FM-200-B Refresh

[fred soop]

I forgot to mention that the LEDs mentioned above are 300 per 16 foot strip and can be cut into 2 inch sections of 3 LEDs each. This is not suitable for replacing fuse type dial lamps. You need the double density, 600 LEDs per 16 feet, that can be cut to one inch sections of 3 LEDs. A 2 inch section will be too long. I don't have the Amazon links handy so it might take a bit of searching.

1428

 

[notdigital]

Very neat, and neat I might add!

 

[nerdorama]

I forgot to mention that the LEDs mentioned above are 300 per 16 foot strip and can be cut into 2 inch sections of 3 LEDs each. This is not suitable for replacing fuse type dial lamps. You need the double density, 600 LEDs per 16 feet, that can be cut to one inch sections of 3 LEDs. A 2 inch section will be too long. I don't have the Amazon links handy so it might take a bit of searching.

Which color temp did you choose? Also curious if you can share a picture of how it looks with the LED's lit up.

Thanks,
John

 

[fred soop]

Which color temp did you choose? Also curious if you can share a picture of how it looks with the LED's lit up.

Thanks,
John

I used the bright white, but I'm a bright white sort of person. I use them to light model railroad passenger cars, putting me at odds with nearly all other modelers that insist on warm white.

I still need to add the foam between the glass and front panel to tame the leaking light. There is another 1 inch of 3 LEDs behind the meter. These are NOT being run on the full 12 volts. The current is knocked down from the rated 20 mA per 3 LEDs to only 3.5 mA or about 9.2 V per group of 3. A reel of these things at 12 volts will light up half a basement well enough to read a newspaper. I did locate the series resistor in a location where it is easily accessible.

1403

1404

 

[AlTinkster92]

Fred that looks great to my eyes, nice receiver as well!

 

[bhamham]

I think I'm leaning to be a bright white person. That receiver is a beauty :thmbsp:

 

[fred soop]

There is a Fisher 600-T restoration thread from last year that is buried somewhere on the forum with all the details.

 

[sruddy]

Not -- Clippy in fact strikes again! The new bridge rectifier is made up of Ultra Fast discrete diodes located on the back side of the new T-strip mounted on the rear of the chassis. I felt that approach made for a very neat and clean look, with secure connections made in the traditional fashion.

Dave

Nice job Dave, I plan on using this rectifier you suggested. I'm thinking of using a wire tie in the holes for the original mount. What do you think about that?

Audio and MPX Circuits

In the underside pic of the unit as originally received, you can see the two output coupling caps used to block the DC at the output of the cathode follower outputs from the output jacks in the lower left corner of the pic. Not the easiest caps to get at and remove, particularly if you remove their compete leads rather than just snip them out. But, they should certainly be replaced in any full refurbishment.

Ditto for the MPX subchassis. The 1 uF composite signal electrolytic coupling cap always gets the proper attention to be replaced (as it did from the previous tech), but the pilot signal coupling cap and audio output coupling caps rarely get any mention, let alone replacement. But these caps are of the same kind that get loudly decried to be replaced in the general audio circuits, and with good reason. They don't often develop any leakage (although they can), but you can bet they will eventually become intermittent. Therefore, these caps too should be replaced with any full refurbishment effort. Also not the easiest to get to to replace with a neat, finished appearance, but well worth the effort in terms of long term dependability.

So, all the old film coupling caps have been replaced in both of these areas now. With that and the power supply circuits finished, all that remains then are about a half dozen caps in the Auto Stereo and Microtune control circuits. A complete alignment check will top off the project after all the work is complete.

But, with the parts in now for the buffer circuit of the X-202B project, it will move back to center stage for the moment to keep it on track. A few pics show the progress:

1. The finished audio circuits.

2. The MPX circuits showing the 3 caps to be replaced.

3. The new pilot signal coupling cap.

4. The new L & R audio output coupling caps.

5. The finished MPX section.

Back when there's more to report.

Dave

Who makes those yellow caps? When I first started working on tube gear I used orange drops but noticed different brands used in Jim's kits now I see you using the same yellow ones as him. I want to use the best parts and am wondering if the yellow ones are better than orange drops.

Whoa yeah -- starting with the units of serial number 20001 and up, the MPX 100 converted to using a somewhat more complicated, but basically topologically identical time division design, similar to that used in the sub-chassis units.

As long as the MPX interconnect is kept short, then the FM 200 and the later MPX 100 decoder should perform identically with the FM 200B. In that case then, the 200B just represents a nice, complete package, rather than the separate units that the 200 requires.

Dave

I have a much nicer looking FM 200 with a latest model MPX -100 I was going to use the tuner for parts but know I think I will restore it and do a comparison!

Waiting......and Odds and Ends

After the recap, the tuner was put back into service, with a few details noted to take care of:


2. Some techs don't realize what fanatics we Fisher fans are! This unit had the typical 8 volt Fuse Style bulbs SOLDERED in place for the dial lamps, because someone along the way apparently used the fatter festoon lamps in this unit than were called for, which broke out (or required the breaking out of) the dial glass side of the lamp well to accommodate them. This ruined the four sockets, and meant that the proper festoon lamp, or even the Fuse Style lamps would no longer snap and hold in place, requiring the previous tech to solder in the existing fuse bulbs. It works, but is hardly convenient when change out time comes.

Different options were examined to try and fix the broken out sides of the socket wells to have them work as Fisher intended them to, but all were involved, and hardly left a stock look to the fix. At that point I realized that by disconnecting and removing the clip from each well, and simply reversing them -- so that they clamped the bulb between the clip and the remaining in tact side the lamp well, a fix could be had with no one really the wiser about it. It worked perfectly!

Dave

Sweet!!! I was going to try and glue the Bakelite but will do your fix instead. I broke mine jamming in the 6.3v fuse lamps I got at parts express. I have since found warm white LED with the proper dimensions.

 

[AlTinkster92]

This FM200B still sits proudly in my living room and performs perfectly. Thanks again to our Professor Dave! Al

 

[vendo81]

Sweet!!! I was going to try and glue the Bakelite but will do your fix instead. I broke mine jamming in the 6.3v fuse lamps I got at parts express. I have since found warm white LED with the proper dimensions.

Where did you buy the LED's? I'd like to try them out in my FM-200B.

 

[dhrob]

Hi, just signed up here as I have become recently an owner of a unrestored FM200B.
I just ordered all the caps that will replace the older ones. Thanks so much for posting this out here!

If anyone is still listening, I have a question..
I slowly powered up the FM200B using a variac to see if it was functioning as I got with a huge layer of dust and all kind of attic-stuff on it. Happy to say that the units works and is receiving from an in house aerial I put up (where lots of modern tuners won't pick up the classical station I am currently listening to on the Fisher).
Thing is that after powering up it lasts about 2 to 4 minutes for the left channel to come alive after a soft click. Any idea what might be the reason and are chances that it will be solved when all original caps are replaced?

Thanks in advance,
Rob

 

[dcgillespie]

Hi Rob -- Welcome to the AK Fisher Forum! You'll find lots of great folks and Fisher enthusiasts here to help you with your gear, and its always nice to add new folks to the list!

If you will, please provide the serial number of your 200B, and how many positions (settings) the front panel Selector switch your unit has (3 or 4), but invariably it will be a version that resides within the range that is lower than 49999, and possibly lower than 59999. Units of 49999 and lower (and possibly 59999 and lower -- I don't have a manual for this version to know with certainty) employ a special 3PDT relay to (in part) switch the audio output signals between either a stereo or mono output as the front panel Selector switch setting and received station conditions so dictate. Invariably what has happened is that the relay's audio contacts are intermittent in making their contact in one of the modes, so that either with a little heating, or possibly the unit switching to the opposite mode, contact is then made and the sound either resumes or appears in the left channel.

This is a common problem in these units. Cleaning the contacts will resolve the problem for a while, but is typically a poor long term solution unless the unit gets regular use on a nearly daily basis. This is because the contacts in question carry no current through them at all, and therefore, there is no natural cleaning action from the micro-arcing that normally occurs when switching state with relay contacts that do in fact pass current through them. Fisher was clearly aware of this problem, as later versions (at least from 60001 on) employ electronic switching with a diode matrix array that completely solves the problem. There is still a relay involved, but a much simpler one with contacts that are always passing current (not audio signals; now acting simply to control the state of the diode array), eliminating the problem of the older design.

The good news is that older units can in fact be retrofitted to the newer design -- but it is not a simple modification to perform when done properly. It is certainly very worthwhile to do however if you want utterly dependable stereo/mono switching action from your 200B. My own unit suffered from this very problem, so after finally tiring of cleaning the relay contacts, I converted my unit to the later design, allowing use of it on a much more regular basis now without always wondering if or when a channel would cut out.

When looking at the relay (located near the Selector switch), check also that a appropriate amount of tension is present in both positions of the rotor (moving) contacts so that positive contact is made -- although this is usually not a problem unless someone as tried to adjust it and damaged the relay in the process.

If your unit is of a version that already has the electronic switching installed, the same symptoms can be created by intermittent coupling caps in the audio output amplifiers -- but this is only a remote possibility. By the time these units were produced, Fisher's coupling caps were generally quite dependable relative to leakage and intermittent operation. The great likelihood is that your unit employs the 3PDT relay, and its contacts are the source of your problems.

I hope this helps!

Dave

 

[dhrob]

Hi Dave,

Thanks for quick reply, and a lengthy one as well. Much appreciated.
I took a picture of the serial number as can be seen on top of the chassis. It is 20495A, if I read it correctly. The selector has 3 positions and I have seen the relays when cleaning it. You can hear them clicking when dialling in for stereo despite the lamps are probably broken. I will have a look if cleaning will solve the issue. I am a enthusiastic listener for classical music on a local station here in Holland, so am not tuning a lot for other stations..
The unit is missing the jewels and some of the knobs, unfortunately. I saw that these are offered on marketplaces but those prices.. fascinating. As well the tuning lights and lamps are broken or missing. Only one lamp alive, it is the one behind the tuning indicator, lucky me.
I will check, clean and get back. Thanks!

Rob

 

[Patrice B]

I've cleaned the relays on mine with a simple little piece of paper, maybe it could help. Going well since then...

 

[dhrob]

Hi Dave, well, cleaned the contacts of the relays and it has something to do with that because now the left channel will not come alive anymore within almost 15 minutes. :-(
I attached a picture of the relay before cleaning. I do not have any reference for it, but it looks like the spring is still okay and the coil must be functioning otherwise I would not hear the relay click? The middle contact seems a little bent? Do you know which of the three is related to the left channel?
Just to explain how I cleaned it: I detached the spring so I could slide the three contact a bit to the side and so reach top and bottom contacts for cleaning. I used contactspray on a small sheet of rice-paper and slide it back and forth between the contacts. Lots of dirt came off (but not enough?).

And thanks Patrice!

Thanks,
Rob

 

[Patrice B]

Maybe not enough contact in the relay? Maybe Mr Gillespie will chime in soon. I didn't removed the springs on mine, just put the paper back and forth between contacts.

 

[dhrob]

Might be.. maybe it has a bad spot at the point it makes contact.
Or.. and this is what I just learned.. Music suddenly faded away, first left channel and right to follow. When pushing the metal small housing on top (next to the ECC88 and 6CW4) suddenly both channels came back. Coincidence?

 

[dcgillespie]

You certainly want to clean all the tube sockets as well. In tuners in particular, dirty sockets seem to abound (particularly if they've sat idle for a long time) that will either make for a completely dead unit, or cause strange operation for sure. Don't forget to clean the Nuvistor sockets as they can be some of the worst offenders.

If pushing on the chassis at any place causes the sound to return then clearly something is intermittent. The problem is, it can often be anywhere in the chassis as many times, just the slightest movement or flexing of the chassis is all it takes to restore operation -- temporarily anyway.

Your relay is the earliest, and most problematic type. Later units (like mine) used a relay that had contacts that were slightly magnetized to help ensure contact integrity in either state, but while that did help with the problem, it did not complete eliminate it with any finality. Final units then had the electronic switching which did. The inner most contacts (relative to the interior of the unit) are the contacts that handle the Left channel (Channel A). The middle set of contacts handle the Right channel, while the contacts closest to the edge of the chassis handle turning the Stereo Beacon Lamp on and off.

Dave

 

[dhrob]

Hi Dave,
Thanks again. I did clean tubesockets using contact spray. Forgot about the Nuvistors though.. so will do that as well.
I think (no, hope) that I found the culprit. An equivalent of E88CC, the CV2493, was used in the first stage. When touching/pushing the chassis music faded away and came back. I replaced that one with a genuine 6DJ8 and now that problem is solved: pushing the chassis has no effect anymore on sound. I will see tomorrow morning if the left channel is still slow at turning on after a night cooling down..

Sorry for asking so much.. I do have experience with amplifiers and tubes and such, not with tuners though.
Do you know what the brown wires' function is coming out of the metal box? It is not attached anywhere and on other pictures it seems the same? I can not find it in the service documentation.. is it some kind of antenna or should it be connected somewhere?

Thanks again, Rob

 

[dcgillespie]

The metal box is the "RF Front End" of the tuner, where the 6DJ8 you replaced and the Nuvistors resides. It is completely shielded to promote frequency stability, and prevents its circuits from being influenced by or influencing other circuits around it (primarily from the local oscillator circuit contained within it). It was built and aligned on a completely separate assembly line, and then assembled into the tuner proper as a complete assembly at the appropriate time during production. The brown wire with a hook on the end of it is a test point that the factory used in aligning the front end assembly. It appears on the schematic as Test Point #1 within the dashed line box that represents the front end portion of the design. Such test points appear on the FM front end unit of many Fisher FM MPX Stereo tuners, but most are never used in any kind of routine servicing or alignment procedures -- except for the 200B, where it is used because of the Nuvistor tubes used. It is also used on most versions of the 500C receiver for the same reason (even though the alignment instructions in my service manual for that model don't mention it as the instructions are a carryover from the earliest 500Cs that did not use Nuvistors). It also used in the FM-1000 of course because of its Nuvistor front end as well. The test point hook lead normally protrudes from the front end box touching or connected to nothing, and should be left alone.

Dave