ElectroBOOM! CuriousMarc Tries (and fails) to fix an old HP182C Oscilloscope -- Words of Wisdom for all Homebrewers

"You try your best to improve something that already almost works... and then you ZAP it entirely in the process.  This is the worst feeling ever.  But don't kick yourself.   This is our lot.  We are made to suffer." CuriousMarc

Indeed.  Take heart homebrewers.  Even CuriousMarc (who is a ham!) has been there and done that. 

This particular CuriousMarc episode was, I think, especially good: 

-- It reminded me of WHY I gave up on my beloved Tek 465 and went with Rigol DSO scopes.  I found I was fixing the Tek scope too often.  Plus, my Tek 465 had PLUG-IN TRANSISTORS.  Yikes!  One false move and you would insert 2 or 3 new problems into the already broken 'scope.  The high voltage in there was really scary.  I had to borrow a high voltage probe from Alan W2AEW.  I survived, but we shouldn't have to risk our lives for hobby test gear!

-- I would advise all homebrewers to be more careful around the really high voltages you will find in old 'scopes and TVs.  Remember the lesson of Ross Hull:

https://www.wia.org.au/members/contests/rosshull/documents/Ross%20Hull%20-%20VHF%20Pioneer.pdf

Read the article that starts on page 7:

 https://www.rsp-italy.it/Electronics/Magazines/QST/_contents/QST%201938_11.pdf

-- Marc struggled with a junction FET.  This reminded me of the raging J310 debate on the Discord channel for the SolderSmoke Direct Conversion Receiver. 

-- We see the oscillator signal flat-topping when it turns on the diodes -- again DC RX memories. 

-- Marc had trouble seeing how the oscillator would start.  I too had trouble understanding how an oscillator would get going. 

-- At one point Marc replaced a transistor with a device that grounded the drain.  This will happen if you switch too quickly from say an RD06 to an IRF-510.   With the IRF-510 you need to insulate the tab from the grounded heat sink.    

It will be great to see, in subsequent episodes, how Marc makes it work.  It is really great to see someone present an unvarnished view of how troubleshooting really works.  

Thanks Marc.   73 

Here is Marc's YouTube channel:

https://www.youtube.com/@CuriousMarc