Re: TEK 475: Dead on Start Up.


Michael W. Lynch
 

Tom is spot on. I have repaired dozens of these scopes and do not subscribe to the "shotgun" approach of replacing all tantalum's. When they fail, tantalum caps usually do so in spectacular fashion and typically announce failure with a quantity of "magic smoke". I replace tantalum caps only if the related supplies or circuits exhibit symptoms that can be contributed to no other source. 2X voltage rating or more is best. That scheme has worked for me and I have seen relatively few failures. The Bulk filter caps are typical failure points so that is where you can spend your initial investigation. I have found that you can solder a good cap across the pads of the bulk filter cap of the offending supply and restore function as "proof" that the filter cap is the issue. it is possible that the bridge rectifier for the +15V circuit is bad, but that will become apparent upon testing of the bulk filters. Check ripple on all supplies while you are at it. and repair as needed. Good luck! ,

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Michael Lynch
Dardanelle, AR

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