MF-300 & Remote Control Acquired

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

  1. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    1,176
    Location:
    Tioga, TX
    Good news! I just received the copies of the MF-300 Owner's Manual and the Service Manual from Bob McCrae. He was generous enough to share copies with me. I will be scanning them in ASAP and get them to the Fisher database on AudioKarma after some amount of clean-up. I was pleased to see that Fisher did actually put out a complete service manual on the MF-300. When I worked for a dealer years ago I only had an addendum document to work from. This is far better as there is no need to refer to more than one schematic and parts list etc.

    The last few days it has been rather cold and I have stayed inside and worked on my son-in-law's Philco 46-1226 AM/SW radio-phonograph. I discovered an open resistor in the B+ circuit and have to order a replacement. So for now I will get back to the MF-300 documents and the Electra equipment cabinet for my granddaughter.

    Joe
     
    Last edited: Nov 25, 2017

     

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  2. audmod01

    audmod01 AK Subscriber Subscriber

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    More good news. I found a scanned copy of the RK-20 Wireless Remote Control and hand unit. It was not the best of copies, so I have spent a couple of days re-drawing it in Adobe Photoshop to make it easy to read and follow. I need to get it to the database manager here so it can be listed in the Fisher equipment. I am currently trying to identify the Amp? connectors on the back of the RK-20. I need a current source for these connectors and their contacts so I can build an interconnect cable to go between the MF-300 and the RK-20. The RK-15 wired manual remote hand unit's schematic is shown on the same page with the RK-20.

    Joe
     
  3. audmod01

    audmod01 AK Subscriber Subscriber

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    I thought I would try attaching the *.png version of the RK-20 file here. It may or may not be very legible after it goes through the mill here.
    RK-20.png
    Joe

    P.S.: I see after attaching it and then opening the file that it is not legible here, so I will have to pursue sending it to the database manager as a full *.pdf file at 300dpi. Sorry it did not work well here.

    Joe
     
  4. vendo81

    vendo81 AK Subscriber Subscriber

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    Hi Joe. I can help you out with the plug as both of my RK20 's have them.
     
  5. audmod01

    audmod01 AK Subscriber Subscriber

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    Keith;

    Thanks for being willing to help. I will contact you by PM. I did learn something today by contacting Gary Stork of thevoiceofmusic.com. Many of the older record changers used this type connector for the power to the changer. He has the 4-contact type but not the 3-contact type. They were made by what was the AMP Corporation at the time. These were part of their AmpLock series of connectors and contacts. After I carefully cleaned the connector of a 6-pin from the Electra 490-T that I had removed I could make out the name AMP and just to the right of that AC-6, where the number 6 represented the number of contact positions in the connector shell. The biggest problem is that the 3-contact cable is the hardest size of this type to locate. Gary has some 4-contact types he is willing to sell me but does not have the 3-contact type. The cable to go between the RK-20 and the MF-300 chassis is the 3-contact type. It has to have a female connector shell with the 3 rectangular male pins on each end. I actually have used pins from the connector I removed from the Electra 490=T chassis interconnect cable. I have just enough to make one cable, which is all I would need. The 4-contact connector on the back of the RK-20 is for connection to the RK-15 wired remote that then allows it to operate the same control functions as the RK-20 wireless hand control. Since I do not have an RK-15 I don't need the 4-wire connector.

    I am going to check with RadioDaze and Mark Oppat's site to see if either of them might have the 3-connector female housing and contacts for it. There might be one or two more places to check also.

    Joe
     
  6. vendo81

    vendo81 AK Subscriber Subscriber

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    Hi Joe.
    Great info on the use on turntables. The plugs are also the same as used on some Fisher consoles. I'm sure they were used on the turntable connection as well. Here's a photo of the RK-20 plug (left) and the plug from a Fisher console amplifier. They are EXACTLY the same down to the 3 molded ridges in the connector. They only use 2 of the contacts for speaker connections leaving the center unused. I've sent a PM with all of the information and more photos to you as well.

    RK-20 plug 3.jpg
     

     

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  7. walyfd

    walyfd Well-Known Member

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    Looks similar to the power antenna connection on my old Cadillac...
     
  8. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    Location:
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    walyfd;
    Yes I remember seeing a number of different kinds of products that incorporated this brand and type of connector. I remember seeing these connectors on many brands of televisions too. They used to be quite common on other brands of audio equipment also. It appears that now the only source is from parts donor chassis and some lines of speakers.
    Joe
     
  9. hammr7

    hammr7 AK Subscriber Subscriber

    Joe,

    Although I won't be starting until after Thanksgiving, I have some old consoles I am planning to gut. If you haven't found an appropriate connector let me know and I'll see if I can find a spare or two.
     
  10. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    Location:
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    hammr7;

    Thank you for your kind offer. Keith says he believes he has some, so I may have them soon. This is such a great and helpful group!

    Joe
     
  11. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    The RK-20 Service Data document is now in the AK Database. Thanks again to our moderators and support people on this site!

    Joe
     

     

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  12. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    Some observations on the internal circuitry of the MF-300:
    The Tune Left (or down in frequency) wiring inside the tuner uses a violet lead from the S8-A switch contact behind the front trim panel for Tune Left which activates the K1 relay.
    The Tune Right (or up in frequency) wiring inside the tuner uses a yellow lead from the S8-B switch contact behind the front trim panel for Tune Right which activates the K2 relay.
    The same color leads are used from the rear of the chassis Remote Tuning connector for Tune Left (Violet) and Tune Right (Yellow) functions.

    Inside the RK-20 the same colors are used at its rear chassis TO REMOTE TUNING JACK connector, so the Violet wire inside the RK-20 is for Tune Left and the Yellow wire is for Tune Right. Fisher was consistent with assignment of the wire colors and their functions. That is good to know.

    The bridge rectifier, SR1, used in the MF-300 S/N 101764 that I have is not a flat pack as seen in my 202-R or the FM-200-B. Instead, it looks more like circuit breakers seen in some televisions of the period.

    The I3 lamp, P/N AS50451-1, designated on the schematic is a 2.5V lamp attached to the dial pointer and has a 47 ohm resistor in series with the 6.3VAC from the filament string. On the chassis I have, the wires to/from the dial pointer lamp are both blue and fit into small spring-loaded Fahnestock clips on top of the chassis behind the front panel.

    The tuning drive motor, M1 P/N P-882, used on the MF-300 chassis is rated at 25VAC and is powered from a 25VAC tap of the power transformer.

    The Service Manual that I have for the MF-300 covers 10000 to 19999 serial numbers inclusive. I do not know if there were later serial numbers of the MF-300 or whether its production stopped at 19999 and perhaps the MF-320 superseded the MD-300 in later year(s) production.

    I cleaned the RK-20 cover inside and out. The inside had considerable dust and disintegrated foam rubber coating its surfaces. The foam rubber was from the hardened foam rubber that used to cushion the RK-20 internal power transformer.

    Joe
     
  13. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    Location:
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    Vendo81 sent me the interconnect cable that couples the tune left/right from the RK-20 to the MF-300 tuner. It arrived today in good condition, so now I have everything I will need to start checking out the system except the battery for the hand-held remote unit. That will be next. There is a battery specialty store in Sherman, TX that I plan to visit and see what they might have that I could use.

    I am making good progress on the schematic for the MF-300 clean-up and as soon as I have that done I can send the completed service manual file to the AudioKarma.org database.

    Joe
     
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    DAMN JOE! Smart, can reverse engineer schematics, and your wife says you are good looking (I'll have to take her word on that).:confused: And this is a HOBBY???????? Don't let your Grand-Daughter see this one. She'll probably want it for those lazy couch potato days. :bigok:
     
  15. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    Location:
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    This morning I finished the work on the service manual for the MF-300. I sent a message to the database administrator to ask about best method of sending the 32.2MB file for inclusion in the Fisher database. The pages are all in black & white as that provides the smallest size file. There are eleven pages. It should be used in combination with the RK-20 Remote Control service data file already in the Fisher database.

    Toward the end of the clean-up of the schematic on page 5 my wireless mouse began to act up. It is one of those that uses a USB port with a small plug-in to communicate with the mouse. The mouse is somehow sealed with no provision for opening it up and cleaning or repairing the internal circuitry, so I need to make a trip to get a new one. I have never gotten along with the touch-pad of my laptop computer.

    Joe

    P.S.: I sent a invitation link to ak.pdfs@gmail.com
    from my dropbox account share folder. I hope that is the correct way to do the transfer for larger files.
     
    Last edited: Nov 23, 2017
  16. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
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    Location:
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    I learned that the 20MB size limit on PDF documents for the AK database is a hard and fast rule. So I had to go back and reduce resolution on most pages except for the schematic pages. I finally got the complete file size down below 20MB and hope this time it will make it onto the database.

    I opened each page in Adobe Reader and the lower resolution pages are still easy enough to read at 150dpi or 175dpi. I kept the schematic pages at 300dpi so that if a user downloads the file to a memory stick and asks a commercial printer such as FedEx, UPS or Kinko's to print it on a larger size of paper it will still be decent copy on the larger paper sizes.

    Joe
     

     

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  17. audmod01

    audmod01 AK Subscriber Subscriber

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    The service manual for the Fisher MF-300 was successfully loaded to the AK Database today! In combination with the RK-20 service data already posted there, the information available will allow restorers to access information easily and proceed confidently with restoration work.

    Thanks to njcanuk, Rich, for his tireless efforts supporting this site!

    Joe
     
  18. audmod01

    audmod01 AK Subscriber Subscriber

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    How does the Fisher RK-20 achieve the tune up or volume up operation?

    After examining the schematic of the remote hand unit and ultrasonic receiver I believe I understand how Fisher's design works. Looking at the hand unit you can see that if the hand unit is held just level or tilted to the left that the mercury switch inside the hand unit does not place C28 and C29 in circuit. This is the default Tune or Volume down mode. If the remote hand unit is tilted to the right (clockwise) it places C28 and C29 into the base circuit of the Q8 oscillator and adds an audio frequency modulation note to the overall output of the remote transmitter. I suspect that this may be 60Hz modulation as the alignment information on the RK-20 advises listening to the hand unit for a "Buzz" which would indicate a fairly low frequency. So whether you press the Volume or Tune button there is either a pure ultrasonic frequency output or an ultrasonic frequency plus audio frequency modulation present in the output of the hand unit's transducer.

    Looking at the RK-20 Receiver unit, there is a common connection between Q4 and Q5 that feeds that low impedance point to the base of Q6 whose output is rectified by voltage doubler circuit of CR2 & CR3 and applied to the base of Q7 whose Collector output drives the activation of the K2 Reverse relay or not.

    When I first thought about the RK-20 system I thought that Fisher was using some sort of sophisticated means of polarizing the output signal of the remote hand unit and determining the received signal polarity to provide for reversal of volume or tuning. Instead it turns out to be a very simple presence or absence of audio modulation on top of the basic ultrasonic Volume 41.805kHz signal or the Tune 38.285kHz signal. With 60Hz modulation presence, the Volume Up or Tune Up function is activated. Without the 60Hz modulation Volume Down or Tune Down is the default mode.

    Granted, I have not yet used my oscilloscope to verify these comments, but I believe this is the way the system actually achieves its modes of operation. I plan to visit a local battery specialty business to find some pieces I can use to substitute for the original battery that goes into the remote hand unit. Then with power for the hand unit I can use my scope to verify how the system operates.

    Joe
     
    Last edited: Dec 2, 2017
  19. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    It will be interesting to see what you find out!

    Dave
     
  20. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Now all you need to do is to make a plate mounted on a spring centered gimbal. Build a small box with a F-16 sidestick handle on top. Mount it on the arm of your recliner in a neutral position, drop in the remote control, and then kick back and relax. Add an eject mechanism to the recliner:rolleyes: (closes the recliner by pushing one of the armament buttons) and you're all set. :banana:
     

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