surprise STF refurb

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stween
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Re: surprise STF refurb

Post by stween »

ijor wrote: Mon Apr 18, 2022 12:49 pm2 - Can you replace the TOS chips with a later version of TOS, even TOS 1.02. This will probably not fix the problem, but because of a bug that TOS 1.0 has, the behavior might change and will give us more clues about the problem. Conceivable, even when not likely, your TOS chips might be corrupt. But this is not the main reason I recommend to try a later TOS.
Yeah I might buy a set of 1.4 ROMs. I don't have a set here spare for this machine.
3 - What pullups do you have at the CPU buses?
stween wrote: Mon Apr 11, 2022 4:09 amI've now swapped out RP1, 2, 3, 4, 7, 8, and 9 with 2.2k resistor packs. RPs 1-2 and 3-4 are rigged in parallel so they actually provide 1.1kohm resistance, but from what I interpret, that's likely still fine. Desoldering some of these was a real pain and I'm not the best solderer, but the resistances now all read as they should.
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Re: surprise STF refurb

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stween wrote: Mon Apr 11, 2022 4:09 amI've now swapped out RP1, 2, 3, 4, 7, 8, and 9 with 2.2k resistor packs. RPs 1-2 and 3-4 are rigged in parallel so they actually provide 1.1kohm resistance, but from what I interpret, that's likely still fine. Desoldering some of these was a real pain and I'm not the best solderer, but the resistances now all read as they should.
I haven't checked which signals you are referring to, but just to be sure.. The address & databus resistors should not total less than 2.2K.

2.2K in parallel with 10K for 1.8K seems to be fine but I haven't done much testing below 2.2K. Either way your boarding on creating new DMA (and likely other ) issues below 2.2K values. The DMA on the STE definitely malfunctions with 1K resistors.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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stween
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Re: surprise STF refurb

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exxos wrote: Mon Apr 18, 2022 1:56 pm
stween wrote: Mon Apr 11, 2022 4:09 amI've now swapped out RP1, 2, 3, 4, 7, 8, and 9 with 2.2k resistor packs. RPs 1-2 and 3-4 are rigged in parallel so they actually provide 1.1kohm resistance, but from what I interpret, that's likely still fine. Desoldering some of these was a real pain and I'm not the best solderer, but the resistances now all read as they should.
I haven't checked which signals you are referring to, but just to be sure..
1-2 and 3-4 are in the same position as this board. It was tricksy to find info on what to do with this arrangement, I'll admit!
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Re: surprise STF refurb

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stween wrote: Mon Apr 18, 2022 1:43 pm For the 1K I looked at the page on the bad DMA investigation and based on the text at the top about a 1K SIL, I opted for that. (Now I see that this post says 10K, so I can find time later in the week to pick that back out and try again!)
Yikes.. yes, the DMA investigation was indeed exactly that. That page is not really a "how to guide" but more of a progress report of the investigation spanning the years. In fact a lot of information on my website is actually outdated or slightly wrong as to what is posted on the forum in the mandatory fixes.

It does mention 1K.. That was likely the value I tried originally. But later I found on some machines that it actually caused issues as well. So I opted for 10K in the end as it worked the best overall. 10K is what is mentioned in the mandatory fixes, but obviously my website has not been updated for the past few years.

Without trying to derail the thread, this is exactly why I am creating a new Wiki to correlate and update all information properly in one place as people are indeed getting confused all the time. The website will ultimately be taken down in favour for the wiki as I do not have the time to maintain multiple locations of information. I probably won't be doing "progress reports" or similar type of content any more either, as again it just confuses people more than anything.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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Re: surprise STF refurb

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exxos wrote: Mon Apr 18, 2022 2:34 pmThat page is not really a "how to guide" but more of a progress report of the investigation spanning the years. In fact a lot of information on my website is actually outdated or slightly wrong as to what is posted on the forum in the mandatory fixes.

It does mention 1K.. That was likely the value I tried originally. But later I found on some machines that it actually caused issues as well. So I opted for 10K in the end as it worked the best overall. 10K is what is mentioned in the mandatory fixes, but obviously my website has not been updated for the past few years.
Yeah I totally get it. I have one billion tabs open, between board schematics and board photos (because no schematic I can find matches this board), pinouts for various chips, and a heap of forum posts. In that moment I landed on the text at the top of your investigation and took it as a sort of conclusion.

No harm done! This is all a for-fun resurrection project. Easy to swap that out when I get time.

So far: precisely nothing has changed on the floppy behaviour. I'd expect something non-deterministic by now, but the garbage file listing is the same every time.

JbTfLKC.jpg
JbTfLKC.jpg (406.55 KiB) Viewed 1216 times
Without trying to derail the thread, this is exactly why I am creating a new Wiki to correlate and update all information properly in one place as people are indeed getting confused all the time. The website will ultimately be taken down in favour for the wiki as I do not have the time to maintain multiple locations of information. I probably won't be doing "progress reports" or similar type of content any more either, as again it just confuses people more than anything.
FWIW I like the step-wise investigation from A-to-B-to-C, but also apparently I needed a box at the top with red text and alarm bells telling me what to take from it :D
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Re: surprise STF refurb

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stween wrote: Mon Apr 18, 2022 1:39 pm
It's one thing I'd like to try, but I don't have a spare here without removing one from an STE :shock:
If I'm honest, my money is on a bad DMA, and whilst doing the mandatory fixes is a good thing, not to mention all the other stuff like continuity checks etc, it's a lot quicker to just swap the chip out. I know you don't have a spare as such, but if you can find one without desoldering from another working machine, it's the faster option. just be bloody careful desoldering the old DMA as it's really easy to damage these boards, just ask @BrettRogersUK!

I would also add that I have had the following as reasons for a bad FDD:
  1. Bad DMA
  2. Bad GLUE
  3. Bad WD1772
Don't forget that the sound chip has FDD select signals on pins 19 & 20 so they are worth checking too.
stween wrote: Mon Apr 18, 2022 1:39 pm Also something I don't have; I'm at the max of what my tools can do for me! Might be my reason to finally pick one up though.
Depends on how often you are likely to use a scope versus the cost. I use one a lot, so it was worth the investment, but for a single use, probably not.
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Re: surprise STF refurb

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rubber_jonnie wrote: Mon Apr 18, 2022 2:54 pmIf I'm honest, my money is on a bad DMA
I'm leaning that way, but then I'm only feeling my way around. I've had fun learning the ins and outs of this board in a way I've never had to in the past!

Might be easier to source a replacement DMA next time I'm in the UK. I'm really not compelled to risk an STE unless I have to.
I would also add that I have had the following as reasons for a bad FDD:
  1. Bad DMA
  2. Bad GLUE
  3. Bad WD1772
Noted. At least I've been able to test a replacement glue and 1772.
Don't forget that the sound chip has FDD select signals on pins 19 & 20 so they are worth checking too.
Poked some YM pins last night and they have continuity. Checked all the other DMA connections, and they look good too.
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Re: surprise STF refurb

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stween wrote: Mon Apr 18, 2022 2:45 pm So far: precisely nothing has changed on the floppy behaviour. I'd expect something non-deterministic by now, but the garbage file listing is the same every time.
I think you have continuity checked and replaced pretty much everything by now ? I have not been following this thread much unfortunately.

Of course you have the floppy drive - ribbon cable 1772 - DMA - databus. GLUE controls a lot of stuff, and you have the YM chip with AB selects.

I assume you have also ran YAART to test the RAM ?

Indeed 1K on the DMA bus will not help. again I have not checked, but make sure you are on the bus between the DMA and 1772, and not the bus between the DMA and CPU.. As they are separate data buses.

Indeed you should be using TOS104. Then you can repeatedly press ESC and see what corruption you get exactly. Then what I generally do is just go around for the main chips like 1772, DMA, GLUE,CPU etc which a scope on X1 and keep pressing ESC and see if the corruption suddenly changes when you are on any particular pin. If you can replicate any sort of change consistently by having the probe on or off a pin then it can give a major clue as to what part of the system is malfunctioning.

Past that that your literally into "desperation territory". Random bit flips are incredibly difficult to diagnose because the whole board is just inherently buggy / noisy. You would have to start with adding 33pF caps on all any suspect signals. I generally do that with a fly lead with a 33pF cap on it so I can quickly go around all the pins on various IC's. I then repeat the same with a 1K pullup resistor and see if anything changes.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: surprise STF refurb

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exxos wrote: Mon Apr 18, 2022 3:10 pm
stween wrote: Mon Apr 18, 2022 2:45 pm So far: precisely nothing has changed on the floppy behaviour. I'd expect something non-deterministic by now, but the garbage file listing is the same every time.
I think you have continuity checked and replaced pretty much everything by now ?
Not literally everything but I've continuity checked a lot, working back from the floppy: pins sticking out of the floppy ribbon back through things like the 1772/7406/DMA/CPU/HD port/glue/YM/anything else the schematics suggest I should have continuity to. Everything seems to beep that should beep.
I assume you have also ran YAART to test the RAM ?
Yeah, YAART gives the machine a pass.
Indeed 1K on the DMA bus will not help. again I have not checked, but make sure you are on the bus between the DMA and 1772, and not the bus between the DMA and CPU.. As they are separate data buses.
*nods* yes, I put this between the DMA and the 1772. I'll swap out the 1k in favour of a 10k this week.
Indeed you should be using TOS104.

Then you can repeatedly press ESC and see what corruption you get exactly. Then what I generally do is just go around for the main chips like 1772, DMA, GLUE,CPU etc which a scope on X1 and keep pressing ESC and see if the corruption suddenly changes when you are on any particular pin. If you can replicate any sort of change consistently by having the probe on or off a pin then it can give a major clue as to what part of the system is malfunctioning.

Past that that your literally into "desperation territory". Random bit flips are incredibly difficult to diagnose because the whole board is just inherently buggy / noisy. You would have to start with adding 33pF caps on all any suspect signals. I generally do that with a fly lead with a 33pF cap on it so I can quickly go around all the pins on various IC's. I then repeat the same with a 1K pullup resistor and see if anything changes.
Since I have no skin in this game, I expect I'll end this if a 10k on the DMA lines, TOS 1.4, and a replacement DMA don't fix it.
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Re: surprise STF refurb

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stween wrote: Mon Apr 18, 2022 3:30 pmSince I have no skin in this game, I expect I'll end this if a 10k on the DMA lines, TOS 1.4, and a replacement DMA don't fix it.
I have a heartbeat!
  1. I put the 10K pull-up on the DMA lines, and no change.
  2. I sourced TOS 1.4, and that made no change.
  3. I sourced a spare DMA chip, and I'm off to the races.
Well, almost: drive access is much closer to working correctly now yay!

sk3iSDi.jpg
sk3iSDi.jpg (271.9 KiB) Viewed 1218 times

But the quick test on the cartridge test is giving me some errors and TOS flags occasional read errors e.g.

sctYwfR.jpg
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H35HN43.jpg
H35HN43.jpg (164.24 KiB) Viewed 1218 times


Two drives, both the same symptoms. Nevertheless, it's MUCH happier than it was, so I'm marking this as progress and putting the root cause of misbehaving floppy access as a bad DMA after all.

I don't totally trust the current behaviour until I replace the RP1+RP2 and RP3+RP4 pull-ups again, this time for something higher than 2.2kohm each since they read as wired in parallel (it's this motherboard layout).

Presumably putting 4.7k in each will give about 2.35k on those lines, which sounds like a more typical setup on other motherboard layouts.

Might be able to do more this week. All fun; thanks for following my roundabout exploration of this board :D
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