Philco 50-T1403 with focus problem

[dreyfoos]

I don’t have a Simpson or a Triplett now but I do have a very contemporary old Hickok 203 volt-ohm-capacity-milliameter. Hadn’t gotten around to recapping it. I put the meter in the focus coil circuit and it jumped up but there was an obvious hitch in its get-along.

Maybe this meter maintenance issue deserves a new topic…a cursory web search didn’t find anything. I think that I need to get up to speed on cleaning and lubing that very delicate meter movement.

In the old days I suppose it would have been carbon tet and sewing machine oil – two things that aren’t likely to be found around the house these days.

BTW Don, I will triple check the wiring around the new electrolytics – some had been installed by the previous owner before I dived in and recapped the rest. Of course, I never make a mistake myself.

And, I’ll play around with that unwanted ripple in the alternate supply.

Roger

[Don Lindsly]

Avoid lubricants on the meter movement. Clean with ether or carbon tet in a sterile work area. Look for small stuff stuck between the movement coil and magnet. Fixing meter movements is a craft all its own. Some other members may have something to offer.

[dreyfoos]

Progress? report:

First, a puzzling observation: the 100 ohm focus coil shunt (Sam’s R127, Rider’s R65) seems, at this time, to be superfluous. No difference in the raster focus whether it’s in or out of the circuit. I subbed all the way down to 0 ohms and up to several hundred with no effect on focus. I know manufacturers aren’t in the habit of spending extra pennies for nothing. Seems significant to me – could this be the missing piece of the puzzle?

It was noticed as I was inch-worming my way through the circuitry to verify every connection and component. I have found nothing out of place so far. All electrolytics are fresh and polarity double-checked.

I also rigged up for smoother DC from my breadboard supply to the focus coil. I used two 22uF 350V’s with the secondary of a filament xmfr in between as the inductor. There’s still a ripple but it’s much reduced – appears as one or two bands instead of six or eight.

It took 30 VDC indicated on my Variac and confirmed with the VTVM to get perfecto focus using the lower ripple breadboard supply. The current measured 195mA with the digital ammeter. This same alternate supply - without the new filtering - gave perfect focus at 160mA and 33VDC.

(I’m still trying to get an ammeter to confirm what I’m now getting with the digital. I took out the meter on my old Hickok and it seemed to be moving freely once I could hold it in my hand and subject it to gravity from different directions. Now I need to check all the shunt resistors in the range circuits and then there are the contacts and connections to clean up before I put it back together.)

Don, you said, "Try a 10-20 uf electrolytic on the 5U4 side of the B+ source when measuring total TV current drain.” I’m not clear on where I should put that cap relative to the meter. Do you mean in series with the digital meter lead?

Roger

[Don Lindsly]

Roger:

I would just put it from pin 8 to ground to clean up both sides of the power supply. You could also just put the ampmeter is series the choke on either side. It all amounts to the same thing.

If the 100 ohm resistor does not do anything, then it is probably because the focus control is at one end where it routes the most current through the coil.

First try a 150-200 ohm, 5 watt in series with the end of the focus control that is connected to the filter choke. That should center the control action.

Don

[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

[dreyfoos]

I have now delved further.

Disassembling the yoke-focus coil stack on my #1 version of this Philco revealed an extra layer of nuts between the yoke and the magnets - based on what I found in the #2 set. That changed the presumably critical spacing between the yoke and the focus coil bolted on behind it. That extra nut shifted the focus coil's position over the gun by about 3/16 inch aft. Now, having "corrected" that, to duplicate the spacing found in my #2 set and having assembled the magnets from #1 with the yoke from #2, I find that the focus from the original situation appears to have changed slightly – now it’s 100% perfect at the extreme CW end of its focus control rotation. But it should be around the mid-point of the control rotation, as with magnet #2, and that still leads me to think that the permanent magnet from #1 is not up to snuff. So, on the one hand, I've got sharp scanning lines! On the other hand, no headroom in the focus control.

There are some contradictions to clear up. I will delve yet further.

Roger