Repair of Fluke 6060B RF signal generator

[TheDefpom]

Hi all,  I thought I would just share my repair videos here for this unit, in case anyone is interested.

https://youtu.be/0aMK52UX1AM

There are 5 videos in total, this is the first in the series.

[wn1fju]

Nice videos.  Fortunately, mine was a bit easier to diagnose and repair.  It threw errors 5 and 13 (left and right displays), but a first look with the spectrum analyzer at 100 MHz showed everything was working properly.  It wasn't until I hit >245 MHz that I saw the problem - harmonics that were only 3 dB down from the fundamental and an output that didn't track the amplitude setting.  Plus the modulation looked overdriven.  I simply took a scope and probed my way along the signal path until the waveform first looked distorted.  On the output PCA, there is a three-stage 20 dB amplifier.  The 150 ohm collector resistor on the second amplifier transistor changed value to 750 ohms.  This starved the transistor of gain and the ALC circuit tried to compensate by overdriving the hell out of the signal before it got to this amplifier.   Anyway, pretty amazing that the entire 6060B was brought to its knees by a single lousy resistor!

[TheDefpom]

I certainly enjoy a good fault finding session, but this was a bit longer to resolve than I wanted!

If I had stopped working on it as soon as I found the faulty MC10131P it would of been better, as I spent a lot of time trying to trace the 20MHz offset fault, originally thinking it was a separate problem, once I realized it was likely connected I stopped working on it until the new part arrived.