1L5/Repairs

I obtained a nonfunctioning 1L5. The output was a flat line, no deflection. The sequence of steps was as follows.

1. Confirm that the 5 kHz calibration source is functioning by setting the VOLTS/CM switch to the CALIBRATE position and measuring the voltage waveform at terminal BP on the calibrator board.
2. Confirmed that the the first LO is functioning. I connected the front panel OSC OUT to a frequency counter, put the VERTICAL DISPLAY switch in LIN position, set Hz/CM to 200, and set the sweep mode to MANUAL. I confirmed that first LO could be swept by rotating the MANUAL knob and watching the counter.
3. Checked the output of the first IF amplifier, saw no signal.
4. Checked the voltage waveform at the base of Q30, saw no signal.
5. Wiggled Q20 in its socket.
6. Checked the voltage waveform at the base of Q30. Signal look just like in the manual.
7. Checked the output. Still no deflection. Note: When using the internal calibration source, deflection should be maximized when the first LO (and OSC OUT) frequency is 2995 kHz.
8. Checked the output of the variable resolution amplifier. Looks good.
9. Put the 1L5 VERTICAL DISPLAY switch in VIDEO mode, which sends the input signal to the mainframe, like a regular amplifier plug-in. The VIDEO mode output is good. 5 kHz is appearing at the mainframe.
10. Put the 1L5 VERTICAL DISPLAY switch into LIN mode.
11. Checked the voltage waveform at the collector of Q400 in the output amplifier circuit. Looks good.
12. Checked the DC level at the collector (can) of Q410. It was close to the +350 V rail, and the transistor was cold.
13. Wiggled Q410 in its socket (with the power off).
14. Checked the DC level at the collector (can) of Q410. It was 165V.
15. Checked the output of the 1L5. Now deflection works.

The 1L5 is functioning. Of course it needs to be calibrated.