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Monday, October 24, 2022

Realistic STA-180 Receiver Restoration

Unit: AM/FM Stereo Receiver
Manufacturer: Realistic
Model: STA-180
SN: 07002284

One of my customers brought in a rather rare vintage Realistic STA-180 stereo receiver for restoration. His son-in-law bought this beautiful receiver on the action and gave it to him for his birthday. The receiver is still in excellent cosmetic condition and brought back many good memories. It's definitely worth restoring.

Realistic STA-180_After Restoration

The Realistic STA-180 has many unique features. There is a separate front end, two dial scales, and two thumbwheel knobs (similar to Marantz's "Gyro-Touch-Tuning") for AM and FM. The variable FM muting control allows you to select a muting level for tuning weak or stronger stations (pretty unique!). The FM dial pointer changes its color to indicate a stereo reception (a very cool feature but PITA to replace burned lamps). It also has a "Flip-Top" door at the top rear allowing you to make all connections from the front of the receiver. The list price in 1972 was $399.95 (Ref. Radio Shack Catalog, 1972, ver.1, page 14).

I was not able to find a service manual for this receiver. Currently (October 2022) even the schematic is not available online. There is only one thread on AudioKarma.org about servicing this model. Also, some info is available in the 1972 Radio Shack catalog.

Realistic STA-180 - inside view before restoration

Realistic STA-180_inside view_01

Realistic STA-180_inside view_02

Power Supply Board

The power supply has three aluminum electrolytic capacitors: C01, C02, and C07.  I replaced them with low impedance Nichicon UPW caps. The original e-caps were tested with an Atlas ESR70 capacitance meter and the results are below. Two out of three capacitors have a tolerance outside the factory specifications.

Test results on original capacitors removed from the power supply board:

C01: rated capacitance – 220uF, measured – 303uF, ESR – 0.09Ω, deviation: +38%
C02: rated capacitance – 220uF, measured – 261uF, ESR – 1.02Ω, deviation: +19%
C07: rated capacitance – 220uF, measured – 278uF, ESR – 0.46Ω, deviation: +26%

The regulating transistor TR01 installed on this board is 2SC1061. This transistor is on my list of transistors that are prone to failure and I replaced it with a new Fairchild MJE15032G. The MJE15032G is a "bulletproof" transistor and can dissipate twice the power of the original transistor: 50W vs. 25W.

Note that the plastic sleeve of the original resistor R05 has significant discoloration. I measured the voltage drop across this resistor under normal operating conditions to calculate the current flowing through it. The voltage drop was ~46.4V. The nominal resistance of R05 is 2.2kΩ. Therefore, the current flowing through resistor R05 is 46.4V / 2.2kΩ = 21mA. And the electrical power dissipated by this resistor is 46.4V x 21mA = 0.97W. The original metal oxide resistor installed in this position has a rated power of 2W. So, it should be enough to efficiently dissipate the heat without overheating. I measured the resistance of R05 and it is still very close to the nominal. I decided to replace the original resistor with a new 3W metal oxide KOA Speer resistor as a part of "preventive maintenance".

The original (2.2kΩ/2W) and new (2.2kΩ/3W) metal oxide resistor R05

Realistic STA-180_Power Supply Board_R05_before servicing

Realistic STA-180_Power Supply Board_R05_after servicing

Power supply board - before and after

Realistic STA-180_Power Supply Board_before servicing

Realistic STA-180_Power Supply Board_after servicing

Pre-Amplifier Board

There are nineteen aluminum electrolytic capacitors on the pre-amplifier board: C03, C04, C05, C06, C11, C12, C13, C14, C15, C16, C17, C18, C31, C32, C33, C34, C37, C38, and C39. All these capacitors are ordinary aluminum electrolytic capacitors. And it's very confusing, why didn't the manufacturer install low leakage or solid tantalum capacitors in the signal path on this board? Generally, when an aluminum electrolytic capacitor is used in a coupling or decoupling circuit, only low leakage or solid tantalum capacitors are used to reduce the noise generated in the circuit. This noise depends on the leakage current of the capacitor. Less leakage current produces less noise. The typical leakage current of ordinary aluminum electrolytic capacitors is nearly 10 times higher than that of low leakage or solid tantalum capacitors. Perhaps the cost savings is the reason why low leakage or solid tantalum capacitors were not installed on this board. I don't know. In fact, none of the boards in this model (pre-amplifier, equalizer, or main amplifier) use low leakage or solid tantalum capacitors. In any case, it always makes sense to replace the capacitors in the signal path with modern low leakage or polyester film capacitors to reduce the noise generated in the circuit.

As I mentioned earlier, I was unable to find a schematic or service manual for this receiver. Thus, it was not clear which capacitors should stand in the signal path. However, an educated guess can be made that all electrolytic capacitors with a capacitance of 4.7uF or less are likely installed in the signal path. So, based on this assumption I replaced six e-caps with a capacitance of 1uF (C05, C06, C31, C32, C37, C38) with film polyester WIMA caps. The other four e-caps with a capacitance of 4.7uF (C15, C16, C33, C34) were replaced with modern low leakage Nichicon UKL caps. And the remaining nine capacitors were replaced with low impedance Nichicon UPW/UPM caps.

All controls on this board were cleaned and lubricated with DeoxIT FaderLube 5% spray.

Test results on original capacitors removed from the pre-amplifier board:

C03: rated capacitance – 10uF, measured – 17uF, ESR – 0.58Ω, deviation: +70%
C04: rated capacitance – 10uF, measured – 17uF, ESR – 0.61Ω, deviation: +70%
C05: rated capacitance – 1uF, measured – 1.7uF, ESR – 3.8Ω, deviation: +70%
C06: rated capacitance – 1uF, measured – 1.6uF, ESR – 4.3Ω, deviation: +60%
C11: rated capacitance – 10uF, measured – 17uF, ESR – 0.44Ω, deviation: +70%
C12: rated capacitance – 10uF, measured – 17uF, ESR – 0.46Ω, deviation: +70%
C13: rated capacitance – 10uF, measured – 17uF, ESR – 0.84Ω, deviation: +70%
C14: rated capacitance – 10uF, measured – 17uF, ESR – 0.46Ω, deviation: +70%
C15: rated capacitance – 4.7uF, measured – 8.9uF, ESR – 1.18Ω, deviation: +89%
C16: rated capacitance – 4.7uF, measured – 8.8uF, ESR – 1.3Ω, deviation: +87%
C17: rated capacitance – 10uF, measured – 17uF, ESR – 0.42Ω, deviation: +70%
C18: rated capacitance – 10uF, measured – 17uF, ESR – 0.52Ω, deviation: +70%
C31: rated capacitance – 1uF, measured – 1.6uF, ESR – 4.5Ω, deviation: +60%
C32: rated capacitance – 1uF, measured – 1.6uF, ESR – 4.2Ω, deviation: +60%
C33: rated capacitance – 4.7uF, measured – 8.4uF, ESR – 1.14Ω, deviation: +79%
C34: rated capacitance – 4.7uF, measured – 8.8uF, ESR – 1.2Ω, deviation: +87%
C37: rated capacitance – 1uF, measured – 1.7uF, ESR – 3.6Ω, deviation: +70%
C38: rated capacitance – 1uF, measured – 1.7uF, ESR – 3.5Ω, deviation: +70%
C39: rated capacitance – 100uF, measured – 131uF, ESR – 0.08Ω, deviation: +31%

As can be seen, all electrolytic capacitors installed on this board are out of factory tolerance spec.

The six NPN transistors (TR01 to TR06) installed on this board are the notorious 2SC458 transistors. This transistor has different types of failure modes: leakage, noise, and/or static. I replaced every 2SC458 transistor with a modern low-noise Fairchild KSC1845. Keep an eye on the pinout of the replaced transistors when servicing this board. The original transistor is BCE and the new one is ECB.

Pre-amplifier board - before and after

Realistic STA-180_Pre-Amplifier Board_before servicing

Realistic STA-180_Pre-Amplifier Board_after servicing

Main Amplifier Board

The Realistic STA-180 has two main amplifier boards. And each board is secured in the slot. This is certainly a service-friendly design.

I removed these boards from their slots and noticed that one board is marked "F" (failed?) and the other has significant discoloration around the TR04 transistor. This transistor was replaced in the past with the same type. I tested all electronic components on each board and didn't find any failed ones. Except for the electrolytic capacitors being out of factory tolerance spec, all other components are still good. So, I replaced only electrolytic capacitors on these two boards and lubricated each trimming resistor with DeoxIT FaderLube 5% spray.

Each board has four aluminum electrolytic capacitors: C01, C02, C03, and C05. The e-cap C01 is installed in the signal path. I replaced it with a high-quality film polyester WIMA cap. The remaining aluminum capacitors were replaced with low impedance Nichicon UPW/UPM caps.

Test results on original capacitors removed from the main amplifier board:

left channel:
C01: rated capacitance – 1uF, measured – 1.5uF, ESR – 5.6Ω, deviation: +50%
C02: rated capacitance – 100uF, measured – 138uF, ESR – 0.07Ω, deviation: +38%
C03: rated capacitance – 220uF, measured – 343uF, ESR – 0.21Ω, deviation: +56%
C05: rated capacitance – 47uF, measured – 61uF, ESR – 0.16Ω, deviation: +30%

right channel:
C01: rated capacitance – 1uF, measured – 1.5uF, ESR – 4.1Ω, deviation: +50%
C02: rated capacitance – 100uF, measured – 139uF, ESR – 0.08Ω, deviation: +39%
C03: rated capacitance – 220uF, measured – 434uF, ESR – 0.24Ω, deviation: +97%
C05: rated capacitance – 47uF, measured – 60uF, ESR – 0.21Ω, deviation: +28%

As expected, all electrolytic capacitors installed on this board are out of factory tolerance spec.

Main amplifier boards from the left and right channels - before restoration

Realistic STA-180_Main Amplifier Board_Left channel_before servicing

Realistic STA-180_Main Amplifier Board_Right channel_before servicing

Main amplifier boards from the left and right channels - after restoration

Realistic STA-180_Main Amplifier Board_Left channel_after servicing

Realistic STA-180_Main Amplifier Board_Right channel_after servicing

Equalizer Amplifier Board

The equalizer amplifier board has seven aluminum electrolytic capacitors: C01, C02, C07, C08, C13, C14, and C17. Two of them (C01 & C02) are installed in the signal path. I replaced the C01 & C02 with modern low leakage Nichicon UKL caps to improve the signal-to-noise ratio. The remaining aluminum capacitors were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the equalizer amplifier board:

C01: rated capacitance – 3.3uF, measured – 5.5uF, ESR – 3.8Ω, deviation: +67%
C02: rated capacitance – 3.3uF, measured – 5.9uF, ESR – 3.4Ω, deviation: +79%
C07: rated capacitance – 47uF, measured – 69uF, ESR – 1.2Ω, deviation: +47%
C08: rated capacitance – 47uF, measured – 69uF, ESR – 1.1Ω, deviation: +47%
C13: rated capacitance – 100uF, measured – 148uF, ESR – 0.3Ω, deviation: +48%
C14: rated capacitance – 100uF, measured – 141uF, ESR – 0.3Ω, deviation: +41%
C17: rated capacitance – 100uF, measured – 142uF, ESR – 0.1Ω, deviation: +41%

Again, all electrolytic capacitors installed on this board are out of factory tolerance spec.

Equalizer amplifier board - before and after

Realistic STA-180_Equalizer Amplifier Board_before servicing

Realistic STA-180_Equalizer Amplifier Board_after servicing

Power Transistors

The power transistors in this unit were a mixture of the original Hitachi 2SC897 and the replacement ones 2SC1051 (see picture below). I removed all transistors and tested them with an Atlas DCA55 semiconductor analyzer. The measured DC current gain on both original Hitachi transistors met the specifications in the datasheet. But the other two transistors (2SC1051) did not pass the test since their current gain was rather low (6 and 14, respectively). So, I decided to replace these transistors with new 2SC897s from the old stock. I installed two original Hitachi 2SC897 transistors in the left channel and two new 2SC897s in the right channel.

Power transistors in this unit before servicing:

Left channel:
gain = 63 (2SC897, Hitachi)
gain = 14 (2SC1051)

Right channel:
gain = 57 (2SC897, Hitachi)
gain = 6 (2SC1051)

Realistic STA-180_Power Transistors_before servicing

Power transistors in this unit after servicing:

Left channel:
gain = 63 (2SC897, Hitachi)
gain = 57 (2SC897, Hitachi)

Right channel:
gain = 67 (2SC897, Marantz)
gain = 64 (2SC897, Marantz)

Realistic STA-180_Power Transistors_after servicing

FM Dial Pointer

As I mentioned earlier, the FM dial pointer has a unique design. Inside the dial pointer holder are two small incandescent bulbs. One of them is wrapped in red tape. When the tuner is not tuned to a stereo station, only the bare lamp is on and the dial pointer is white. However, when stereo reception is achieved, the bare lamp dims and the "red" one lights up. The dial pointer is red. Isn't that cool? Yes! But trouble comes when one lamp burns out and needs to be replaced. The lamp wrapped in the red film was burned out in this receiver. And it took me at least a few hours to replace it. This is a rather time-consuming process since everything is very small and fragile.

FM dial pointer - two lamps inside the holder

Realistic STA-180_FM Dial Pointer_two lamps inside the holder

FM dial pointer - a new lamp is installed

Realistic STA-180_FM Dial Pointer_new lamp installed

Dial and Meter Lamps

To replace the dial lamps in the STA-180, you need to remove the front panel and unscrew the two small screws on the top, and four more screws on the sides holding the small clips. Then, the dial scale can be removed from the chassis. There are eight dial lamps in total (four for AM and four for FM). I replaced the original incandescent lamps with warm white LED lamps.

Unscrew two small screws on the top, and four more screws on the sides to release the dial scale

Realistic STA-180_Dial Scale_top screws

Realistic STA-180_Dial Scale_side screws

Dial lamps - original incandescent and new warm white LED, AM and FM sections

Realistic STA-180_Dial Lamps, AM Scale_original lamps

Realistic STA-180_Dial Lamps, AM Scale_warm white LED lamps

Realistic STA-180_Dial Lamps, FM Scale_original lamps

Realistic STA-180_Dial Lamps, FM Scale_warm white LED lamps

Meter lamps can be replaced much easier. One should just unscrew two screws behind the meters and the holder can be released. I replaced the two original incandescent lamps with warm white LED lamps.

Holder for the meter lamps - just unscrew two screws and release the holder

Realistic STA-180_Signal Strength and Tuning Meters

Selector Switch Lamps

Be aware that the selector switch lamps in the Realistic STA-180 are non-standard long "fuse type" lamps rated at 10V, 0.33A. The original selector switch lamp is 43mm long while the "standard" vintage "fuse type" lamp is 30mm long. I was able to find a modern bright white LED lamps with a similar length.

Standard (30mm), non-standard (43mm), and non-standard LED (41mm) "fuse type" lamps

Standard, non-standard (43mm), and non-standard LED (41mm) fuse type lamps

New LED lamps are installed

Realistic STA-180_Selector Switch Lamps_new warm white LED lamps

Adjustment of Idling Current and Voltage at Intermediate Point

As I mentioned earlier, no schematic or service manual for this receiver is available online (October 2022). But, the amplifier section in STA-180 has a similar design as in the integrated amplifier Hitachi IA-1000. So, I used the service manual from that amplifier as a reference.

To adjust the idling current one should remove the fuse from the left (right) channel and connect the DC ammeter between the terminals of the fuse holder. I connected the DC ammeter between pin #3 and the positive terminal of the filter capacitor to measure the idling current as these are the same test points but with better access. Then the idling current was adjusted to 30mA with the trimming resistor VR02.

The voltage at the intermediate point can be adjusted if the DC voltmeter is connected between pin # 7 and the chassis. I adjusted it to ~37V on each channel with the trimming resistor VR01.

Idling current on the left and right channels after restoration

Realistic STA-180_Idling Current_Left channel

Realistic STA-180_Idling Current_Right channel

The voltage at the intermediate point on the left and right channels after restoration

Realistic STA-180_Voltage at Intermediate Point_Left channel

Realistic STA-180_Voltage at Intermediate Point_Right channel

Output Power Test

The final output power test was performed at the end of my restoration. The receiver was loaded with a low inductance 8Ω/100W dummy resistor for each channel. The oscilloscope was connected across the speaker terminals and a sine-wave signal of 1kHz was applied to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 17.03 VRMS (left channel) and 17.07 VRMS (right channel). It corresponds to the output power of 36.3W on the left channel and 36.4W on the right channel.

Output power test

Realistic STA-180_Output Power Test

As usual, all the knobs and the front panel were gently cleaned in warm water with dish soap. All controls have been cleaned with DeoxIT 5% contact cleaner and lubricated with DeoxIT FaderLube 5% spray.

The final result can be seen in the photos below. The receiver looks pretty cool and sounds awesome! Please watch a short demo video at the end of this post. Thank you for reading.

Realistic STA-180 - after restoration

Realistic STA-180_After Restoration

Realistic STA-180_After Restoration_with parts

Demo video after repair & restoration

Wednesday, October 19, 2022

Fisher 201 Receiver Restoration

Unit: AM/FM Stereo Receiver
Manufacturer: Fisher
Model: 201
SN: 73398

Another classic stereo receiver made by Fisher Corp came on my bench for restoration. The Fisher 201 "Futura Series" was introduced in 1972 and produces 20 watts per channel into 8 ohms with less than 1% total harmonic distortion. The optional walnut veneer cabinet for this model is 21-UW. The list price in 1972 was $249.95 (Ref. High Fidelity Magazine, April 1972).

Fisher_201_After restoration

Power Supply Board

The power supply board provides +15.5V DC for the tuner section, +31.5V DC for the pre-amplifier and control amplifier, and +53V DC for the power amplifier. This board has three aluminum electrolytic capacitors: C01, C02, and C03. I replaced them with low-impedance Nichicon UPW caps. The original e-caps were tested with an Atlas ESR70 capacitance meter and the results are below. All original capacitors still have very low ESR, but the capacitance tolerance is outside the factory specification.

Test results on original capacitors removed from the power supply board:

C01: rated capacitance – 47uF, measured – 57uF, ESR – 0.11Ω, deviation: +21%
C02: rated capacitance – 47uF, measured – 61uF, ESR – 0.08Ω, deviation: +30%
C03: rated capacitance – 100uF, measured – 131uF, ESR – 0.14Ω, deviation: +31%

The regulating transistor Q01 mounted on the heat sink is a 2SC1226 transistor. In my experience with restoring Fisher 201/202 receivers, the intermittent or unstable operation of the tuner section is often caused by the aging of this transistor. I replaced it with a new Fairchild MJE15032G transistor.

Power supply board - before and after

Fisher_201_Power Supply_before servicing

Fisher_201_Power Supply_after servicing

Power Amplifier Board

Similar to the Fisher 202, each channel in the Fisher 201 has a separate driver board inserted vertically into the slot. This makes the servicing of these boards very easy.

Each driver board has four aluminum electrolytic capacitors: C01, C02, C03, and C04. I replaced the e-cap C01 installed in the signal path with high-quality film polyester WIMA cap. The remaining aluminum capacitors were replaced with low-impedance Nichicon UPW caps.

Test results on original capacitors removed from the power amplifier boards:

Left channel:
C01: rated capacitance – 1uF, measured – 1.6uF, ESR – 5.2Ω, deviation: +60%
C02: rated capacitance – 47uF, measured – 48uF, ESR – 0.42Ω, deviation: +2%
C03: rated capacitance – 100uF, measured – 141uF, ESR – 0.74Ω, deviation: +41%
C04: rated capacitance – 47uF, measured – 69uF, ESR – 0.18Ω, deviation: +47%

Right channel:
C01: rated capacitance – 1uF, measured – 1.8uF, ESR – 4.4Ω, deviation: +80%
C02: rated capacitance – 47uF, measured – 59uF, ESR – 0.22Ω, deviation: +26%
C03: rated capacitance – 100uF, measured – 142uF, ESR – 0.62Ω, deviation: +42%
C04: rated capacitance – 47uF, measured – 66uF, ESR – 0.87Ω, deviation: +40%

The capacitance tolerance of all original capacitors (except C02 from the left channel) is outside the factory specifications.

Driver boards - before and after

Fisher_201_Power Amplifier_before servicing

Fisher_201_Power Amplifier_after servicing

Power Transistors

The original Hitachi 2SC1030 power transistors were removed, cleaned, and tested with Atlas DCA55 semiconductor analyzer. The measured DC current gain on all transistors met the specifications in the datasheet. Each pair of transistors was also very well matched within ~4%. Not too bad for 50+ old vintage gear! I mounted all the transistors back on the heat sink and applied fresh thermal paste. The old thermal pads were also replaced with new Mica ones.

Original power transistors with new Mica pads and fresh thermal paste

Fisher_201_Power Transistors_after servicing

Pre-Amplifier Board

The pre-amplifier board has seven aluminum electrolytic capacitors: C01, C02, C11, C12, C13, C14, and C19. Four of them (C01, C02, C13, C14) are installed in the signal path. I replaced these capacitors with modern low-leakage Nichicon UKL caps to improve the signal-to-noise ratio. The remaining capacitors were replaced with low-impedance Nichicon UPW caps. Note that the filtering e-cap C19 is soldered on the foil side of the PCB.

Test results on original capacitors removed from the pre-amplifier board:

C01: rated capacitance – 10uF, measured – 17uF, ESR – 1.73Ω, deviation: +70%
C02: rated capacitance – 10uF, measured – 16uF, ESR – 2.41Ω, deviation: +60%
C11: rated capacitance – 100uF, measured – 149uF, ESR – 0.44Ω, deviation: +49%
C12: rated capacitance – 100uF, measured – 145uF, ESR – 0.52Ω, deviation: +45%
C13: rated capacitance – 10uF, measured – 15uF, ESR – 0.78Ω, deviation: +50%
C14: rated capacitance – 10uF, measured – 16uF, ESR – 0.74Ω, deviation: +60%
C19: rated capacitance – 47uF, measured – 74uF, ESR – 0.33Ω, deviation: +57%

Again, the capacitance tolerance of all original capacitors from this board is outside the factory specifications.

Filtering e-cap C19 is soldered on the foil side of the PCB

Fisher_201_Pre-Amplifier_C19_soldered on the foil side

Pre-amplifier board - before and after

Fisher_201_Pre-Amplifier_before servicing

Fisher_201_Pre-Amplifier_after servicing

Control Amplifier Board

The control amplifier board has nine aluminum electrolytic capacitors: C503, C504, C511, C512, C513, C514, C517, C518, and C525. The e-caps installed in the signal path (C513, C514, C517, and C518) were replaced with film polyester WIMA caps. The other four e-caps installed in the signal path (C503, C504, C511, and C512) were replaced with modern low-leakage Nichicon UKL caps. And the remaining filtering capacitor C525 was replaced with a low-impedance Nichicon UPW cap.

Test results on original capacitors removed from the control amplifier board:

C503: rated capacitance – 10uF, measured – 15uF, ESR – 3.1Ω, deviation: +50%
C504: rated capacitance – 10uF, measured – 15uF, ESR – 3.0Ω, deviation: +50%
C511: rated capacitance – 4.7uF, measured – 9.6uF, ESR – 5.2Ω, deviation: +104%
C512: rated capacitance – 4.7uF, measured – 9.7uF, ESR – 2.2Ω, deviation: +106%
C513: rated capacitance – 1uF, measured – 1.3uF, ESR – 4.1Ω, deviation: ++30%
C514: rated capacitance – 1uF, measured – 1.4uF, ESR – 3.7Ω, deviation: +40%
C517: rated capacitance – 1uF, measured – 1.4uF, ESR – 3.6Ω, deviation: +40%
C518: rated capacitance – 1uF, measured – 1.3uF, ESR – 4.1Ω, deviation: +30%
C525: rated capacitance – 220uF, measured – 311uF, ESR – 0.05Ω, deviation: +41%

As expected, the capacitance tolerance of all original capacitors from this board is outside the factory specifications. The measured capacitance of the two e-caps (C511 & C512) is almost double their nominal capacitance! Yeah, everything ages and electronic components are no exception.

The 2SC458 NPN transistors installed on this board are prone to failure. A typical failure mode of 2SC458 is noise and/or static. I replaced every 2SC458 transistor with a modern low-noise Fairchild KSC1845. Keep an eye on the pinout of the replaced transistors when servicing this board. The original transistor is BCE and the new one is ECB.

All controls on this board were cleaned and lubricated with DeoxIT FaderLube 5% spray.

Control amplifier board - before and after

Fisher_201_Control Amplifier_before servicing

Fisher_201_Control Amplifier_after servicing

Dial, Meter, and Stereo Indicator Lamps

To replace the dial lamps in Fisher 201 just unscrew two small screws on the top of the dial scale. Then slide the dial lamp bracket to the rear and drop the bracket to get to the lamps. I replaced the original incandescent bulbs with warm white LED lamps to maintain the original look and decrease heat.

Old incandescent dial lamps

Fisher_201_Dal Lamps_original

New warm white LED lamps

Fisher_201_Dal Lamps_warm white LED lamps

The meter and stereo indicator lamps in this receiver burned out. I replaced them with new incandescent lamps.

Two original meter lamps

Fisher_201_Meter Lamps_original

New meter lamps are installed

Fisher_201_Meter Lamps_new lamps installed

Two original stereo indicator lamps

Fisher_201_Stereo Indicator Lamps_original

New stereo indicator lamps are installed

Fisher_201_Stereo Indicator Lamps_new lamps installed

Center Voltage Test

The driver boards in the Fisher 201 do not have trimmers to adjust the center voltage. The service manual simply recommends doing a center voltage test to make sure the amplifier works properly. The test is very simple. First of all, the supply voltage should be measured between pin #3 and the ground. In this unit, the measured supply voltage was ~51.8V. Then, the center voltage should be measured on each board between pin #5 and the ground. This voltage should be half of the supply voltage within +/- 2V. As can be seen from the pictures below, the measured voltage on the left and right channel driver boards were 25.12V and 24.86V, respectively. So, it is approximately half of the supply voltage within +/- 1V. The unit passed the center voltage test, and both channels work properly.

Supply voltage measured between pin #3 and the ground

Fisher_201_Supply Voltage_pin #3 and the ground

Center voltage measured between pin #5 and the ground (left channel)

Fisher_201_Center Voltage_pin #5 and the ground_left channel

Center voltage measured between pin #5 and the ground (right channel)

Fisher_201_Center Voltage_pin #5 and the ground_right channel

Output Power Test

The final output power test was performed at the end of my restoration. The receiver was loaded with a low inductance 8Ω/100W dummy resistor for each channel. The oscilloscope was connected across the speaker terminals and a sine-wave signal of 1kHz was applied to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 10.69 VRMS (left channel) and 10.60 VRMS (right channel). It corresponds to the output power of 14.3W on the left channel and 14.0W on the right channel.

Output power test

Fisher_201_Output Power Test

As usual, all the knobs and the front panel were gently cleaned in warm water with dish soap. All controls have been cleaned with DeoxIT 5% contact cleaner and lubricated with DeoxIT FaderLube 5% spray.

The final result can be seen in the photos below. Please watch a short demo video at the end of this post. Thank you for reading.

Fisher 201 - after restoration

Fisher_201_After restoration

Fisher_201_After restoration_with parts

Demo video after repair & restoration