KIO2 Malfunction

[KT4G]

Hello all,

I'm having problems with my KIO2.  The unit was functioning normally until recently, then suddenly failed to connect to my PC.

I pulled the unit, set the rig to the settings recommended in the manual, and measured the following voltages:

U1: All voltages within normal range EXCEPT:
Pin 5   -0.03 (-8.0 is normal)
Pin 8   -3.4 (-9.0 is normal)

J1: All voltages within normal range EXCEPT:
Pin 2   -0.02 (-8.0 is normal)
Pin 4   6.0 (4.5 is normal)

J2: All voltages within normal range EXCEPT:
Pin 7   6.0 (4.5 is normal)

Diodes:
D1A   -3.3 (-9.0 is normal)
D1C   0.0 (0.1 is normal)
D2A   -3.3 (-4.0 is normal)
D2C   -1.9 (0.1 is normal)
D2A   -1.9 (-4.0 is normal)
D2C   0.0 (0.0 is normal)

Oscillator is normal.

I highly suspect U1 (MAX1406) is the culprit, since I'm getting the proper voltages from U2 and Q1.  I just want to make sure that it failed on its own and not due to the failure of another component.  Is there somebody out there who could possibly shed some more light on the issue before I risk smoking another '1406?

BTW, I'm running the KIO2 through a USB-RS232 converter.

Thanks in advance,
Larry KT4G (K2 4431)  

[Don Wilhelm-4]

Larry,

First remove any connector from the DB9 that may be plugged in and
re-check the voltage at U1 pin 8.

You should not assume that U1 is the culprit (but it may be).  Even
though the DC voltages at Q1 may be OK, it could be producing less
oscillation than normal because of a faulty crystal or a faulty Q1.  D4
could be leaky which would cause the RF voltage level to be less than
normal. (the only function this oscillator has is to provide an RF
source that can be rectified for the negative voltage).

You could be correct that U1 is to blame, and if you have good
desoldering tools, the best check is to remove it and see if the voltage
at D1 anode increases significantly.

If you decide to replace U1 anyway, even by cutting its pins, do check
the voltage at D1 anode before putting the chip back in.
In the KIO2, about the only source of damage to the MAX1406 chip comes
from outside the K2 - you might be wise to check your adapter before
plugging in a computer connection.

73,
Don W3FPR

KT4G wrote:

> Hello all,
>
> I'm having problems with my KIO2.  The unit was functioning normally until
> recently, then suddenly failed to connect to my PC.
>
> I pulled the unit, set the rig to the settings recommended in the manual,
> and measured the following voltages:
>
> U1: All voltages within normal range EXCEPT:
> Pin 5   -0.03 (-8.0 is normal)
> Pin 8   -3.4 (-9.0 is normal)
>
> J1: All voltages within normal range EXCEPT:
> Pin 2   -0.02 (-8.0 is normal)
> Pin 4   6.0 (4.5 is normal)
>
> J2: All voltages within normal range EXCEPT:
> Pin 7   6.0 (4.5 is normal)
>
> Diodes:
> D1A   -3.3 (-9.0 is normal)
> D1C   0.0 (0.1 is normal)
> D2A   -3.3 (-4.0 is normal)
> D2C   -1.9 (0.1 is normal)
> D2A   -1.9 (-4.0 is normal)
> D2C   0.0 (0.0 is normal)
>
> Oscillator is normal.
>
> I highly suspect U1 (MAX1406) is the culprit, since I'm getting the proper
> voltages from U2 and Q1.  
>

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[KT4G]

Hello Don,

Thanks for the insight.  I checked D4 and it seemed to be ok.  I went ahead and removed U1 and the voltage on the D1 anode rose from -3.3 to -11.5!  U1 must be bad.  The only question is what made it that way?

I'm going to order a couple of 1406's from Mouser and see if that indeed fixes the problem.  If the original chip suffered from a latent defect (in other words, was the proverbial "time bomb" waiting to go off), then I should be ok.  If the failure was due to another faulty component then at least I've got a spare...

Anything else I should look for before I proceed?

Thanks again!

Larry, KT4G
 

[Don Wilhelm-4]

Larry,

Other than that negative voltage supply, the 5 volt regulator, and the
12 volt line, there is just not other places to look for a problem.  The
MAX1406 just handles two RS-232 signals in this application, TXD and
RXD, so there is nothing on the board to stress the chip.

73,
Don W3FPR

KT4G wrote:

> Hello Don,
>
> Thanks for the insight.  I checked D4 and it seemed to be ok.  I went ahead
> and removed U1 and the voltage on the D1 anode rose from -3.3 to -11.5!  U1
> must be bad.  The only question is what made it that way?
>
> I'm going to order a couple of 1406's from Mouser and see if that indeed
> fixes the problem.  If the original chip suffered from a latent defect (in
> other words, was the proverbial "time bomb" waiting to go off), then I
> should be ok.  If the failure was due to another faulty component then at
> least I've got a spare...
>  
>

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[KT4G]

Don,

That's indeed good to know.  I went ahead and cut the pins to the original 1406 so I wouldn't screw up the PC board.  The 1406's are on order now.  I'll let you know how it goes when they get here.

Thanks again!

Larry KT4G


<quote author="Don Wilhelm-4">
Larry,

Other than that negative voltage supply, the 5 volt regulator, and the
12 volt line, there is just not other places to look for a problem.  The
MAX1406 just handles two RS-232 signals in this application, TXD and
RXD, so there is nothing on the board to stress the chip.

73,
Don W3FPR