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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