[SMCARA] Trouble Shooting Help

[Tom Shelton]

Hi All – I need some help from the technically minded...

Many years ago I was re-arranging my shack.  I had an ASTRON RD-35A power supply that I was moving around.  My bad – it was still turned on and I set it down on top of a screwdriver which promptly shorted the rectifier diodes (Motorola 1N1184A) to ground.  I went to my back-up power supply and set the RS-35A aside for later repair.

Well, 12-15 years later (today) I finally got around to checking it out.  I unsoldered and removed the two 1N1184A’s and checked them with a cheap Radio-Shack multimeter.  I set the meter on the ohms setting (2Mohms range) and here’s what I saw.

The first diode I checked showed 1.2 Mohms forward and an open reverse.  The second diode looked like a capacitor, as in the forward direction the multimeter gave an initial reading of around 1.2 Mohms, then quickly increased in resistance until it maxed out the meter.  When I reversed the leads, I saw a discharge, evidenced by a short circuit followed by an open...

I expected a bad diode to to show open in both directions.  I also expected a good diode to show something better than 1.2 Mohms.  Is this normal?  I fully expect to have to replace both of these diodes (about $7.00 each), but want to be sure – and also see if there is something else I need to check.

Your help is greatly appreciated.

Tom Shelton 

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