Morion MV89A Oscillator Repair

While testing three Morion MV89A oscillators I got from eBay, I found that one of them had a weak output

After carefully opening the case with a small propane torch, it did not take long to find the problem while tracing the output circuit. The very first component found, a capacitor, was blocking the signal. The value not being critical, I replaced it with a new 10nF one. Not surprisingly, the expected 7dBm output appeared. Although not needed, I couldn’t resist opening also the inner shell:

There are six posts connecting and holding the PCB inside the inner shell on top of the main PCB. There are a few thick traces and four posts soldered, appart from five connections in the center that go probably to the actual oscillator. It would have been very interesting to see behind that smaller PCB, but I did not want to take the risk.

Unwanted Signals

I noticed the oscillators had different uwanted signals around the main 10Mhz. The strongest are around 50dB lower than the 10Mhz signal so not a problem, but I expected all oscillators to show similar spectra. The first plot is from the one that had the capacitor replaced: