[Elecraft] RS232 problems with KPA100

[Matt Osborn]

The high voltage bias supply on the KIO2 is between -6v to -12, so
your 19.4 is probably sufficient, but the KIO2 Vss, U4 pin 8 is -9v on
my KIO2. The MAX1406 wants from -13.2 to -10.8, but the absolute max
ratings are from +0.3 to -14.0, so you're probably OK with the -5.87.

The real suspect is that U4 pin 12 should be reading +5V from the
AUXBUS on the control board.  The only other use of AUXBUS on the
KPA100 is U1 pin 28 (RB7 Serial Programming Data).

It would be worth checking out AUXBUX line for a short (C25) or an
open P1 pin 1.

On Sat, 25 Jun 2005 16:06:46 -0400, "Frank Van Cleef W1WCG"
<w1wcg at snet.net> wrote:

>Greetings, all you I/O experts out there -- I need some advice, please....
>
>I'm using K2 #2634 with a  KPA100 and KAT100; therefore the RS232 I/O is done by the MAX1406 chip on the KPA100.  I've done computer control in the past but not for some months, so today I was rather surprised when I went to try out a new CAT program and could not get it to control or read out from the K2/KPA100.  A breakout box showed no signal coming from the KPA100, and the TXD line from the computer indicated signals until I connected the KPA100; then the line seemed to be dragged down almost to 0v by the KPA100.
>
>After verifying continuity between the computer end of the RS232 cable and the RF chokes on the KPA100 board (RFC6, RFC7) I meaured voltages on the MAX1406 chip.  Except for the 5 and 12v supply voltages they were not what the chart in the manual described.  The pin voltages on the MAX1406/U4 chip were:
>
>    1 -    +12.54         2 -    -0.43              3 -   -0.03            4 -    -0.43
>    5 -    -0.44            6 -    0.44               7 -   -0.44            8 -    -5.87
>    9 -    0.00            10 -   0.00              11-    0.10           12 -    -0.13
>  13 -    -0.09          14 -   0.00              15-   -0.09           16 -    4.96
>
>The voltage on pin 8 (-5.87) is at the very low end of the expected -5 to -25v range shown on the schematic, and even the +30v on the HV bias supply is low at 19.54v --almost as though whatever is wrong in the chip is dragging
>down the -25v and and the rest of the HV bias.
>
>Resistance on the TXD/RXD leads at the chip is about 100 ohms to ground with the power removed.
>All measurements made with a FLUKE 87 DMM.
>
>I don't know how but I'm afraid I've somehow crisped the MAX1406. Is there anything else I should try before replacing the chip???
>
>TIA, all
>
>Van, W1WCG
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