Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!


Dave Peterson
 

Yes, intermittent transient problems are the worst.

I figure any recovered parts scope comes with 0 assumptions. When it at first did nothing I wasn't the slightest bit surprised. I was more surprised that it did work - and is working pretty darn well. My primary guess is that the "Regulating Range Selector" - the jumper in the main fuse holder? - was the culprit. That removing and reinstalling it broke whatever surface corrosion was interfering. The power switch had already been cycled a few times (without power) during the disassembly/reassembly process. Should it be taken back out and and cleaned? Sure, along with every other contact surface in the scope? I'm not that patient and thorough, yet.

It's doing a lot of off-nominal things that can't be of any surprise: pots being "jumpy", etc. I have to wonder how long this thing has been sitting on a shelf in the most non-ideal conditions. There have been a lot of water spots on internal metal parts. I think mostly likely condensation. The boards have appeared rather pristine, though it also appears to have had some boards and shields removed. Obvious solder work on the wires and BNCs necessary to disassemble/reassemble. I suspect several attempts to fix it have been made before.

Things are cleaning up as I use it - position pots are settling down with use, BNCs are being noisy and intermittent, but getting better. Small oxidation and corrosion on contacts has to be expected. I'll get into cleaning methodologies as I get into the calibration and determine what is and isn't working.

Just part of the fun!
Dave

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