[dreyfoos]

And now, ta-da, sweet success, I’ve got excellent focus (see photo). It’s been a long road and along the way I’ve received outstanding guidance and suggestions from those of you who for whatever reason are travelling this same road. Special thanks to Don Lindsly out in Colorado.

To catch y'all up: I had let this thread slide for a month as I took a different tack to get at this focus problem. For most of you, what follows will be old hat. But there may be a youngster or novice reading this…I’m no youngster but not much more than a novice either.

Strategies for solving a defect in a TV that’s way past old enough to vote depends on several approaches. If you have the knowledge of an engineer or “reverse engineer” you may know how to zero in on a few likely components as the culprit(s). Years of hands-on experience in the trenches and on the benches also goes a long way. Knowing what to measure and how can get you off to a fast start – if you have a good suite of reliable instruments. What makes the senior, or retired, or aged TV receiver so “interesting” is that it’s no longer anywhere near “factory-fresh” – boasting virtually all new parts with only one failure point for us to detect. That’s why those of us afflicted with old TV’s usually do a wholesale replacement of the statistically likely failure points – like all paper caps and electrolytics – and of course, a tube check. (BTW, I’m in the camp that feels no shame with having lots of shiny new Asian electros or orange drops showing. How do you re-stuff a bumblebee anyway? …but I’m sure someone has done it.)

Where it gets interesting, is when the part is not easily tested nor readily available as a new part. In this case, I did have a permanent magnet part of the focus assemble but with no way to make a definitive measurement (it would still hold a paperclip). I also had no new part to “sub” that final piece of the puzzle. I say “final” piece in the style of old Sherlock, who deduced from “the dog that didn’t bark.” In this case it was the permanent magnet part of a combination PM/ electro-magnet combination to handle the focusing. My books (from the era) told me that the PM does the heavy lifting in that PM/EM combo. I wanted to eliminate that PM as the point of failure. But I had no duplicate part with which to sub. Then, just in the nick of time, a twin of my Philco 50T1403, code 125 popped up on eBay. I decided to go for it – first, because I just like this model. But also, it would have the correct PM that I could use for a sub and eliminate that as the problem in the set which was taking up too much time and space on my bench. Of course, there was also the possibility that I would just end up with twin sets having the same tough-dog focus problem. Bottom line: got the twin, the sub worked and the focus is perfect – somewhere in the middle of the focus pot’s range. But is the case closed? No. I only have one good PM and two Philcos that need it. Anyone have a spare focus PM? The one that is around the outside of the EM (EM Philco part number 76-2622-3 or Merit number MF-1). I assume that there is no separate part number for the PM.

What causes a PM failure anyway? Temperature is mentioned. A hard knock is mentioned. Anything else that might be associated with age? Where would one take that magnet to get it refilled with the magic? Somewhere, I saw the word “saturation” referring to magnets. Does that mean the somewhat “unsaturated” magnet should be put in an appropriate magnetic field until it’s “full”? And where would I find a magnetism station where I can “fill ‘er up”?

One other factoid that bothers me: the PM with the problem has four scribe marks at the point where the EM wires exit the assembly (see photos). It made me wonder whether there is an orientation problem with the first set’s two magnets. Is alignment between the two critical? A month ago, I tested that by changing the alignment and noticed no difference but those scribe marks still bother me. The magnet assembly from the second Philco does not have any scribe marks. Someone, probably after it left the factory, made those scribe marks. Did they know it was critical to get that back to the factory position? But why are there four marks? Should I start rotating the old PM, one degree at a time? I really need some enlightenment (wild and crazy ideas) from the forums before I try to delve further.

Well, thanks for your interest. I’ve learned from this – hope you have – and that we’ll learn more.

(P.S., you can view the test pattern photo without the artifacts if you hover over the "zoom" icon in the lower right hand corner of the pix and click.)

Roger