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MF-300 & Remote Control Acquired

Today I tried some other parts such as C28 the .05uF cap and that made no difference. I also increased the load resistance to the transducer circuit by adding a 10K ohm resistor as a load - all with no oscillation from the oscillator circuit. I removed the RCA SK3004 transistor and installed a 2N4403 silicon PNP transistor - still no oscillation. C25, C27 and C30 check good so I do not suspect any problem there. The switch contacts were cleaned early on in the investigation. I am about to suspect that the oscillator coil may have some shorted turns in it. It is a potted core ferrite construction. There is a tuning slug in the center, but I have not made any attempt to move it. I may reinstall the 2N632 transistor and try changing the tuning slug of the oscillator next.

Matt is sending his units to me to restore, so I will get a chance to examine one more remote hand unit and another RK-20 for comparison. If the oscillator coil in my hand unit is bad I am hoping his remote hand unit has a good coil so I can check resistance readings to compare the two.

For now I am frustrated and am taking a break from it. I find that usually helps. Going back to look at an item another day often helps by starting with a clear mind and progress is made.

Joe
 
I removed the oscillator coil from the board and checked resistances, recorded same and then put back in board with the OEM 2N632 oscillator transistor. I am waiting for Matt's remote pieces so I can compare resistance readings of the oscillator coil in circuit.

I did receive the ultrasonic transmitter transducer I ordered from DigiKey yesterday. I had taken apart the OEM transducer to look at the metalized mylar disc. It had many damaged areas scattered about the center portion of the disc and around the outer edges much of the metalized surface was worn away where the circular metal backing plate touched it. So the OEM transducer has real problems. However, even with the transducer disconnected, the oscillator circuit will not oscillate, so there are still problems with the oscillator circuit. Things are pointing to the coil assembly being defective at this point.

As a backup measure I am considering using 555 timer ICs to generate the desired frequencies that would be needed to talk to the RK-20 receiver circuits. 555 timers are very stable in operation and so would make a good choice for such service. They could be housed in a small plastic project case. I could still keep the original remote hand unit for looks. If it turns out the 555 timer circuits were small enough to house inside the Fisher remote hand unit case, I would do that instead.

Joe
 
There is usually some slight logic to Fishers naming conventions. Anyone care to guess at "MF" as in MF300? I guess for that matter RK ought to be RC...
 
R for AM/FM Tuner
FM for FM only Tuner
MF for Multiple Frequency (Band) Tuner?
RK for the Remote considering the "GERMAN" Engineer's. Remote Kontrol? Kathode=Cathode?!?!
 
R does seem appropriate for AM/FM models based on a number of example Fisher chassis.
FM seems self explanatory and there are numerous examples of Fisher's FM only tuners.
MF - doesn't seem to apply in the case of the MF-300, which is an FM only tuner. The later R-200-B AM/SW/FM tuner is a multiband Fisher tuner. Is there a German word for automatic that begins with "M"? Maybe Magic FM?
RK=Remote Kontrol does seem logical. Fisher used the same mnemonic for their wired remote controls so there was definitely a precedent there.

Joe
 
I guess it could be arbitrary but scaling with position in the lineup like the numbers associated with the different receivers 400, 500, 800, or integrated amps 100, 101, 202, 1000, or tuners for that matter 50, 90, 100, 200, 300, 1000. All manufacturers seem to have an element of this bigger is better approach, but Marantz with their 70's silver face line has an element of the literal to it one finds them selves trying to reason out of the numbers
 
I am pretty certain that the oscillator coil in the remote hand unit I have is bad. I have been investigating using 555 timer ICs to generate the required frequencies to create the two primary frequencies of 38.285kHz and 41.805kHz. I need to determine the modulating frequency that activates the reverse relay and use another 555 timer for that. I need to get some perf-board so I can build up the circuits. They may well be small enough to mount inside the original remote hand unit case and that way would look original. Lots of work lies ahead. I got a good buy on some 555 timer ICs and bought 100 of them. I will eventually have a use for them for other projects. The frequency stability of the 555 timers are quite good as long as good quality resistors and capacitors are used with them. Silver mica, polypropylene or polystyrene capacitors are some of the most stable.

Joe
 
The 555 timers arrived today in a long box from Mouser Electronics. I could not understand why they used such a long box until I opened it and saw the ICs were in a long anti-static plastic tube. They arrived in good shape though, so I am glad to have them.

Joe
 
Well, half the naming mystery of the MF-300 is solved - it's called the "Motor Tuner" on a manual I saw.
 
Today I got around to looking at the remote hand unit of rufleruf's RK-20 system. I measured the resistances of the oscillator coil in the hand unit and it measures virtually identical to the one in my unit:
1 to 2 = 114.5 ohms
1 to 3 = 1.8 ohms
1 to 4 = 0.70 ohms.
Mine measured:
1 to 2 = 115.8 ohms
1 to 3 = 1.98 ohms
1 to 4 = 0.71 ohms
So with both units measuring so close in resistance to each tap, I believe that the coils are likely OK. More checks ahead.

I cleaned the battery connections and tried the remote hand unit with my RK-20 receiver which works using an audio signal at the correct frequencies. I installed the 4.5VDC battery and no output appears to be getting to the RK-20 receiver. I will do some more detailed tests tomorrow.

Joe
 
Some more details on rufleruf's RK-20 remote hand unit:

I have installed a new 25uF@16VDC electrolytic for C31 using an axial lead electolytic from Mouser P/N 75-TE1157.1 which is virtually the same physical dimensions as the original Frako part.

I cleaned both battery terminals on the PC board of the hand unit as I spotted some resistance between the spring contact and the rivet, then re-tinned the battery spring contacts and resoldered underneath the board to the traces.
The R30 in this hand unit is a 27K ohm as shown on the schematic whereas the R30 in my hand unit had been changed to an 18K ohm.

Q8 in this unit is a Raytheon 57D1-?? (no other numbers other than a 6104 date code visible). Q8 in my unit is a 2N632 as shown in the schematic. Q8 checks OK with the ohm meter and readings are very similar to the Q8 in my hand unit.

Next step will be to change C29 which is only in circuit when the hand unit is rotated until the remote hand unit body is vertical, which engages the internal mercury switch to "On" to activate the modulation for reversing volume or channel motor tune direction. I have already cleaned the contacts that are activated by the push-buttons.

If no oscillation is seen I will try substituting the new transducer I ordered from DigiKey.

Joe
 
Joe - thanks for the update - I'm looking forward to getting the MF300 together with maybe my X-1000 as my living room set up for a while.
 
Matt;

Great news! After lunch I became brave and decided to try your remote hand unit with my repaired RK-20 receiver. It works!!!

I still need to change the 0.47uF electrolytic in your hand unit and retry the reverse functions again. I tacked the new transducer that I had ordered from DigiKey into my hand unit and it appears to be working now also.

The next step is to order the remaining electrolytics for your RK-20 receiver and get it operational. I will also be getting another 4.5VDC battery made for your hand unit. It will be another 3-5 days to get the ordered parts from Mouser. I will get those parts on order this afternoon. I still need to make sure the transducer in your hand unit will work at a distance before I pronounce it completely OK. I also need to recheck the frequencies being output to make sure it does not need tweaking. I had to clean the small mica compression trimmer in your hand unit and I may have gotten the frequencies off a bit.

Joe
 
I made an interesting discovery when I opened up Matt's RK-20 receiver. There was a small paper label at the front of the etched circuit board that said:
"This device is manufactured under Admiral's U. S. Patent No. 3,027,497 and other patents pending. 4DD155-420". So Fisher contracted the remote control parts to Admiral Corporation. This explains the 57D1-nn designations on the Raytheon transistors in these units. Those beginning characters are very indicative of Admiral part numbers and even some of their model numbers. This does not mean that they were not made for Admiral and Fisher by a company in Western Germany. The presence of Frako electrolytics does at least show that they used some parts supplied by a West German company even if the assembly was done in the USA.

Joe
 
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After the success with Matt's remote hand unit, I decided to work on mine again.
I had the ultrasonic transducer made by Murata that I had ordered from DigiKey. I had no exact way to mount it and had not tried replacing the original transducer in my hand unit. I removed the original transducer and set that assembly aside. I attached flexible wire leads to the new Murata transducer and connected them into the oscillator output circuit, then installed the battery in the spring clips on the circuit board. My RK-20 remote receiver was already sitting on the bench from testing Matt's remote hand unit. I pressed the channel and volume contacts on my remote hand unit's board and my hand unit is now working!:jump:

I remembered from my days working on RCA televisions with ultrasonic remote controls that their most common problem was with the ultrasonic transducers going bad. In the case of the Fisher hand unit this is true too. When the transducer goes bad it stops the oscillator circuit from working. I was lucky that the Murata part I selected works in this circuit. The Fisher service data does not state the impedance or other characteristics of the transducer to make selecting a new replacement an easy task. I spent several days looking at different parts on the internet before choosing the Murata part. Not only does it have to operate in the desired frequency range, it also has to fit the dimensions of the small phenolic molded bracket that Fisher used in the remote hand unit. It has to be about 9.9mm in diameter to fit into the bracket.

The Murata MA40S4S is just small enough to fit after the metal ring on the back side of the phenolic bracket is swaged and filed a small amount. In the end I got mine to fit without undue strain on the transducer case. The back side of the transducer is a bit deeper than the OEM part and the wire leads have to be bent at 90 degrees to clear other parts behind it. When bending the leads the leads have to be held tightly with small needle nose pliers to keep from placing any stress on where the leads actually enter the transducer body. I will add a couple of small drops of plastic glue to help retain the transducer in the phenolic bracket. some wires will be attached to the metal ring on the back side of the transducer bracket to secure the bracket to the circuit board. Fisher used two heavy wires originally to hold the transducer to the circuit board.
I will take some pictures of the modified mounting bracket to show how I did this for posterity.

I am now resting from the tension of dealing with such tiny delicate parts!!:bowdown:

Joe
 
The light at the end of the tunnel is the 5:00 express heading Westbound. :jump:

Seriously Joe. Damned nice job on getting not only yours running , but Matt's too. Let's just hope not too many of these things start popping up all over. :biggrin:

Larry
 
Excellent news Joe!!! If the Murata part is inexpensive, maybe you should put one in an envelope and tape in somewhere in my receiver unit.

I'm going to have to move the MF300 project up in my queue!
 
Matt;

I will be glad to do as you suggested. I do not foresee any significant problems with your RK-20 receiver. Now that I have done mine, I know my way around in there and parts are available easily enough. This is one time that discrete transistors are nice. It makes studying a schematic easier to follow. There are some parts that are internal to the "modules" in the receiver, but normally they are not going to go bad. Fortunately these are soldered into the circuitry rather than being plug-in circuits. Some manufacturers tried to go the route of plug-in modules and the connectors proved to be a primary cause of problems over time.

Joe
 
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