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Restoring the Yaesu FT100D

Discussion in 'Radio Circuits, Repair & Performance' started by HAMHOCK75, Nov 4, 2018.

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  1. HAMHOCK75

    HAMHOCK75 QRZ Member

    Although I have done many restorations from the 1950’s vintage Heathkit DX35 up to 1980’s vintage rigs like the Kenwood TS440SAT and Icom 735, none of them was as challenging as the FT100D circa year 2000 due to its tiny size and its use of perhaps 95% surface mount components.

    This FT100D came from eBay a few years ago. It worked fine at that time. After several months, 2M suddenly failed. The through hole output pin diode for 2M had failed. It fell out as two pieces when it was unsoldered,. The glass had cracked. It appeared that the leads on the part had not been spread apart enough for the part to drop in so an assembler forced it into the holes. The diode had been under stress for many years.

    This diode is available but it took six months to obtain one. The factory, Microsemi in Massachusetts, only makes one batch of these diodes per year. All the distrubutors were out of stock. Meanwhile, I used a lower power pin diode and kept the output power reduced.

    Next the 70 cm band failed, then 6M failed, finally 2M failed again on transmit. It was noticed that 6M receive is also failed although it receives well in every other band. I have been able to determine that none of the failures is related to the output power devices. For example, the HF output from the mainboard is about -5 dBm except on 6M where it drops to -40 dBm. The 2M and 70 cm signals vanish somewhere in the preamp area of the power amplifier board.

    Below is a photo the FT100D with its switching power supply.

    [​IMG]

    As may be seen above there are a myriad of flat cables and coax cables internally. Yaesu used RF connectors internally for the coax cables made by only one Japanese company, Taiko-Denki. The plug is part number TMP-K01X-A1. These have been discontinued but I was able to obtain a few samples to make the TMP to SMA cable shown below which makes it much easier to test the signal levels in the unit with a spectrum analyzer.

    [​IMG]

    Below is a drawing with the locations of the TMP connectors on the mainboard. The inputs are LO1, LO2, LO3, HFRX, and V/U RX. The outputs are HFTX and V/U TX. HFTX is the output for 160 through 6M, V/U TX is the output for 2M and 70 CM.

    [​IMG]

    Regarding the flat cables; while it may be tempting to just pull out the flat cables like a ribbon cable, these cables actually have a mechanism in the mating part on the pc boards which release the tension so the cable can be easily removed. The image below shows the connector in locked position with the red arrow pointing to the top cap that releases the cable.
    [​IMG]

    In this photo the cap has been lifted up at both ends as shown by the vertical red arrow. This releases the cable so it can be removed with out tension.

    [​IMG]

    A problem can already be seen in preparing to remove the mainboard from the casting. At the red circle on the right side there appears to be a chip capacitor that has broken in half on a daughter board in the image below.

    [​IMG]
     
    US7IGN and W1TRY like this.
  2. G3YRO

    G3YRO Ham Member QRZ Page

    All useful stuff that I must download and save . . .

    I bougt an FT100 recently, just because it was absurdly cheap (it was on a small website and nobody was interested in it, so they had dropped the price a few times)

    It all works fine as received . . . but I was very realistic that I might not be able to repair it if anything does go wrong. (which goes against my usual philosophy about equipment)

    But for what I paid I figured it was worth the risk, as I'd only ever use it as a small rig to take abroad on holiday.

    Roger G3YRO
     
  3. HAMHOCK75

    HAMHOCK75 QRZ Member

    The prices for the FT100 plain and D vary from about $240 to $450 depending on condition over here. The lower priced ones generally have some problems. The D adds a tone decoder ( that's the little board in the last image above next to the XF-118S crystal filter ), a larger speaker which creates a bulge in the top cover, and the 500 Hz CW filter is standard. The service and operation manuals can be found at the Fox Tango site on this page.

    http://www.foxtango.org/ft-library/FT-Library/nineties/Nineties.htm

    I intend to write generally about what is not mentioned in any manual. Partly this was inspired by your earlier thread and comment that there is not much written about the FT100's. What little I found mostly involve the finals. Fortunately I have never had an issue with the finals.

    With the mainboard removed, it is much clearer that two capacitors are damaged and missing from the daughter board 6M-FIL-UNIT. The remnants of C1708 fell under the shield for the HFTX amplifier. That shield was carefully removed using 2 mm solder wick. Under that cover are two leaded 10K resistors that appear to be factory modifications.

    [​IMG]

    All the voltages in both transmit and receive on the 6M-FIL-UNIT board were checked before removing it. It helps to have very sharp, narrow probes that do not slip off the item under test. Nothing else seems amiss except that Yaesu seems to have mis-numbered the connector at the bottom. While checking the voltages and location of pin 1 on the mainboard, the labeling on the daughter board seems reversed as shown below. The fact that C1706 and 1708 are missing explains why there is no receive on 6M. They are part of a high pass filter in front of a 6M rf amplifier, Q1701.

    [​IMG]

    Yaesu does not show the high pass filter response by this is what is looks like with Spice analysis. The corner frequency is about 45 MHz. Spice shows a 6 dB loss in the passband but that is from the voltage dropping in half from a 50 ohm source into a 50 load. The two series resonant shunt arms produce the notches in the response below 45 MHz.


    [​IMG]
     
  4. HAMHOCK75

    HAMHOCK75 QRZ Member

    Earlier I though that these two leaded parts under the shield cover of the mainboard were 10K resistors. They are actually .01 mfd capacitors according to the capacitance meter.

    [​IMG]

    These capacitors modify the HF preamp for 10-160M as shown below. Although the schematic shows L1048 and L1050 as 220 uH, this board has 6.8 uH parts. The material list does show 6.8 uH and 220 uH under the same reference designator.

    [​IMG]


    The back side of the mainboard has an assortment jumpers and another leaded capacitor ( or resistor, need to check )

    [​IMG]

    and what looks like a bunch of chip capacitors soldered over a piece of masking tape.

    [​IMG]

    The shield cover removed from over the HFTX amplifier has a piece of masking tape also.

    [​IMG]
     
  5. HAMHOCK75

    HAMHOCK75 QRZ Member

    It looks like the masking tape additions are Yaesu fixes. Another piece of masking tape separating T1016 and T1017 can be seen in the image below. In trying to identify the purpose of the three added capacitors on the backside of the mainboard it was found that the mainboard has 12 jumpers ( both solder connections and with connectors ) none of which show up in the schematic or interconnection diagram. They do show up in the upper side of the PCB drawing which locates components. These connections are labeled from A to M and each side of the connection bears the same designator. The A connection is not used. The location of the wires for these intraboard connections is shown below. The added capacitors appear to bypass three lines from the H connector.

    [​IMG]

    At the lower left are two, two pole monolithic crystal filters which form the roofing filter at the first IF of 68.985 MHz.
     
  6. HAMHOCK75

    HAMHOCK75 QRZ Member

    This is another change in the mainboard that does not show up in any documentation. There is a green wire with a series 100 pF capacitor from the mainboard, daughter board HPF, to pin 3 of Q5001 on the LPF Unit as shown below.

    [​IMG]

    It is not easy to either see or photograph but one end of the green wire appears to be soldered directly to the daughter board as shown below.

    [​IMG]

    Since Q5001 pin 3 is driven by Q5002 ( MC14028 BCD to decimal converter ) pin 7 which is an output, this wire appears to carry an output from the LPF Unit to the daughterboard.
     
  7. HAMHOCK75

    HAMHOCK75 QRZ Member

    Here are some tools that help with manipulating these tiny 0603 size surface mount components used by Yaesu. These components must contain some ferrimagnetic material because a magnetized tool will pick them up and not let go. The demagnetizer is essential to prevent that happening. The normally closed tweezers help a lot in holding these parts from moving around while soldering them.

    [​IMG]
     
  8. HAMHOCK75

    HAMHOCK75 QRZ Member

    I was able to find replacement capacitors for the 6M-FIL-UNIT board locally. 6M receive was restored and tested. A 0.1 uV CW signal from an HP8656B synthesizer was easily readible

    After removing the remnants of C1706 and C1708 that fell and lodged themselves under the shield cover in the area of the yellow box below, it was found that the 6M transmit output from the mainboard was also restored.

    [​IMG]

    About -5 dBm is typical of the HFTX ( 160M to 6M ) output from the mainboard. The 6M output is shown below.

    [​IMG]
     
  9. HAMHOCK75

    HAMHOCK75 QRZ Member

    After checking that the HFTX output of the mainboard is good from 160M to 6M, the V/U TX output of the mainboard was also checked and looked good. I decided to check the V/U output of the FT100D from its V/U pigtail output on the rear panel and was surprised to find a full, 50 watt output on 2M and about 0.3 watts on 430 MHz. Then I checked the V/U output at the PA board before the signal goes to the LFP Unit for clean up. The 2M output was still 50 watts but the 430 MHz output was 4 watts.

    Because this was done with a spectrum analyzer it was pretty obvious that the 430 MHz signal was losing phase lock and not stable.

    The service manual for the FT100D can be found at the link below,

    http://www.foxtango.org/ft-library/FT-Library/nineties/yaesu_ft100_100d_tech_supplem_sch_pdf-.pdf

    The voltage for the VCO on the 70 cm band was out of specification. From page 14 of the service manual, at 449.999.99 MHz, the voltage on TP2001 should be +7.4 VDC +/- 0.1 V. Measured was +7.25 VDC. Adjusting TC2005 corrected the situation. Unfortunately, both the 2M and 430 MHz output from the PA board dropped down to the fraction of a watt range again. Looks like this might be an intermittent issue.
     
  10. HAMHOCK75

    HAMHOCK75 QRZ Member

    One problem in the V/U section of the power amplifier has been identified. The schematic shows a jumper J3502. The adjustments section of the service manual describes inserting an ammeter between the two jumper pins. The ammeter will show the collector and drain current of the first four transistors in the V/U amplifier when the FT100D is keyed. That current should read between 1.5 to 1.6A. This unit reads 0.23A. VR3501 on the schematic is used to adjust the drain current of Q3504 which is a Motorola MRF5015 FET. VR3501 is identified on the silkscreen of the pcb as VR501. It adjusts the voltage on the gate of Q3504 between about 2.6 to 4 VDC.

    [​IMG]

    Adjusting VR3501 though its entire range had no effect on the current at J3502 although the voltage on the gate did change and was correct. Below is the gate to drain current characteristic of the MRF5015. The initial voltage measured on the gate was 3.68 VDC.

    [​IMG]
    The 0.23A appears to be the sum of the collector currents of the first three devices, the MRF5015 appears to be open circuit. However, since full power does appear intermittently, it is possible that there may be cold solder joint involved. Fortunately, it appears that the MRF5015 can be removed without taking the PA board out.
     
    Last edited: Nov 14, 2018

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