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Re: 4MB MMU Adapter Issue
Posted: 14 Oct 2020 12:57
by exxos
Have you done all the mandatory fixes in the tweaks and fixes forum ?
Re: 4MB MMU Adapter Issue
Posted: 14 Oct 2020 13:21
by rubber_jonnie
I'm pretty sure that there is no direct connection from the MMU to the floppy as I traced a lot of the pins between chips the other day on the schematics for a floppy problem I'm looking at.
There are connections from the WD1772 to a 74LS02, a 74LS06, the YM2149 and the DMA, but none that I have found go direct to the MMU.
Of course there are data lines between the DMA and the MMU, but no direct connection to the FDD controller itself.
I'd suggest that the mandatory fixes as suggested by exxos are probably a good step to make sure there are no floating data lines between the DMA and WD1772.
Re: 4MB MMU Adapter Issue
Posted: 15 Oct 2020 08:54
by MonoJono
Oh no this quick ten minute upgrade isn't going well! :D
I've looked through the tweaks and fixes and given my circumstances ie:
1 - STFM
2 - Recapped PSU
3 - Currently Using GOTEK Externally Powered
4 - All Diag Tests Pass Perfectly (ex floppy) Including GemBench and YAART
5 - No Issues Before Upgrade
I think only 3 could apply.
1 - DMA Pullup
2 - 1772 Pullup
3 - Bus Resistors
Would you have any order you suggest I try these in - ie most to least likely to fix it?
Does EXXOS stock the parts for these fixes, or should I just go to Farnell and find them?
Alternatively would the other Exxos RAM upgrade where the old RAM is unsoldered and 4MB board is soldered onto the mobo be less likely to cause issues?
Cheers
John
Re: 4MB MMU Adapter Issue
Posted: 15 Oct 2020 09:10
by rubber_jonnie
@MonoJono Just get the SILs from your usual supplier, there is nothing unusual or special about them. Just get the values recommended in the mandatory fixes post.
You should do all 3 really.
However you should also consider that your PCB had had a lot of handling lately. I know from personal experience that manhandling a board can break it, so you should consider testing all of the connections from the WDD1772 to the FDD internal and external ports for continuity, and also look at doing the same for other connections from the FDD to DMA to YM2149 etc.
I've attached a schematic for you, download and remove .txt from the end, as that is just a cheat to upload a PDF.
Re: 4MB MMU Adapter Issue
Posted: 16 Oct 2020 14:18
by MonoJono
@rubber_jonnie
Hi Jonnie - I can't use your full name - just cant do it! :D
First off I just wanted to say thanks for the all the replies - you've been incredibly helpful - Exxos is lucky to have you! I hope he gives you lots of free stuff! :D :o ;)
I did some digging around inside the machine with a multimeter last night and everything looked fine, but I am not entirely sure what I am doing at any moment so...yes enough said
But.... I have managed to get the machine to work (ish) - but its the strangest thing... I have an ultrasatan. It was plugged into this machine (but turned off). I unplugged it just out of desperation and booted - up came the floppy drives - everything perfect! I plugged it back in, they disappear. Tried turning the US on and booting - no drives. Did this a few times to be sure and its 100% - US cable in and I see no drives out and its fine. I've checked the US on my other machine and its working fine so I cant imagine there is anything wrong with it/the cable.
Could the impendence from this ribbon cable be causing a marginal signal to not be strong enough? Given this is there something I should look at first?
Cheers
John
Re: 4MB MMU Adapter Issue
Posted: 16 Oct 2020 14:24
by exxos
MonoJono wrote: 16 Oct 2020 14:18
Could the impendence from this ribbon cable be causing a marginal signal to not be strong enough? Given this is there something I should look at first?
This is why you need to do the Mandatory fixes...
Re: 4MB MMU Adapter Issue
Posted: 16 Oct 2020 15:17
by rubber_jonnie
MonoJono wrote: 16 Oct 2020 14:18
@rubber_jonnie
Hi Jonnie - I can't use your full name - just cant do it! :D
First off I just wanted to say thanks for the all the replies - you've been incredibly helpful - Exxos is lucky to have you! I hope he gives you lots of free stuff! :D :o ;)
I did some digging around inside the machine with a multimeter last night and everything looked fine, but I am not entirely sure what I am doing at any moment so...yes enough said
But.... I have managed to get the machine to work (ish) - but its the strangest thing... I have an ultrasatan. It was plugged into this machine (but turned off). I unplugged it just out of desperation and booted - up came the floppy drives - everything perfect! I plugged it back in, they disappear. Tried turning the US on and booting - no drives. Did this a few times to be sure and its 100% - US cable in and I see no drives out and its fine. I've checked the US on my other machine and its working fine so I cant imagine there is anything wrong with it/the cable.
Could the impendence from this ribbon cable be causing a marginal signal to not be strong enough? Given this is there something I should look at first?
Cheers
John
No problem, I'm here to help because I enjoy helping :)
What you have here is a classic case showing the necessity of the mandatory fixes. I have had Ultrasatan cards become corrupted for no other reason than the pullups just aren't up to the job, and it can show itself in floppy drive problems as well.
I have a big reel of SIL resistor packs so that I can re-do the pullups whenever a machine comes my way.
It's simply one of the problems that Atari STs have, and it manifests in several ways, and is particularly noticeable when a hard drive like US is in the mix.
I think you'll find once the mandatory fixes are done, you will be just fine.