Re: LED Tuning light

Gary DeBock

Hi Brian and Kevin,

An LED that it not lighting (when it should) usually has two possible
causes-- either the LED itself is burned out, or the active device
(diode or transistor) driving the LED circuit has failed. Usually a
technican would use a voltmeter to determine whether or not the LED
input circuit has a positive voltage (to ground) when the LED should be
lighting. If there is the normal positive voltage, the LED itself is
probably bad. If the voltage on the input circuit is missing at all
times, most likely the diode or transistor (or sometimes IC) driving
the circuit has probably failed. You will need to locate these
components on your schematic diagram, Brian, then check for that LED
input voltage (either on the circuit board, or LED input pin).

73, Gary

-----Original Message-----
From: dhsatyadhana <dhsatyadhana@...>
To: ultralightdx <ultralightdx@...>
Sent: Sun, Mar 27, 2011 5:48 pm
Subject: [ultralightdx] Re: LED Tuning light

Hi Brian:

Alas, all I can give is qualitative suggestions - I am probably about
as handy with true tech work as you are, so wouldn't feel comfortable
going any further. Anyone else???


--- In ultralightdx@..., "Jerry"
<brianalexmiller@...> wrote:

Hi Kevin -

Thanks for the reply.

I am so green on radio surgery that I'm not even quite sure what
the "trace" is. The wires coming from the pcb to the led?

What do I test with?

I have the service manual for the radio. I had to get it to figure
out how exactly to route the tuning dial string. I was amazed I was
able to actually do it after a few tries.

I've looked at the manual for awhile and can't figure the
indicator light out from looking at the schematic, but again, I am far
from a technician.

I guess what might help me most is if you or someone could tell me
the general concept behind what causes the indicator to light, where it
usually would connect to.....

anyway -
&gt; Thanks again

--- In ultralightdx@..., "dhsatyadhana"
<dhsatyadhana@> wrote:

Hi Brian:

Have you tried testing the LED itself? Not sure if these
burn out.

Disconnecting the trace to the LED (to test the LED) would
allow you to test if there is voltage coming to the LED as well?
&gt; >
Kevin S

--- In ultralightdx@..., "Jerry"
<brianalexmiller@> wrote:
&gt; I know this is the ultralight DX board, but it is the
most active DX message board I know of so maybe someone can answer me
even though this is not about ULR's.

My question is about a red LED tuning light on a
portable Sony analog AM/FM radio - TFM-7250W.
I got the thing at a garage sale last year for five
bucks and I took it apart to clean it and to retro-fit it with an 18"
outboard ferrite antenna.

Everything is working great except for I cannot get the
little red tuning led to light anymore.
&gt; >
All of the connections look good to me but obviously I'm
missing something.

I guess my question is if anyone knows where that kind
of a connection would be made generally.


Brian Miller

Berkley, MI
&gt; USA

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