RCA Theremin Service Notes

(14) MAIN ASSEMBLY CONTINUITY TESTS

Remove Radiotrons and disconnect cable – Refer to Figure 8 – A D. C. voltage is used in making the tests and the resistance values given are D.C.

Circuit	Test Terminals	Correct Effect	Incorrect Effect
			Indication	Caused by
Grid	G1 to frame	5000 ohms	Open	Open No. 1 oscillator coil or 5000-ohm resistor or both Shorted 0.5 mfd. condenser
	Control grid No. 2 or G3 to frame	5000 ohms	Open	Open No. 2 oscillator coil or 5000-ohm resistor or both Shorted 0.5 mfd. condenser
	G4 to frame	5000 ohms	Open	Open secondary audio transformer No. 1, or open ground connection Shorted or grounded transformer secondary
	G5 to filament 5	Shorted	Open	Open connection
	G5 to frame	100000 ohms	Shorted	Shorted 0.5 mfd. condenser or grounded lead
	G6 to frame	110 ohms	Open	Open grid oscillator coil or 625-ohm resistor or 420-ohm resistor Shorted fixed or trimmer condenser
	G6 to P6	Open	Shorted	Shorted fixed or trimmer condenser
	G7 to frame (Play-Off switch open)	5000 ohms	Shorted	Closed or defective “Play-Off” switch grounded or shorted secondar No. 2 audio transformer Open audio transformer secondary
Plate	P1 to frame	Open	Shorted	Shorted 2 mfd. condenser
	P1 to P2	1100 ohms	Open	Open 10,000-ohm resistor or No. 1 audio transformer primary
	P1 to P3	5 ohms	Open	Open plate coil of fixed or variable pitch oscillator
	P1 to Lug 1 (Green)	1000 ohms	Open	Open plate coil variable pitch oscillator or open 10,000-ohm resistor
	P2 to Lug 1 (Green)	1000 ohms	Open	Open primary first audio transformer
	P4 to frame	105,000 ohms	Open	Open primary second audio transformer or open 100,000-ohm or 420-ohm resistor Shorted 0.5 mfd. condenser
	P5 to Lug 3 (Black)	1000 ohms	Open	Open 1000-ohm resistor
	P5 to frame	Open	Shorted	Shorted 2 mfd. condenser
	P6 to Lug 3 (Black)	1000 ohms	Open	Open plate coil of volume control oscillator
	P6 to frame	Open	Shorted 1000 ohms	Shorted 2 mfd. condenser Shorted 1 mfd. condenser
	P7 to Lug 2 (blue)	Shorted	Open	Open connection
	P7 to frame	Open	Shorted	Grounded lead
Cathode or Filament	C1, C2, C3 or C4 to frame	Closed	Open	Open connection or lead
	F5 to frame	100,000 ohms	Open	Open connection or 100,000-ohm resistor or 420-ohm resistor
	F6 or F7 to frame	Open	Shorted	Grounded lead
Heater	H1, 2, 3, and 4 to frame	Open	Shorted	Grounded lead or connection
Miscellaneous	Pitch control rod to G1	Open	550 ohms	Shorted oscillator resonant coil fixed condenser
	Volume control loop to G6	Open	150 ohms	Shorted oscillator resonant coil fixed condenser