IKA combimag RET stirring is broken - Page 1
Forum section: electronics / repair

author: louchedeal
author_rank: Newbie
timestamp: December 28, 2024, 11:02:29 pm
content: Hi there,i was just wondering if anyone has any experience with my issue as im more of a chemistry wizard.i recently purchased a broken heat and stirring plate as it was cheap. I bought it thinking it was probably a broken or corroded connection but alas.now i sit here broken hearted () with a broken stirring plate and a project that has been ground to a halt.so the problem is that it heats fine, but it doesnt stirr at all. i looked at the connections and it seems to be fine. i have found a schematic (see attachment) online but, again, i suck at understanding this.this may be a shot in the dark, but if any of you all has a clue or experience with this sort of machinery i would be delighted to try anything. luckily i have acces to a multimeter.thanks already for your time and i look forward to reading your replies.louchedeal

author: tooki
author_rank: Super Contributor
timestamp: December 29, 2024, 03:36:14 pm
content: I am actually the electronics technician for a university chemistry department, and I have mag stirrers in for repair all the time, though I haven’t had one of that exact model.I assume that you’re not getting any motor movement at all? (And not, for example, motor vibration, but no movement with the stirrer rod.)General troubleshooting tips:- check fuses. If blown, check for signs of overheating on other parts (for example, darkening of a PCB)- check voltages. Make sure there is power everywhere there should be. Luckily your schematic tells you the voltages. (The little arrows pointing to different nodes in the circuit.)- check switches and potentiometers. “Exercise” them by moving them back and forth several times.- check triacs and diodes for short circuits. These love to fail short.- check capacitors. Electrolytic caps often leak and lose capacitance. Film capacitors, often used for motor starter capacitors, also lose capacitance with time (but at least don’t leak).Mag stirrer troubleshooting tips:- because it’s common for chemicals to spill onto these, or for chemical vapors to attack them, switches and potentiometers are a bit more likely to go bad than in non-lab equipment. So give those parts extra attention.- I’ve had a surprising number of units fail due to simple resistor failure, which I suspect may also be due to chemical vapors.Tips for this model specifically:- be careful when measuring, as it has mains voltage on the PCB!! If you don’t feel confident around that, find someone knowledgeable to help you.- note that the schematic says to set it to 600rpm for measurement.- check motor capacitor C7.- disconnect the motor and measure the resistance of each motor winding by measuring between each combination of two wires. They should be approximately the same. If one is significantly higher or lower than the others, the motor may be bad.- disconnect potentiometer P3 and measure it across the ends to make sure it’s about 50k ohms, and then put the wiper in the middle and make sure you’re getting around half on each side.- make sure the photointerrupter disc on the motor shaft is clean, and that the photointerrupter itself is not blocked by any dirt or debris.