Electronics > Repair
Wavetek 2520a 0.2-2,200MHz RF sig gen repair
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hAudi:
Thanks for the info on the NVRAM.  It is helpful to know about Test 20.  This blog series should be helpful for anyone else wanting to get their 2520A back in operation.

I had another failure yesterday that threw me for a loop.  The gen would not output below 137.5MHz which uses the 500MHz VCO which is in the aluminium enclosure to the right as viewed with the top lid removed.  Upon opening the module, the VCO is in the small section of the enclosure.  Probing the VCO stripline with my sniffer probe there was no 500MHz output with the SG set to 100MHz.  The screen also read unleveled and unlocked.  After studying the schematic I figured out the feed through pins that lead into the smaller 500MHz VCO section.  There is a 595 serial to parallel shift register on the main top side board that controls the band switching.  That voltage toggled from 0 to 2v as the frequency went back and forth through the 137.5MHz point so the micro was flipping the 595 as expected.  I was perplexed why the voltage high was not 5v as expected so I flipped the machine over and probed the 595 chip VCC pin only to find it measured 2v also.  It turned out the problem was the 5v regulator that I replaced earlier in the week (pulled from my old junk box stash) failed early.  I replaced that reg again and all was well again with the SG.  I usually use parts that I got from Digikey or Mouser however hamfest cheap finds also populate my junk box.

I'm going to let the machine run for a few days to be sure it is finally stable.  It is a PITA to remove all of the screws to pull the bottom covers.
The self test and self calibration was a big selling point for the generator.  That and the spin knob were important to me. Test 18 ran quickly and passed.  I plan on feeding all of my equipment with a Trimble cell site pulled GPS standard 10MHz reference when I get around to adapting and old Grass Valley video DA for multiple outputs.
dazz1:
Hi
Glad it is all working.
I got good at removing the screws, pcbs etc.   These SGs have that hand made look and feel about them. 
For anyone else fault finding this make/model SG, get the manuals.  I would rate them as essential items.

There are two things I like about 80's/90's vintage test gear.  I can fix them and they are old enough to retain their value.  If I buy a new item of test equipment, it loses at least 50% value before I switch it on.  When it is superseded by the next model, the value depreciates even further.    The depreciation is offset by the capability provided by modern test gear, and the benefit to cost ratio of modern gear is astonishing.  So not knocking modern test gear at all.

I have considered GPSDO but it is not required for my use cases. The inbuilt oven oscillator is good enough for me.
These days I only buy test gear if it adds capability that I know I will use.
Buying an SG added significant capability that I didn't have.  A GPSDO does not add capability that I would use.  It is a personal thing and there is no right answer for everyone. 

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