Help diagnosing this Corning hotplate stirrer that the motor doesnt spin - Page 1
Forum section: electronics / repair

author: artvandalai
author_rank: Regular Contributor
timestamp: March 03, 2025, 12:38:35 am
content: Is there any schematics for this Corning pc-420 hotplate stirrer? All of a sudden the motor doesnt want to spin. It has this flashing light when ever i move these cables i circled and a sound like they are making a short. Im not sure if I damaged these cables crushing them when i screwed the bottom cover on or damaged the pcb. The top pcb where the potentiometers are is okay since i switched that pcb with another working pc-420 to double check it wasn't the problem. Any advice on how to diagnose this problem further?

author: Dougmc
author_rank: Contributor
timestamp: March 03, 2025, 12:53:13 am
content: The red 2 pin connector on the left tc1 looks to be at an angle. Maybe not fitted correctlyOr it's mating connector has pulled looseFrom the pcb.Another note the screw next to it is missing.Sometimes the ground to chassis is made thruThese screws. Try putting in a screw 1stDoug

author: artvandalai
author_rank: Regular Contributor
timestamp: March 03, 2025, 01:25:49 am
content: Heres the back of that pcb board

author: MathWizard
author_rank: Super Contributor
timestamp: March 04, 2025, 05:46:54 am
content: Do you have a DMM and some experience on such things? You could check a lot of it unpluged, and it's not a very big circuit. It could be a loose solder joint some where, like if some wires got pushed the wrong way.It looks like power comes in through a fuse, and there's a little transformer like in a microwave oven, for the low voltage supply. And is that a relay connected to a heater element ? And then there's probably a speed controller and temperature control. There's no display, so maybe there's not a microcontoller.But yeah maybe it's just some loose or dirty connections.

author: benj38
author_rank: Frequent Contributor
timestamp: March 05, 2025, 04:59:32 pm
content: @artvandalai, given that you opened another topic in the "Beginners" section of the forum, where you ask how to reinforce the connection of one of the wires in this PCB, I assume that you have found the problem.

author: tooki
author_rank: Super Contributor
timestamp: March 05, 2025, 06:55:36 pm
content: Quote from: artvandalai on March 03, 2025, 12:38:35 amFirst of all, stop creating new threads about the same repair. Three is approximately two too many.Anyway, in the thread about the broken pad, you posted this image:And that could be your problem. That relay shows a significant bulge (above the "9508" date code, as seen in the picture). So that's where I would begin diagnosing.

author: floobydust
author_rank: Super Contributor
timestamp: March 05, 2025, 08:57:47 pm
content: The relay master-enables power for the heater and fan. It looks damaged from poor contacts overheating and would explain the zzzt sizzling sound OP hears.The small triac switches the fan motor, the bigger triac on the heatsink switches heater power.Replace it with a ? HascoSSD110PH-DC5has a kooky pcb footprint.I'm not sure why people multi-post about the same issue.

author: artvandalai
author_rank: Regular Contributor
timestamp: March 07, 2025, 05:43:05 am
content: I have not found the problem yet. Unfortunately im still a novice with electronics diagnosing and testing. I only have a multimeter to help me but a schematic would be the most helpful. I opened that post for another Corning hotplate stirrer im having touble with ripped pads but both im having problems with the motor not spinning.

author: artvandalai
author_rank: Regular Contributor
timestamp: March 07, 2025, 08:19:13 am
content: You all motivated me to go fix the ripped pad from the pin. I tried it out on both hotplate stirrers and both spin and heat. I'm still not sure yet whats wrong with the pcb that doesnt spin the motor.

author: benj38
author_rank: Frequent Contributor
timestamp: March 07, 2025, 08:23:32 am
content: Quote from: artvandalai on March 07, 2025, 08:19:13 amFirst, congratulations!Second, now that you have working units to compare to, finding the problem in the faulty PCB should be much easier by doing comparative measurements.

author: floobydust
author_rank: Super Contributor
timestamp: March 07, 2025, 06:14:38 pm
content: In that pic, the soldering for the crimp press-fit pegs looks fractured, I would resolder that as well.

author: artvandalai
author_rank: Regular Contributor
timestamp: March 15, 2025, 09:32:06 pm
content: An update, i replaced the relay and both hot plate stirrers work now.