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KPA100 voltage measurements?

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CTMorton

KPA100 voltage measurements?

Hello All,

Am on page 23; KPA100 test points and have two problems:

U5 Pin 1 should be 0 to 0.1; I get 2.4

U6 Pin6 should be 0 to 0.5; I get 28v!

Any ideas or where to look? All other measurements were either right on or
within the +/- 10%.

73

Tom

K6CT

"Once one has reached the point of no return--Reality then begins".

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Don Wilhelm-2

Re: KPA100 voltage measurements?

Tom,

I have not yet seen a reply on the reflector to your questions, so I will
try to give you some information.

The voltage at U5 pin 1 will depend on the reflected voltage sensed by D17
and the setting of R27 - if you are measuring the voltage under transmit
conditions, do you have a good dummy load connected? Pickup on an antenna
wire connected to the output MIGHT do strange things during receive periods
too. You should have the same voltage on U5 pin 1 and pin 3 because U5A is
a unity gain op amp. If the voltage on pin 1 is much different than the
voltage on pin 3 the problem will be found after the op amp U5A, but if they
are the same, the problem is in the SWR bridge or its adjustments.

I am at a loss to explain 28 volts on U6 pin 6 - that is another op amp and
it is powered from a 5 volt supply, so the pin 6 voltage will never be
brought higher than 5 volts by anything in U6 itself. A regular RS232
computer cable plugged into the KPA100 and connected to a computer might
cause that kind of voltage - DO NOT USE A REGULAR COMPUTER SERIAL CABLE -
BAD THINGS WILL HAPPEN. Check for something tied into the VRFDET line
somewhere in the base K2 or on the KPA100 board's AUX IO umbilical cord
and/or the DB-9 connector. Follow the PC board traces from U6 pin 6 to the
connection with the cable and the DB-9 connector for a short to an adjacent
trace or solder pad.

That is all I can tell you with the info I have right now.

73,
Don W3FPR

----- Original Message -----

>
> Am on page 23; KPA100 test points and have two problems:
>
> U5 Pin 1 should be 0 to 0.1; I get 2.4
>
> U6 Pin6 should be 0 to 0.5; I get 28v!
>
> Any ideas or where to look? All other measurements were either right on or
> within the +/- 10%.
>

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CTMorton

RE: KPA100 voltage measurements?

Don,
Yours has been the only reply though I did talk to Richard at Elecraft. The
setup for the test is no antenna, no xmit, no other cables connected other
than the 4 inch cable from K2 P4 to KPA 100 P1. I reheated the offending
pins and double checked the components in that circuit for good soldering,
no bridges and correct values on resistors and caps. I just rechecked and
nothing has changed, i.e., U5 pin 1 @2.4v and U6 pin6 at 28v...I followed
the schematic thru the VRFDET and found that J8 (aux I/O) pin 7 has 28v as
does P1 (to Ctrl Board) pin 10 has 28v.
Any suggestions?
73
Tom

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Wednesday, July 21, 2004 3:02 PM
To: [hidden email]; Elecraft
Subject: Re: [Elecraft] KPA100 voltage measurements?

Tom,

I have not yet seen a reply on the reflector to your questions, so I will
try to give you some information.

The voltage at U5 pin 1 will depend on the reflected voltage sensed by D17
and the setting of R27 - if you are measuring the voltage under transmit
conditions, do you have a good dummy load connected? Pickup on an antenna
wire connected to the output MIGHT do strange things during receive periods
too. You should have the same voltage on U5 pin 1 and pin 3 because U5A is
a unity gain op amp. If the voltage on pin 1 is much different than the
voltage on pin 3 the problem will be found after the op amp U5A, but if they
are the same, the problem is in the SWR bridge or its adjustments.

I am at a loss to explain 28 volts on U6 pin 6 - that is another op amp and
it is powered from a 5 volt supply, so the pin 6 voltage will never be
brought higher than 5 volts by anything in U6 itself. A regular RS232
computer cable plugged into the KPA100 and connected to a computer might
cause that kind of voltage - DO NOT USE A REGULAR COMPUTER SERIAL CABLE -
BAD THINGS WILL HAPPEN. Check for something tied into the VRFDET line
somewhere in the base K2 or on the KPA100 board's AUX IO umbilical cord
and/or the DB-9 connector. Follow the PC board traces from U6 pin 6 to the
connection with the cable and the DB-9 connector for a short to an adjacent
trace or solder pad.

That is all I can tell you with the info I have right now.

73,
Don W3FPR

----- Original Message -----

Kurt Cramer

RE: KPA100 voltage measurements?

In reply to this post by CTMorton

Tom,

With the amp disconected from the control board J4, what is on J8 pin 7?
That's with both the K2 and the Amp powered.

73, Kurt

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