On 9/4/22 18:58, John Lyles wrote:
I was using the Hp 436A in the 1980s, and the 438A was a significant improvement, in being able to read forward and reflected power from a dual directional coupler, for example, with built in math abilities. I didn't see the 437A until the 1990s. We bought a few of them, and quickly found that they are not as reliable as their predecessors. I have scrapped more than one dead 437A while the 438A models are still going.
One problem in the 437B design is that some parts of its power supply are powered up whenever the instrument is plugged in, but the front panel power switch is "off". I've had several 437Bs, three or four, and I've had one fail because of this. The 4700uF capacitor in the 5V power supply, before the power switch, had dried out. Replacing it solved the problem.
-Dave
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Dave McGuire, AK4HZ
New Kensington, PA
Dave McGuire