[Elecraft] RS232 problems with KPA100

[Jack Brindle]

On second look...

On Jun 25, 2005, at 1:06 PM, Frank Van Cleef W1WCG wrote:

> 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


Pins 3, 5 and 7 of the MAX1406 are RS232 Tx Outputs. They should  
either be at a level above +3 volts, or below -3 volts. More  
specifically, the inputs for T1 and T3 are at ground, meaning that  
the outputs should be at the +12V rail. The measured voltages are NOT  
valid for a properly working circuit. I bet the chip is getting  
pretty hot, or has already disconnected itself (internally) from the  
pertinent supply.

On another note, removing C38 should cause the amplifier to return to  
its normal operating voltages except for the RS-232 circuit. Now the  
question is that if indeed the MAX1406 is bad, how did it happen?

-Jack Brindle, W6FB
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