FT-1000mp MARK-V very low receive issue solved

Discussion in 'Radio Circuits, Repair & Performance' started by KD8UYQ, Jun 15, 2019.

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  1. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello all,

    This radio was part of a large amateur radio estate willed to us at the Museum of Radio and Technology from a SK in the northern part of the state.

    The Mark-V had virtually no receive on all bands with only the strongest signals barely bleeding through to the speaker plus there was no activity on the S-meter. However, if you pushed the IPO button (Intercept Point Optimization) then the receive sensitivity came back and the S-meter showed activity. I did a master reset of the radio's micro-processor but that didn't change anything. After working on this radio on and off for about 8 weeks and going down several rat holes I finally figured out what was happening and repaired the problem.

    Reading the Main Receive circuit description in the FT-1000mp MARK-V technical supplement it talks about three high-frequency RF amplifiers on the RF Unit. These three RF amplifiers are separated by low bands, mid bands, and high bands. For example if your push the 3.5 button on the radio to select the 80/75 band the low band RF amplifier (Q1018) is turned on and the other two RF amplifiers for the mid and high bands are turned off.

    Pushing the IPO button turns off all three RF amplifiers and the receive signal if shunted directly to the 1st mixer from the BPF circuits bypassing the RF amp section completely. So, I figure out early on that there is a problem with the RF amplifier section or the logic that turns on or off these amps. This is when I stared chasing my tail. If I had read the circuit description more carefully I would have picked up on this: (Note - If "Flat" is selected in the Menu Program 8-4, RF signal input is sent to the mid-band amplifier circuit) thus saving a lot of wasted effort. Page 44 of the operators manual has a section titled Front End Selection: were it describes in detail how the IPO function works, when to use it, and how the "tuned" RF amplifiers operate. Of particular note, the mid-band RF amplifier is used as a broadband amplifier for ALL bands when "Flat" is selected in the program menu. This explains why I could hear nothing on any band when the IPO button was not activated.

    The gotcha is (it got me anyway) "Flat" is the default setting in the program menu. Resting the micro-processor will not help you troubleshoot the problem in this situation. I went to section 8-4 in the program menu and changed the default from Flat to Tuned and bingo! The low and high bands immediately came back to full sensitivity with the IPO button turned off. Now I knew that there was nothing wrong with the logic circuits controlling the RF amplifiers eliminating the Control Unit and most of the RF Unit. My problem was with the mid-bands RF amplifier section.

    Long story shortened, switching transistor Q1023 had opened so that the mid-band amplifier could never turned on.

    I wanted to pass this along to others that might find themselves in a similar situation.

    BTW it took the Service Manual and Operators Guide to put this puzzle together.

    Ripley
     
    KJ4NOO, KB1YFD and W4FBI like this.

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