| Indication |
Cause |
Remedy |
| Radiotrons Fail to Light |
No supply voltage |
Test with A.C. voltmeter at loudspeaker auxiliary power receptacle (operating and safety switches should be closed) |
| Defective safety switch |
Test as above. Repair or replace |
| Defective operating switch |
Test as above. Replace |
| Defective Power Transformer |
Check by continuity tests (Section 13). Replace |
| Defective Radiotrons |
Replace |
| UX-120 (only) fails to light |
Low emission UX-280 or 171-A (no. 6) tube not oscillating. (A Neon glow lamp - such as the Cooper Hewitt type G10, 115-V - is a convenient test for oscillation. The brass base of the lamp should be held in the hand and the glass bulb near the pitch control rod or volume control loop). Circuits out of adjustment |
| Defective wiring |
Check by means of continuity tests, Sections 12-13 |
| Tubes light - Theremin fails to play |
Defective "Play-Off" switch |
Replace |
| Loudspeaker defective or disconnected |
Connect O. K. speaker |
| Tube Nos. 1, 3, or 6 not oscillating |
Test tubes and continuity of circuits, Section 12 |
| Defective audio input transformer |
Check with continuity test |
| Grounds or opens |
Check continuity Sections 12-13 |
| Control grid connection open at UY-224 |
Attach contact cap |
| Distorted Reproduction |
Low emission or defective Radiotrons |
Replace |
| Poor wave form of A. C. supply current |
Try resistances from 500 ohms to 2000 ohms in series with control grid of UY-224 |
| Open 550-ohm resistor |
Replace |
| Defective audio transformer |
Replace |
| Open or imperfect chassis ground |
Repair |
| Improper audio voltages at audio sockets |
Check with tables Sections 10-11, Isolate trouble by continuity test Section 12 |
| Defective Loudspeaker |
Replace |
| Hum |
Defective Radiotrons |
Replace |
| Open or shorted center tapped fixed condensers |
Repair or replace |
| Open by-pass or filter condensers |
Test and replace |
| Shorted filter reactor |
Check by resistance measurement. Replace |
| Open chassis grounds |
Check from diagrams Figures 7-8 |
| Loose laminations in power transformer |
Repair or replace |
