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uBITX v3 Low Output

Hugh Debo
 

Hello all,
I have been reading this group for a while, but have just joined. Thanks for the add.
I've been a ham for only a couple of years, so this has been a lesson learned:

A couple of weeks ago I was experimenting on JS8 with a new antenna and produced enough 
common mode current to fry my Raspberry Pi and uBITX.  The RPI was replaced as were the finals
in the uBITX, but I had only about 1W output. I replaced the finals a second time, but the low output continues.

I downloaded the Diagnostic Guide and have measured all the TX Testpoints (Thanks Farhan!).
Using a battery at 12.3 VDC to power the uBITX, most Testpoints' measurements showed voltages slightly higher 
(+ 0.1-0.4 VDC) than the values listed in the Guide.

Others showed these differences:
Q911-3, Q912-3, Q92-3, Q93-3, & Q96-3 measured 11.9 VDC instead of 10.9 VDC.
Q94-2 & Q95-2 measured 12.3 VDC instead of 11.3 VDC.
Q94-1 measured 12.3 VDC instead of 3.1 VDC.
Q95-1 measured 3.2 VDC instead of 3.3 VDC.
U2-1 measured 5.0 VDC instead of 4.2 VDC.
U2-3 measured 12.2 VDC instead of 10.9 VDC.

I've examined the components leading up to Q94-1 and they all seem externally okay to me. My ohm meter says they are
connected from one to the next.

My only electronics education is from reading and small experiments (I was a registered nurse before retirement), so I don't really know what to do next.
Can you all please help me figure this out?
I welcome your suggestions!

Thx, 
Hugh WM5J

P.S. I've constructed a toroid choke balun!!
H

iz oos
 

I would check the values of the resistors around Q94


Il 06/giu/2019 04:20, "Hugh Debo via Groups.Io" <hughdebo=rocketmail.com@groups.io> ha scritto:
Hello all,
I have been reading this group for a while, but have just joined. Thanks for the add.
I've been a ham for only a couple of years, so this has been a lesson learned:

A couple of weeks ago I was experimenting on JS8 with a new antenna and produced enough 
common mode current to fry my Raspberry Pi and uBITX.  The RPI was replaced as were the finals
in the uBITX, but I had only about 1W output. I replaced the finals a second time, but the low output continues.

I downloaded the Diagnostic Guide and have measured all the TX Testpoints (Thanks Farhan!).
Using a battery at 12.3 VDC to power the uBITX, most Testpoints' measurements showed voltages slightly higher 
(+ 0.1-0.4 VDC) than the values listed in the Guide.

Others showed these differences:
Q911-3, Q912-3, Q92-3, Q93-3, & Q96-3 measured 11.9 VDC instead of 10.9 VDC.
Q94-2 & Q95-2 measured 12.3 VDC instead of 11.3 VDC.
Q94-1 measured 12.3 VDC instead of 3.1 VDC.
Q95-1 measured 3.2 VDC instead of 3.3 VDC.
U2-1 measured 5.0 VDC instead of 4.2 VDC.
U2-3 measured 12.2 VDC instead of 10.9 VDC.

I've examined the components leading up to Q94-1 and they all seem externally okay to me. My ohm meter says they are
connected from one to the next.

My only electronics education is from reading and small experiments (I was a registered nurse before retirement), so I don't really know what to do next.
Can you all please help me figure this out?
I welcome your suggestions!

Thx, 
Hugh WM5J

P.S. I've constructed a toroid choke balun!!
H

Evan Hand
 

I would check C261.  It may have shorted.  That is the only way I can see to get 12v on pin 1 of Q94.

note: you can replace the SMT with through hole devices if you bend the leads right, and are careful when soldering.

FWIW, good luck and good hunting:)
73
Evan
AC9TU