Macintosh IIfx explosive RAM

[The House of Moth]

Currently in the process of fixing this and very curious, what could cause this in a RAM socket?
Whatever happened blew a hole straight through the board. Leaving one heck of a burn on the case even.

 

[The House of Moth]

Might as well give a few updates on the repair
Removed part of the socket, cleaned some debris from the crater.
Pins 1 and 2 no longer exist, 3 is in rough shape. Some traces 2 layers down got destroyed.

 

[The House of Moth]

More cleanup of the burnt board material and exposing the traces underneath. These will have to be dug out so I can probe them to figure out where they go and attach wires to ‘em

 

[The House of Moth]

Some more cleanup and prep. Figured out where everything connects to thanks to an old Bomark (I think I got that right?) schematic and help from @Branchus decyphering it.

 

[The House of Moth]

Started building up the board with solder mask. This will build up until I get to the height of the traces, then wires will be applied.

RAM socket has also been completely removed by now and replacement was ordered.

 

[trag]

The 64 pin SIMM socket was also used by Apple for ROM modules and, I think, by Amiga for another type of incompatible memory.

Guessing, someone installed something other than a IIfx SIMM in the socket and caused a dead short from 5V to GND.

Or something close to that.

I have a PM9600 board with a melted DIMM socket and a hole in it, where someone forced 3.3V memory into a 5V slot....

Nice restoration.

 

[Kai Robinson]

Might as well give a few updates on the repair
Removed part of the socket, cleaned some debris from the crater.
Pins 1 and 2 no longer exist, 3 is in rough shape. Some traces 2 layers down got destroyed.

Looks like someone shot a Xenomorph next to that IIfx!

 

[The House of Moth]

A new day, more of the same. Apply solder mask, cure, apply solder mask, cure... A good amount of layers went into this hole. Finally got to a height where I could rebuild the traces.

 

[The House of Moth]

A bunch more layers on top and the board is whole once again. The two ground pins will be drilled out once the replacement sockets come in or I may just run a wire from the legs to the ground, we'll see.

 

[The House of Moth]

The 64 pin SIMM socket was also used by Apple for ROM modules and, I think, by Amiga for another type of incompatible memory.

Guessing, someone installed something other than a IIfx SIMM in the socket and caused a dead short from 5V to GND.

Or something close to that.

I have a PM9600 board with a melted DIMM socket and a hole in it, where someone forced 3.3V memory into a 5V slot....

Nice restoration.

Hell of a whammy for just 5V but wrong SIMM is the most logical explanation, tnx!

 

[Zane Kaminski]

Wow, this is an amazing repair. I usually tape down bodge wires against the board with kapton tape. I always thought that was a fairly low-profile solution. I had never considered laminating the repair into the board! Amazing... I have to try your technique of building up the mask goop next time I'm fixing a board with a hole in it.

 

[The House of Moth]

Wow, this is an amazing repair. I usually tape down bodge wires against the board with kapton tape. I always thought that was a fairly low-profile solution. I had never considered laminating the repair into the board! Amazing... I have to try your technique of building up the mask goop next time I'm fixing a board with a hole in it.

It’s fun and satisfying! Do share when you get around to it

 

[trag]

A bunch more layers on top and the board is whole once again. The two ground pins will be drilled out once the replacement sockets come in or I may just run a wire from the legs to the ground, we'll see.

Would you mind linking to the product you're using to build up mask layer? And is it a UV cure or a two component mask?

That sounds like mighty useful stuff.

 

[The House of Moth]

Sure thing!
I get the UV curing mask from amazon or ebay, whichever has the best price at the time and brands vary.

Green for the vintage stuff: https://www.amazon.com/dp/B01MUB4PJL

Black for the modern stuff: https://www.ebay.com/itm/PREMIUM-BL...d-UV-Curable-Curing-Solder-Mask-/282637383153

Laser pen to cure it quickly: https://www.ebay.com/itm/UV-Glue-Cu...Laser-Ultraviolet-405nm-Pointer-/132809688246

Note: The black mask takes considerably longer to cure and must be applied much thinner so the UV can penetrate all the way. I also recommend wearing UV blocking glasses unless you're watching your work on a screen through a camera.

 

[trag]

Sure thing!
I get the UV curing mask from amazon or ebay, whichever has the best price at the time and brands vary.

Green for the vintage stuff: https://www.amazon.com/dp/B01MUB4PJL

Fantastic. Thank you.

I don't suppose you have a link for a plunger and nozzle? Many of the reviews note the lack. I can improvise if necessary.

 

[The House of Moth]

Ah no, sorry. I don't use nozzles but a very small paintbrush to just dip into the tube (and even then I typically get too much). My pinky is the plunger haha

 

[trag]

Ah no, sorry. I don't use nozzles but a very small paintbrush to just dip into the tube (and even then I typically get too much). My pinky is the plunger haha

Ah, cool. I often use the tip of a toothpick in situations like that.

 

[Alf Torp]

Currently in the process of fixing this and very curious, what could cause this in a RAM socket?
Whatever happened blew a hole straight through the board. Leaving one heck of a burn on the case even.
View attachment 1209

I can only assume this was where the porn was stored in RAM.

 

[GiGaBiTe]

I've had DIMM memory modules get shorted RAM chips that burn pins out in the RAM socket, but never seen one blow a hole in a PCB.

I guess the thicker pins in a SIMM socket facilitate more current being able to pass through the board.

 

[LeadedSolder]

That’s amazing: structural solder mask. I can’t even get the stuff to go smoothly over trace repairs!