K2: Power control KPA100/KAT100 - have I fried the EL5146C?

[Sverre Holm (LA3ZA)]

My KPA100/KAT100 is located 5-6 meters away from the K2 and I am afraid I have gotten RF into the VRFDET line and fried the output buffers on both of them. The Power display on the K2 does not reach full value especially on 15, 12, 10 meters. In  this setup I think it is the voltage from the KPA100 that controls the K2's power output.

When I measure the KAT100 without the KPA100 (easier to measure than the KPA100) I have the following input/output relationship on  the VRFDET amplifier, U2,  at 7 MHz:

0.5 W: in 0.5V out 0.85 V
1 W: in 0.77 V out 1.2 V
5W: in 2.0 V out 2.2 V
10W: in 2.4 V out 2.3 V

As the amplifier is supposed to have a voltage gain of 2 I think this is suspect, so have I fried the EL5146C (probably on both the KPA100 and the KAT100)?


Sverre
LA3ZA


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[Don Wilhelm-4]

Sverre,

It sounds like you are working in the right area, but something seems
inconsistent to me.
Before concluding that the EL5146C is defective, check for something
else (in the base K2) that may be loading down the VRFDET line.  The
KAT2 and K60XV as well as D9 and its associated voltage divider
resistors on the K2 RF board can drag down that line.

If you have the KAT2 installed, try changing its R6 value to 470 ohms as
a first step.
If the K60XV is installed, be certain that its VRFDET output is NOT
being enabled when the KAT100 is installed and the low power output is
not being used.
Check RF board D9 to be certain it has not been damaged.

The reason for these thoughts - the input vs. output voltages for an op
amp should have close to the same ratio, even if that ratio is
incorrect.  Your ratios vary all over the place which causes me to think
that the op amp may be OK.  I may be proven wrong, but I believe it is
easier to make some other checks before going to the trouble of changing
the suspect component only to find that the problem is still present.

73,
Don W3FPR

Sverre Holm wrote:

> My KPA100/KAT100 is located 5-6 meters away from the K2 and I am afraid I have gotten RF into the VRFDET line and fried the output buffers on both of them. The Power display on the K2 does not reach full value especially on 15, 12, 10 meters. In  this setup I think it is the voltage from the KPA100 that controls the K2's power output.
>
> When I measure the KAT100 without the KPA100 (easier to measure than the KPA100) I have the following input/output relationship on  the VRFDET amplifier, U2,  at 7 MHz:
>
> 0.5 W: in 0.5V out 0.85 V
> 1 W: in 0.77 V out 1.2 V
> 5W: in 2.0 V out 2.2 V
> 10W: in 2.4 V out 2.3 V
>
> As the amplifier is supposed to have a voltage gain of 2 I think this is suspect, so have I fried the EL5146C (probably on both the KPA100 and the KAT100)?
>
>
> Sverre
> LA3ZA
>
>  
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[Sverre Holm (LA3ZA)]

Thanks Don for the tips:

> If you have the KAT2 installed, try changing its R6 value to 470 ohms as a first step.
> If the K60XV is installed, be certain that its VRFDET output is NOT being enabled when the KAT100 is installed and the low power output is not being used.
> Check RF board D9 to be certain it has not been damaged.

The KAT2/R6 is already 470 ohms and the K60XV has been replaced by its Unmodule to eliminate that possibility. The measurements I had in my past mail were under these conditions.

D9 measures output voltage for the base K2 and that's the only power control circuit that works as it should, so I'm pretty confident that D9 is fine.


Sverre
LA3ZA




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