Also find info below at:
Those IKA-Works stirplates cost upwards of a $1K. So, yes worth repairing . We see lots of these, mostly with buffer/saline spills, or the DPST powe r switch has died. For the more involved fails:
The quick cheap fix is: replace the entire guts, two PCBs with a permanent ribbon between, Part No. 5008001, PCB Assy for stirplate number RTC-B-S1 $156.00 (2012 price)
IKA Works 2635 North Chase Pkwy SE Wilmington, NC 28405-7419 Phone: (910) 452-7059
See PCB Photo w/notes:
Safety shutdown
The LM358 dual op-amp compares the setting of the safety-temperature pot wi th the output of the main sensor thermistor. If the two values approach too closely, or if the safety pot is set too low, the op-amp will drive the ba se of the SOT23 BC817 (NPN transistor) low to shut off the safety relay; re moving 120VAC from heater.
A second BC817 NPN in series must pull the above NPN's emitter to below app rox 5V in order to drive the safety relay on. The second BC817 is driven by the Q-output pin5 of the 74123 retrig 1-shot, which is kept constantly hig h-triggered by the LED scan signal from the CPU. And, its own emitter in tu rn is pulled low by being connected to the 5pin DIN's pin3. The pin3 must be grounded in order for the rest of the circuit to drive the safety relay to supply 120VAC to heater (you must add a jumper between pin3 and pin5 on the rear DIN.)
Common error msgs
ERROR-6: Missing temperature probe. You must enable the stirplate by instal ling the LCD thermal probe assembly, or the small grey jumper plug. Or, jus t ground pin-3 on the rear connector by using a bent piece of solid wire #1
6ga to jumper from pin-3 to pin-5. See pin diagram on the PCB photo above.
ERROR-25: Processor thinks it can't turn triac on/off, or no AC at heater/t riac section. Caused by: heater-coil failed or unplugged, or the triac or h eater relay is dead, or the safety-relay is forced off (because of 1K therm istors wrong or unplugged, or safety-tempr pot set wrong, or the DIN connec tor's shorting-plug missing.)
User manuals (no, not service manuals)
IKA Works catalog page