http://elecraft.85.s1.nabble.com/RS232-problems-with-KPA100-tp379774p379775.html
However, the measurements I gave you for U4 Pin 12 is correct. On My
steady 5V with the PC disconnected. Pin swings from 0 to -8V only if
should read whatever is coming from the PC. I noticed that Pin 6 is
>Hi Matt,
>
>Thanks for your quick response!
>
>Looking at the schematic on page 62 of the KPA100 manual, in the lower
>left-hand quadrant, I believe pin 12 of U4 is the input side of the TXD
>inverter that drives the RS232 interface, and should be 0 or +5v depending
>on the state of the RS232 serial signal going from the K2 to the interface.
>The AUXBUS lead comes in on the pin of P1 on the opposite side of the
>connector from the TX lead and goes to the MCU and pin 6 of J8 (the 9-pin
>RS232 connector)through RFC 9, but does not actually connect to U4. I
>believe the AUXBUS is OK because the KAT100 works just fine. I have not
>looked at U4 pin 12 with a scope to see if it varies at all, but it is
>slightly higher in voltage at 0.13v than the others, which suggests that
>it's receiving a logic zero from the K2. The output on pin 5 (T2OUT) should
>be near one of the RS232 supply voltages of either +12.54 or -5.87 (as
>measured at pins 1 and 8) but instead there's only 0.44v. It's also very
>strange that the voltages on pins 2, 4, 6 and 7 are all about the same, as
>well as pin 3 which is an anomaly -- all these pins should be at one RS232
>level or the other. That's why I'm thinking the chip may be kaput. The
>other really bad thing is that connecting the receive side from the computer
>(which works fine with other devices such as a chip programmer) drags the
>voltage on the receive line almost to zero -- this line is an input to the
>MAX chip and the input should be high-impedance and not affect the voltage
>on the line at all -- but it does. Gotta keep looking, I guess.
>
>Thanks again for your response, Matt, and I'll put a note on the reflector
>when I do find out what happened. Any suggestions always welcomed!!!
>
>73, Van W1WCg
>
>
>----- Original Message -----
>From: "Matt Osborn" <
[hidden email]>
>To: "Frank Van Cleef W1WCG" <
[hidden email]>
>Sent: Saturday, June 25, 2005 5:46 PM
>Subject: Re: [Elecraft] RS232 problems with KPA100
>
>
>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"
><
[hidden email]> 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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