested.

Here it is in all its half naked glory:

IMG_20211022_151616.jpg
IMG_20211022_151616.jpg (214.69 KiB) Viewed 620 times

So, it isn't working, and I'm hoping it isn't a logic board, however since it is a computer in its own right, I should be able to troubleshoot it on its own, especially since I have a known working one I can use as a reference.

At present, the dead one can be differentiated from the good one because when you power on, the drive has a power light, but doesn't initialise the mechanism like the good one, so no busy light and no motor spin & head twitch.

Time to get the tools out and start measuring things like VRM output, signals on the connections from the board to the drive etc, and IIRC I have the old rom from my working drive after upgrading it to a Happy, so I can try that too.

I should probably also test the mechanism from the dead drive in the good, as then I can at least rule that part out.

Looks very much like it's been recapped, as there was some fairly awful soldering, which I've also cleaned and refreshed. Schematics also downloaded, I'll see if I can find the service manual too.
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 » Fri Oct 22, 2021 5:10 pm

First pass and according to the service manual, TP 13 and TP 14 should have 5v and 12v respectively and they do.

I also found that the disk inserted microswitch is a bit erratic and that compared to the working drive when it does operate, there is a really high resistance across it, so a new one of those is on the way.

Slightly more concerning is that when left standing with power on, the PIA, a 6532, gets extremely hot. I have a spare 6507 and ROM so they would be easy to switch, but not so the 6532, so I need to source one of those too, and I suspect they may be harder to find.

What I didn't realise was that the 6532 is also known as the RIOT chip, also used in the Atari 2600 alongside the 6507, so essentially the Atari 1050 FDD is 2/3rds of an Atari 2600 :)
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 » Fri Oct 22, 2021 6:05 pm

Deciding to take a gamble, I just bought a 2600 for spares for the princely sum of £20, so fingers crossed it'll yield a 6532 for me in case that's what's dead in the 1050.
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 Oct 31, 2021 1:52 pm

OK, progress, turns out the 6507 socket was an old single wipe type and the CPU practically fell out of it when I went to test a spare one.

New double wipe socket installed and its now actually initialising the drive correctly on power up.

What is now the problem is that it isn't recognised by the Atari, so I think next I'll give the ID switch a clean out with Electrolube and also, given the fact that the rest of the sockets are single wipe, I'll pull those too and replace with double wipe parts just to be on the safe side.

I'll also check the SIO sockets for bad solder joints as they do take a bit of punishment when the cables are plugged in.
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 » Wed Nov 03, 2021 9:47 am

Ok, so the replacement for the snapped chip viewtopic.php?f=18&t=4786 arrived today, so I quickly dropped it in and powered it on.

The drive still initialises, so that's a good start, next I need to test to see if the Atari recognises it, which it didn't before.
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 PhilC » Wed Nov 03, 2021 10:39 am

rubber_jonnie wrote:
Wed Nov 03, 2021 9:47 am
Ok, so the replacement for the snapped chip viewtopic.php?f=18&t=4786 arrived today, so I quickly dropped it in and powered it on.

The drive still initialises, so that's a good start, next I need to test to see if the Atari recognises it, which it didn't before.
Pleasantly surprised to see you can still get a replacement :)
If it ain't broke, test it to Destruction.

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Re: Yet another FDD on the bench - Atari 1050

Post by rubber_jonnie » Wed Nov 03, 2021 11:09 am

PhilC wrote:
Wed Nov 03, 2021 10:39 am
rubber_jonnie wrote:
Wed Nov 03, 2021 9:47 am
Ok, so the replacement for the snapped chip viewtopic.php?f=18&t=4786 arrived today, so I quickly dropped it in and powered it on.

The drive still initialises, so that's a good start, next I need to test to see if the Atari recognises it, which it didn't before.
Pleasantly surprised to see you can still get a replacement :)
It's a slightly different version, a 2797 rather than a 2793 but I was advised by a chap on FB they can be used interchangeably. Also the datasheet only refers to a 279X, so covers all the variants.

Thankfully the replacement doesn't have the same fragile construction.
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 » Sat Nov 06, 2021 5:35 pm

Hmmm, it seems I may have jumped the gun slightly.

The drive isn't properly initialising as the track zero test isn't happening, and there are no control pulses at all to the head stepper motor like on the working one.

Interestingly, it does it without the 2787, and looking at the block diagram, that isn't in play during initialisation.

So, back to the service manual for me.
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 » Tue Nov 16, 2021 10:51 pm

Finally got some time to sit down and look at this in a bit more depth. Luckily I have a working one, which sure has helped.

Checking the CPU address bus after boot, I noticed a number of address lines just doing nothing compared to the working drive.

Since the chip I snapped then replaced isn't required for initialisation I removed it and noted that nothing changed.

I noted that some of the address lines on the CPU didn't match the working drive, and working my way along the bus, matched the behaviour all the way along the bus at the ROM and RAM, with the same address lines misbehaving all the way along.

It was at that point I also noted the 6532 (RIOT chip as used in the 2600) was really hot, so I powered off and removed it, then checked the contacts in the socket for a short and PB6 came up as shorted to ground.

Not good, so that was traced back to U1, a 14 pin 5 transistor array package (A UA3086). I removed that and the short is now gone, so I'll order a replacement, though it still isn't setting the heads to track 0, and is still pulsing the drive motor, so the track 0 seek may be my next line of investigation. At this point the signals at the stepper motor plug do seem to match the good one, so not totally sure what's going on there, and also, given the physical drive mechanism does work with the good logic board I know the stepper is ok.

Feels a bit like progress, but since U1 doesn't appear to be crucial for initialisation, and the address lines go bad again when I put the 6532 in, there is more I think going on with that, but too tired to do any more now, other than order some replacement UA3086s.
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 » Tue Nov 16, 2021 11:41 pm

Bit more digging and there is a pair of UDN 5713 peripheral drivers that are used to control the stepper motor, so I need to check those for shorts and correct operation compared to the good one.

Not so sure they'll be that easy to find! Though I have read that SN75478s can be used instead and the service manual does seem to back that up, as do the datasheets.

I'd better check U11, a 74LS02, as this enables the stepper control chips so if it's dead that would be an easy one to swap and I probably have them in stock.
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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