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T1 Tuner Kit Control Board final check issues

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Erik Tkal

T1 Tuner Kit Control Board final check issues

I just assembled the T1 kit, but am having an issue in the final check phase of the Control Board.

"Resistance across capacitor C19: between 137 K-ohms and 148 K-ohms. Press S2 and confirm reading drops to between 117 K-ohms and 135 K-ohms.”

I’m getting around 60K or 43K with my Fluke 117, depending on which way I connect the leads. Each of R10 and R11 individually test ok, and I don’t see any solder bridges or missing joints, and I’ve reflowed anything suspicious that might be related. Has anyone seen this or could offer an explanation before I start pulling parts or digging out the oscilloscope?

The second check is also off.

"Resistance between D3 anode (end without the band) and the “ –“ pad near D7 (ground) where the black wire is attached: > 100 K-ohms (may show open or infinite on some DMMs). Press S1 and confirm the reading drops to between 117 K-ohms and 130 K-ohms. If the resistance is higher, try reversing your DMM leads.”

Attaching the red lead to D3 shows infinite resistance and pressing S1 reads 170K. Reversing shows about several M-ohm initially, but then pressing S1 gives 180K. Note that if I use normal automatic ranging it won’t get a lock on the second S1 measurement (with black lead on D3 and red on Ground), I had to use manual range. This makes me think the DMM circuitry may be interfering in some way.

The third check on the LED voltage drop succeeds,

Any suggestions?

Thanks and 73,
Erik Tkal - W1QED

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Don Wilhelm-5

Re: T1 Tuner Kit Control Board final check issues

Erik,

Check and double check the orientation of the diodes. That is the most
likely reason for you measurement results.

73,
Don W3FPR

On 5/23/2021 5:39 PM, Erik Tkal wrote:

> I just assembled the T1 kit, but am having an issue in the final check phase of the Control Board.
>
> "Resistance across capacitor C19: between 137 K-ohms and 148 K-ohms. Press S2 and confirm reading drops to between 117 K-ohms and 135 K-ohms.”
>
> I’m getting around 60K or 43K with my Fluke 117, depending on which way I connect the leads. Each of R10 and R11 individually test ok, and I don’t see any solder bridges or missing joints, and I’ve reflowed anything suspicious that might be related. Has anyone seen this or could offer an explanation before I start pulling parts or digging out the oscilloscope?
>
> The second check is also off.
>
> "Resistance between D3 anode (end without the band) and the “ –“ pad near D7 (ground) where the black wire is attached: > 100 K-ohms (may show open or infinite on some DMMs). Press S1 and confirm the reading drops to between 117 K-ohms and 130 K-ohms. If the resistance is higher, try reversing your DMM leads.”
>
> Attaching the red lead to D3 shows infinite resistance and pressing S1 reads 170K. Reversing shows about several M-ohm initially, but then pressing S1 gives 180K. Note that if I use normal automatic ranging it won’t get a lock on the second S1 measurement (with black lead on D3 and red on Ground), I had to use manual range. This makes me think the DMM circuitry may be interfering in some way.
>
> The third check on the LED voltage drop succeeds,
>
>

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Don Wilhelm-5

Re: T1 Tuner Kit Control Board final check issues

Since that is the case, check the value of the resistors and check out
the soldering under magnification.

73,
Don W3FPR

On 5/24/2021 3:08 PM, Erik Tkal wrote:
> Hi Don,
>
> Nope, D3 and D4 are correct, and the LEDs check out per the test...

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Erik Tkal

Re: T1 Tuner Kit Control Board final check issues

Hi Don,

Everything appears correct and in place, already used magnification to check, and individual resistors all seem to measure correctly. I still think it's my multimeter in auto mode. I went back and retried the initial test using manual ranging and if I set the range to 600K it shows a reasonable value. I suspect the caps in the circuit are fooling it, will have to google that and see if there is an adjustment. The second test still shows a bit high as well, but if I measure from the *cathode* of D3 instead of the anode then I get a reasonable value as well; perhaps the difference in meter currents used for measurements is messing up due to the diode being in the circuit as the check is worded?

Thanks and 73,
Erik Tkal - W1QED

On May 24, 2021, at 15:32, Don Wilhelm <[hidden email]> wrote:

Since that is the case, check the value of the resistors and check out the soldering under magnification.

73,
Don W3FPR

On 5/24/2021 3:08 PM, Erik Tkal wrote:
> Hi Don,
>
> Nope, D3 and D4 are correct, and the LEDs check out per the test...

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Don Wilhelm-5

Re: T1 Tuner Kit Control Board final check issues

Erik,

Yes, using auto ranging on the DMM can cause false readings. Try to set
the fixed range a bit above the highest expected resistance for the best
results. It all depends on the voltage the DMM applies to the circuit.
Too high a voltage can make ICs and transistors conduct causing a low
reading.

73,
Don W3FPR

On 5/24/2021 5:52 PM, Erik Tkal wrote:

> Hi Don,
>
> Everything appears correct and in place, already used magnification to
> check, and individual resistors all seem to measure correctly. I
> still think it's my multimeter in auto mode. I went back and retried
> the initial test using manual ranging and if I set the range to 600K
> it shows a reasonable value. I suspect the caps in the circuit are
> fooling it, will have to google that and see if there is an
> adjustment. The second test still shows a bit high as well, but if I
> measure from the *cathode* of D3 instead of the anode then I get a
> reasonable value as well; perhaps the difference in meter currents
> used for measurements is messing up due to the diode being in the
> circuit as the check is worded?
>
> Thanks and 73,
> Erik Tkal - W1QED
>
>
>
> On May 24, 2021, at 15:32, Don Wilhelm <[hidden email]
> <mailto:[hidden email]>> wrote:
>
> Since that is the case, check the value of the resistors and check out
> the soldering under magnification.
>
> 73,
> Don W3FPR
>
> On 5/24/2021 3:08 PM, Erik Tkal wrote:
>> Hi Don,
>>
>> Nope, D3 and D4 are correct, and the LEDs check out per the test...
>
>

Erik Tkal

Re: T1 Tuner Kit Control Board final check issues

Hi Don,

Yeah, I don’t often perform measurements on components already installed in a circuit, so the behaviour was confusing. I thought I bought a nice DMM but I guess it was just a fluke… ;-)

Anyway, I got it finished and everything is operational, now just have to wait for the IC-705 interface cable!

Thanks and 73,
Erik Tkal - W1QED

On May 24, 2021, at 18:01, Don Wilhelm <[hidden email]> wrote:

Erik,

Yes, using auto ranging on the DMM can cause false readings. Try to set the fixed range a bit above the highest expected resistance for the best results. It all depends on the voltage the DMM applies to the circuit. Too high a voltage can make ICs and transistors conduct causing a low reading.

73,
Don W3FPR

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Elecraft mailing list

Re: T1 Tuner Kit Control Board final check issues

And for the bands to cooperate!! :-)

Congrats, Erik.

> On May 25, 2021, at 1:01 PM, Erik Tkal <[hidden email]> wrote:
>
> Hi Don,
>
> Yeah, I don’t often perform measurements on components already installed in a circuit, so the behaviour was confusing. I thought I bought a nice DMM but I guess it was just a fluke… ;-)
>
> Anyway, I got it finished and everything is operational, now just have to wait for the IC-705 interface cable!
>
> Thanks and 73,
> Erik Tkal - W1QED
>
>
>
> On May 24, 2021, at 18:01, Don Wilhelm <[hidden email]> wrote:
>
> Erik,
>
> Yes, using auto ranging on the DMM can cause false readings. Try to set the fixed range a bit above the highest expected resistance for the best results. It all depends on the voltage the DMM applies to the circuit. Too high a voltage can make ICs and transistors conduct causing a low reading.
>
> 73,
> Don W3FPR
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]