KPA100 Problem still exists, but some new measurements

[GS-3]

Hi there,

I'm still on page 43 in the process and I have now narrowed the problem area. You remember, I measured a negative voltage of 0.15V on J3+.

Now: I removed Z1 and found the voltage measured at the collectors of Qs 1 and 2 to be -0.4V (J3+ is ok now). I don't know where it could come from. Shorting the collectors to ground via 1k resistor it takes 3 seconds to eliminate the voltage. I measure 0V. Removing the resistor it takes abt. 20 seconds for the voltage to go to -0.4V again.

T2-4,5 are ok. The base of the transistors are ok, 0V. The emitters also, 0V. The body of T2 also has -0.4V.

Any idea and testing procedures appreciated!

Kind regards


Gerhard Schwanz
DH3FAW
mailto:[hidden email]
http://www.gs-personal.de


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[Don Wilhelm-3]

Gerhard,

That small negative voltage may be coming from the AC ripple on the '90-150
V' supply to the TR switch that is being coupled through the RF chokes and
capacitors into the Q1 and Q2 collector circuit and then being rectified by
the transistors themselves.  If that is the case, it may not be a problem at
all once you connect a +12 volt supply.

Put an RF probe on the cathode of D13 and see how much RF voltage is present
there (it would be at the approximate frequency of X1).

73,
Don W3FPR

> -----Original Message-----
>
>
> Hi there,
>
> I'm still on page 43 in the process and I have now narrowed the
> problem area. You remember, I measured a negative voltage of 0.15V on J3+.
>
> Now: I removed Z1 and found the voltage measured at the
> collectors of Qs 1 and 2 to be -0.4V (J3+ is ok now). I don't
> know where it could come from. Shorting the collectors to ground
> via 1k resistor it takes 3 seconds to eliminate the voltage. I
> measure 0V. Removing the resistor it takes abt. 20 seconds for
> the voltage to go to -0.4V again.
>
> T2-4,5 are ok. The base of the transistors are ok, 0V. The
> emitters also, 0V. The body of T2 also has -0.4V.
>
> Any idea and testing procedures appreciated!
>

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[Mike Harris-9]

G'day,

Did you have a light shining on the PA transistors?  J3+ on my KPA100
had -0.18V.  Apparently something to do with illumination of the PA's.
Well noted by others.

Regards,

Mike VP8NO

----- Original Message -----
From: "Gerhard Schwanz" <[hidden email]>
To: <[hidden email]>
Sent: Friday, February 04, 2005 10:42 AM
Subject: [Elecraft] KPA100 Problem still exists, but some new measurements


Hi there,

I'm still on page 43 in the process and I have now narrowed the problem
area. You remember, I measured a negative voltage of 0.15V on J3+.

Now: I removed Z1 and found the voltage measured at the collectors of Qs 1
and 2 to be -0.4V (J3+ is ok now). I don't know where it could come from.
Shorting the collectors to ground via 1k resistor it takes 3 seconds to
eliminate the voltage. I measure 0V. Removing the resistor it takes abt.
20 seconds for the voltage to go to -0.4V again.

T2-4,5 are ok. The base of the transistors are ok, 0V. The emitters also,
0V. The body of T2 also has -0.4V.

Any idea and testing procedures appreciated!

Kind regards


Gerhard Schwanz
DH3FAW
mailto:[hidden email]
http://www.gs-personal.de


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[Ward Willats-3]

>Now: I removed Z1 and found the voltage measured at the collectors
>of Qs 1 and 2 to be -0.4V (J3+ is ok now). I don't know where it
>could come from.


Hi Gerhard:

Dunno if this is related, but I got a small voltage J3 by shining a
bright light on the final transistors. There is some sort of
photoelectric effect.

Your numbers are close to what I measured then:

http://www.ac6rm.net/mailarchive/html/elecraft-list/2003-11/msg00574.html


-- Ward


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[GS-3]

Well, um, yes.

And I noticed another thing which led me think everything is fine. The
voltage was there, even without power connected to the K2 at all.

All is well now, I neglected the voltage. I will go on air tomorrow for on
air tests. RS232 test is next now, then shield and final assembly.

And thanks to all who helped!!!


Gerhard Schwanz
DH3FAW
mailto:[hidden email]
http://www.gs-personal.de


----- Original Message -----
From: "Mike Harris" <[hidden email]>
To: "Gerhard Schwanz" <[hidden email]>; <>
Sent: Friday, February 04, 2005 5:14 PM
Subject: Re: [Elecraft] KPA100 Problem still exists, but some new
measurements

> G'day,
>
> Did you have a light shining on the PA transistors?  J3+ on my KPA100
> had -0.18V.  Apparently something to do with illumination of the PA's.
> Well noted by others.
>
> Regards,
>
> Mike VP8NO
>
> ----- Original Message -----
> From: "Gerhard Schwanz" <[hidden email]>
> To: <[hidden email]>
> Sent: Friday, February 04, 2005 10:42 AM
> Subject: [Elecraft] KPA100 Problem still exists, but some new measurements
>
>
> Hi there,
>
> I'm still on page 43 in the process and I have now narrowed the problem
> area. You remember, I measured a negative voltage of 0.15V on J3+.
>
> Now: I removed Z1 and found the voltage measured at the collectors of Qs 1
> and 2 to be -0.4V (J3+ is ok now). I don't know where it could come from.
> Shorting the collectors to ground via 1k resistor it takes 3 seconds to
> eliminate the voltage. I measure 0V. Removing the resistor it takes abt.
> 20 seconds for the voltage to go to -0.4V again.
>
> T2-4,5 are ok. The base of the transistors are ok, 0V. The emitters also,
> 0V. The body of T2 also has -0.4V.
>
> Any idea and testing procedures appreciated!
>
> Kind regards
>
>
> Gerhard Schwanz
> DH3FAW
> mailto:[hidden email]
> http://www.gs-personal.de
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft
>
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> Elecraft web page: http://www.elecraft.com
>

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