Fox Tango International FT-102 

Service Manual, Circuit Board Descriptions and Trouble shooting Tips

 Compiled by Wim Penders PA0PGA &  C.L Maher W4CLM





Download FT-102 Service Manual Here

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Circuit Board Descriptions

RF Unit PB-2342B

PB-2342A, RF Unit Receiver:

The incoming signal from pin 2 of J-1004is fed trough RL-1001 (RF amplifier on/off relay) to the preselector circuit selected by the band switch. Then the signal goes through T/R relay RL-1002 to the gate of the RF amplifier Q-1002. AGC is applied to the gate of Q-1001. Q-1001 and Q-1002 (2SK125Y) are together used as a RF amplifier, in a dual gate FET arrangement, ( not unlike a cascode VHF amplifier in earlier days). It combines a low-noise amplification with large signal handling.

The signal is then fed through the RF amplifier relay RL-1003 and T/R relay RL-1004 to one of the band pass filters, selected by two sections of the band switch.

When the RF amplifier is switched off, the signal is passed directly from RL-1001 to RL-1003, and to the band pass filter, bypassing the RF amplifier and giving a still better great signal handling.

From the band pass filter the signal is fed through the T/R relay RL-1005 and transformer T-1031 to the active balanced mixer, Q-1005 and Q-1006 (2SK125Y). Here the signal is mixed with the first LO signal from the Local Unit.

The resulting 8.2 MHz mixer product is then passed through transformer T-1030 and XF-1001, a monolithic crystal filter with a bandwidth of 20 kHz ( a kind of roofing filter to remove IMD causing products), and transformer T-1029 to the IF Unit.

A sample of the wideband IF signal at T-1030 is buffered by Q-1003 (2SC1815Y) for external monitoring, via the IF-Out-2 jack. A sample of the filtered IF signal at T-1029 is buffered by Q-1004 (2SK125Y) for delivery to the noise blanker circuit on the IF Unit and the FM receiver circuit in the optional AM/FM unit. The transistors Q-1001 through Q-1006 operate all from the 24Vdc supply, used to obtain a very good large-signal handling.


The modulated and filtered 8.2Mhz IF signal is applied to the balanced mixer module Q-1008 (ND487C2 schottky bridge), along with the first LO signal from the Local Unit, resulting in an output signal at the operating frequency. This signal is amplified by Q-1007 (2SC2407), Q-1009 (2SC1589) and Q-1010 (2SC1971) before application to the driver tube V-1001 (12BY7A).

A sample of the input to the driver is fed to the RF-Out jack on the rear panel, for use with a transverter.

Output from V-1001 (12BY7A) is resonated by the preselector on the band, selected by the band switch, and then delivered to the Final Unit.




FT-101 Rectifier "A" Unit


Power transformer PT01 delivers 120, 190 and 250Vac for rectification on Rect A Unit. The 120V input is rectified by D-8006 (10D10) and then filtered to provide grid biases for the driver and the final tubes. VR-8001 adjusts the bias voltage for the finals and the biases are keyed as described in the CW Transmit Operation description. The 190V input is rectified by D-8002 and D-8003 (10D10) and then filtered, after which a portion is pulled down to 180Vdc for the screen voltage to driver V-1001 on the RF Unit. The remainder is passed through diodes D-8004 and D-8005 (10D10) to provide 210Vdc for the screen grids of the final amplifiers. The 250V is rectified by diode D-8001 (SM1-12) and then filtered before delivery (as 300Vdc) to the plate of driver tube V-1001 on the RF Unit.


Rect "B" Unit



Bridge rectifier D1 (S4V10) on the main chassis delivers 15 Volts DC to this board where it is filtered and regulated by Q-8501 (2SA733), Q8502 (uPC78L12) and Q1 (2SB705R on the main chassis) providing 12Vdc as the general VCC supply to all other units and to the cooling fan through the HEATER switch. On the main chassis a portion of the 15Vdc present at the emitter of Q1 is diverted to regulators Q3 and Q4 (uPC7812H); Q3 thus providing 12Vdc for the panel lamps and Q4 providing 12Vdc to pin 2 of the EXT VFO jack on the rear panel for the external VFO supply.

AC voltage from the heater winding of the power transformer is rectified by D-8505 (V06B) and filtered by capacitor C-8509, where the filtered 15Vdc from bridge rectifier D1 is added to result in about 26Vdc. This voltage is regulated by Q-8503 (2SC496Y) and zener diode D-8501 (AW01-24) to provide 24 Vdc for the receiver front end circuits on the RF and IF Units.

A portion of the 24 Vdc is further regulated by Q-8505 (78L15) to provide 15Vdc for the Width Control system. During transmission, 12Vdc is applied to Q-8504 (2SC1815Y) which then grounds the base of Q-8503, dropping the 24Vdc and 15Vdc lines to zero and thus disabling the sensitive receiver front end and the Shift/Width function.

The power transformer 320Vac winding connects to the Rectifier B Unit where the AC is rectified by D-8501 through D-8504 (10D10), and then doubled by capacitors C5 and C6 (on the main chassis) to result in 900 Vdc for the plate circuit of the final amplifiers. Also when a plug is not inserted into the EXT VFO jack on the rear panel, 8 Vdc is delivered from the 8 Vdc supply bus (regulated from the 12 Vdc bus by Q2 (uPC14308), on the main chassis) to zener diode D85-6, producing 6Vdc for delivery to the VFO unit.


Audio Unit  PB-2344

PB-2344: AF Unit Receive:

The SSB or CW 455khz IF signal is detected at D3021-D3024 (1N60), which also receives the 455khz third LO signal from the Local Unit, after buffering at Q-3018 ((2SC1815Y). The CW audio product is then passed through an active CW filter, Q-3020 ((2SC1815GR) and APF filter Q-3024 (AN6551); while the SSB audio product and the detected AM are passed through active filter Q-3022 (2SC1815GR) and amplifier Q-3023 (2SC1815GR); after which each signal is applied to analog switch Q-3019 (MC14066B), which selects the appropriate mode via the MODE selector for further amplification. Finally, the selected output is fed through the muting switch Q-3030 (2SC1815Y) to the audio power amplifier Q-3025 (uPC2002V) and from there to the speaker. A portion of the output signal from Q-3019 is diverted through amplifier Q-3016 for auxiliary output at the AF-OUT jack on the rear panel.


IF Unit PB-2343A, IF Unit

PB-2343A, IF Unit  Receiver:

The 8.2 MHz signal from the RF unit is amplified by the first IF amplifiers Q-2001 and Q-2002 (2SK125Y), which are also operated from the 24V supply to maintain excellent large signal performance. The amplified first IF signal is then passed through the noise gate, composed of two schottky diodes D-2001, D-2002 (1SS97) and a varactor diode D-2003 (FC63) before being applied to the first set of crystal filters.

SSB and CW signals are passed through a 2.9 kHz wide 8-pole crystal filter XF-2001 (XF-8.2HS), while AM signals are passed through a optional 6 kHz wide, 3-pole monolithic ceramic filter XF-2002 (XF-8.2GA). If XF-2002 is not installed, AM signals pass through XF-2001.

When the NAR button is pressed on the front panel, CW signals are passed through one of the optional narrow second filters in location XF-2003: this can be either the 600hz width, 8-pole crystal filter XF-8.2HC, or the narrower 300hz width, 8-pole crystal filter XF-8.2HCN.

When the NAR button is pressed in the SSB mode, the SSB signals are passed through one of the optional narrow SSB filters in location XF-2004, this can be the optional  2.9khz wide 8-pole crystal filter XF-8.2HS, or the narrower 1.8khz wide, 8-pole crystal filter XF-8.2HSN.

All signals from XF-2001, (and AM signals from XF-2002, if installed) are delivered to the second IF amplifier Q-2003 (3SK73GR) when the NAR button is off, or the optional filters are not installed; otherwise CW and SSB narrow signals from the second filters are applied to Q-2003 after narrow filtering. After amplification, the filtered 8.2khz IF signal is applied to the second mixer Q-2004 (3SK73GR) where it is heterodyned with the 8.67 MHz second LO signal from the Local Unit, producing the 455 kHz second IF.

CW and SSB signals are then filtered by a third filter CF-2001, a 2.9 kHz width, 3-pole ceramic filter (CMF455J1); unless optional CW-narrow third filters are installed at XF-2005 (either a 500hz 8-pole filter XF-455C or a 270hz, 8-pole filter XF-455CN) and the NAR button in pressed.

AM signals bypass these filters.

All signals are fed from the third filter bank through the Q-Multiplier, composed of Q-2006 and Q-2007 (2SC1815Y) and notch filter Q-2008 (2SC1815Y) to the 455khz IF amplifier Q-2010 (3SK73GR).

A portion of the amplified signal is then amplified by Q-2011 (2SC1815Y) and fed to the Narrow-Band IF-Out-1 jack, the AM detectors D-2038 and D-2080 (1N60) and the AGC detectors D-2039 and D-2040 (both 1N270). The remainder of the amplified signal from Q-2010 is delivered to the product detector on the AF Unit. The detected AM signal from D-2038 is delivered to the AF Unit for filtering and amplification. The detected AGC signal from D-2039 is amplified by Q-2012 (2SC1815GR), and a portion of the output is fed back to the IF amplifier Q-1001 for gain control, while another portion is further amplified by the S-meter amplifiers Q-2013 (2SK19TMGR) and Q-2014 (2SA564AR) before delivery through T/R relay RL-2001 to meter II.



The double sideband modulated signal from the AF Unit is buffered by Q-2005 (2SK19TMGR) and passed through ceramic SSB filter CF-2001 to mixer Q-2017 (3SK73GR), unless the speech processor is on, in which case the filtered remaining sideband from CF-2001 is amplified by second IF amplifier Q-2017 (also used in the receive path) and Q-2015 (2SC1815Y), a portion of the output of which is diverted to amplifier Q-2023 (2SC1815GR) for COMP indication on meter I. The remainder of the output from Q-2015 is clipped by limiter-amplifier Q-2016 (TA7060P) before being applied to mixer Q-2017 (3SK73GR).

The 8.7 MHz second LO signal from the Local unit is mixed with the modulated 455khz signal at Q-2017 to produce an 8.2Mhz IF, which is then filtered trough XF-2001 in the first bank of filters and amplified by Q-2003 (also used in receive) before delivery to the RF unit.

SSB Mode

The speech signal from the microphone jack is amplified by Q-3001 (2SC732TMGR) and Q-3002 (2SC1815Y). A portion of the speech signal is diverted for VOX operation. The remaining signal from  Q-3002 is further amplified by  Q-3003 (2SC1815BL) and passed through adjustable TX tone filters to tone amplifier Q-3004 (2SC732TMGR). A portion of the output from Q-3004 is diverted to the optional AM/FM Unit, when installed; while the remainder is applied to the balanced ring modulator, composed of Schottky diodes D-3002 to D-3005 (1SS97)

The balanced modulator receives also a 455khz LO signal from the Local Unit after buffering by Q-3017 ((2SC1815Y), and the resulting modulated IF is delivered to the IF unit.


VOX, Anti-Trip

A portion of the amplified speech signal from Q-3002 is amplified for VOX operation by Q-3010 (2SC1815Y), and then rectified by D-3014 (1N60) to produce a DC voltage, whose level varies with the speech input at the microphone.  This DC is amplified at Q-3011 (2SC1815Y), and further amplified at Q-3012 (2SC1815Y) before being applied to switch Q-3009 (2SA733). Te switched output of  Q-3009 then controls a Schmitt trigger composed of Q-3013 and Q-3014 (2SC1815Y), which in turn switches relay control Q-3015 (2SA496Y) to drive T/R relays RL1 and RL2 on the main chassis.

The anti-trip signal is derived from a sample of the output from audio amplifier Q-3025, or from an external source via the A-TRIP IN jack on the rear panel.

This signal is amplified by Q-3006 (2SC1815Y) and then rectified by D-3011 to produce a DC voltage whose level varies with the audio output from the receiver. This DC is amplified by Q-3007 (2SC1815Y) and Q-3008 (2SA733) before being fed into the VOX control circuit at Q-3012, to counter the VOX DC voltage that is produced by audio at the microphone.


CW Mode

The CW carrier is generated by crystal oscillator Q-3026 (2SK19TMGR), activated by analog switch Q-3019 in the CW, AM and FM modes through Q-3029 (2SC380TMY) and applied through amplifier Q-2003 on the IF Unit to balanced mixer Q-1008 on the RF Unit as for SSB operation. Final amplification is the same.

The key lead from the key jack activates side tone oscillator Q-3005 on the AF Unit and also controls switches Q-8001 (2SA639Q), Q-8002 (2SC1815Y) and Q-8003 (2SA639Q) to turn the biases to the final tubes on and off. Q-8002 also keys post TX mixer amplifier Q-3026 and offers a keyed control point at pin 2 of the ACC-1 jack. The side tone oscillator provides an output to VOX amplifier Q-3010 to activate the VOX circuit for semi break-in CW control.


Noise Blanker:

Buffered output from the 20 kHz filter XF-1001 is amplified by Q-2019 and Q-2020 ((2SC1583) as well by Q-2021 (2SC380TMY) before being applied to noise detectors D-2053 and D-2054 (1N60).

A portion of the output from Q-2021 is also rectified by D-2055 and D-2056 (1N60) and amplified at Q-2022 (2SC1815GR) for feedback to Q-2019 and Q-2020 as noise blanker AGC. The time constant of this AGC is adjusted by the NB LEVEL control on the front panel.

Output from the noise detector is buffered by gate control Q-2018 (2SC1815GR) before being applied to the noise gate D-2001-D-2003 who are located between the first IF amplifier and the first bank of crystal filters.


A portion of the output of IF amplifier Q-2003 is buffered by Q-2024 (2SC380TMY) and fed to the transmit monitor mixer Q-2025 (2SK19TMY), which is also fed the second LO signal from the Local Unit. The 455khz output of Q-2025 is then demodulated at Q-2026 ((2SK19TMY), which is also fed a portion of the third LO signal from the Local Unit after buffering at Q-3017 on the AF Unit.

The resulting audio signal from Q-2026 (2SK19TMY) is amplified by Q-2028 (2SC380TMY), which also amplifies a sample of the audio input from the FM detector Q-6008, delivered from the optional AM/FM Unit, when the FM mode is used, as well amplifies the output from the monitor AM detector Q-2027 (2SC380TMY), which receives IF output from Q-2024. The output of amplifier Q-2028 is delivered to the final audio amplifier Q-3025 on the AF Unit for output to the speaker or headphones.





Band switching signals from the BAND selector are delivered through the Counter Unit to J-4001 on the Local Unit, selecting one of the six VCOs Q-4001 Q-4006 (2SC945Q) for the band of operation. The selected VCO oscillates at the first LO frequency, and provides output through buffer Q-4007 (2SC535B) to buffer Q-4008 (2SC2407), which is also controlled by the unlock signal.

Q-4008 provides first LO output at J4002 for delivery to the RF Unit.

A portion of the VCO signal is buffered by Q-4011 (2SC535B) and applied to PLL mixer Q-4012 (SN76514), which also receives a 13.715 to 34.215 MHz  PLL Local signal from buffer Q-4013 (2SC535B), whose frequency is determined by the band, mode, IF shift and VFO setting for the operating frequency. The 1.0 to 4.0 MHz output from PLL mixer Q-4012 is then passed through a band pass filter and buffered by Q-4014 and Q-4015 (2SC535B), before being fed to programmable divider Q-4017 (74LS192). Q-4017 is programmed by band switching signals to provide a output of 500 kHz, regardless of the operating frequency. This output is applied to phase detector Q-4018 (MC4044) which also receives a 500 kHz reference signal derived from 10 MHz crystal oscillator Q-4026 (2SC945Q), buffered first by Q-4028 (2SC945Q) and then divided by 10 at Q-4019 (74LS90) and again by 2 at Q-4020(MC14518) before final buffering at Q-4021 (2SC945Q).

Q-4018 provides a DC output, proportionally to the phase difference between the VCO derived input and the reference derived input. The Dc output is then delivered through active low-pass filters Q-4022 and Q-4023 (2SC732GR) to the varactor of the selected VCO, thus locking the VCO frequency to the reference oscillator

If the output from phase detector Q-4018 is too great to allow locking of the VCO, an unlock signal is delivered through amplifier Q-4016 (2SA733) to the unlock switch Q-4009 (2SC945Q) which disables first LO buffer Q-4008, removing the first LO signal from the RF unit. A portion of the switching signal from q-4009 also switches Q-4010 (2SC945Q) which delivers a blinking command signal to the Counter Unit, causing the display to blink whenever the PLL is unlocked.

The PLL local signal is derived from a 10 MHz reference oscillator Q-4026 and 19,21 MHz VCXO Q-4033 (2SC945Q) along with the VFO input.  Output from VCXO Q-4033, shifted appropriately for the selected operating mode by Q-4032 (2SC940Q) and according the IF shift function, is buffered by Q-4035 (2SC945Q) and applied to PLL local first premixer Q-4024 (SN76514), which also receives a 5.0 to 5.5 MHz signal delivered from the VFO Unit or external VFO jack, through a low-pass filter.

The 13.715 to 14.215 MHz output from pre-mixer Q-4024 is then filtered through a band pass filter composed of T-4001 through T-4003 before being delivered to the PLL mixer ( for the bands below 14 MHz).

For operating on the bands above and including the 14 MHz band; the 13.715 to 14.25 MHz filtered signal is applied to PLL local second premixer Q-4025 (3SK73GR), which also receives a 10 MHz signal, filtered through band pass filter T-4011 (for operating frequencies between 14 and 21 MHz), or a 20 MHz signal from times 2 multiplier Q-4029 (2SC945Q) for operating frequencies on or above 21 MHz.

Both the 10 and 20 MHz signals are derived from 10 MHz crystal oscillator Q-4026, through buffer Q-4027 (2SC945Q). The output from the second premixer Q-4027 is then passed through one or two band pass filter networks, composed of T-4004 trough T-4006 or T-4007 and T-4008 for the 14 and 18; or 21, 24.5 and 28 MHz bands respectively.

The filtered output from the appropriate band pass filter is then buffered through Q-4013 and applied to the PLL mixer Q-4012 as before. Frequency and filter selection is made through diode switches by commands from the BAND selector.

The 8.67 MHz second LO signal is derived from the 19.215 MHz VCXO and the signal from another 10.54 MHz VCXO (actually 10.5466 for USB, 10.5434 for LSB, and 10.545 MHz for AM); with continuous frequency adjustment by the Width system. The output of this 10.54 VCXO Q-410.54 VCXO Q-4036 (2SC945Q) is buffered by Q-4037 (2SC945Q) and applied to second mixer Q-4038 (3SK73GR) which also receives a signal from 19.215 MHz VCXO Q-4033 after buffering by Q-4034 (2SC945A). The 8.67 MHz output from mixer Q-4038 is then buffered by Q-4039 (2SC945Q) and passed through a band pass filter for delivery to the IF Unit from J-4008 and to the AM/FM Unit from J-4009.

The 455khz third LO signal is derived from 10 MHz  reference oscillator Q-4026 and 10.54 MHz VCXO Q-4036. The 10 MHz signal, after buffering by Q-4028 and division by 10 at Q-4019 ( see PLL description) has its 1 MHz square pulse signal filtered through a band pass filter composed of T-4012 and T-4016, to provide an 11 MHz signal for third LO mixer Q-4040 (3SK73GR). Q-4040 also receives a portion of the buffered 10.54 MHz signal from Q-4037, thus providing an output at 455 KHz, buffered by Q-4041 (2SC945Q) and passed through a low pass filter for delivery from J-4011 to the AF Unit.

This unique frequency derivation scheme allows the shift function to tune the second LO at 19.215 MHz VCXO Q-4033, while the width function synchronously tunes the second LO and third LO, commonly derived from 10.54 VCXO Q-4036.

Sample data to the Counter Unit for frequency display is derived from both the VFO signal and the 10 MHz reference oscillator Q-4026. Reference divider Q-4019 provides a 2 MHz square pulse for this purpose, which is filtered at T-4013 to provide a 6 MHz signal to counter sample mixer Q-4030 (3SK73GR), which also receives the VFO signal after low pass filtering. The resulting 0.5 to 1.0 MHz mixer product is passed through another low pass filter before delivery from pin1 of J-4013 to the Counter Unit.

A clock signal for the Counter Unit is also derived from 10 MHz reference oscillator Q-4026 after division by 10 at Q-4019, further division by 40 and Q-4020 (see PLL description), buffering by Q-4031 (2SC945Q) and low pass filtering. This 25 kHz signal is brought out for the Counter Unit at J-4013, pin 3, while a portion of the unfiltered signal is delivered from J-4014 to the receiver input at the EXT ANT jack on the rear panel, providing a MARK signal for the receiver, when the MARK button is depressed.

Second reference divider Q-4020 also provides a 100 KHz signal, delivered from J-4015 to the EXT VFO jack and the ACC-1 receptacle on the rear panel.



VFO Unit


Variable frequency Oscillator module Q-7001 (VFO-1) provides an output of approx. 4.95 to 5.55 MHz, in accordance with the setting of tuning variable capacitor VC-7001; paralleled with temperature compensating capacitors and trimmers and Clarifier varactor D-7001 (1S2236), whose capacitance is varied by changes in the clarifier control adjusted from the CLAR control, when the CLAR function is activated on either transmit or receive. Output from Q-7001 is fed through a band pass filter before delivery from pin 1 of J-7001 to the local unit.




Relay Unit

PB-2354 RELAY Unit

On the Relay Unit the signal is fed through T/R relay RL-9601 to the coaxial ANT jack, with a sample delivered through the PO ADJ potentiometer on the rear panel and the METER SELECT switch to METER I


Final Unit

PB-2355 Final Unit

On the Final Unit the transmit signal is brought up to full power at V-9801 to V-9803 (6146B) before delivery trough the final tank circuit on the main chassis to the

 ALC circuit

On RECT A Unit the grid bias to the final power amplifiers is sampled by Q-8004 (2SC2229). A resulting DC voltage appears whenever the grids of the final tubes are driven positive with respect to the bias voltage, as grid current starts to flow through R8021, causing a voltage drop that is then amplified  by Q-8004 for delivery to the IF Unit.

On the IF Unit a portion of this ALC voltage is fed to the gate of second IF amplifier Q-2003, varying the gain of this stage to limit the drive level to the RF Unit and final amplifiers during transmission.

The incoming ALC voltage is also amplified by Q-2029 (2SK19BL). A portion of the output from Q-2029 is applied through meter amplifiers Q-2031 (2SK19TMGR) and Q-2032 (2SA564A) for delivery through T/R relay RL-2001 to meter II during transmission. The remainder of the output from Q-2029 is buffered by Q-2033 (2SC1815Y) and amplified by DC amplifiers Q-2034 and Q-2035 (2SA564AR) which, together with Q-2030 (2SC1815Y), make up the peak-hold circuit.

Q-2030 gives a constant voltage output proportional to the charge retained at capacitor C-2155, which is charged by the ALC voltage from Q-2033 when the ALC METER peak hold switch on the front panel is depressed. The constant output from Q-2030 is then fed to meter amplifier Q-2031 in the same fashion as normal ALC for meter indication.


Counter (Display) Unit


The 0.5 to 1.0 MHz sample signal from the Local Unit is buffered by Q-5001 (2SC1815Y) and again by a gate in Q-5005 (MC14011B) before being applied to Q-5006 (MC14022B) for gating and division by 8. Output from Q-5006 is then applied to pin 37 of LSI Counter Q-5007 (TC-5070).

The 25 kHz clock signal from the Local Unit is buffered by Q-5002 (2SC1815Y) and divided by 25 and by 50 at Q-5003 (MC14518B). The resulting 1 KHz output is applied to SCAN LOCK pin 22 of Q-5007, while the 500 Hz output is passed to Q-5004 (MC14518B) for further division by 10 and by 50. These outputs are summed in Q-5005 resulting in a gating pulse for Q-5006 and LOAD PRESET input to pin 32 of Q-5007. The 10 Hz output from Q-5004 is also delivered through a gate in Q-5005 to provide a STORE pulse to pin 16 of Q-5007; and to Q-5006 for gating control.

Preset data for Q-5007 is furnished by the band switch through encoders Q-5012 and Q-5013 (MC14081B), and by the mode selector through Q-5011 (MC14011) for a 700 Hz CW shift and plus 500 KHz for appropriate band selections. Digit driver Q-5009 and Segment driver Q-5008 (both TC5066) pass the output of Q-5007 to fluorescent display DS-5001 (FIP9E8), while Q-5008 (TC-5066) passes mode display information to DS-5001.

The 8 volt DC bus is regulated by Q-5015 (78L05) to provide the 5V supply for the ICs, while the 8V bus is applied directly to the DC-DC converter formed by oscillator Q-5014 (2SC1815Y) and T-5001 (E142) supplies negative 10 Volts DC for the display and for delivery from J-5006 to the 10 volt DC bus.


Restoring 28Mhz / 29 MHz to your digital display

If removing a 27 MHz modification from your FT-102 Display then remove the diodes as per this photo. Check CB modification as several other diodes on top of the display may have been cut or removed.  See Notes: Removing CB modifications





PB-2347 Optional AM/FM Unit.

FM Receive

A portion of the buffered IF signal (after the 20khz filter XF-1001) from Q-1004 is delivered through another 20khz width filter XF-6001 on the AM/FM Unit to the mixer section of Q-6008 (MC3359), which also contains limiter-amplifier, discriminator, noise amplifier and AFC sections.

In the mixer section the filtered receiver IF is mixed with the 8.67 MHz  second LO signal delivered from the Local Unit, resulting in a 455khz second IF. This signal is passed through ceramic filter  CF-6001 and fed to the IF limiter amplifier section of Q-6008, where amplitude variations are removed from the signal. The signal is then applied to the discriminator section of Q-6008, resulting in an audio output coinciding with frequency shift in the 455khz IF signal.

When no carrier is present in the 455khz IF, the high frequency noise present at the discriminator output is amplified by the noise amplifier section of Q-6008 and rectified by noise detector D-6004 (1N60). The resulting DC voltage is passed through the SQL control back to Q-6008  which turns off the audio output when no carrier is present.

When a signal is received the audio output from Q-6008 is delivered to audio amplifier Q-3025 on the AF Unit unless the MUTE line grounded, in which case Q-6012 (2SC1815GR) grounds the output signal from Q-6008. AFC output from Q-6008 is filtered and delivered through the METER I for discriminator tuning indication.


FM transmit

The signal from tone amplifier Q-3004 on the AF Unit is also delivered to limiter amplifier Q-6014 (uPC577H) on the AM/FM Unit, where the audio signal amplitude is amplified and limited to a preset level, preventing over-deviation. This signal is then applied to varactor diode pair D-6003 (MV104) to phase modulate 8.2 MHz VCO (voltage controlled oscillator) Q-6006 (2SK19BL) serving as part of a PLL (Phase Locked Loop). One portion of the VCO output is buffered by Q-6004 (2SK19TMGR) and then divided by 256 at Q-6005 (TC5082P) for application to phase detector Q-6013 (TC5081P).

Carrier oscillator Q-3026 on the AF Unit delivers its signal, after buffering by Q-3029 to buffer Q-6002 (2SK19TMGR) which signal is then divided by 256 at Q-6003 (TC5082P) and applied to phase detector Q-6013 along with the signal from Q-6005. Q-6013 then presents a DC output voltage proportional to the phase difference between the divided carrier signal and the divided VCO signal, which is passed through active filter Q-6015 (2SC1815GR) back to modulator varactor D-6003, thus locking the VCO frequency to that of the carrier oscillator.

The remainder of the frequency modulated signal from VCO Q-6006 is buffered by Q-6007 (2SC380TMY) and delivered through IF amplifier Q-2003 on the IF Unit to the second transmit mixer Q-1008 on the RF Unit. A sample of the buffered VCO output from Q-6006 is also delivered to the input of  FM receive detector Q-6008 for IF monitoring of transmitted signals.


AM transmit:

A portion of the amplified and filtered speech audio from the tone amplifier Q-3004 on the AF Unit is delivered to AM modulator Q-6001 (TA7069P) on the AM/FM Unit, which also receives a carrier signal from carrier oscillator Q-3026, buffered by Q-3029 (2SC380Y), also on the AF Unit.

The modulated AM output is then delivered through IF amplifier Q-2003 on the IF Unit to the final transmit mixer Q-1008 on the RF Unit, as for SSB and CW, and final amplification is the same.


Yaesu FT-102

Troubleshooting Tips

General service tips!

First off: When trouble shooting your FT-102 the first thing we would like to you think about is safety as this rig will really pack a wallop on the high voltage (rail) capacitors up to 900 VDC, even long after the rig has been turned off for some time. Many an FT-102 service technician can testify to this first hand!

Second: Be very careful when working in this transceiver as it is very easy to disturb or break wring that has become brittle due to age.  It is very easy to disturb wiring in the rig and wind up with unexpected problems cropping up in the transceiver that you did not have prior to starting your repairs. We highly suggest that you work in small steps and check your work, test the transceiver for normal operation, then move on to the next trouble area. Even though you may have problem with the transceiver, it's important to check the rig and make sure your symptoms have not changed.  So use caution as your proceed, check all wiring as you work.  If the symptoms have changed then go back to the last place your were in the rig as it's highly possibly a wire could have broken loose from a terminal strip or even behind the front panel.

Third: When working on your FT-102, changing relays or troubleshooting for intermittent problems. Carefully check all circuit boards for hairline cracks in solder joints at the point where all the plugs meet up with the circuit boards.  Carefully inspect the boards for poor solder connections. Recently I had a transceiver with an intermittent S-Meter upon close inspection I found several connections that gave up the ghost after some 35 years, note the picture below and carefully solder all connections that don't look solid, use enough heat to flow the solder making a new connection while at the same time be very careful not to bridge any connections that might cause new problems!

RF AMP NOT WORKING: If your RF amplifier is inoperative, turn the volume all the way down on your transceiver, push the RF Amp button thus checking the Relay and control circuit. You should be able to hear the RF Amp relay click on and off with the button.   If after checking the relay your amp is not working it can be assumed re-amp transistors Q01 and Q02 on the RF Unit. FETS on the RF unit (2SK125) could very well be bad.   Data sheet for Sony 2SK125  This was a common failure item on the FT-102. HTML page 2SK125 data sheet below.  Replacement 2SK125 can be bought from B&D Enterprises or as a suggestion you can use try a suitable replacement like the  NTE-312 that meets or exceeds the original Sony specifications.

LOW RX SENSITIVITY: Check antenna input lamp fuse which is a small lamp fuse located on the relay unit in the PA compartment. It is not possible to use any old bulb here as some bulbs may cause several dB attenuation. Recommend replacing the lamp fuse with original equipment

INTERMITTENT LOW RX SENSITIVITY: Suspect the relays on the RF  PCB around the RF amp.  Don't miss RL05 this is the  relay at the front of the board under the shaft of the band switch which is difficult to change.  Cleaning the relays can help but they usually go intermittent again within a few weeks - it's better to replace them if they are available.

PRESELECTOR NOT TUNING CORRECTLY: There is a shaft coupler on the band switch shaft - if the screws in this are loose it is possible for the front and rear sections of this switch to be out of physical alignment.

NO RF OUTPUT (PA DRAWING CURRENT AS NORMAL): The main antenna T/R relay has been known to burn its contacts. .

PA FAULT CONDITIONS, Rig blowing fuses: Check for physical short circuits around the band switch in the PA compartment. Inspect the rear panel fuse socket and see if the ( + ) slot for a screw driver is worn down.  If so this is a good indication that the rig has been blowing fuses thus you possibly have one or more 6146 final amplifier tubes that are failing or arcing occasionally.

ERRATIC CONDITION WHEN LOADING CONTROL IS VARIED, especially below setting of 2 on panel marking.  Varies smoothly when top of final amplifier compartment is removed.  Trouble returns when PA top cover replaced. The loading capacitor frame touches the top cover of compartment. Insulate top cover around loading control.  Check 3~ gang Loading capacitor very closely and make sure no plates are shorting or arcing a carbon path when transmitting.

FLUCTUATING POWER OUTPUT: check 6146 finals for arcing, check PA (RFC) choke.

FT-102 POOR AUDIO WHEN USING LINEAR: Many complaints about poor audio have been received when using a linear amplifier that were traced to RF entering the 102 through a connected phone patch.  Since most people don't use phone patches anymore, the simple fix is just to remove it. the demise of phone patching has all be resulted due to cellular phones and Email.  If you're so inclined to fix the problem properly a little effective filtering to prevent the entrance of RF through accessories should take care of the problem. 

REMOVE CB MODIFICATIONS   SEE: Yaesu mod sheet and reverse all mods. The CB modification allowed the 29-30Mhz range to cover 27-28Mhz and the counter also had to be modified to display CB frequencies, so it will have to be re-worked as well.

NO TX: Check the series pass transistor in the 12v. regulator circuit.  Possible failure of screen grid supply voltage from RECT A Unit. Check for 80ma IC grid current.  Check all voltages on RECT A unit.

NO TX - NO DRIVE: Check RECT A UNIT. Check driver tube after replacement.

POOR NEUTRALIZATION: This can sometimes be a problem if 2 or 3 different types of valves are used in the PA.

PA WON'T NEUTRALIZE: PA screen grid supply to a higher voltage on the rectifier unit, causing this problem.

FREQUENCY SHIFTS WHEN CLARIFIER ON: Dirty contact on RL4001, the clarifier relay.

FM TX WAY OFF FREQUENCY: Failure of Q13 (TC5081P) on AM/FM unit. See Yaesu mod sheet to prevent further failure.

LUMPY VFO DRIVE: Improved can be had  by cleaning and re-lubrication of the tuning mechanism.  If its really bad the drive will probably need to be replaced.

KEY CLICKS: Some of the earlier models suffered from key clicks on CW. To cure this connect a 0.68 microfarad cap between key 1ine on the REC A board and ground.

DRIFT ON CW: Some of the early units suffered from a drift of 50-100Hz during the first couple of minutes of CW transmission. Yaesu suggest removing C153 (3.3 microfarad) on the local unit to cure this problem. It is located between X4002 and T4014.

FT-102 Survival Guide

For a complete summary of these pages and more

 you are invited to down load the Fox Tango FT-102 Survival guide compiled by PA0PGA We recommend you right click and save the file to your computer. You will need a copy of Adobe reader Version 6, 7 or later to view the guide.

Click here to download FT-102SG PDF file (12.3 MB)

**Our sincere thanks to Wim Penders ( PA0PGA) and Dr. Malcolm Eiselman (NC4L) for their dedication and contributions to amateur radio community and their contributions that were used to compile this FT-102 survival guide. Oh Yes, I guess I fit in there too!  ~ C.L. Maher W4CLM Administrator Fox Tango Intl.