LC575 motherboard - working, but ... death chimes on any RAM installed

[Byrd]

Hi all,

I recently picked up a barebones LC575 (the educational model with blanked out optical drive space), missing the HD and motherboard.  I picked it up locally, no cracks or shattered plastic in sight!  I've always liked the LC575 format so am keen to restore this fully.

I had one spare LC575 motherboard (onboard 4MB RAM IIRC) - which laid unused for years - which chimes and boots to ? flashing question mark.  Unusually, if I install any RAM in the 72-pin slot, it will chime then immediately give a death chime, no video.  I've tested several sticks of RAM which work fine in my Colour Classic LC575 board (the same board also works fine in the barebones machine I have here, so it's not the edge connector).

I've cleaned the board thoroughly (and SIMM socket extensively) and notice no leaking caps, but will replace regardless.  Has anyone come across similar issues, short of recapping, has replacement of a SIMM socket been successful?

Thanks

JB

 

[rsolberg]

Sounds like you've done the lion's share of troubleshooting so far-- the only thing I wonder about is missing or bent contacts on the SIMM slot. I've encountered four or five bent fingers on a SIMM slot before, and I was able to gently straighten them and get it functioning again. I suspect the damage may have been caused by someone trying to push a memory module straight down as you would with a DIMM, rather than at an angle.

 

[Byrd]

Thanks for your post rsolberg - yes I think I'll investigate the socket more, and any traces around it.  It looks OK though.  The thought of desoldering the 72-pin socket is another thought, but I also will do the recap however this is surely not related to that ...

 

[Byrd]

I've spent more time on this LC575 board, and there was a reason it sat unused for so long ...

It has a bad solder joint/layer around the VRAM and RAM sockets.  I cleaned the 72-pin socket and it failed to boot, cleaned it again and all good but when I push around the sockets it turns off.  My test LC575 board doesn't do this so it's not the edge connector.

Next up, some resoldering and ... baking?

JB

 

[Macdrone]

baking may do the trick, or hot air on just the areas in question.  depends on the plastic on the slots.  I have not baked a board that had plastic on it at reflow temp.

 

[Byrd]

Thanks Macdrone - I tried hot air/reflow around the ICs surrounding the VRAM and RAM sockets, and it resulted in a more reliable chime but with graphical glitches.

Looking closer it goes have some ? cap corrosion around two ICs which will need further investigation.

If I did bake it - looking over at my benchtop oven - would 200deg @ 15 mins suit?

 

[Macdrone]

If your talking celsius I dont know lol.  I use 425 F so sounds about right, just not sure if the plastic on the sockets will hold up to that.  Its why I suggested hot air gun.