Elecraft

OT - troubleshooting NIR-12

Classic

List

Threaded

9 messages Options

James Hall-2

OT - troubleshooting NIR-12

Hello:

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.

Can somebody help shed some light - voltage ? - here ?

Thanks -

73, Jamie

WB4YDL

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Don Wilhelm-3

RE: OT - troubleshooting NIR-12

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.
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

James Hall-2

RE: OT - troubleshooting NIR-12

Hi Don:

I was hoping you might lend a hand. :) OK, now this may show how much I've
forgotten but for the symbol of a diode, the 'arrow' side is cathode and
'plate' side is anode - right ? The schematic drawing of this unit
definitely shows the 'arrow' side towards the +12v source.

->|-
Cathode - anode Right ?

This would prevent reverse voltage but not forward voltage. So I should not
have seen a different voltage on the 'plate' side of the diode - if I
understand correctly.

73, Jamie
WB4YDL

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Saturday, December 31, 2005 7:32 AM
To: [hidden email]; 'Elecraft List'
Subject: RE: [Elecraft] OT - troubleshooting NIR-12

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

Ron D'Eau Claire-2

RE: OT - troubleshooting NIR-12

Jamie, WB4YDL wrote:

I was hoping you might lend a hand. :) OK, now this may show how much I've
forgotten but for the symbol of a diode, the 'arrow' side is cathode and
'plate' side is anode - right ? The schematic drawing of this unit
definitely shows the 'arrow' side towards the +12v source.

->|-
Cathode - anode Right ?

This would prevent reverse voltage but not forward voltage. So I should not
have seen a different voltage on the 'plate' side of the diode - if I
understand correctly.

----------------------------

It's just the other way around, Jamie. Arrow = anode, line = cathode.
Positive to anode and negative to cathode will produce current flow.

Ron AC7AC

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

N2EY

Re: OT - troubleshooting NIR-12

In reply to this post by James Hall-2

In a message dated 12/31/05 12:56:32 PM Eastern Standard Time,
[hidden email] writes:

> for the symbol of a diode, the 'arrow' side is cathode and
> 'plate' side is anode - right ?

Wrong!

The diode arrow points in the direction of "conventional current flow" -
which is opposite to the way the electrons flow.

The schematic drawing of this unit
>
> definitely shows the 'arrow' side towards the +12v source.
>
> ->|-
> Cathode - anode Right ?
>
>

The "conventional current" flows from the +12 into the radio's innards. But
the electrons actually go the other way.

73 de Jim, N2EY
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

James Hall-2

RE: OT - troubleshooting NIR-12

In reply to this post by Don Wilhelm-3

K3yt

Re: OT - troubleshooting NIR-12

In reply to this post by James Hall-2

easy way to remember....

A...ANODE

A...ARROW

K3YT
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Ron D'Eau Claire-2

RE: OT - troubleshooting NIR-12

In reply to this post by James Hall-2

So I should not have seen a different voltage on the 'plate' side of the
diode - if I understand correctly.

73, Jamie
WB4YDL

---------------------------------------------
Diodes have a forward voltage drop. It depends upon the material used in the
junction and how it is treated or 'doped' in manufacture. It can vary from
less than 0.2 volts to about 0.6 volts for a common silicon diode.

So if you measure 13.8 volts between the positive (anode or arrow) side of a
diode and ground, you'll see something between 13.6 and 13.2 volts between
the cathode side of the diode and ground. This drop is largely independent
of the current being drawn, within limits. It's called the "barrier voltage"
and acts as though a small battery with a voltage between 0.2 and 0.6 volts
is inside the diode, bucking the voltage applied. There's always some small
value of ohmic losses in any component too, so the drop will vary slightly
when there's a large change in the current.

Of course when you reverse the diode, current almost stops. There's some
leakage, usually in the range of a few microamperes, but it's usually
negligible. That is, until you reach the reverse breakdown voltage. At that
point an avalanche of current will occur melting the junction and turning
the diode into a resistor. So in a circuit design it's important to respect
the reverse breakdown voltage specification of a diode.

Some special types of diodes use that effect in a controlled way that avoids
damaging the junction. One common one we see all the time are
voltage-regulating "Zener" diodes. The Zener effect is just that: when
reverse-biased (positive to the cathode, or line side on the schematic and
negative to the arrow side) very little current flows until a specific
voltage is reached. Beyond that the diode begins to conduct heavily,
maintaining a fixed voltage across its junction. Such circuits always
include a current-limiting resistor. Without it, the diode would be
destroyed by the current flow. As long as the current is limited to less
than the maximum rating for the diode, the voltage across the diode will
remain close to the initial zener value. That's why they make quite good
voltage regulators.

Of course, those diodes are used with the connections reversed from normal
diodes: the cathode (straight line on the symbol) goes to the positive
voltage and the arrow goes to the negative voltage. Such diodes are shown
schematically with little extra "wings" on the straight cathode line to
indicate that they are Zener diodes.

Ron AC7AC

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Ron D'Eau Claire-2

RE: OT - troubleshooting NIR-12

You definitely SHOULD see a voltage difference (or drop) of between 0.2 and
0.6 volts, depending upon the type of diode, as long is current is passing
through it.

Ron AC7AC

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ron D'Eau Claire
Sent: Saturday, December 31, 2005 12:27 PM
To: 'Elecraft List'
Subject: RE: [Elecraft] OT - troubleshooting NIR-12

So I should not have seen a different voltage on the 'plate' side of the
diode - if I understand correctly.

73, Jamie
WB4YDL

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com