BAD DMA - Myth or fact ?

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Re: BAD DMA - Myth or fact ?

Postby dhedberg » Tue Sep 29, 2015 10:26 pm

exxos wrote:Do you know which AC issue it was in ?

Judging by the name of the file it looks like it's issue 19.
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Re: BAD DMA - Myth or fact ?

Postby exxos » Tue Sep 29, 2015 10:48 pm

dhedberg wrote:
exxos wrote:Do you know which AC issue it was in ?

Judging by the name of the file it looks like it's issue 19.


of STF yes, he mentioned a article on AC he wrote..
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Re: BAD DMA - Myth or fact ?

Postby dhedberg » Wed Sep 30, 2015 2:56 pm

exxos wrote:
dhedberg wrote:
exxos wrote:Do you know which AC issue it was in ?

Judging by the name of the file it looks like it's issue 19.

of STF yes, he mentioned a article on AC he wrote..

Ah, sorry. I didn't read properly. I found his article in AC issue 5, June 1997. Page 16: Dr. Steve's house of upgrade horrors.
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Re: BAD DMA - Myth or fact ?

Postby mikro » Sat Oct 24, 2015 8:13 am

Hi guys,

I received the famous Best Electronics catalog today and what do I see there:

IMG_20151024_095629.jpg

Have you tried / do you know about that, too?
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Re: BAD DMA - Myth or fact ?

Postby exxos » Sat Oct 24, 2015 8:53 am

mikro wrote:Hi guys,

I received the famous Best Electronics catalog today and what do I see there:

Have you tried / do you know about that, too?


Thats interesting, thanks for uploading it.

Had to tell from the diagram I have, but the resistor pack seems to be pull ups on the AS,UDS,LDS,DTACK BERR,BGACK and a few other lines.

The 33pF seems to be going across data lines which is odd. Though on the DMA stuff, I think D0 had some really screwy issues. In some of my tests while working on CPU boosters, some stuff would only work when the scope probe was on D0. I did not spend much time on it, but it seems was some odd oscillation on D0, and something like 30pF scope capacitance was enough to clap it. But this was on the STFM, not STE. On the STE it seems D2 & D4.

Very interesting page for sure, makes a change from all the "must change DMA chip" malarkey, this actually seems more of a mod I would do. I found all kinds of screwy issues on the 68000 bus ( which is one reason the CPU boosters are taking so long to develop) In some cases I was using a 1K pullup on the bus.

My fixes are on the DMA bus itself, not the 68000 bus though, currently I don't have any drive issues after my mod. I guess there would be no harm in doing it. Wonder why this information stayed hidden for so long :shrug: Defiantly will add that image to my site if thats ok ?
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Re: BAD DMA - Myth or fact ?

Postby DarkLord » Sat Oct 24, 2015 10:30 am

That catalog is one of the best (pardon the pun :) ) ever!

I've still got my old copy.

BTW, was that a new release or did you just order what he had?

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Re: BAD DMA - Myth or fact ?

Postby mikro » Sat Oct 24, 2015 10:58 am

Exxos: feel free to upload the picture wherever you like.

DarkLord: it's still the 10th edition, I wanted to order it since I was a young teenager, time to make dreams reality :)

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Re: BAD DMA - Myth or fact ?

Postby DarkLord » Sat Oct 24, 2015 4:37 pm

That is just Atari "canon" as far as I'm concerned. Read through the whole thing,
but slowly, savoring every last page. :)
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Re: BAD DMA - Myth or fact ?

Postby zmiennik » Fri Nov 13, 2015 7:13 pm

exxos wrote:It is also possible (although I am not sure if it is even verifiable) that early STE's which are supposed to have the "Bad DMA" that the PSU was in those machines was bad to start with. In fact I wouldn't class any PSU of having particularly good regulation even after changing the capacitors. Capacitors years ago were not as good as they are today by far, So its not a far stretch to speculate that some PSU's were pretty poor even when manufactured.


I've got a question. How do we know if the PSU we've got in our STe are worth changing the capacitors? Is it possible that after changing the capacitors in PSU we may still have a problem with floppy/hdd because they're poor manufactured?
I have to decide what to do with my PSU ASAP as my friend (electronic engineer) is about to send back to me my ATARI soon.
He says the capacitors look really bad in that PSU but after reading this I don't know anymore if changing them will fix potential problems with DMA chip (as I've got the "bad one" - however it's been never tested with any HDD/CF before) I just wanted to reduce any potential risk of problems with files transfer, etc before fitting Cosmos Ex as it is still in good hands..
So what's the other way if not changing capacitors? Replacing whole PSU for a modern one?

exxos wrote:I would really try the resistor mod's as listed on my site

Do you mean the mod located in "Part 15 DMA MOD" on your website?

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Re: BAD DMA - Myth or fact ?

Postby exxos » Fri Nov 13, 2015 7:31 pm

zmiennik wrote:I've got a question. How do we know if the PSU we've got in our STe are worth changing the capacitors?


Because they are almost 30 years old. Everyone should be changing them.

zmiennik wrote:Is it possible that after changing the capacitors in PSU we may still have a problem with floppy/hdd because they're poor manufactured?


The PSU isn't poor manufactured, capacitors dry up and go bad after a number of years. This will happen in any electronics equipment.


zmiennik wrote:I have to decide what to do with my PSU ASAP as my friend (electronic engineer) is about to send back to me my ATARI soon.
He says the capacitors look really bad in that PSU but after reading this I don't know anymore if changing them will fix potential problems with DMA chip (as I've got the "bad one" - however it's been never tested with any HDD/CF before) I just wanted to reduce any potential risk of problems with files transfer, etc before fitting Cosmos Ex as it is still in good hands..


You will have problems with floppy drive and hard drive if the PSU has not be fitted with quality capacitors like I suggest on my page, and the DMA resistor mod is not done. As to if it will solve "all problems" I can't say. But it will greatly reduce a lot of already known problems.

zmiennik wrote:So what's the other way if not changing capacitors? Replacing whole PSU for a modern one?


You shouldn't have any problems if you use my guide to upgrade. As long as you have a SR98 or ASP34 PSU then those are the best types to have. I have tested them and upgraded them as stated on my page.

But if you want the best, then I am about to start selling new PSU's shortly.. http://www.atari-forum.com/viewtopic.php?f=28&t=28746

zmiennik wrote:Do you mean the mod located in "Part 15 DMA MOD" on your website?


I mean the SIL resistor mod http://www.exxoshost.co.uk/atari/last/DMAfix/dma2015fix.jpg The capacitor probably isn't needed. I would suggest you read though the page to see why that resistor network is needed.
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Re: BAD DMA - Myth or fact ?

Postby dlfrsilver » Sat Nov 14, 2015 9:03 pm

@zmiennik :

I also recommand what Exxos says, changing the capacitors are doing a lot of good, especially on the color quality display. That's the first thing i noticed when i changed mine (via the caps kit i bought from him).

And the very best, you provide also a plus in term of value to your ST, because the "WANG CAPACITORS" brand is really utter rubbish.

My advice : use Nichicon, Rubycon or Panasonic brands for replacement.
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Re: BAD DMA - Myth or fact ?

Postby qq1975b » Mon Nov 16, 2015 9:04 pm

If someone finally tries the DMA mod told on the magazine, please upload pictures if everything works fine :)
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Re: BAD DMA - Myth or fact ?

Postby exxos » Mon Nov 16, 2015 9:33 pm

qq1975b wrote:If someone finally tries the DMA mod told on the magazine, please upload pictures if everything works fine :)


The BEST one won't work. They say change the pull up resistors on the control lines (basically) I have already tried that even before that article was posted here.

I have spent a couple hours tonight tweaking my page as I regularly get asked about this "buggy DMA" and its driving me nuts. I think I will lose my sanity if one more person emails with the phrase "I have the buggy DMA in my STE, do you sell the 001A?" <insert head banging emotie here>

http://www.exxoshost.co.uk/atari/last/DMAfix/index.htm

There maybe some merit in the 33pf on the dataline, That was basically the same thing I was doing with my original mod. Though I only had issues on the STFM on some boards. I think it would only work if D0 had the scope probe on it or something daft like that. Though I have not seen that problem for a long time now. next time I am probing around, I will try and remember to look into the STE databus more. As it stands, ultra Satan and the floppy drive is perfectly stable with the SIL resistor mod.
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Re: BAD DMA - Myth or fact ?

Postby redhawk668 » Sun Jun 12, 2016 9:15 pm

Well, I seem to have the 'bad' DMA on my 1040 STE too. I bought an UltraSatan and tested it on my STE, with HD Driver 9.xx I could not partition the SD Cards. It would give no errors, but after a reboot no partitions on the SD Cards (1 GB and 2 GB). Then, I've tested the UltraSatan on my STFM, it worked flawlessly, partitioning, etc. Everything works like it should. Hooked it up to my STE, at first booted nicely (tested that several times), seemed to function, but after an hour it started to behave 'wonky'.... After copying some stuff to the C:\ drive it managed to trash the whole partition in just one second..... On my STFM on the other hand it functions like it should, even after long time use....

Could be a wonky PSU, so I've ordered a upgraded PSU from Exxos to rule that out. There is a modification on the board, though. What I've seen is 2 piggybacked 74lsxx IC's with 2 wires going out, one has been soldered to a pin of the MFP and one has been soldered to a pin of the YM2149F. So, I guess the previous owner had some issues with it too....

Hope the new PSU will sort things out...
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Re: BAD DMA - Myth or fact ?

Postby exxos » Sun Jun 12, 2016 9:26 pm

redhawk668 wrote:Well, I seem to have the 'bad' DMA on my 1040 STE too. I bought an UltraSatan and tested it on my STE, with HD Driver 9.xx I could not partition the SD Cards. It would give no errors, but after a reboot no partitions on the SD Cards (1 GB and 2 GB). Then, I've tested the UltraSatan on my STFM, it worked flawlessly partitioning, etc. Everything works like it should. Hooked it up to my STE, at first booted nicely (tested that several times), seemed to function, but after an hour it started to behave 'wonky'.... After copying some stuff to the C:\ drive it managed to trash the whole partition in just one second..... On my STFM on the other hand it functions like it should, even after long time use....

Could be a wonky PSU, so I've ordered a upgraded PSU from Exxos to rule that out. There is a modification on the board, though. What I've seen is 2 piggybacked 74lsxx IC's with 2 wires going out, one has been soldered to a pin of the MFP and one has been soldered to a pin of the YM2149F. So, I guess the previous owner had some issues with it too....

Hope the new PSU will sort things out...


If you think your DMA is bad, then send it to me for testing. I updated my page last week as it seems I could may well have one of those mythical bad DMA chips.

If you have a progressive fault, where it gets worse the longer the machine is turned on, then that will likely be a bad PSU. It still doesn't rule out the possibility of a DMA problem, but at least it rules out one huge issue.
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Re: BAD DMA - Myth or fact ?

Postby redhawk668 » Sun Jun 12, 2016 9:37 pm

Well, it sometimes functions normally, but after some time of use the wonkyness starts to happen. So, it could be a wonky PSU. But, if the wonkyness stays I think I'll send it to you for testing. I live in the Netherlands, so that means proper protection. The case has seen better times, I'd like to recase it some time.
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Re: BAD DMA - Myth or fact ?

Postby exxos » Sun Jun 12, 2016 9:43 pm

redhawk668 wrote:Well, it sometimes functions normally, but after some time of use the wonkyness starts to happen. So, it could be a wonky PSU. But, if the wonkyness stays I think I'll send it to you for testing. I live in the Netherlands, so that means proper protection. The case has seen better times, I'd like to recase it some time.



It does sound like the PSU. As I keep telling others, they are like 30 years old now. I've had them failing for the past several years now and my STFM's are the later revisions aswell. STE's are a bit newer, but again, PSU's are really old now. It should be mandatory for people to update them these days.

If you still have troubles, then yes you are welcome to send your machine over. Though to save postage, I only really need the motherboard. No use shipping the PSU if you have one of my updated ones anyway. I don't need keyboard, or metal work etc. Might be worth sending the floppy drive as a lot of those are dying just as fast as the PSU's.
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Re: BAD DMA - Myth or fact ?

Postby redhawk668 » Sun Jun 12, 2016 9:49 pm

I have a modified Sony MPF920-E floppydrive, it already died on me. The Sony Drive is a 2001 model and works reliable, after the mod. Formatting, etc. Flawlessly.
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Re: BAD DMA - Myth or fact ?

Postby exxos » Sun Jun 12, 2016 9:54 pm

redhawk668 wrote:I have a modified Sony MPF920-E floppydrive, it already died on me. The Sony Drive is a 2001 model and works reliable, after the mod. Formatting, etc. Flawlessly.


920 drives are awesome :)
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Re: BAD DMA - Myth or fact ?

Postby dlfrsilver » Sun Jun 12, 2016 10:07 pm

yes Sony MFP-920 are great drives :) I use them also for dumping and preserving ST, Amiga and PC games :)
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Re: BAD DMA - Myth or fact ?

Postby redhawk668 » Mon Jun 13, 2016 4:51 am

Well, I ordered a PSU. But, it has to be delivered. So, when it arrives I can test again.
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Atari 130XE, stock
Atari 800XL, stock
Atari 600XL, Ultimate 1 MB
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Atari 520 STfm, 4 Mb, TOS 1.04, Blitter, Cosmos Ex with Raspberry Pi2, 2 GB ACSI/SD
Atari 1040 STe, 4 Mb, TOS 2.06, Cosmos Ex with Raspberry Pi3, 2 GB ACSI/SD
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Re: BAD DMA - Myth or fact ?

Postby jd » Mon Jun 13, 2016 2:10 pm

exxos wrote:
ChrisTG wrote:Btw, the "1v pulses" are crosstalk from a nearby line while the particular line is in "floating" state. So just another indication for a bad circuit design concerning the DMA stuff.


Yep , I really wish the internals of the ST chips were published, it would make life so much easier.


So who holds the intellectual property to the internals of the custom chips?

Have they refused/want extortionate amounts of cash or lost to time?

Some of those old atari engineers might have cleared out a cupboard or two recently . . . .

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Re: BAD DMA - Myth or fact ?

Postby exxos » Mon Jun 13, 2016 3:01 pm

jd wrote:So who holds the intellectual property to the internals of the custom chips?
Have they refused/want extortionate amounts of cash or lost to time?
Some of those old atari engineers might have cleared out a cupboard or two recently . . . .


I've tried to track them down, basically nobody knows. Best I got was Curt vandal ? Might have them. He claims he does, but he wanted access to all my work to sell it himself, I basically said no. Later I said "ok" as I was prepared to basically lose all my atari sales and work to gain the documents and he never replied.

I offered him cash initially to scan them, I think the bottom line was he couldn't be bothered. As to if he has the documents or not, who knows. If he does, then hes been the soul cause of much impairment on hardware development for several years. He seems to be a well liked person, but if he is sitting on important documents like that.. then I'm not a fan.

Its because of these lost documents that people like ijor are try to reverse engineer the custom Atari chips. This is going to take years and likely at a huge cost. I've even asked around to get the IC's reverse engineered, and the companies I talked to basically wanted $750,000 just to work out what the chip is, nevermind compiling a schematic from it.

If we had the diagrams we could generate our own versions of the chips, improve on them and still keep the ST working 100% as the original. FPGA clones seem the only future or PC emulators. But they are never going to emulate the real hardware 100%.

Its really sad that great things could happen if we had the source documents, but sadly, it seems its never going to happen Yellow_Colorz_PDT_32
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Re: BAD DMA - Myth or fact ?

Postby redhawk668 » Thu Jun 16, 2016 9:30 pm

Well, tested my STE with a new upgraded power supply. It still has the problem :cry: Did some copying on my UltraSatan and data got corrupted again on the SD Cards. Seems to have a buggy DMA.... Maybe I need to find a STE with a good DMA.....
Total Retro Nut, my collection:

Atari 130XE, stock
Atari 800XL, stock
Atari 600XL, Ultimate 1 MB
Atari 1050 FloppyDrive
SIO2SD
Atari 520 STfm, 4 Mb, TOS 1.04
Atari 520 STfm, 4 Mb, TOS 1.04, Blitter, Cosmos Ex with Raspberry Pi2, 2 GB ACSI/SD
Atari 1040 STe, 4 Mb, TOS 2.06, Cosmos Ex with Raspberry Pi3, 2 GB ACSI/SD
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Re: BAD DMA - Myth or fact ?

Postby exxos » Thu Jun 16, 2016 9:38 pm

redhawk668 wrote:Well, tested my STE with a new upgraded power supply. It still has the problem :cry: Did some copying on my UltraSatan and data got corrupted again on the SD Cards. Seems to have a buggy DMA.... Maybe I need to find a STE with a good DMA.....


You need to try the SIL mod on my page before you conclude faulty DMA. http://www.exxoshost.co.uk/atari/last/DMAfix/index.htm
4MB STFM 1.44 FD- VELOCE+ 020 STE - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - various clutter

http://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
http://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.
http://ataristeven.exxoshost.co.uk/Steem.htm Latest Steem Emulator


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