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Control board U4 8v regulator issue

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WE0H

Control board U4 8v regulator issue

Has anyone else had a 8v regulator (U4) on their control board show a
lower voltage than it should? Mine shows 7.61v with the board in the
radio or on the bench with a 14v supply connected to the input of that
regulator. All components and soldering look correct. The 5v regulator
is at 5.00v. All functions in the test procedure work as they should
except the AGC voltage couldn't be set to 3.80v because of the 8v buss
being at 7.61v, the AGC voltage changed as it should but was lower than
the 3.80v suggested for setting R1 to.

Nothing runs hot or smells hot. What do you guys think? Bad regulator or???

Many thanks,
Mike
WE0H
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WE0H

Re: Control board U4 8v regulator issue>Solved problem

I replaced the regulator and now have 8.30v output from U4. The original
regulator only put out 7.61v. Thankfully I had a used regulator on a
parts board from a security system!!! hi hi...

Mike

Mike-WE0H wrote:

> Has anyone else had a 8v regulator (U4) on their control board show a
> lower voltage than it should? Mine shows 7.61v with the board in the
> radio or on the bench with a 14v supply connected to the input of that
> regulator. All components and soldering look correct. The 5v regulator
> is at 5.00v. All functions in the test procedure work as they should
> except the AGC voltage couldn't be set to 3.80v because of the 8v buss
> being at 7.61v, the AGC voltage changed as it should but was lower than
> the 3.80v suggested for setting R1 to.
>
> Nothing runs hot or smells hot. What do you guys think? Bad regulator or???
>
> Many thanks,
> Mike
> WE0H

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Don Wilhelm-4

Re: Control board U4 8v regulator issue

In reply to this post by WE0H

Mike,

The regulator is a 10% tolerance part, so any voltage between 7.2 and
8.8 volts meets the spec for the regulator. They have been running on
the low side of the 8 volt nominal rating for some time now, and cause
no harm other than the AGC Threshold voltage cannot be adjusted up to
the level indicated in the manual.

Everything is proportional, and since the IF amplifier (which is
controlled by the AGC) also runs off the 8 volt regulator, setting the
AGC Threshold at its maximum setting works just fine. The real
consequence of low AGC Threshold voltage is that the S-meter setting get
a bit 'squirrelly' when the voltage is lower. If you are able to adjust
the CAL S LO and CAL S HI for proper S-meter action, then all is well.

If you have trouble with the S-meter settings, add a 10k to 15k resistor
across Control Board RP5 pins 3 and 4 - then readjust the AGC Threshold.

73,
Don W3FPR

Mike-WE0H wrote:

WE0H

Re: Control board U4 8v regulator issue>Solved problem

In reply to this post by WE0H

I want to thank all you people for the tips, mods & suggestions that you
emailed direct. Much appreciated. The radio is testing 100% now with the
new used regulator which puts out 8.30v. I saved the original 7.61v
regulator along with the mod procedure to make it work if I need to. A
shame the regulator manufacturer sells a 8v regulator that is barely at
the minimum end of it's spec's, but it is good that the K2 can be
modified to work with the lower voltage regulator if need be.

Now onto stuffing the other components into the RF board...

Mike
WE0H
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David Woolley (E.L)

Re: Control board U4 8v regulator issue>Solved problem

Mike-WE0H wrote:

> shame the regulator manufacturer sells a 8v regulator that is barely at
> the minimum end of it's spec's, but it is good that the K2 can be
> modified to work with the lower voltage regulator if need be.

It's a shame that the K2 doesn't work when its components are all in
tolerance! There should be no need for a fix.

--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
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WE0H

Re: Control board U4 8v regulator issue>Solved problem

Oh mine was working excellent last night for it's first time listening
on the air 40m. Heard South Africa and some South Pacific islands on 40m
after I peaked the 40m bandpass filter. The only issue I had was that
regulator & that was a piece of cake to troubleshoot & repair. So far I
am totally impressed with this kit & it's design, well worth the money
spent.

Mike
WE0H

David Woolley (E.L) wrote:

> Mike-WE0H wrote:
>
>
>> shame the regulator manufacturer sells a 8v regulator that is barely at
>> the minimum end of it's spec's, but it is good that the K2 can be
>> modified to work with the lower voltage regulator if need be.
>>
>
> It's a shame that the K2 doesn't work when its components are all in
> tolerance! There should be no need for a fix.
>
>