I recently began repairing VLT's and soft starters and would appreciate any tips or advice, links etc. We are based in Uruguay S.A.Thank you

A few things come to mind. Good information from the customer about the circumstances of the failure and application history is always helpful. Mechanical parts are the weakest link to include fans or pumps for cooling, the customer keypad interface, contactors for pre-charge and bypass. Find a design for an SCR tester to give you the ability to determine SCR failures quickly. One thing to keep in mind when working with 3 phase power semiconductor circuits is the realization that you are troubleshooting the same similar circuit for each device so insure your troubleshooting method has a method. Intermittent problems are always the hardest to detect. In order to detect these it is best to have a storage oscilloscope and utilize the triggering on a circuit that will ID the event. Good grounding at clients site!

Thanks for that Dave. Do you have any suggestions for the SCR tester ? I ask because the other day I had a WEG SSW03 that had suffered from a brownout and the symptom was that the motor we use to test the starters would jump all over the place. I tested the SCR's and they seemed ok, So I connected three fans to simulte a three phase motor and could see that one worked fine and the other two were intermittent. I concluded I had two dud SCR's that didn't fail on a simple test.

When the spares arrived I couldn't remember which were the faulty ones so I decided to replace them one by one. After I replaced the first one the starter funcioned perfectly !

Conclusion, I need a better method to test the SCR

Thanks for that Dave. The circuit described is similar to the way I had tested the SCR's and they passed that test but failed under real conditions. I probalby need to use 220v and a 60w lamp ir something similar to give a more realistic test. What do you think ?

Additional Loading may help. Sounds like a gate failure. I have not noticed an increased voltage with that type of device giving me better results.

Thanks Dave and Mark for your comments.

I had pretty much ruled out a PBC failure by swapping the connectors around. When I changed places, the fault shifted to a different fan, I agree, bulbs would be better.

Also I had measured the SCR on the highest meg range on my tester and there was nothing to suspect a short. This starter had been affected by a huge brownout so I suspected the SCR could have been affected in unusual ways.

We are a Manufacturer of Soft Starters based in the UK and we are currently expanding in to South America - I would be happy to help you with any enquiries and potential sales oppurtunities. We can provide full technical training in our products should this be useful to you. Fairford Electronics Ltd, Devon UK. contact me at rollen.flood@fairford.com