[SMCARA] Trouble Shooting Help

[Tom Clarke]

Hi Tom,

Mouser Electronics has them for $4.78 each, no minimum order. I lost the 
diodes in an Astron 20 to a lightning strike. Easy fix.
Any big surge can blow the diode junction and give all sorts of strange 
readings! If that doesn't fix it, the pass transistors
(usually 2N3771 or similar) may have gone also.

73 Tom/W4OKW





On 5/13/2011 6:06 PM, Tom Shelton wrote:
> 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
>
> No electrons were harmed in the sending of this message, although several were terribly inconvenienced.
> Draco Dormiens Nunquam Titillandus
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