Posted by
Don Wilhelm-3 on
Jun 26, 2005; 2:19am
URL: http://elecraft.85.s1.nabble.com/RS232-problems-with-KPA100-tp379774p379781.html
Frank,
Can you make a comparison of the voltage on U4 pin 8 with what you had at
some time previous. All other voltages except that one seem in order with
no computer connected. The only pins used on the chip are 1, 5, 6, 8, 11,
12, and 16. Pins 9 10 and 14 are grounded, but the rest are floating.
You may be correct that the negative supply is being dragged down, but I
know of no way to confirm that except by removing U4. Yes, the reduced
negative supply voltage should be resolved because that will cause improper
T/R switch operation at higher power levels. The KPA100 should function
normally with U4 removed (except that you will have no computer interface
function).
Your assumption that U4 may be toast may indeed turn out to be correct, but
I really can't tell from the info I have right now.
I did see another note on the reflector indicating that you may want to look
at the AUXBUS line - that signal does not appear on U4 and is not a part of
the RS-232 function. If you hear relays click in the KPA100, the AUXBUS is
working.
73,
Don W3FPR
> -----Original Message-----
>
> 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???
>
>
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