Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: SB-34 restoration  (Read 1071 times)
KH6VP
Member

Posts: 65


WWW

Ignore
« on: September 22, 2018, 05:33:49 AM »

Hi,
I have two working SB-34’s but am trying to repair a third SB-34 that has a weird problem.
When it turns on, it seems to be in TX mode, or rather no Rx sound on the speaker.
On the power line checks, TP5 has 13V not a maximum of 1V as the maintenance manual says.
I have touched both the audio transistor and the driver and I can hear sound so they are ok.
I have replaced Q16 with a 2N2222 but still no change.
All power supply voltages are fine.
I removed both the blue wires on the TUNE board to see, but still no change.
I have replaced the driver tube; no change.
Anyone who is an expert in the SB-34 has any suggestions?
Thanks!
Logged
W6EM
Member

Posts: 1941




Ignore
« Reply #1 on: October 02, 2018, 06:49:31 PM »

Since the SB-34 was a hybrid radio, chances are you have a shorted switching transistor or a component like a capacitor that is shorted causing the radio to key up.  1V on a TP that should be 13V is a strong clue.  Start by checking voltages on collectors of all transistors associated with the PTT circuits.  13V or so if off.  0.5 to 1V if on.  Opposite for PNPs.  Work back to the microphone connector.  You should be able to find the problem that way.  Also, check for change in voltages when the PTT switch is depressed.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!