Replacement Mode Switch for FT-101ZD
Before we look at the various boards in your FT-101ZD I would like to take a quick look at the FT-101ZD mode switch. We get many requests here at Fox Tango International from members looking for a replacement mode switch for this rig. After much research some members have reported having good luck using the following replacement part #C4D0806N-A made by Electroswitch, can be purchased through Allied Electronics, www.alliedelec.com SKU# 873-1010. 6 position switch for the MK II & MK III radios. Allied electronics, Digikey, and Mouser have this part. If you need more information on this switch you can down load the switch datasheet here in PDF format.
Switch, Rotary (Non-Shorting), C4 Series, 08 Poles, 02-06 Positions
RF boards PB1960A and PB2154A
|PB-1960A RF board component side||PB-1960A RF board solder side|
Contains the RF pre-amplifier, the receiver and transmitter mixer and a buffer stage, The mixer output of 8.9875Mhz goes to the IF board. The in and output tuning of the RF amplifier is done by permeability-tuned circuits, resulting in high sensitivity and excellent rejection of unwanted out-of-band signals.
The difference between the two boards is the mixer. The PB1960A uses a balanced mixer with 2 Fet’s, the later PB2154A board uses a diode ring mixer, for a better big signal behavior.
PB-2154A RF board component side
IF board PB1963B/C
The IF board is the heart of the transceiver, and is the same in every type of FT-101ZD. The signal is first passed trough a monolithic filter with a bandwidth of 10 kHz, to have a wide band point for noise blanking. The signal pass then the noise blanker gate and is fed trough the SSB filter or the optional CW filter to the IF first mixer. Here the incoming signal is heterodyned with a 19.7475 MHz local signal. This local signal is delivered from a XCO and the resulting mixing frequency is 10.76 MHz. This 10.76 MHz signal is fed trough a second SSB filter, and mixes with the same 19.7475 MHz local signal back to the original IF frequency of 8.9875 MHz. The 19.7475 MHz XCO is tuned with a varicap over a close range, and the result is that the pass band of the first and second filter shifts along each other, so in effect making the pass band smaller or broader, depending of the frequency of the XCO. It is a very useful item, you can make the band pass as low as 300 Hz, and as high as the original pass band of the first filter. (SSB 2.4 kHz, CW 300 or 600 Hz). The skirt of the filters add, so the filter pass band improves too. The output from the second IF mixer is fed to a 2-stage IF amplifier, and is delivered to the AF unit. On the board are also a AGC amplifier and S-meter amplifier, the SSB Tx IF filtering and the speech processor with filter. The board has the SSB filter installed, and there is room for installing a 300 or 600 Hz CW filter.
NB-Fix unit PB1961
This board is also used in every FT-101ZD, and contains the noise blanker circuitry and a crystal oscillator for 2 fixed frequencies. The fixed frequencies are sideband dependent, so the operating frequency is on LSB 3 kHz higher than on USB at a given crystal frequency. The necessary crystals have to be in the VFO (5 – 5.5 MHz) range.
AF Unit PB1964
The AF unit board contains the SSB/CW diode ring demodulator and the carrier oscillator: USB, CW rx 8989 kHz LSB 8986 kHz CW Tx 8988.3 KHz The audio signal is amplified and delivered to the internal or external speaker. On the AF board is also the marker generator, who provides a 25 kHz marker signal for alignment and testing purposes. The TX microphone amplifier with sideband generator, and a 800 Hz side tone generator for CW are also a part of the AF unit. The AF unit board is used in every model.
VFO Unit PB1440B-3420
The VFO uses a modified Colpitts type oscillator to generate a 5 –5.5 MHz VFO signal, producing a 500 kHz tuning range. The VFO tuning is extremely linear over the entire range, no small feat with the use of a “normal” tuning condenser. Stability is very good, and tuning is very exact with the smooth precision gear. The VFO is one of the reasons for the good overall stability of the transceiver. The VFO frequency can varied by a small amount, providing a offset of +/- 2.5 KHz, by a varicap diode and a controlling voltage. (Clarifier), very useful when you are in a net, if all members are not exactly at the same frequency. Can be used in TX and Rx mode, or both. This VFO unit is used in all the FT-101ZD series transceivers. Premix Local Unit PB1965
This is the newer plug-in board, used in FT-101ZD MK2 and MK3, that has all amateur bands including the W.A.R.C. bands 30m, 17m, and 12m. This board has no WWV or a optional AUX band.
Premix Unit PB1962, PB2152
Used in production runs 16- to the end in the 101ZD This counter uses a custom LSI chip, the OKI MSM9520RS, which has all the possibilities of the older counter including the frequency offset in one chip. The rest of the board is used for the transistor digit and segment drivers. The LED displays in this counter are multiplexed.
AM Unit PB2040The AM print has a AM detector and audio preamplifier, and at the transmitting side the necessary circuits for the production of a AM signal. This board is used in the FT-101ZD MK1, MK2 and MK3. It is a optional board, so it is not used in all transceivers.
FM Unit PB2219This optional board is used for receiving and transmitting in FM mode. The board uses the same connections as the AM board, which must be removed (if installed) when installing the FM board. One board can be installed at a time, so you must make a choice. Installing is rather easy. This board can be installed in production runs from 24 up, the FT-101ZD MK3
Power Supply PB1967 Rectifier A board.
This board delivers all the high and low voltages used in the transceiver, so be careful, there are points with 900 Volts dc on this board, and that voltage can do serious damage to a unsuspecting Ham to say the least. Discharge all filter capacitors, preferably through a load resistor before starting to work at this circuits. The board is positioned in the underside of the transceiver and delivers the various low voltages (6, 8, 12 Volt dc) and the 900Vdc for the Power Amplifier. This board is used in all models of the FT-101ZDPB1968 Rectifier B board
APF/NOTCH unit PB2217
The APF unit is placed in the audio circuit by the APF/Notch switch on the front panel. For APF operation forms it a selective active filter, to narrow the pass band of the receiver. The notch function eliminates selective some audio frequencies, like carriers or other interfering signals. The center frequency of the APF/Notch is adjustable from the front. This unit is used only in the MK3 model.
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