4MB MMU Adapter Issue

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MonoJono
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4MB MMU Adapter Issue

Post by MonoJono »

Hi

I just got around to installing a 4MB MMU adapter I bought from here a couple of months back. Everything seemed to go fine, but I have issues now...
The machine is a 520STFM with a CO70789 mobo, so all fairly standard.
Unfortunately I now get a full row of bombs across a white screen after it tries to start up. I get this whether or not I have a floppy installed. I tried booting from my ultrasatan but get the same issue. If I remove the FDD completely I just get a white screen and not a blank desktop.
I have an exxos diag cart and running the diagnostics on that weirdly it is almost fine - everything comes up and passes including RAM tests, all floppy tests work, BIOS, video etc, BUT... it only thinks it has 1MB (the board is still on its default position of 4MB no switch wired to it)...
Also weirdly I get the same bombs again when I try to run up YAART from the cart - almost as if YAART may be trying to load itself into RAM and any attempt to do this fails????

I haven't removed the old RAM or tied off the resistors etc yet - as I understood it the machine should boot and work without doing this, its just advisable as it puts less stress on the PSU?

Any thoughts or similar issues from anybody I would love to hear.

Cheers
John
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exxos
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Re: 4MB MMU Adapter Issue

Post by exxos »

Have you recapped the PSU ? We have a whole topic on mandatory fixes which should be done.

Also you shouldnt run 2 banks of RAM in parallel, you need to do as it says in the guide, skipping steps is only going to cause headaches.
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
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.
MonoJono
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Re: 4MB MMU Adapter Issue

Post by MonoJono »

Ah OK. I watched a Gadget UK video and he stopped halfway to check everything was ok and got I desktop, but maybe his PSU was in better shape?

I do have a recapped PSU in my other machine. I will swap it in and try again. If that doesn't work I will complete the steps to disable the old RAM. Just wanted to make sure this was going to work before doing anything more difficult to reverse to my old ST! Once I was happy was going to unsolder it completely. It has had the RAM repaired and socketed really badly by somebody years ago and so removing all completely would be good.

Cheers
John
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rubber_jonnie
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Re: 4MB MMU Adapter Issue

Post by rubber_jonnie »

I think you'll need to do as exxos suggests and disable the old RAM first, having the original and new banks enable together won't work very well with 4MB enabled.

You also need to check the fit and orientation of the MMU adaptor to ensure it is making a good connection, and that pin 1 is correctly lined up with pin1 if the MMU. Same goes for the shifter adaptor, only there is only a 50/50 chance of installing that round the wrong way, though we have seen it on here before.

If you can, add some pictures, and if you do have a known good PSU then that will help 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...
MonoJono
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Re: 4MB MMU Adapter Issue

Post by MonoJono »

Will do.
As I get a picture and everything passes with flying colours when I run the diag cart I guess there can't be too much wrong with the fitting - certainly the shifter and adapter is in the right way!
When I get a minute I will swap out the PSU and disable the old RAM then post a message here to say how it went. Hopefully everything will be fine.
Cheers
John
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rubber_jonnie
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Re: 4MB MMU Adapter Issue

Post by rubber_jonnie »

MonoJono wrote: Mon Oct 12, 2020 8:34 am
" certainly the shifter and adapter is in the right way!"
I know is seems daft to ask that you check, but another user recently posted that their 4MB upgrade wasn't working, but the photo they posted showed the Shifter adapter was in the wrong way round, so 180 degrees out. I used to work on aircraft, so the adage was "never assume, check", something I've stuck to that has served me well :)

Of course the MMU adapter is a little harder and has 4 positions where it will fit, but 3 of them are wrong.

As you can see in my picture, pin 1 is opposite the ribbon cable connector. Any other way won't work:

MMU_Adapter.JPG
MMU_Adapter.JPG (79.79 KiB) Viewed 3713 times

Be aware that not all ST mainboards have the MMU facing the same direction, so do check the pin numbers around the edge. This picture is from my 520ST, and pin 1 points towards the front of the mainboard, but for other STs, some have pin1 facing left, some right, so just double check.

Also, i recommend you remove the mainboard, including the metal under tray and place it on a hard flat surface in order to insert the MMU adapter. It prevents the board flexing and makes it easier to insert smoothly.

Once you've disabled the onboard RAM, try powering on, you should get a black screen and white border, which indicates no RAM installed. Then you're good to move on to fitting the rest of it.

I'll keep fingers crossed it all goes smoothly
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...
MonoJono
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Joined: Sun Oct 11, 2020 10:01 am

Re: 4MB MMU Adapter Issue

Post by MonoJono »

All looks to be working perfectly once I disabled the old RAM. :)

Thanks for your help! I should have just done the whole thing and not stopped halfway through! I really thought the chap (gadgetuk) in the video stopped after installing it and before disabling the old ram to test everything worked - I guess I was wrong. Now I have an ocean of memory and should be able to use my UltraSatan with this machine as well as my STE. Happy days!

Cheers
John
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exxos
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Re: 4MB MMU Adapter Issue

Post by exxos »

:bravo: :goodpost:
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
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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rubber_jonnie
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Re: 4MB MMU Adapter Issue

Post by rubber_jonnie »

Fantabulous :)

:girldance: :girldance: :girldance:
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...
MonoJono
Posts: 8
Joined: Sun Oct 11, 2020 10:01 am

Re: 4MB MMU Adapter Issue

Post by MonoJono »

Sorry to be the harbinger of doom but Fantabulousness was short-lived....

I plugged the floppy drive back in later and it didn't show on the desktop - hmm odd...
So thought must be the PSU not coping driving it and the new RAM so plugged in my gotek and powered it from an external 5V mains adapter. Still got same thing.

Ran the diag cart and it is clearly partially there - it spins up when I do a speed test and reports back the correct 200 RPM. But when I try to do a Disk Exerciser it comes back 'F0 Not selected'.

I checked all the ribbon connector pins and they all have continuity. I guess one of the pins that control some aspect of the FDD on the MMU adapter isn't either connected to the adapter or the mobo properly now maybe? Or I guess a line on the now socketed shifter could not be getting through?

All other tests on the diag cart pass as does running YAART from the diag cart now too, so its very close!

I'm really loathe to pull the whole thing off as it took considerable force to get it on there and I'm not sure how many times those notoriously finicky old PLCC sockets can cope with that.

Anything you can suggest I look at? A line I can check for continuity from the MMU or shifter - I dont have a scope but am ok with multimeter :)

Cheers
John
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