520st stopped recognising my gotek

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Noah199
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520st stopped recognising my gotek

Post by Noah199 »

So, a couple of days ago I got my first Atari st: A 520st from 1985. It has ROM TOS 1.0. For loading software, I opted for a Gotek, which i connected to the st with one of these 34-pin to DIN 14 adapters you can find on ebay and a twisted floppy cable. This setup worked for about an hour, although I noticed that occasionally, it would just not recognize the disk drive and boot to an empty desktop (no disk icons) upon reset. Then I decided to open the computer up to check if everything was in order. After finding nothing that seemed out of place, I put it all back together to do further testing, but it now completely stopped recognizing the disk drive and its activity light would stay dark. After changing the gotek's jumper from DS1 to DS0, manually routing the Atari's Drive A select to DS0 and using a straight cable, the activity light now lights up for about 4 seconds after reset (as i think it should without a disk inserted). The Atari still doesn't recognize the Gotek though. I've now done a bit of probing and here's what i found out:

-Motor on on the FDC always stays low, yet the inverted motor on output from the 7406 also always stays low
-Since the gotek only cares about the Drive Select signals, it sends out data and index as normal during those afformentioned 4 seconds, which do arrive at at the corresponding FDC pins
-There is no step signal whatsoever
-If i manually step the drive to a higher track and then reset the computer, it doesn't step back to track 0

The most perplexing question to me is: How does the St even detect whether there's a disk drive attached?
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rubber_jonnie
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Re: 520st stopped recognising my gotek

Post by rubber_jonnie »

Out of curiosity what jumpers do you have set on the Gotek?

From what I recall and I have posted elsewhere on the site, you only need S0 set to set the drive ID to 0.

Nothing else needs jumpering.

Are you using FlashFloppy firmware on the Gotek?
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...
Noah199
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Re: 520st stopped recognising my gotek

Post by Noah199 »

Yes, I'm using FlashFloppy and only S0 is jumpered. The Disk images are all good, by the way.
ijor
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Re: 520st stopped recognising my gotek

Post by ijor »

Noah199 wrote: Sun Feb 25, 2024 2:54 pm After changing the gotek's jumper from DS1 to DS0, manually routing the Atari's Drive A select to DS0 and using a straight cable
What do you mean by "manually routing"? I hope you know what you are doing because this might be dangerous. In particular, the chip that outputs the drive select signal (the PSG) is quite sensitive and there is no additional buffering.
-Motor on on the FDC always stays low, yet the inverted motor on output from the 7406 also always stays low
Are you 100% sure about that? If so that would suggest that either the 7406 is damaged, or you are somehow forcing this signal low, perhaps with a bad connection to ground.
-There is no step signal whatsoever
This is not good. How are you measure the signals? What happens if you boot without any drive connected at all?
-If i manually step the drive to a higher track and then reset the computer, it doesn't step back to track 0
How you do that?
The most perplexing question to me is: How does the St even detect whether there's a disk drive attached?
As most computers do, monitoring the TRACK0 signal.
http://github.com/ijor/fx68k 68000 cycle exact FPGA core
FX CAST Cycle Accurate Atari ST core
http://pasti.fxatari.com
Noah199
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Re: 520st stopped recognising my gotek

Post by Noah199 »

The Shugart-Atari adapter had solder pads for this, but i managed to rip them off, so I connected the pins with a small isolated wire, I tested for shorts multiple times before powering up.

The motor on signal on the FDC does actually very rarely come up upon powering the computer on, as i just discovered. Whenever it does, it seems to stay high indefinitely, not even the reset button changes it. Only powering cycling the computer causes it to go into that state where it is indefinitely low again.

None of the 7406's outputs are not shorted to ground.

I'm measuring the signal with an analog scope to see exactly what they do over time and a digital multimeter to measure exact voltages. Sadly, neither can measure peaks. The FDC's step output as well as the 7406's inverted step output stay low when nothing is connected. The step output is pulled up to 3.7 volts if the Gotek is connected.

I step it manually by tapping the step signal on the gotek with a probe connected to a multimeter in Amp mode, the other probe grounded. I know it's not ideal, but the 7406's step output is fed through a resistor and 74LS series logic is supposed to be robust.

Oh, and TRACK0 is at 2.6 volts with only the gotek powered up and at 5 volts with the computer powered up too. Regardless wether the gotek is on track 0.
Noah199
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Re: 520st stopped recognising my gotek

Post by Noah199 »

The 7406 is replaced now and nothing has changed.
It's outputs are all low, despite not being shorted to ground and despite the chip comming out of a 100% working commodore 64c.
I am going to put the Atari's 7406 into my c64 and report my findings later, but I'm starting to run out of ideas. Should i buy another 7406? Should I bite the bullet and replace the FDC?
ijor
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Re: 520st stopped recognising my gotek

Post by ijor »

I'm not sure what you are describing makes much sense. Either you are having serious hardware issues, or either you are not measuring correctly.

It is still not clear to me which kind of instruments are you using. Are you measuring with a multimeter? I don't think this is the right instrument for the task. What do you exactly mean by an "analog scope"? An analog scope should provide enough voltage accuracy. Anyway ...

Noah199 wrote: Fri Mar 01, 2024 9:13 pm The 7406 is replaced now and nothing has changed.
It's outputs are all low, despite not being shorted to ground and despite the chip comming out of a 100% working commodore 64c.
The 7406 outputs are open collector, and the computer has no pullups on these signals. If you are trying to measure the 7406 outputs without the Gotek, the signals might be floating and what you would measure would be not reliable. Measuring the signals with the Gotek depends, of course, on the Gotek and the cable. Which means that if you get a low state it doesn't necessarily means a problem with the 7406 itself, it might be a problem at the Gotek side.
http://github.com/ijor/fx68k 68000 cycle exact FPGA core
FX CAST Cycle Accurate Atari ST core
http://pasti.fxatari.com
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rubber_jonnie
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Re: 520st stopped recognising my gotek

Post by rubber_jonnie »

I think what would help here are photos of everything. So Gotek Jumper block, any cables/adapters you're using, how you're connecting the Gotek to the ST, how the Gotek is powered etc.

I'm assuming this is an external drive as you've said it's a 520ST and that you used a 14 pin to 34 pin cable.

Did I read correctly that you have removed the cable with a twist? I'm sure the twist is not required for any of the ST drives and they should all be set to DS0.
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...
Noah199
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Re: 520st stopped recognising my gotek

Post by Noah199 »

So, here are some photos. The soldering is quite poor, but all the connections are good and there are no shorts.
rubber_jonnie wrote: Mon Mar 04, 2024 9:28 am Did I read correctly that you have removed the cable with a twist? I'm sure the twist is not required for any of the ST drives and they should all be set to DS0.
Yes, I'm now using a straight cable.
ijor wrote: Mon Mar 04, 2024 2:26 am The 7406 outputs are open collector, and the computer has no pullups on these signals. If you are trying to measure the 7406 outputs without the Gotek, the signals might be floating and what you would measure would be not reliable. Measuring the signals with the Gotek depends, of course, on the Gotek and the cable. Which means that if you get a low state it doesn't necessarily means a problem with the 7406 itself, it might be a problem at the Gotek side.
Thanks for explaining that, I had just assumed the output must always be the opposite of the input, but looking at how transistors work, this behaviour now makes sense to me. Anyways, with the Gotek powered and connected, the outputs I thought to be broken were indeed pulled up.

The thing i find weird now is that despite receiving track 0, data and index signals just fine, there are no step signals on the FDC. Even if the step signals are too brief for me to measure them with my analog scope, the inverter should be fine and the gotek too, so it should step tracks if there's a step signal. Also, the motor on signal on the FDC stays low for about 30 seconds upon booting, then it goes high. It's inverted version on the 7406 stays low, probably because it isn't pulled up (this happens with the gotek connected)

And by the way, it has a ram expansion as you can see on the photos.

FDC and replaced 7406
FDC and replaced 7406
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IMG_20240304_133209.jpg
IMG_20240304_133209.jpg (193.44 KiB) Viewed 584 times
IMG_20240304_133218.jpg
IMG_20240304_133218.jpg (256.46 KiB) Viewed 584 times
Gotek jumper configuration, the wires are for dial and buzzer
Gotek jumper configuration, the wires are for dial and buzzer
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IMG_20240304_133414.jpg
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Current setup, the bottom shield is attached, btw
Current setup, the bottom shield is attached, btw
IMG_20240304_133531.jpg (306.11 KiB) Viewed 584 times
Multimeter used for measuring
Multimeter used for measuring
IMG_20240304_133730.jpg (257.35 KiB) Viewed 584 times
Analog osciloscope used for measuring
Analog osciloscope used for measuring
IMG_20240304_133756.jpg (231.31 KiB) Viewed 584 times
Power supply for the gotek, it's voltage is fine
Power supply for the gotek, it's voltage is fine
IMG_20240304_133705.jpg (244.85 KiB) Viewed 584 times
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rubber_jonnie
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Re: 520st stopped recognising my gotek

Post by rubber_jonnie »

First off, and don't take this as a dig BTW, but the amount of bare wire you have showing at either end of the green wire is not good and could easily have led to a short causing the floppy circuits to die on either the Gotek or the ST.

Where that much wire is showing you should use heatshrink or insulation tape to cover the bare wire when you finish soldering.

Secondly, what flux was used? I have seen instances of plumbers flux used in the past, and this looks a little like that. Electronics flux and plumbers flux are very different.

The problem is, it's extremely corrosive when it is used with electronics, and given the way the pads and other stuff on the adapter PCB look, it could be that there is unseen corrosion and the adapter board is broken beyond repair.

That is something you will struggle to diagnose at all.

Personally I'd look for an original external drive, it doesn't have to be an Atari one, on eBay. I have a Datel drive, but there are many other brands available. That way you can test with a real floppy intended for the machine.

Even if the drive doesn't work and won't load software, you can hopefully see activity on boot, such as head seek and activity lights etc. You can also then drop the gotek in the casing when you're up and running.

I also find the Atari diagnostic cartridge helpful here, because you can run repeatable floppy drive tests, and it will give you error data as well.
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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