Fisher 440-T Alignment Questions

[jadney]

I'm trying to finish the refurb of a Fisher 440-T that I worked over a few decades ago. It had some problems that remained, but I think I have fixed each of them, except for two.

Fisher 440-T (transistor) SN: 34xxxB. I have the service manual beginning SN 20001, which seems to be the appropriate one, but there's no mention of the B at the end. Anyone know what that means? I've found a couple mistakes in the service manual and can share them if anyone cares.

The amp and preamp all work now, and the tuner does FM mono just fine.

Remaining problems are: no indication on the signal strength meter and no FM stereo output or "Stereo Beacon" lamp lite.

Because the signal strength meter signal comes from the IF strip, I'm starting there, but I've run into a couple questions. Under IF Alignment, third paragraph, it says, "AdjustZ303 (Bottom core)..." but then in paragraph 5 it says to adjust "bottom core of Z303". The top core of A303 is not mentioned anywhere, so I suspect that one of these should refer to the Z303 top core. My GUESS is that paragraph 3 should refer to Z303 top core. Looking at the schematic, there are up and down arrows next to each IF transformer winding. I'm GUESSING that these arrows are supposed to indicate which cores are on top and which are on the bottom. Because I suspected a problem in Z303, I've had it apart, so I know that the secondary is on top, not on the bottom as the schematic arrow seems to indicate. Am I completely wrong about what the arrows mean?

There was no problem inside Z303. I even measured the two capacitances, which each came out to within 10% of the indicated 47 pF. There were no shorts anywhere and the included diode was still good. I've read that these can have "SMD" or Silver Mica Disease, but I'm not sure what else I should do to check for that. If someone would care to explain exactly what SMD is and how to identify it, I'd love to hear from you.

I have checked all the components leading from the IF strip to the meter and they are all good. When I check the IF output pin, TP302, the voltage there is zero, even with a strong local station. If I inject a voltage there with my VOM, the signal meter deflects.

I'm hoping that getting the signal strength meter working will bring the multiplex back to life, but I don't think there's any point in worrying about that until I get the IF fully working. If it doesn't, I'll deal with that later, once I get some advice on the IF strip problem.

Thanks for any insight you care to offer.

 

[larryderouin]

Silver Mica disease commonly occurs in Silver bearing (usually Mica) capacitors. Silver migrates and the cap goes open. As you got the appropriate response in Z303, no indication of SMD is apparent (yet).

The "B" at the end of the Serial is not relevant to finding a Service Manual. We've been pulling hairs out over this (I know Thered1 has) for 15 or more years now and haven't come up with a conclusive answer. Don't worry about it.

The transistors on the IF Strip are all 2n2654's which are germanium. Bets are at least one or more of the 5 on the board are weak or bad. Gonna be a Gold plated biotch trying to find something equivalent WITHOUT using NTE. NTE 160 is their cross ref. HOWEVER! NTE-160, like most all of NTE's semi's are not exact replacements. More like within the same county vs on the same block. Should work tho.

The 440-T 47001 and up manual has the same mistake. I'm thinking of a similar gaff in the 400 receiver late model. Based on that, Para 3 should be bottom, and Para 5 top. But just to be sure, do para 3 adjusting Z304 1st then either of the Z303. Which ever one that peaks is the correct side. Mark your twiddler and the IF can so you can put the non responding coil back where you started. Make corrections in manual.

 

[jadney]

There was one bad 2N2654 when I first worked on this 440-T a few decades ago. I replaced it with a Delco transistor that I had bought way back in the early 70s and never used. It was in the same package and seemed to work. These days it was easy to buy some NOS 2N2654s on ebay to restore the IF strip to OE condition. I had hoped that might fix the problems, but it made no difference.

I will test out the alignment as you suggested.

 

[fred soop]

There could be some units available for parts only or one that is being parted out that might have the proper transistors available. Searching for one may take some time and patience. Try contacting Joeoldaudio as he may have something that has not been listed. I bought a preamp board from him for the pots. Also bought an IF board from someone to get a transformer and it may have had the same transistors.