Re: K3 - FSK in not working - KIO3 boards

[HP]

R2 is open and is blackened like it has been over dissipated . Now the $64,000 question is how can one over dissipate a 220 ohm resistor fed from 5 volts thru 10K ohms ???

Even if there was no resistor fed from 5 v it would be a tad under 1/8 watt - which is probably on the edge for a 0508 SMD chip resistor .  R98 on the RF board feeding P35 is in fact 9980 ohms and the runner to P35 is Ok. The other end of R98 shows 4.97 volts from  U12 so the 5V  regulator is OK .  There are 1000 pfd caps to ground from the 15 pin ACC connector before the 220 ohm resistor so unlikely RF could have done it plus I have a 2.4 inch #31 core with 14 T right at the connector before it runs to the N1MM FSK keying box with the standard open collector NPN to FSK in.

So its beyond me - off to   FRY's Electronics to  see if they have 0508 220 ohm strips hanging on a nail .

Welcome any ideas .  Maybe same  gremlin that blew a 1N4007 D35  reverse spike diode  on the 12 ACC jack with the P3 only thing ever on it , two weeks after I fired  up the K3

73 Hank K7HP



  Thanks -- I pulled it out and there they are -- 73 Hank K7HP



  The voltage on the FSD in line is "floating" at about 3.2 volts and even finger leakage pulls it down so its from a very high sourfce impedance and does niot key the FSk.

    I have tracked from J23 ACC connector  to P90/J90 on the KIO3 Dsub RS232 IO board  the  PTT in , KEY out , AUX and all are the nominal 220 ohms shown on the schematic . Pin 16 FSK in is about  6 megohms. This would indicate that R2   220 ohms is open or something along that line is open .

    My question is where the  heck is R2 ? Or maybe more to the point - Is R2 on the back side of the horizontal board marked  "KIO3 Remote I/O Module "  with J23 (15 pin) and J24 (9 pin RS232) that then plugs into J90 on the KIO3 vertical Main board ?

    I hate to pull all that apart and find its somewhere else ?? Of course it could be a lousy solder joint somewhere in the run (incidentally the 5v is solid at pin 20 J90 and at pin 3 of J35/P35 on the RF board.

    Thanks -  if I don't hear anything guess it will be tear it apart and see !

    Hank K7HP
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[Don Wilhelm-4]

Hank,

You might want to check the output of that NPN transistor circuit before
you connect it to the K3 FSK input again.
If there is a base to collector short, it could put the full RS-232
level on the FSK input pin, and that is quite likely to fry something in
the K3 (like that 220 ohm resistor).
That NPN transistor should show open circuit during non-keyed times and
show as a short when it is turned on by the RS-232 signal line. It
should never show any voltage at all in either state.

The base K3 circuits are protected with a series reverse polarity
protection diode (the KPA3 does not because of the diode voltage drop).  
However, if the FSK Keying box were connected and powered at the same
time as the reverse polarity event, there could have been some strange
current flow between the K3 FSK input pin and the FSK box.  The full
circuit would have to be analyzed to know the answer for certain.

73,
Don W3FPR

On 4/19/2014 3:58 PM, Pfizenmayer wrote:
> R2 is open and is blackened like it has been over dissipated . Now the $64,000 question is how can one over dissipate a 220 ohm resistor fed from 5 volts thru 10K ohms ???
>
> Even if there was no resistor fed from 5 v it would be a tad under 1/8 watt - which is probably on the edge for a 0508 SMD chip resistor .  R98 on the RF board feeding P35 is in fact 9980 ohms and the runner to P35 is Ok. The other end of R98 shows 4.97 volts from  U12 so the 5V  regulator is OK .  There are 1000 pfd caps to ground from the 15 pin ACC connector before the 220 ohm resistor so unlikely RF could have done it plus I have a 2.4 inch #31 core with 14 T right at the connector before it runs to the N1MM FSK keying box with the standard open collector NPN to FSK in.
>

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