Help with FM-1 alignment

Hi,

I have been on this crusade for a few years now, and have previously posted on AA about this.
I have a FM-1 with multplex, and am trying to align it. A year ago I replaced the failed PS cap with discrete caps, replaced the plate resistors for the tubes on the PC-8 board, replaced coupling caps C29, C31, C82 and C83. I did a tabeltop alignment by the manual, the issue came with aligning T73. The stereo light would stay lit the entire time. I could hear the signal go from mono to stereo and back to mono as i turned the slugs from bottom to top, and left them in the middle of the two phase switches. It worked fine, with the stereo light on all the time and after i resoldered L-1, reception was very good.

Fast forward to now. I now have an old signal generator, set it to 10.7000**MHz and tried to align the IF stages properly with the tuning eye. The issue is the bottom of T1. There was no movement of the eye when i turned the slug. If i went ALL the way up OR down, i could get a small closing change. The other T1-T4 slugs behaved normally. I did not remove the gimmick, should I have? Is there something else causing the bottom of T1 to not respond?

I did not replace anything on PC-7.

[quote="studeb"]Hi,

I have been on this crusade for a few years now, and have previously posted on AA about this.
I have a FM-1 with multplex, and am trying to align it. A year ago I replaced the failed PS cap with discrete caps, replaced the plate resistors for the tubes on the PC-8 board, replaced coupling caps C29, C31, C82 and C83. I did a tabeltop alignment by the manual, the issue came with aligning T73. The stereo light would stay lit the entire time. I could hear the signal go from mono to stereo and back to mono as i turned the slugs from bottom to top, and left them in the middle of the two phase switches. It worked fine, with the stereo light on all the time and after i resoldered L-1, reception was very good.

Fast forward to now. I now have an old signal generator, set it to 10.7000**MHz and tried to align the IF stages properly with the tuning eye. The issue is the bottom of T1. There was no movement of the eye when i turned the slug. If i went ALL the way up OR down, i could get a small closing change. The other T1-T4 slugs behaved normally. I did not remove the gimmick, should I have? Is there something else causing the bottom of T1 to not respond?

I did not replace anything on PC-7.

You may very well have some issues with PC-7 and possibly PC-8 the main issue being grounding. You need to make sure that your ground planes are well soldered to the chassis, check the screw adjustment on C8 it needs to have a very tight contact to the threads, double check the screw adjustments on C1 those need to be adjusted exactly as they are explained in the manual.

Keep us posted on your results.

By the way be careful with PC-8 it's signal and ground planes are very close.

Your timing is interesting, I just did this same thing to a FM-3 last weekend. I sent 10.7 MHz in through pin 6 of V2 (with tube removed) and then adjusted the bottom slug of T1 to obtain peak eye closure. The problem was, like you I couldn't see much of any eye movement either. I actually did a frequency scan initially and found that peak eye closure was around 11.0* MHz, but I knew it couldn't be that far off. I went back to 10.7 MHz and slowly worked my way up in amplitude from -130 dB. At I believe it was -80 dB or so I saw the first glimpse of the tuning eye movement/change. I could then adjust the bottom of T1 and was able to discern peak eye closure, but it was very small movement. I then did a "by the manual" alignment except I never touched the bottom of T1 again.

I made a bunch of other changes at the same time, power supply caps, coupling caps, and probably most importantly new/correct PEC modules from C. Epperson. Everything about the tuner is dramatically better then it was before. This was an Ebay gamble and ALL of the tubes are the original Dynaco/Mullard/Telefunken ones! So, I'm still not confident that how I set T1 was optimal, but it certainly seemed to make a big improvement. For me, the rear screw on C1 was both touchy and *critical* to good performance. All of the other adjustments seemed pretty easy to discern the optimum position.

This was the first time I've ever aligned a tuner, so take that for what it's worth.

Also, I did not remove the gimmick capacitor when aligning the IF transformers. The gimmick should be removed before aligning the discriminator and reinstalled afterwards per the Dynaco manual.

Hi,

Thanks for the replies! I am inserting the signal through pin 6 of V2, which should eliminate most of PC-7.

I will check the ground joints, and while I am there the rest of them on PC-7. I guess if L1 had a cold joint, there could be others.

I am re-wiring the output of my signal generator, the attenuator was non-functional, and the insulation is so brittle it falls off just looking at it. I will see if that helps at all. Maybe there was too much signal for the first coil?

I think you identified a likely cause of the issue. I had to supply the bare minimum signal amplitude necessary to see the response of adjusting the bottom slug of T1 in the tuning eye. I had a scope hooked up concurrently with the SG output and if I remember right it was in the 5 mV P-P area; I wish I had paid closer attention now so don't put too much stock in that number. This was using a near mint HP 8640B generator; not the best in the world but very far from the worst.

I would get your SG attenuator issue straightened out and then try working up from minimum output. Another indication I had was that when I was just above the "optimum" level the stereocator began to flicker. If I backed down ~10 dB I was then in the ballpark. Hopefully that gives you something to at least try.

I've had the chance to do some more listening and the improvements have really been substantial. I also have almost zero drift when starting up from cold; it would take a good 20 minutes to stabilize before. The mods and alignment were well worth the effort!

i replaced the output wire, and cleaned the pot. still have to get some BNC connectors to replace the amphenol ones. On the scope i can see the signal go from about 200mV p2p down to less than 10 before the signal goes out. But on the tuning eye, there is no difference. I tried changing freq to see where the peak was, it was up about 11.0. I brought it down to about 10.7ish, this brings the bottom slug about 1/3 up from the bottom. This resulted in a large change in the top of T1 when i did the back tuning. The sg is not boxed back together yet, and i am running unshielded wire from the output to the board which i know is less than ideal. It may also be this SG just isn't good enough, but i want to get the attenuation down before i shop some more, or cave in and have a shop do it for me.

There were some cold solder joints, C12 and the PC-7 side of the jumper to PC-8. There is also some dodgy looking flux i will clean.

thanks again for the help.

If you still have issues or can't find a shop willing/capable of doing the work, let me know. I used the need to do this alignment as a good excuse to finally buy a real signal generator, knowing I would have some more uses for it down the road. You'll probably have much more luck talking to Ham folks vice any hi-fi shop if you're trying to find someone local to do it.