31-08-2019, 09:34 PM
Peter
The first step is a visual examination of the electros from the top side of the PCB. Check for any that have 'peaked' metal tops instead of flat tops. Secondly, look at the PCB around the electros' bases and see if there has been any 'gunk' (technical term for discharged electrolyte, often brown or black in colour) released from one or more of them. If either is true then it will be worth the effort in prying the PCB loose from the case to replace them.
Don't ignore the smaller electros around the PWM controller part of the PCB either. The bigger output ones may be ok but smaller ones (eg 4.7uF..) could be unexpected causes.
The SMPS supplies are a pain to troubleshoot but since you have the 340V DC present, that makes the PWM controller part the most likely culprit. If it isn't the output filter area electros bad (& you already know that the switching transistors/FETs are OK because you get the 3V out of the supply itself), it will probably be part of the output sensing back into the PWM's control input or the supply to the PWM chip.
Do-able.
The first step is a visual examination of the electros from the top side of the PCB. Check for any that have 'peaked' metal tops instead of flat tops. Secondly, look at the PCB around the electros' bases and see if there has been any 'gunk' (technical term for discharged electrolyte, often brown or black in colour) released from one or more of them. If either is true then it will be worth the effort in prying the PCB loose from the case to replace them.
Don't ignore the smaller electros around the PWM controller part of the PCB either. The bigger output ones may be ok but smaller ones (eg 4.7uF..) could be unexpected causes.
The SMPS supplies are a pain to troubleshoot but since you have the 340V DC present, that makes the PWM controller part the most likely culprit. If it isn't the output filter area electros bad (& you already know that the switching transistors/FETs are OK because you get the 3V out of the supply itself), it will probably be part of the output sensing back into the PWM's control input or the supply to the PWM chip.
Do-able.
Doug VK4ADC @ QG62LG51
http://www.vk4adc.com
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If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.