EEVblog #804 - HP1740A Oscilloscope Repair - Part 2

Follow Dave as he tracks down an elusive intermittent thermal fault in a HP1740A analog oscilloscope.
Can you figure out the culprit before Dave does?
Part 1: https://www.youtube.com/watch?v=Cmz8bzUsj7E
Forum: http://www.eevblog.com/forum/blog/eevblog-804-hp1740a-oscilloscope-repair-part-2/
https://teespring.com/warrantyvoid2
Original HP Journal article on the HP1740A:
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1975-12.pdf
How not to blow up your oscilloscope:
https://www.youtube.com/watch?v=xaELqAo4kkQ

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