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Trouble pushing 4MB MMU board into socket

Upgrade your RAM from ST to Falcon.
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sandord
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Re: Trouble pushing 4MB MMU board into socket

Post by sandord »

rubber_jonnie wrote: Fri Sep 26, 2025 5:36 pm
sandord wrote: Fri Sep 26, 2025 5:13 pm It turned out I had to use Chrome instead of FireFox.

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That spacer looks far too thick to me, will it plug in without?
I tried it without the spacer and it didn't seem to make any difference.
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Re: Trouble pushing 4MB MMU board into socket

Post by rubber_jonnie »

sandord wrote: Fri Sep 26, 2025 5:41 pm
rubber_jonnie wrote: Fri Sep 26, 2025 5:36 pm

That spacer looks far too thick to me, will it plug in without?
I tried it without the spacer and it didn't seem to make any difference.
I'd suggest then that your pins are not properly aligned, the socket looks normal.
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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Re: Trouble pushing 4MB MMU board into socket

Post by exxos »

Can you take a picture of the MMU board at a angle so we can see where the pins are aligning to the socket?

Looks like you have a typical 70789 style board. That's the type I use for testing.
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Re: Trouble pushing 4MB MMU board into socket

Post by exxos »

This is mine...

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Re: Trouble pushing 4MB MMU board into socket

Post by sandord »

Here are some alignment pictures.

By the way, the outer bracket doesn't fit over the socket, on one edge the bracket is something like 1.5mm too small.
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Re: Trouble pushing 4MB MMU board into socket

Post by exxos »

sandord wrote: Fri Sep 26, 2025 6:38 pm Here are some alignment pictures.
Looks fine to me..
By the way, the outer bracket doesn't fit over the socket, on one edge the bracket is something like 1.5mm too small.
Its because the socket is warped.
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Re: Trouble pushing 4MB MMU board into socket

Post by rubber_jonnie »

Try removing the MMU and inserting it to take a bit of tesnion off then remove the adapter, refit the MMU and try again.

It's possible the socket is warped as suggested by @exxos
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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Re: Trouble pushing 4MB MMU board into socket

Post by exxos »

rubber_jonnie wrote: Fri Sep 26, 2025 9:12 pm Try removing the MMU and inserting it to take a bit of tesnion off then remove the adapter, refit the MMU and try again.
Ah yes that's what I did. It's a very tight fit by design.. It has to be. It has to go on straight down as well.. Trying to hook one side on first and then the other actually makes it harder work.. so you have to push the adapter down almost vertically.. Equal on each side because that is the best way to fit, but of course the socket being warped will make this very difficult.
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Re: Trouble pushing 4MB MMU board into socket

Post by sandord »

I think I managed to do it! Here's what I did:
  • Pull the MMU chip out of the socket (thanks for the suggestion)
  • Push the MMU chip half-way back into the socket
  • Place the inner bracket on top
  • Put the upgrade board on top
  • Push the entire stack down until firmly locked in place
The next steps are disabling the old RAM, testing and then removing the old RAM.
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Re: Trouble pushing 4MB MMU board into socket

Post by rubber_jonnie »

Well done.

it 'looks' about right, but I guess that the proof will be once the old RAM is disabled. The old RAM doesn't have to be removed BTW.
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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