Re: VE9BP: RE: K2 #6155 Resistance check page 55

[ArtLinux]

Gary

Thanks for the timely response. Comments after your text:

On Mon, 2007-09-07 at 10:34 -0700, Gary Surrency wrote:
> I see 271.6 ohms between U6-8 and ground on my K2, using a Fluke 179 digital
> meter. So there is no misprint in the manual.

My measurements were with an Ideal 766 true RMS DMM

>
> It is fairly common for me to find a reversed 78L05 regulator at U8, so look
> for that.

No reversal of U8
>
> Your soldering iron should have a grounded tip

Using Hakko 936 ESD protected
>
> Do NOT press the transistors down too close to the PCB or their leads may
> short together or break off. Leave a small gap between the device and the
> top of the board.
>
> Do NOT remove parts without good reason to do so

Part removal was a last resort in the interests of isolating the part of
the circuit that was causing the low U6-8 resistance.
>
> Be sure the PLL thermistor board is not installed wrong

With the thermistor board removed the U6-8 resistance remaiins low
>
> Did you ever try turning on the power to see what would happen? Sometimes
> that is a good (or the only) way to determine if there is a problem or not.
> The 5V and 8V regulator IC's will self-limit the current and usually a part
> will not be damaged unless it is installed in reverse or at the wrong
> location. Look closely for such an error before removing any part or
> applying power.

I was trying to avoid the smoke test!

Gary, could you comment on my detailed work procedure at least in the
summary at the end or maybe in the procedure with results provided in
detail. Without your insight, I do not know what else to try!!

Thanks again for the quick reply to my email, Gary

Arthur VE9BP

>
>
> --
> 73, Gary AB7MY
> =========
> [hidden email]
> Elecraft Technical Support  
>  
>
>
>
> -----Original Message-----
> From: Arthur Gunn [mailto:[hidden email]]
> Sent: Saturday, July 07, 2007 4:34 PM
> To: [hidden email]
> Subject: K2 #6155 Resistance check page 55
>
>
> Hello
>
> My building has progressed well up to the point of resistance check at U6
> pin 8 just prior to alignment & test part 2. Instead of >100 Ohms, I
> measured 39 Ohms.
>
> After a suggestion by Don Wilhelm on the email reflector, I performed the
> following steps:
>
> 1. Checked physical position of all devices Q,U,D;
> 2. Examined the board for solder bridges
> 3. Checked resistance of any resistors connected to bus 8B points in the
> schematic diagram
> 4. After 1,2, & 3 the same measured value at U6 pin 8 was observed.

>  5.Followed a program of one-at-a-time component removal to locate / isolate
> the component or section causing the low resistance, as follows:

>  5.1 U6 and resistance increased to 40.6 Ohms

> 5.2 Thermistor board
> 5.3 RFC16, C103, U8
> 5.4 R33
> 5.5 R9
> 5.6 R15, R13, R14
> 5.7 U3 - the only damage created by the exercise caused the pin 5 to break
> mid way up its lead and the pin 1 to bring with it the the sleeve from the
> circuit board hole. I believe by good luck that neither may have an effect
> on the K-2 operation. Can you confirm that?


>  5.8 Q19 upon removal, measured
> 18k Ohm from U6 pin 8 to ground. When I temporarily replaced Q19 with
> another identical part the measurement increased to just 41 Ohms. I removed
> the temporary part. Now possibly isolated, I investigated the components in
> that area as follows:

> 5.8.1 Lifted R20 measuring it and RFC14 continuity;

> 5.8.2 Lifted and measured C86 as .04 nF


>  5.8.3 Lifted and measured R21


> 5.8.4
> Measured RP2 1-2

> 5.8.5 Measured RP2 3-4 5.8.6 Measured continuity of C85 to
> be 12 meg Ohms
>
>
> In summary, except for the big resistance change in 5.8 following Q19
> removal, NOTHING else had more than a 2 Ohm change from the 39 Ohms first
> read.
>
> My first question is to the >100 Ohms given in the resistance chart, and
> whether it is a misprint.
>
> My second question is what can I do to further look for the cause of the low
> resistance value.
>
> 73

--
Arthur Gunn VE9BP

74 Mill Bank Road
Nasonworth NB  E3C 2C6

H 506 459-5336
W 506 457-2020
F 506 457-2035

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