MAXTEMP BED Error

[tfg 0]

First post on the forum, even though I've been signed up here for quite a while. So - hello to everyone.

 

I bought a UMO kit in July 2012. Then life got in the way. So I only started to build it late last year. By then, I'd added an Ultimaker HBK kit to the pile, so that got included as I built the kit, along with a Flex3Drive head, as the head construction that was part of the original kit didn't match the instructions (I think it was a very early version of the head) and it didn't look as though it would work well anyway.

 

Last week, I finally got to the point were I could power it all up. Everything seemed to work, at least in basic function. It turned out that the glass bed plate wasn't flat, so I had to make some modifications, but that seems better now. When I was bed levelling, I pre-heated the nozzle and bed to the default operating temperatures. Everything seemed to be working OK, then the Ulticontroller showed a "MAXTEMP BED" error. I switched everything off and reset. Initially, it would still pre-heat the bed to about 80-85C (target temperature was set at 95C), then the temperature readings would vary wildly for a few seconds, then the error would flag up. Now, the error is permanently on, even when the bed is cold. Also, when I view Pronterface, it connects and shows the nozzle and bed temperatures in the title bar as approx. room temperature for the nozzle, but 1,100C (!) for the bed. It also permanently indicates "Detecting baud rate", but never establishes a connection. Resistance across the bed temperature sensor is showing around 110 or 111 ohms when at room temperature.

 

I seem to be going backwards with getting the printer to run. What's my best course of action?!

 

Matt

[tfg 0]

Update: I've followed the troubleshooting advice on the UM Error pages and swapped the connectors over between TEMP1 and TEMP3. The error then becomes a simple MAXTEMP displayed on the Ulticontroller, so from this I assume that the fault lies with the bed rather than the control board(s).

 

So I've stripped the bed down and checked the resistances across the various connections and terminals. Measured at the tails at the back of the connector block on the heated bed plate, the PT100 sensor is showing a steady 108.3 ohms at approx. 19C room temperature. The main heater track gives a reading of 3.2-3.3 ohms, but as that has been heating up OK I don't think there's a problem. Both of the sensor wires that run from the bed to the heater control board show very good continuity. The 3-pin cable running from the heater board to the main board also shows good continuity for all wires, even when I measure across pins on the boards sockets.

 

I'm running out of ideas here. Any ideas where the fault may lie?