Can you be more specific. What kind of HKB are you talking about (self build or the UMO heated bed kit from ultimaker?). Do you have a multimeter so you measure at the connection to see what is going on?
@msurunner: Assuming you mean the UM HBK. You drive it with both power supplies and do not have the Ultimaker shield power connected to the new pcb, correct? But you have made the logic connection with the cable which is mounted to the heater 3 (or bed heater) clamps on the UM shield pcb and by a connector to the HBK pcb, correct too?
You also made sure you didn't mess up the connections on the heater pcb (print stage)? Then, as @zoev89 suggested, please check for a voltage signal on the heater pcb. If you get one and the bed still doesn't heat, you may check resistance between the connectors of the heater pcb when the printer is switched of and the heater pcb disconnected.
Gotcha... See here I was thinking the "SWITCH" was wired to the physical switch on the shield to disconnect power from the PCB... Now that makes sense... Wow...
Is there not a power disconnect to the small PCB?
The new pcb gets its power directly from the new psu. Only unplugging the new psu de-powers the new pcb (unplug the psu on the AC side, not on the DC side!). It's not so elegant. I recommend to plug everything into a switchable multiple socket and use this switch only for (de-)powering the UMO.
Gotcha. Then the only connections between the Original shield and the smaller HBK PCB are the logic coming from the Heater 3 header to the "SWITCH" terminal and the temp being TEMP 3 terminals, correct?
There are always two connections; the first one is the 'heater' connection between 'hot bed' terminals on the shield and the connector marked 'switch j4' (see hbk manual page 13). There is not much power running through that cable, so I call it a logic connection. The second connection is the one between the temp3 connector on the shield and the temp connector J1 on the hbk pcb (page 14 right side). This one is for the temp sensor.
If you run your UMO with only one extruder, you can establish a third connection which is described on the left half of page 14. It's a power connection which brings 19V from the hbk pcb to the shield and makes the old psu obsolete. In your case, there are two hotends which is too much for the new psu to drive and you should not make this third connection but use both psus.
This description might have been a bit too detailed for you but maybe it will help some newbies...
Hey, there IS a manual for the kit! I was super confused, because the link on the product sheet is to assembling a whole UMO+... Dang, I was making inferences on that and trying to figure out how it was designed to be incorporated into older electronics...
IMHO a printed manual should be in the kit (which is not, at least not in the kit I used). It's certainly not a big cost factor to have a few A3 sheets printed and stitched together...
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