EUROTHERM 3504 Process Controller Repair

They are designed to control industrial and laboratory processes via input sensors which measure the process variables and output actuators which adjust the process conditions. 3504 controller can handles input types of Digital inputs, Thermal couple inputs, Pt100 inputs, 0-20mA analog inputs and many more. if you interested about full description, datasheets are available from manufacturers website.

I received this unit for repair in full dead condition. there were no any physical damage. After removing the cover, i did not see any visible damage on the board. 

There  were very complex board arrangement inside. i had to carefully disconnect and remove all boards to test components of main power supply.

Testing procedure starts from AC line input. fuse, NTC and filter capacitors were fine. DC bus had 320V DC. but secondry side seemed dead. no voltage across filter capacitors at all.

I tested supply voltage rails of SMPS switcher. that also showed 0V. but that can't be happen, because DC bus must provide starting supply voltage to switcher. I had to manually inject voltage to switcher and found 47uF filter capacitor getting heated.

47uF capacitor was the problem. that had an internal short circuit.

 

replacing the capacitor solved the problem.

* Use good spare parts. remember, build trust. trust builds businesses. saved cents do not. *