[Heathkit] SB-303 Report - 1

[Michael Waldrop]

You might check to see if the local crystal heterodyne oscillators on all
bands is working. If you do not have a frequency counter you can use
a separate receiver that will tune the frequency of each bands heterodyne
oscillator crystal. As an example, place the band switch in 3.5Mhz position,
tune the separate receiver to 12.395Mhz, place a piece of wire in the
separate receivers antenna connection and the other end of the wire
near the 303's heterodyne oscillator board and power up the 303. If the
heterodyne oscillator is working you will hear the 12.395Mhz signal in
the separate receiver. Do this for all band switch positions on the 303.
If no signal is heard then the 303's heterodyne oscillator is not working
and you will not hear any signals including the 100Khz calibrator
signal.

This same procedure can be performed for the RTTY, LSB and
USB/CW local oscillator crystals, all controlled through the mode switch.

My 303 had this same problem and found the heterodyne oscillator
was not working due to bad contacts in the band switch plus bad
connections in the board finger contacts and recepticles on the 
backplane. Cleaning the contacts fixed the problem.

If you eventually get the receiver to receive signals, I recommend performing
the voltage adjustments outlined in the manual on page 112.

73's
Mike
W5RKL



kiyoinc at attglobal.net wrote: This is the SB-303 that followed me home from the recent Howard County 
Hamfest.

This was from a smoking shack.  It does not reek as badly as #2 did but 
will require desmoking.

Took a brush and cleaned the face and knobs.  The radio had layers of 
dust on it, several decades worth.   This one should clean up nice.

There's a nicely done spinner attached to the main turning knob.  All 
controls are smooth, even the hairline adjustment.

Hooked up the SB-303 to a longwire antenna and speaker.  Turned it on. 
The dial lights did not light but there was a hum and hiss from the 
speaker.

Turned up the audio and R.F. full, the hiss stayed about the same.

Pulled the case and checked the voltages.  +15, -10 were OK but there 
wasn't any reading on the 35 V terminals.

Removed the power supply board.  It looked fine and the capacitors 
looked new. Using the SB-303 extender board, checked the voltage at the 
main capacitor, the 2000 ufd 40 VDC was 34 V, close enough.

When probing at the 35 V connectors on the wiring harness, the speaker 
made popping sounds.

Sprayed all the connectors with Deoxit and reseated the two big boards. 
   The AF gain increases the hiss but there are no signals heard,  not 
even from the Crystal Calibrator.

Now have 35 VDC.  The radio is still dead.

The wafer switches have a layer of black oxide on them.  It comes off 
easily.   Applied Deoxit and worked the switches.


de ah6gi/4
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