Hello EEVBlog Forum,
New member, getting more into EE and purchased a Tektronix 465B. Everything seems to function normally, but there is a noticeable amount of ripple on the display and it isn't quite as sharp as others I've seen on the forum and on YouTube. Thinking of Dave, I decided to Take It Apart and test the power lines and run through the calibration routine in the service manual.
The good news is the +55V, +15V, +5V, and -8V are all perfect and clean. The 110V line, however, reads with my Fluke meter as 101.6V, well out of tolerance (manual says 106.7 to 113.3). I borrowed the Rigol DS1054Z from work this weekend and took some readings and discovered that there are some huge dips in the 110V rail. See attached screenshot taken at test point TP4340, where you see 40V drops, so the 109V max becomes 102V RMS (at least that's how I read the Rigol output).
Can anyone tell me if the unregulated 110V supply is supposed to be fully rectified before it reaches the Q4425 Regulator ? Mine definitely is not.
Looking at the Block diagram on page 3-26 of the service manual I checked the incoming voltage at the diode CR4431, and that is 129V RMS with a huge ripple, then at the Base, Collector, and Emitter of Q4425 everything reads 102V RMS (the same as at the test point).
The block diagram doesn't show the 110V line going through a Rectifier--so I wasn't sure what to expect at this point in the circuit.
I'd love to clean this bit up since everything else seems to be functioning well.
thanks for your help,
-kai