[bars] When is a fuse not a fuse?

[Geoffrey Feldman]

It would be interesting to know what “The fuse” really is and what purpose it is there to serve.  Semiconductor junctions can change when stressed.

 

This brings up something which I feel is really important in electronics.   Terms such as “Resistor”, “Capacitor”, “Transistor”, “Diode” , “Inductor” are really ideals of what the thing really is.   Capacitors have inductance. Inductors have capacitance.  Transistors and diodes have capacitance.  Resistors have inductive properties. Conductors together on a board have all of the above.  We need the ideals to simplify our thinking but we need to know – there is more to it than that.  By the way, not all fuses are alike and none of the above die a natural death.

 

A favorite experiment is that LED’s actually can produce current when exposed to light.  This actually is important in developing LED lighting because light reflecting back into the LED can increase current and reduce efficiency.   The other fun thing is that LED’s are sensitive to light in a near but not exact wave length to what they produce.    A fun Arduino type project is to pulse an LED just a the margin of producing light.  This builds a charge in the junction.  The Arduino can measure this charge. The charge dissipates quicker if the LED is exposed to light near the wave length it emits.   So where are the ideals now?

 

This type of clip and measure process is one that I have used myself. Though, It can produce a poor customer response when the thing is “Fixed”.  A more patient approach of observing whether voltages make sense on a schematic is another option.

 

W1GCF

Geoff

 

From: bars [mailto:bars-bounces at w1hh.org] On Behalf Of Tim KC1RET
Sent: Monday, August 22, 2022 9:35 AM
To: BARS Reflector
Subject: [bars] When is a fuse not a fuse?

 

The saga of my 'dead' TS-2000 continues.

So after hours of deciphering schematics and finally performing a radio autopsy on my kitchen counter I was struck with this conundrum... How could the supply voltage read 13.8v at the connector, but only 5.2 where the wire connected to the main board?

At first I suspected the filter caps. They are soldered directly to the back of the connector inside the radio, dead-bug style. I cut they leads, one-by-one and they were all good & no change to the voltage reading. In a fit of desperation, I checked continuity between the board and the back of the PS; + was good, GND, not-so-much. Huh?? It was measuring 2.5k ohm! I disconnected the PS lead from the radio, 2.5k between the PS lead connector and PS terminal. Ah HA! (he says - well, I really said something else quite a bit more expressive but I'll leave the specifics to your imagination) I pulled the inline fuse out - Yup, it read not open, not short, but 2.5k. I replace the fuse and the rig fired right up!

So, when is a fuse not a fuse? When it is a resistor!

That is a new experience for me -- I'm def. NOT going to forget it.

73,

T.



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