Instructions for MK2a Heated Bed Upgrade?

On my SD3 I thought this was fairly simple in the end... I taped the new bed on top of the aluminium plate, and now use glass directly on top of the PCB heater. It's much hotter than it was!

* You'll have to have prepared knobs for the bottom of the levelling screws, as this method precludes access to the levelling screws from the top.
* I reused the existing thermistor, so had to rip the old bed apart - but if you have a new thermistor, you don't need to do this.
* I routed the thermistor wiring back through the middle of the Al plate to get it out of the way of the hot bed quickly, and so I didn't have to bend the thermistor legs right up against the glass bead.

When I write it out in steps it sounds a bit more complex than it really is...

A. Disassembly of existing bed:

(1) Undo the levelling screws completely, disconnect bed from mainboard, remove whole plate+heater from printer
(2) Pull off fibreglass insulation (it's stuck on with double-sided tape)
(3) Working gently, peel the silicone mat heater off the back of the bed. Mine was still working, so I wanted to keep it for other jobs (e.g. chamber heating, filament drying) - in your case go to town, that thing's going in the bin.
(4) Untape the thermistor from the back of the bed, gentle with the fine wires.
(5) Cut the heated bed wiring off the heated bed (if you wish to re-use it for the new bed)

B. Preparation of new bed:

(6) Solder wiring onto PCB bed - instructions are printed on the bed. Note Solidoodle is 12V.
(7) Sit the PCB heater on top of the bed as you wish it to be finally oriented (I'd recommend electrical connections at the back, overhanging the Al a little to allow room for the wires and minimise the chance of shorting on the bed), and use a fine tip pen to mark the thermistor hole (the one in the middle) on the aluminium
(8) Drill a 3mm+ diameter hole through the Al at this mark, clean up the edges with a larger drill bit (no sharp edges allowed!)
(9) Run the thermistor through this hole
(10) Put a piece of tape (masking, electrical, kapton, etc.) on the top surface of the PCB heater, covering the thermistor hole
(11) Glue the thermistor into the hole in the PCB heater with RTV sealant (or similar; high-temp epoxy like JB-weld is also good, but will be less removable than the sealant). Allow to set. Remove tape masking.

C. Assembly of new bed:

(12) Reassemble the aluminium bed back into the printer with the levelling screws and springs (once the bed is stuck down, these will not be accessible). Glue your levelling knobs back onto the bottom of the screws.
(13) Using a few pieces of VHB tape (e.g. 5952: a double-sided high-strength foam mounting tape, rated for 120C, and is quite common), stick the PCB to the top of the Aluminium, ensuring the thermistor is aligned with the hole in the plate and the wiring has been pulled through nicely.
(14) Tape the thermistor wiring to the bottom of the aluminium bed (it's a bit of a squeeze to get in there, but if you have the levelling screws right up it is possible).
(15) Reconnect everything, level the bed, and you're done.

Great post! Very detailed. I appreciate it. Looks like I need some double sided tape and maybe a new power supply.

on the old ones it didn't really matter which wire went where. Same for the thermistor.

On this MK2, make note of which wire is placed where - perhaps some black heat shrink on the far end of the negative wire to help you remember and you should be fine.

Dont forget to build in some strain relief for those wires on the board. make small loops and tape them to the underside of the board so the solder joint is not stressed with movement.

Excellent! Thanks everyone. Just waiting on the RTV to set and then I will plug it in and see what happens.

Proceed with a picture, then order a relay to decrease the load on the board.
Or are you saying it is shorted on the board?  Does it seem alright with the heater unplugged?

Just got the melted junk off of there and tried putting the wires directly to the pins, it's still heating up (the wires). Maybe it's wired up wrong.

Sure.. It was so melted it pretty much disintegrated. So I'll need a new connector, if you happen to know what that connector is called I can order one up, also which relay do you recommend if that is indeed what I need to do.

Check your PM