Crackling Noise FT 857

Discussion in 'General Technical Questions and Answers' started by K7KXI, Mar 8, 2010.

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  1. K7KXI

    K7KXI Ham Member QRZ Page

    hello all,

    I have a Yaesu FT 857D. Its about two years old. Over the past year, the radio has developed a loud crackling and popping noise. The popping and crackling overrides the AGC.

    The noise is intermittent, sometimes occuring right at power-up, other times not happening at all.
    Noise occurs with or without antennas attached, occurs when running on batteries or power supply, and also occurs when there are no known sources of noise. Occurs day or night, wet or dry weather, summer or winter.

    I've shut the power down in the house, ran the radio on batteries, and disconnected everything.

    The noise is on all bands 1.8 to 440 mHz.

    The popping and crackling has not effected transmission.

    ANY ideas?

    Thanks,

    Todd
    KE7KXI
     
  2. N2VPC

    N2VPC Ham Member QRZ Page

    Sounds like a loose connection or cold solder joint somewhere.
     
  3. 2E0BSL

    2E0BSL Ham Member QRZ Page

    I had this on my 857. I returned it for repair, it came back unrepaired. This happened 3 times. Eventually, after 3 months they replaced the whole radio as they couldnt find the cause. A freind of mine has has had the same issue on his and Im waiting to see if he returns his.
     
  4. MW0UZO

    MW0UZO Ham Member QRZ Page

    I have an FT-857 with this problem - crackle across all bands and modes, sounds like RF stage crackle not audio crackle. The crackle is present with the antenna coax removed from the main board, so the problem is on the main board.

    When rig is cold, crackle is minimal, once warm crackle is fairly continuous at peaks of S6 to S7, making the radio unusable.

    Does not appear to be poor joints or soldering either. have examined closely both sides of main board.

    Any solutions would be greatly appreciated!
     
  5. W5HTW

    W5HTW Ham Member QRZ Page

    Usually that type of noise is a capacitor going bad. The most likely cause is an electrolytic, but some other types can cause that noise as well.

    If the noise is controllable by the volume control, then it is before the AF output stage. If it is controllable by the RF gain, then it is before the IF state.

    If it is not controllable by the volume control, it is in the AF output stage.

    One thing you can do, though it is more difficult on SMT systems, is apply gentle heat to various components. While a capacitor is most likely the cause, some solid state components can do it, too.

    The old way, and still valid, is to use freeze spray (sparingly!) on suspected areas of the boards. Most likely applying such spray (sparingly!) to various areas will eventually hit a component that when cold, corrects the problem. You may then have to be more careful not to hit areas of the boards, but specific components.

    Freeze spray can also help in locating bad connections, loose plugs and bad solder traces.

    Not sure where you can find it today, but look around. It is a very valuable troubleshooting tool. When I was doing consumer electronics servicing (stereo, TV, etc) I went through about a can a week.

    Ed
     
  6. K9ASE

    K9ASE XML Subscriber QRZ Page

    It sounds like a bad capacitor in the radio's internal power circuit like it is "leaking" a similar thing happened with my Samsung tv and it turned out to be a common issue with those tv's due to the use of cheap capacitors
     
  7. WF7A

    WF7A Subscriber QRZ Page

    Don't have a bowl of Rice Krispies nearby while operating.
     
  8. MW0UZO

    MW0UZO Ham Member QRZ Page

    Thanks for the advice Ed. I've been using a can of butane lighter gas as makeshift freezer spray - the nozzle is great for applying localised amounts of the liquid. Not good for any potential sparks though....! :D

    Information noted on the possible capacitor problems too.

    The fault has been traced to the AM filter CF5 on the main board. A replacement is on its way, will post back if the repair is successful.

    My next concern is getting the old one off. Desoldering through hole components from the thick pcb I have alway found very difficult, even with solder wick and a very hot iron. The pcb just conducts the heat away too quickly for the solder to become molten enough to flow properly.
     
  9. MW0UZO

    MW0UZO Ham Member QRZ Page

    The cause of the crackle was the AM filter. After fitting the replacement, the crackle has disappeared. I broke apart the old filter - an internal piece of ceramic had shattered, causing the crackle.

    Desoldering was tricky. I used a hairdryer to preheat the board and solder wick to desolder the two signal pins. The ground pins would only desolder at the surface, so the filter has to be broken apart, the pins removed with pliers and the blocked holes drilled through with a 1mm drill at high speed in a pillar drill.

    Hope this helps anyone experiencing the problem. The faulty filter is question can be identified by noting the loudness and crispness of the crackle in the USB, LSB and AM modes. Heating and tapping the filter may directly cause the crackle if you are lucky, mine became mechanically sensitive for a short period.
     
  10. MW0UZO

    MW0UZO Ham Member QRZ Page

    Can a mod please move this to the Mods, Tips and Repairs section. :)
     
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