K2 kaputt

[Raimon-3]

Dear Don
I refer again to my problem with K2/100
You wrote on 02/09/07:
"The oscillation possibility is an 'educated guess', so do change C31
and then if a problem persists, we can offer additional assistance if
you give us data and your observations/conditions"

I substituted C31 with two 0.1mf capacitors in parallel (my local
supplier had run out of stock of 0.22 mf capacitors.
Now things have improved, as voltages in diodes D1 trhough D14 are all
right, but the problem persists.

I remember to you what is the problem and my observations:
Recently I upgraded the KPA100 with KPA100UPKT, it passed all tests (I
did not realign it), and it worked perfectly for two weeks.
One day I worked in the morning without any trouble, but when in the
afternoon I fired it up again, the KAT100 was unable to tune: relays
clicked, diodes did not light, tune was not obtained.
I disconnected KAT100 and observed that K2/100 was not working right.
Connected to a dummy load, power and swr readings in the LCD display are:
   Setting  9 w         Read  9.8 w   swr  1.2.1
   Setting 30w         Read  27 w    swr  1.8.1
   Setting 90w         Read   64 w   swr   2.4-1     first appears HiCurr
Connected to the same dummy load through an external wattmeter, swr
readings are negligible, but the power indication is very high (120w)
The bare K2 (disconnected from KPA100) shows no problem. Connected to
the same dummy load and to an OHR qrp wattmeter, power indications agree
in both LCD and wattmeter and swr is negligible.

I guess there is a bad performance of the swr reading circuit of the KAT100.
Where do you think that I should look for a cure?
Your assistance will be greatly appreciated.
73  Raimon
EA3EZO
[hidden email]




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[Don Wilhelm-4]

Raimon,

If it were on my workbench, the first thing I would do at this point is
to replace KPA100 D16 and D17, then check the operation of the wattmeter
again.

If I understand correctly, it did work at one time, so no additional
calibration of the wattmeter should be required.  If the new diodes do
not correct the bad readings, then you should look for an unsoldered or
poorly soldered connection in the wattmeter circuits - R26, R27, U5, U6,
Q10 and Q11 as well as the associated resistors and capacitors.  Check
the schematic to see which components are connected to the listed
devices.  Check the lead tinning and soldering of T4 at the same time.

After the KPA100 is working correctly, add the KAT100 and check the
combination.  If you have to obtain 1N5711 diodes to replace the ones in
the KPA100, order 2 for the  KAT100 at the same time so you will have
them available in case they are needed.

73,
Don W3FPR

raimon wrote:

> Dear Don
> I refer again to my problem with K2/100
> You wrote on 02/09/07:
> "The oscillation possibility is an 'educated guess', so do change C31
> and then if a problem persists, we can offer additional assistance if
> you give us data and your observations/conditions"
>
> I substituted C31 with two 0.1mf capacitors in parallel (my local
> supplier had run out of stock of 0.22 mf capacitors.
> Now things have improved, as voltages in diodes D1 trhough D14 are all
> right, but the problem persists.
>
> I remember to you what is the problem and my observations:
> Recently I upgraded the KPA100 with KPA100UPKT, it passed all tests (I
> did not realign it), and it worked perfectly for two weeks.
> One day I worked in the morning without any trouble, but when in the
> afternoon I fired it up again, the KAT100 was unable to tune: relays
> clicked, diodes did not light, tune was not obtained.
> I disconnected KAT100 and observed that K2/100 was not working right.
> Connected to a dummy load, power and swr readings in the LCD display are:
>   Setting  9 w         Read  9.8 w   swr  1.2.1
>   Setting 30w         Read  27 w    swr  1.8.1
>   Setting 90w         Read   64 w   swr   2.4-1     first appears HiCurr
> Connected to the same dummy load through an external wattmeter, swr
> readings are negligible, but the power indication is very high (120w)
> The bare K2 (disconnected from KPA100) shows no problem. Connected to
> the same dummy load and to an OHR qrp wattmeter, power indications
> agree in both LCD and wattmeter and swr is negligible.
>

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