Troubleshooting the Wurlitzer 200 Series Amplifiers
This text is directly taken from the Wurlitzer 200 Service Manual notes.
Electronic Piano Note #23
April 15th, 1971
200 Series Amplifiers
| 1. | Dead Amplifier (Pilot light does not light) | A |
| 2. | Blows line fuse | B, C, D |
| 3. | Blows output transistors | J, L, M, N, O, P - See Note #1 |
| 4. | Distortion | D, E, S |
| 5. | Low Volume | E, S |
| 6. | Static | E, F, H, I, J, K, T |
| 7. | Hiss and noise (can control with volume control) | E, F, H, I, J, K, T |
| 8. | Hiss & noise (cannot control with volume control) | C, I, J, K, U |
| 9. | Hum | C, E, F |
| 10. | Tremelo dead | Q, R |
A. AC line fuse open
B. Shorted rectifiers D-2, D-3
C. C-6
D. Shorted output transistors
E. Cracks or poor solder joints on PC board
F. Poor ground on input cable
G. TR-1 (use GE style 11-0778 or 651891 yellow or green)
H. R-40, R-36, R-45, R-66 (replace with deposited carbon)
I. R-14, R-7, R-8
J. C-9
K. C-18 too close to R-14
L. R-14 (noisy)
M. R-10 high in value
N. D-4
O. Burr on heat sink puncturing mica washer
P. Use one mica under output and driver transistors with heat sink
compound on both sides
Q. TR-4
R. C-53, C-46, D-5
S. Open or shorted coupling capacitors
T. Reed striking pickup
U. TR-5, TR-6
Note #1. Inspect C, J, L and follow P prior to turning piano on after replacement of output TR'S.
ELECTRONIC PIANO 200A
Before ordering a new AC power cord for a model 200A, check to see which type of pins is used in the receptacle of your piano. Recently, a new connector has been introduced which features rectangular shaped pins rather than the traditional, round ones. Including the description "round pins" or "square pins" on your parts order will insure the proper type of cord to be sent.
Model: 200, 203, 206, 207
Subject: Failure Output Transistors
References: Schematic - Piano Amplifier (11-0783)
When called upon to change output transistors in the Electronic Piano, check the following items to ensure they are in good functioning order. Check for the following:
| C-6 | 1000 mfd. | 50 VDC | Intermittent |
| C-9 | 500 mfd. | 50 VDC | Intermittent |
| R-14 | 200 mfd. | 5 watt resistor | Noise |
| R-8 | .68 ohms | 5 watt resistor | Noise |
| R-7 | 200 ohms | 5 watt resistor | Noise |
| R-10 | 2.7 ohms | 1 watt resistor | Open |
MODEL: 200 Series Electronic Pianos
Subject: Connecting external amplifiers
Reference: 200 Series amplifier Schematic No. 11-1305-S-1
The most satisfactory point to obtain a signal for driving an external amplifier is at the auxiliary output jack. As the piano is wired, this signal is taken from point 7 (signal) and point 1 (ground). It has been noted that in some cases this circuit does not supply sufficient drive signal to the external amplifier input. In other cases a hum is introduced into the external amplifier. The following circuit has been found to correct these conditions. Change the 100K resistor between points 6 and 7 to a 6.8K and the 15K resistor between points 1 and 7 to a 2.2K. The maximum signal is approximately .5 volts peak to peak. If there is no D.C. voltage at the external amplifier input, a cleaner drive signal can be obtained by removing the 5MFD capacitor between pins 5 and 6 and replacing it with a jumper wire.
Model: 203-203W, 214
Subject: Baffle Board Wiring
If you should encounter a piano which has apparent low volume, check speaker wiring to ensure they are all in phase. The orange wires should be connected to the speaker terminal with the color dot. The black wires to the unmarked speaker terminals.