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eHam Forums => Boat Anchors => Topic started by: KH6VP on September 22, 2018, 05:33:49 AM



Title: SB-34 restoration
Post by: KH6VP 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!


Title: RE: SB-34 restoration
Post by: W6EM 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.