Question mark over checkerboard pattern on SE

[elemenoh]

This SE has a flashing question mark *on top of* a checkerboard pattern on an SE. The MLB looks like it was reworked, maybe to support different RAM configs?

I tried removing each set of RAM and swapping them around. Any config other than both installed results in various sad Mac codes.

Any ideas where the trouble might be?

 

[rplacd]

Others know the SE better than I do, but do you need to have a shunt installed on the 2/4M pins?

 

[elemenoh]

If I jump the left two pins, it does boot but only recognizes 512K RAM. If I jump the right two pins, I get the checkerboard pattern. I tried a different set of RAM and got the same result.

 

[elemenoh]

After reading through this article, it looks like the jumper should not be set for 2.5MB which this machine has. I'll try again with a different set of RAM to see if it's just bad SIMMS or something broken on the MLB.

 

[elemenoh]

All 256kb and all 1MB configs work okay but not 2.5MB. It’s filled with and working okay with 4MB at the moment but it’d be good to know why 2.5 is not. Maybe a bad resistor somewhere?

 

[quorten]

Elsewhere on the forum I believe mention of a similar problem with checkboard pattern pointed to bad address multiplexers.  You could try replacing the address multiplexers and see if that works, but I'd defer to looking at that forum post first.  Here is the link to the forum post I saved on my personal blog, but alas, the link is broken!  Go fish and see if you can search it out of the forum.

https://68kmla.org/forums/index.php?/topic/58398-se30-vertical-stripes-death-chimes/

 

[quorten]

Ah, yes, link hacking magic, the working link has been restored.  Yes, it's an SE/30 instead of an SE.  But I see there is SE/30 on your exterior case from the photo.  (No mention of checkerboard here actually, but helpful advice.)

https://68kmla.org/forums/index.php?app=forums&module=forums&controller=topic&id=58398

 

[jimjimx]

On my SE the jumper is removed, and works with 4MB. 

 

[LaPorta]

Does the thing actually boot past the floppy question mark?

 

[elemenoh]

I see there is SE/30 on your exterior case from the photo.

This is a regular SE board in a SE/30 case.

Does the thing actually boot past the floppy question mark?

Yes it works fine with the jumper off and 4MB RAM installed. It doesn't work with the jumper on and 2.5MB RAM installed.