Q7 base resistance test - low reading

[Tim Logan]

Hi folks -
I just completed the RF board and am doing the resistance checks on page 71.  For Q7 base it requires 2.5 - 3.0 k.  My DVM onky meausres  .4 ohms - no where near 2300 - 3000 ohms. I assume this means I have a short.  There is no short between the soldered pads on Q7 and I rechecked the mounting screw hardware to make sure each part was correctly in place. All other measurements for the RF board are OK.
Not being anything but a paint-by-number solderer, am I reading the table correctly? That does mean 2500 - 3000 ohms write?  If so, I very stumped because a short on this component should be very obvious - but I don't see it. Can someone offer some help please? Thank you very much in advance.
73/Tim NZ7C

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[M1DIC]

Tim,

Yes, the resistance should be between 2500 & 3000 ohms. As you say a short
on Q7 itself should be obvious, so if nothing looks bad, then after having a
look at the schematic a good place to look may be around T4. There is a
ground connection to winding 3-4, so a short around here to winding 5-6
would put a ground onto the base of Q7.

Good hunting

73 Don, M1DIC
K2/100 #3082

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of [hidden email]
Sent: 30 January 2005 18:56
To: [hidden email]
Subject: [Elecraft] Q7 base resistance test - low reading


Hi folks -
I just completed the RF board and am doing the resistance checks on page 71.
For Q7 base it requires 2.5 - 3.0 k.  My DVM onky meausres  .4 ohms - no
where near 2300 - 3000 ohms. I assume this means I have a short.  There is
no short between the soldered pads on Q7 and I rechecked the mounting screw
hardware to make sure each part was correctly in place. All other
measurements for the RF board are OK.
Not being anything but a paint-by-number solderer, am I reading the table
correctly? That does mean 2500 - 3000 ohms write?  If so, I very stumped
because a short on this component should be very obvious - but I don't see
it. Can someone offer some help please? Thank you very much in advance.
73/Tim NZ7C

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[Rich Lentz]

Try taking off the heat sink, i.e. unmount the transistor, and then measure
the resistance again.  This will determine if the mounting has introduced
the short.  DO NOT USE THE STAR WASHERS. One of the options indicates this
but it is not in the manual yet.  I had the same problem and found a VERY
SMALL piece of metal on the insulator, needed a magnifying glass to see it.
After removing this small piece of metal all was fine. I guess this is why
they now recommend not using the star washers.

Rich,
KE0X

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[Tim Logan]

Don Lerche was right and I thank him so much! Although I could not SEE
the short I disconnected the T4 windings one by one until the Q7 base
resistance shot up to 2.6k. Then I resoldered one by one - measuring Q7
after each new solder joint. Finally I redid all of the page 71
measurements and I'm back in business! It is so nice to be able to get
some help on a Sunday afternoon and go to Alignment Part III!!!!
73/Tim NZ7C

Don Lerche wrote:

>Tim,
>
>Yes, the resistance should be between 2500 & 3000 ohms. As you say a short
>on Q7 itself should be obvious, so if nothing looks bad, then after having a
>look at the schematic a good place to look may be around T4. There is a
>ground connection to winding 3-4, so a short around here to winding 5-6
>would put a ground onto the base of Q7.
>
>Good hunting
>
>73 Don, M1DIC
>K2/100 #3082
>
>-----Original Message-----
>From: [hidden email]
>[mailto:[hidden email]]On Behalf Of [hidden email]
>Sent: 30 January 2005 18:56
>To: [hidden email]
>Subject: [Elecraft] Q7 base resistance test - low reading
>
>
>Hi folks -
>I just completed the RF board and am doing the resistance checks on page 71.
>For Q7 base it requires 2.5 - 3.0 k.  My DVM onky meausres  .4 ohms - no
>where near 2300 - 3000 ohms. I assume this means I have a short.  There is
>no short between the soldered pads on Q7 and I rechecked the mounting screw
>hardware to make sure each part was correctly in place. All other
>measurements for the RF board are OK.
>Not being anything but a paint-by-number solderer, am I reading the table
>correctly? That does mean 2500 - 3000 ohms write?  If so, I very stumped
>because a short on this component should be very obvious - but I don't see
>it. Can someone offer some help please? Thank you very much in advance.
>73/Tim NZ7C
>
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com
>
>
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
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>
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com
>
>  
>

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