[Elecraft] OT - troubleshooting NIR-12

[Don Wilhelm]

Jamie,

If the diode is in series with the power line (as a reverse voltage
protection diode), and if the unit is being fed with a positive voltage, the
anode lead should be connected toward the +12 volt supply side.  Since you
said there was voltage on the cathode but none on the anode, it would seem
to me that the diode may be installed backwards - and that would produce the
result you are observing.

73,
Don W3FPR

> -----Original Message-----
>
> I know this has nothing to do with Elecraft gear, but having built the 3
> radios, I knew this is the place to come for experienced
> troubleshooters. I
> have an old JPS NIR-12 DSP unit, that, after applying power, decided to
> quit. The power lamp will not now light. This unit does not have
> a fuse. So
> I decided to get out the DVM and attempt to see what's going on.
>
>
>
> The DC power jack goes to a T-network consisting of two 0.1 uf caps with a
> bead inductor before going to a DPDT switch. Beyond this is a 0.1
> uf cap in
> parallel to ground and then a series 1N4004 rectifier diode to a 1000 uf
> electrolytic capacitor in parallel to ground. From there it branches to a
> couple of  voltage regulators to get different voltages. When voltage is
> applied, I get 13.7 volts on the cathode side of the diode, but
> zero on the
> anode side (and beyond). I initially thought that this diode was at fault
> and desoldered it and replaced it with another 1N4004. But, alas, this was
> not the culprit. I desoldered the 1000uf electrolytic, but my capacitance
> meter reads it correctly at 1000uf.
>