MF-300 & Remote Control Acquired

Discussion in 'Fisher' started by audmod01, Nov 2, 2017.

  1. audmod01

    audmod01 AK Subscriber Subscriber

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    Matt;

    I don't think so. The problems with my hand unit are two-fold. Most importantly, the amplitude of the output signal is much lower than that of your hand unit with an OEM transducer. Second, the replacement transducer I bought has metallized Mylar film which is too thick, thus preventing adequate 60Hz modulation from the oscillator circuit. So the only real solution is to have a transducer that is fully capable of higher energy output (by providing the proper capacitive load & Impedance to the oscillator circuit) and capable of responding well to the 60Hz component when selecting tune down or volume down functions.

    If I could change the modulating frequency from 60Hz to say 1kHz or so, it might be possible to change the reverse tune or volume down function detection to work with a 1kHz modulation, however even that may be a problem. I will have to see what I can do toward rebuilding the OEM transducer first. If I am unsuccessful, then I may pursue another approach. It may still be possible to create a new hand transmitter using 555 timers as I had mentioned before. I have plenty of them on hand and could probably create a toroid transformer to step up the output voltage sufficient to drive a transducer to a high enough level to guarantee good distance operation of the system. I would say that the system should be capable of sending and receiving a signal up to 30ft. to be adequate for most room situations.

    Joe
     

     

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  2. gadget73

    gadget73 junk junkie Subscriber

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    metalized mylar, don't potato chip bags and balloons use that? No clue what film thickness those use, but maybe a trip for a bag of chips of your favorite type is worth the experiment.
     
  3. audmod01

    audmod01 AK Subscriber Subscriber

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    Yes many of them do, but most all those items are 1mil or 2mil thickness and thus too thick for this application. There are plenty of sources for those thicknesses. The problem with modulating a 40kHz signal with a 60Hz frequency is compounded by having such a small diameter membrane area to manipulate. The smaller the diameter, the more difficult it is to modulate it successfully the thicker the membrane becomes.

    Joe
     
  4. audmod01

    audmod01 AK Subscriber Subscriber

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    I have done some more investigation of the OEM transducer from my hand unit. It goes together somewhat like a sandwich. The rear-most part is a metal bracket with a hole cut in the center and includes 4 holes for mounting screws plus a solder lug. This establishes one connection for the transducer. Next forward of that is a thin metal plate which appears to be aluminum, but I am not sure. It has a circle cut in its center also. On its back side the Mylar metallized film is applied. Next is the front metal grill which has tiny perforations in it and is concave toward the rear. The metal grill is fastened to the backside of the Phenolic Bracket with two tubular brass rivets. The space between the Mylar film and the center of the front metal grill piece is .009" as far as I can tell. Viewed from the front the Left rivet is used to provide a connection to the grill which is the other connection for the transducer.The metal plate the Mylar film is adhered to and the front metal grill form the capacitor that measured 88pFd on my capacitance meter. I have drawn a diagram of the parts in an exploded view so you can see how they go together. Transducer Detail web.jpg
    I have an order of metallized Mylar sheets coming which are 0.5mil or 12.5um thick. That was the thinnest metallized Mylar sheet material I could find at anywhere near a reasonable cost. I can afford to experiment with mine since it was not working anyway. I will not mess with Matt's transducer in his hand unit since it works and forms the "standard" that I will try to duplicate. I can try different methods of reassembly on mine without worry about ruining anything, Matt's unit serves as a visual reference for how the assembly is put together.

    Joe
     
  5. audmod01

    audmod01 AK Subscriber Subscriber

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    Here are a couple of pictures of the Transducer assembly viewed from the front and rear. In the front view you can see the 18AWG wire was inserted into the rivet and soldered. In the rear view you can see part of the solder lug the other lead to the Transducer is soldered to. That lead is the one that goes down to the center front trace of the PC board.
    Transducer Assy Front View web.jpg
    Transducer Assy Rear View web.jpg
    Joe
     
  6. audmod01

    audmod01 AK Subscriber Subscriber

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    Looks like I will soon get to try rebuilding the transducer in my hand unit. The package of metalized Mylar sheets arrived in the mail today. I spent most of the morning mowing the property but had to stop around noon with the arrival of thunderstorms. This afternoon is being spent resting. I may work on the transducer tomorrow. I will still have to find some rivets or very tiny screws and nuts to mount the front grill piece.

    Joe
     

     

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  7. audmod01

    audmod01 AK Subscriber Subscriber

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    I just ordered some #0-80 brass screws 1/4" long and some brass #0-80 nuts which I can use in place of the brass rivets to reassemble the transducer. If it turns out that there are some problems of fit afterward then I can pursue finding some tubular brass rivets similar to those used in the original assembly. However I think that will be problematic. I was looking on a clock & watch supply company website called Timesavers. They had solid brass rivets, but not tubular ones. There could still be some suppliers out there, I would just have to do more searching.

    The screws and nuts will work at least for a try as I can mount the parts and assemble them outside of the original hand unit plastic case. The only problem I can foresee is the nut stack-up thickness might push against the anodized aluminum grill on the front of the hand unit when the PC board assembly is reinstalled in the plastic case. I might be able to file them down enough to fit interference free.

    Joe
     
  8. audmod01

    audmod01 AK Subscriber Subscriber

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    One aspect of the transducer mounting in the hand unit is that the original design depended on the two 18AWG wires to mount and stabilize the phenolic bracket and transducer to the PC board. When I installed the trial Murata transducer I did not have any 18AWG wires, so I used some plastic glue to adhere the bottom edge of the phenolic bracket to the PC board. This worked quite well. If I need to remove it I can separate it from the PC board with a knife without damaging the board.

    Joe
     
  9. audmod01

    audmod01 AK Subscriber Subscriber

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    Today I found sources for brass and copper rivets in the range I need and ordered some. These can also be used to repair circuit traces on PC boards that have lifted. There are sizes that can take care of most circuit board through-holes and tie down the circuit trace to the board again.

    Joe
     
  10. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    Location:
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    Today I received my order of #0-80 X .25" screws and #0-80 nuts to use in reassembling the transducer in my remote hand unit. I also have orders of three different sizes of brass/copper hollow rivets in the same general size range coming from other sources. The smallest of the rivets I ordered can also be used to reattach circuit board traces that have lifted. This was a technique I used many years ago to repair circuit boards damaged by either power resistors applying too much heat to thru-holes in boards or someone applying too much heat in soldering operations.

    I plan to make some peak-to-peak AC voltage measurements in the two hand units. Again Matt's hand unit is the standard against which I will compare. I will try to take some scope pictures and post them here. It is useful to know approximately what signal level to expect at the transducer when the hand unit is operated.

    In case the metalized Mylar film that I have now is still too thick to work properly, I learned of another source of significantly thinner metalized Mylar film available from a group which is into test equipment to measure Gamma particles. The sheets they offer are much closer to the physical size I need in area dimension, so there would not be as much trimming to do with those. It helps to reach out to others for more sources even if their interests don't exactly line up with one's own.

    I have had to be busy mowing our property and repairing outside equipment for a number of days. Everything seems to need attention at once!

    Joe
     
  11. gadget73

    gadget73 junk junkie Subscriber

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    they must be using that as a cover for the detector. If its for gamma it has to be for really low energy stuff, usually that penetrates pretty well. Alpha and beta are more difficult, alpha especially has very little penetration ability.
     

     

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  12. audmod01

    audmod01 AK Subscriber Subscriber

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    Yes, it is a cover for the detector. They are experimenting with several different crystal structures to try to find the most sensitive and then a calibration method.
     
  13. audmod01

    audmod01 AK Subscriber Subscriber

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    As promised, today I used Matt's hand unit as a standard and connected my oscilloscope probe directly across the transducer. I was amazed at how high the indicated voltage is. I had my scope probe set on the X10 position and the displayed waveform was filling the screen on 50V/Div! One picture shows the CW tone (no modulation) of the Volume Up button engaged. The second image is of the Volume Down button mode with the unit rotated CCW to engage the 60Hz modulation. You can see that the modulation is also very strong.
    Volume Up CW web 02.jpg
    In this image the timebase is adjusted to show the purity of the oscillations at the 41.805kHz frequency.
    Volume Down Modulated 03.jpg
    In this image the timebase is set back to the milisecond range to show the low frequency modulation of the 41.805kHz frequency. The signal is still coming through very strong with the probe set on X10 mode.

    Joe
     
  14. gadget73

    gadget73 junk junkie Subscriber

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    Wow, quite a bit of voltage output.

    Crystals, thats scintillation detection. Scintillators are sort of interesting. The rock actually flashes when a photon strikes it, and the instrument actually reads the flashes using some form of photo sensor. Usually thats used for low level contamination or activity.
     
  15. audmod01

    audmod01 AK Subscriber Subscriber

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    Today after several tries I finally managed to get a round piece of the 0.5mil metalized Mylar cut and mounted using the brass #0-80 X .25" screws and nuts plus the original screws and nuts that hold the back plates together. The tiny brass screws took solder readily and I made sure I kept some siezers on the wire lead I was attaching to carry away the heat of soldering quickly. I did the same with the attachment to the solder lug of the metal back plate. Making sure that there are no shorts between the front and back metal sides of the Mylar proved to be tricky. I kept trying and finally got one disc cut and sandwiched between the back plates and the front convex grill piece successfully! That is the key it appears to reassembly and tightening of the 4 screws for the back plates is critical to avoiding wrinkling the film. I found that going clockwise in sequence tightening each one an equal amount produced the best results. When I reached each step I would stop and measure with my ohm meter to make sure that I still showed infinity between the two sides of the transducer.

    So far, I now have as much signal voltage appearing at the transducer with the same oscilloscope probe in X10 mode as I did with Matt's hand unit. That is true for both station tune up and volume up, where before with the Murata transducer the amplitude was only about a 1/10th that of Matt's unit. It also appears that I may have something intermittent as I try moving it about I loose some of the amplitude. The spring metal switches for tune and volume have been cleaned, but there might be another issue near them. I will clean them again and give it another try.

    For now I need to take a break. I went through considerable frustration getting the metalized Mylar disc mounted and became really tensed up - developed a headache. That is a good sign to stop while I am ahead. Tomorrow I may achieve some success with the modulation for tune down and volume down.

    Joe
     
  16. audmod01

    audmod01 AK Subscriber Subscriber

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    Speaking of scintillating, when I worked with RCA, we found that some capristors (a .001 disc ceramic combined with a resistor in one package) which were used in the AC input circuitry of some of their color TV sets would oscillate at an RF frequency and create lots of interference on the screen. RCA referred to the condition as "scintillating capristors". It was partly due to dendrite growth of the metals used to form the capacitor. The same effect was also involved in the naked mica capacitors that caused the "silver mica disease" in IF transformers. The capristors had part of their metal surfaces not covered by insulation and humidity and air contaminants went to work. The solution was to replace them with alternate parts that had been manufactured properly with good insulation to keep air and moisture away.

    Joe
     

     

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  17. audmod01

    audmod01 AK Subscriber Subscriber

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    Today I spent some time looking at my hand unit again with its rebuilt transducer. I see equal output level on "tune up" and "volume up" when compared to Matt's hand unit. However when I rotate the control to activate the low frequency modulation the amplitude is about 25% of Matt's unit and instead of about a 60Hz buzz I hear a higher tone, probably a multiple of 60Hz. I need to check some of the other capacitors in my hand unit to make sure they measure as marked. I could have a capacitor that is no longer the value marked on it.

    I have not measured the capacitance of the rebuilt transducer either, so I need to do that also. I may have to order thinner metalized Mylar film.

    Joe
     
  18. rufleruf

    rufleruf AK Subscriber Subscriber

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    There's an MF300 (10951A) w/out remote set up on eBay right now for $450 if you want to join the club! A lot more reasonable than 10251A at $1200 asking.
     
  19. audmod01

    audmod01 AK Subscriber Subscriber

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    Matt;

    Yes I spotted that one too. Even without the remote ut is still a good tuner to restore. I hope it goes to a good home.

    Joe
     
  20. gadget73

    gadget73 junk junkie Subscriber

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    I still wonder if a cell phone can produce the frequencies required. If so an app might be possible to sub a phone for the genuine article. I have my doubts that it can make the high frequencies though.
     

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