M9998K tuner issue

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k2j

k2j

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This is a strange one...

While working on my new (to me) m9998k with the cover off the back, I accidentally dropped the screw driver i was holding and it fell onto the tuner board. Not a far drop maybe 5 inches. The radio was on at the time and when it hit the tuner PCB the radio started emitting the station but with a feedback sub sound.

Now, when I flex the tuner PCB board where it sticks out up and down the FM stations change. I'm not moving the board much just enough to flex it a bit. I wouldn't mind if the stations would just change tune, BUT under certain flex positions and now resting position the sound does that super bassy feedback noise. If I flex up or down slightly the station changes up/down the dial and locks in and out of tune. ugh.

Sound familiar to anyone? This is a bizarre one... I can try to make a video to put up somewhere if I can figure that out.

:blush:
 
k2j

k2j

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baddboybill said:
Is noise just from tuner or deck and line in as well?
Click to expand...
Its more an FM tuning issue only.

Superduper said:
Is everything normal if you leave it alone?
Click to expand...
Sort of.

Let me try to better describe. hmmm I'm so bad at this. ANY flex of the board sends it up or down the tuning scale slightly and in doing so whenever it is even just slightly out of 'tune' I get a loud bad bassy feedback sound. If you don't flex the board it goes bassy feedback, so you must push up or down on the circuit board for it to jump and lock into stations.

I'm still working on getting a video together, bare with me please!

thanks!!
 
J

jimmyjimmy19702010

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May 5, 2012
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+ 1. Norm is definately the person to ask.

In the mean time:
So you're saying that is was fine before you dropped the screwdriver onto the board? Does flexing the board pull on the tuner cord? Maybe you have an earth issue. I would try removing and cleaning all wire connectors to the tuner board. I would also check the soldered wires from/to the tuner board. I had an issue with a Hitachi tuner board today that was resolved by reflowing some suspect IC solder joints and cleaning the wire connections. From your video, it looks to be a mechanical problem as apposed to a failing component/components causing the fault.

If you're feeling confident, you could trying pulling the 9998K tuner board so you can get a better look at the underside of the board to check everything out. Also check the AFC circuit. I had a box that had a dirty AFC switch that would cause the channels to drift in and out when you wiggled the switch. If the AFC wires from the tuner board have been knocked, that can in turn have the same affect on the tuner locking in on a station. You will probably have up to 6 separate sets of wires from the tuner board. Any of those could have been affected by the screwdriver. Be careful not to disturb any tuner board components in the process.

Good luck,

James.... :-)
 
Superduper

Superduper

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I suspect that two things could have happened. Either or both together might be causing this:

(1) The screwdriver impact caused a mechanical defect in either a component, or that components' solder joint. Flexing the board might either break the connection or improve it.... whichever might be the issue. Remember that component leads could fracture inside the component too. Rather than flex the board, you might try to touch individual components carefully to see if one particular component displays that symptom.

(2) Tuner component placement, lead length, etc. are all important factors in a tuners alignment. Typically, the components are installed, the tuner aligned, and sensitive components are set in wax to prevent future movement. Something as subtle as bending a weird angled transistor back straight could throw off the alignment ever so slightly. I wonder how many tuners have been inadvertently misaligned due to an uninformed hobbyist attempting to straighten all components and coils for aesthetic purposes during cleaning. One component that is usually manipulated to align a tuner are those copper coils. They look like a copper wire that was looped around a pencil a few times, then installed. These coils play an important part of the tuner alignment process and they are adjusted by stretching, pinching or otherwise distorting. If your screwdriver hit it -- it would likely affect the band coverage or bandwidth. Now, tuners also happen to be very sensitive to capacitance changes. Touching a tuner board could change the capacitance enough to cause a slight bandshift. Distorting the board can change capacitance. Also applying additional pressure during the touch would likely intensify the effect.
 
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