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MF-300 & Remote Control Acquired

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

  1. audmod01

    audmod01 Super Member

    Messages:
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    Location:
    Tioga, TX
    Larry and Gadget;

    Yes, sometimes I feel like my hands and tools are just like using a crowbar! Originally the unit did not have K3 engaging as soon as power was applied. This happened after I measured the DC voltage on C8. I don't know what I did to cause it but have to find the problem and repair that before going on to other things within. Someone suggested using a 2N1307 to replace the 2N632 transistor in the remote hand unit. Another person suggested an NTE160 if I remember correctly. In any case I am studying the available parts to see what might work best. I have to get the hand unit working before tackling the receiver to any great effort.

    Joe
     

     

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  2. audmod01

    audmod01 Super Member

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    I just found and made a correction for connection of C17 on the phenolic board. The current version posted is the most recent.

    Joe
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    How was it wrong? Is this a correction you made to the original schematic?

    Dave
     
  4. audmod01

    audmod01 Super Member

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    Location:
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    Dave;

    No, I had C17 connected to the wrong solder lug 11, top row on the illustration instead of lug 10. I also had forgotten several jumpers from lug to lug. On the bottom row, lugs 14 & 15 are connected; lugs 17, 18 & 19 are connected; lugs 20 & 21 are connected; and lugs 23 & 24 are connected. I worked from a hand sketch of the board and was duplicating it in Adobe Photoshop and stopped my work at one point, thus loosing my place in the process - sorry! I probably should go back to the schematic and add dashed lines around the Q6 & Q7 related parts on the phenolic board, then post an updated version of the schematic with the lug numbers designating either top or bottom row lugs. I also need to make an illustration of the bottom side of the phenolic board since there are some wires there that I am not sure were duplicated on the top side.

    Joe
     
  5. audmod01

    audmod01 Super Member

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    Location:
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    To clarify issues related to the Phenolic Board further, I examined the underside of the board.
    There are numerous connections on the underside of this board as follows:
    Solder lug 1 connects to solder lug 17
    Solder lug 15 connects to solder lug 20
    Solder lug 19 connects to solder lug 9
    Solder lug 9 connects to solder lug11
    Solder lug 12 connects to solder lug 13
    Solder lug 26 has a light blue wire that connects to a lug on Black Relay K2
    Solder lug 8 has a red wire that connects to a terminal on K3 and a terminal on K1.
    Some of those jumper wires have black Cambric sleeving on them while some are bare wires. Obviously it is important to watch lead dress very carefully when reinstalling and securing the Phenolic Board to the chassis. It would be very easy to short out or pinch either the red wire or the light blue wire to the board or the chassis. Also, C8 being underneath the board, has to be carefully positioned so that it does not interfere with other parts such as the relays under it. The new parts used to replace existing electrolytics should be chosen smaller physically if at all possible to free up space and make assembly less critical.

    Cambric sleeving is pretty tough, but if replacing items such as C8 the 250uF@35VDC electrolytic It may be wise to use Teflon sleeving on its leads.

    I have made additional notes on my hand sketch of the chassis related to the physical components such as the volume control & motor assembly, the relays, power transformer, bridge rectifier and some related terminal strips and connectors. I will be working on an illustration of these parts showing some of the interconnecting wiring for a future post. Everything is so compact and packed that tracing wires and parts is quite a task. Anyone who tackles one of these needs to be really on guard to make sure they are tracing the correct wires to various parts. Some wires are the same color and only differ by the wire gauge used to connect certain parts.

    I have mentioned that there are two flat washers that go between the Phenolic Board and the chassis mounting tabs under the board. Today while handling the unit a third flat washer fell out of the chassis and so far I have been unable to locate a spot where it may have come from. It has no marks on it to indicate that it was ever used in fastening any other parts such as a screw or terminal strip ground lug. I am beginning to suspect that it may have fallen loose into the chassis at the factory and has been lying inside ever since.

    K3 and K1 are small white relays very similar to what Fisher used in their 500-C and 800-C receivers. K2, the reverse relay, is larger and has a thin black plastic cover over the top of it. The relays are arranged in this order: K3 (Volume) is close to the volume control motor, K1 (Tuning) is just behind K3 and K2 (Reverse) is behind K3.

    I first thought that the center relay was K3, but instead it is K1 used for activating the tune feature. I need to check to see if K1 is still activating as soon as power is turned on. If it is not, perhaps the extra flat washer that fell out was causing that relay to turn on.

    Joe
     
  6. audmod01

    audmod01 Super Member

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    Here is a picture that shows some of the component locations of the RK-20.
    Component Locations.jpg
    Joe
     

     

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  7. audmod01

    audmod01 Super Member

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    Here is an illustration of the underside of the Phenolic Board so that you can see the jumpers that were added there.
    RK-20 Phenolic Board Underside.jpg
    Joe
     
  8. audmod01

    audmod01 Super Member

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    Location:
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    Here is a drawing that shows some of the power wiring of the RK-20. Most of the wire colors are consistent with others carrying the same voltage or function, but there was one exception in the orange wire to the solder peg connecting to the - terminal of C13 on the Etched Circuit Board. On that board the peg was labeled "RED". This orange wire connects to the same terminal of K1 that has a RED wire connected to it from K3. I suspect that in other units that a RED wire was used here instead of an Orange one. I think this drawing will be helpful to people who may be servicing their own units. The chassis wiring is quite congested and not easy to trace out.
    Components Illustration.jpg
    Joe
     
  9. rufleruf

    rufleruf Poor Impulse Control Subscriber

    Messages:
    1,158
    Joe - I'm happy to see how far you got on this project because I bought MF-300 10291A yesterday with remote and remote receiver. It's not as nice as yours but came with the whole kit, and will be fun to mess with!
     
    vendo81 likes this.
  10. audmod01

    audmod01 Super Member

    Messages:
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    Location:
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    Ruffleruf;

    I saw that one briefly on eBay and noticed the next morning that it was gone. Glad to hear that someone in this group now has it in their collection. Lets stay in touch. I have been temporarily sidetracked to deal with a 1946 Philco for my son-in-law. I am applying finish to the cabinet now and hope to be done with it so I can get back to the MF-300 and RK-20. I have found that there are some PNP transistors I can get through eBay and some other sources. I need to start with the hand unit first. I suspect that it needs new capacitors in it as a starter. I also need to do some more with the illustrations of the components in the ultrasonic receiver for those of us who have these.

    I noticed that the unit that you bought needs the dial cord restrung. The manual on the AudioKarma.org database shows that detail if I remember correctly. Good luck!

    Joe
     
  11. vendo81

    vendo81 AK Subscriber Subscriber

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    This is great information Joe! Great work.
     

     

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  12. vendo81

    vendo81 AK Subscriber Subscriber

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    Great Matt. That's the one that came out of the President that was found in Los Angeles a few weeks back. When you told me about it the other night I had forgotten about the one Jose had.
     
  13. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    Got any inside info about it? He reported it worked, but I think that was just the tuner part of it. I suppose the 400 CX 2 Jose has listed is the match for this?
     
  14. vendo81

    vendo81 AK Subscriber Subscriber

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    Jose told a friend that he had dropped the MF-300 off at his tech to be looked over. He said the tuner worked before it was dropped off but nothing about the remote items. Yes the 400CX2 he has was in the same President cabinet. The MF-300 is quite a tuner. When working well they sure are sensitive and have very good sound. I use my MF-300 more than any other tuner.

    I'm sure I can make you a diagram for restringing the tuner as the dial cord wraps around the rear drive motor. I know the restringing chart is not in my owners manual.
    Congrats on the nice find with the remotes :beerchug:
     
    Last edited: Mar 24, 2018
  15. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    Neat - there is a local tech who went through an MF300 for a guy I know - worst case it can go there. I've been using an R-200-B for a while as by daily driver - mostly too lazy to do the reconfig necessary to be using the TFM-1000 and Cornwalls.
     
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  16. vendo81

    vendo81 AK Subscriber Subscriber

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    Matt, your MF-300 is serial number 10291A. Joe's is 10176A and mine is 10224A. Both of our MF-300's came out of the same year President console. Joe's was a stand alone unit. I can tell from "THE FISHER" on the face of the remote control receiver. I had purchased a stand alone unit from a person in Denmark several years ago that had the same remote equipment as Joes with the brown/white hand held. Everything worked on that one until the battery went dead. I swapped that MF-300 to a friend when I got the duplicate. The one I bought last August from a President is identical to your remote receiver and the hand held is red/white. Is your hand held red/white, or brown/white?
     
    Last edited: Mar 24, 2018

     

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  17. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    That's a pretty narrow group of serials! Tracking says the the MF300 will be here today - I'll let you know about the remote. Maybe its arrival is the kick I need to move things around.
     
  18. audmod01

    audmod01 Super Member

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    Location:
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    I have been working on another illustration of components in the RK-10 receiver and made an interesting discovery this morning. On the circuit board containing the M1 module and labeled 14E325-1, there is a silicon diode, V1112, labeled CR1. It is not shown on the schematic for the RK-20 receiver. My first measurements showed the diode to be open, but when I lifted one end and used a different ohm meter, it did show a good front to back measurement. Then when re-checked with my Fluke 8500A digital ohm meter it then showed a good front to back measurement. However, the cathode end of CR1 is not connected to anything but a solder peg labeled "GREEN" which has no wire connected to it nor any other component. The anode end of CR1 connects to pin 1 of the M1 module. The only thing I can think of is that CR1 was originally connected as a spike suppressor across at least one of the relays, but was determined not to be necessary.

    I may have the extra component layout illustration done later today.

    Joe
     
  19. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    The plastic body of my remote is beige. I don't recall the exact number, but my receiver has serial number around 10400.
     
  20. audmod01

    audmod01 Super Member

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    Location:
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    As promised, here is another illustration of components in the RK-20 receiver. Like the previous illustration, it is not to scale but is intended to show relative positions of the parts and the wiring to/from them.
    Circuit Bd 14E325-1 Connections.jpg
    I also took some voltage measurements which show mostly good transistors, but I may have problems at Q4 and Q5:
    Q1 e=-2.57V b=-2.75V c=-8.55V
    Q2 e=-2.10V b=-2.70V c=-9.30V
    Q3 e=-1.66V b=-1.80V c=-11.50V
    Q4 e=-0.27V b=-0.15V c=-13.30V
    Q5 e=-0.27V b=-.0002 c=-0.32V
    Q6 e=-2.22V b=-2.30V c=-5.59V
    Q7 e=-0.12V b=-.074V c=-14.25V
    So this set of measurements represents my starting point. The DC voltage in the power supply is at -14.4VDC with 120VAC input.

    Joe
     
    Last edited: Mar 26, 2018

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