Predicta Predicament

[Down Under]

Ok,

Here's what happens. With everything connected, pin 5 of the damper measures 230V, which is of course, B+. Pin 3 measures 300V. As I remove the damper from an operating set, the picture quickly shrinks to a vertical line before fading out completely. Being a series string set, everything dies.

Removing the yoke increases B+ to 260V, which is still a bit shy of the supposed 275V. I have a Princess or a Debutante the that I could take yokes out of, to sub for the one in the Holiday, but I haven't looked at how similar or compatible they are yet. I know the plug certainly looks the same.

The horz windings of the yoke measure ok, but I know that with AC, inductance also plays a part, just as it does with the flyback. As to the boost cap, that's been replaced, I assume it's ok. With the damper removed, B+ jumps to 280V, pin 3 changes from 300V to 3.5V.

Cheers,

Adam

[bandersen]

All the Holidays and Tandems I've worked on have low B+. One as low as 240 volts but the whole screen is filled and HV is OK, so I wouldn't worry about that.

[old_coot88]

Adam,
Does the flyback show any evidence of having been replaced?

[Down Under]

Thanks Bob for that interesting piece of info, I didn't know that they could operate with B+ that low and still produce full raster. BTW your Philco radio videos are very interesting.

As to the flyback, I think it's original. There's a story with it though. When flaking all the tar off to recoat it, I discovered a hair thin wire sticking out of the side of the over wind. It was near the inner core of the wind, next to where the wire from terminal D (HOT plate) comes in. I'm assuming I broke something when I removed the tar, and the logical place for this strand of wire to go was to the wire that comes in from D. So I connected it there, but who knows, I may have it wrong and be causing my own problems. I'll look at subbing a yoke this weekend, but I'm suspicious of the flyback.

UPdate: I carefully cleaned the side of the over wind with alcohol, looking for a potential other end of that loose strand. I couldn't see one, so I severed the connection I had made and tested. The 360 ohm reading between D and the rectifier cap is now infinity, and when powering up, B+ still drops to 230V. I'll redo my repair to the fly and sub in another yoke. I'm less suspicious of the flyback, but it still may be a problem, just not where I thought. Glad I haven't coated it yet!



Apart from this major issue, I think I have the rest of the set working, as near as I can tell.

Cheers,

Adam

[old_coot88]

Originally Posted by Down Under

As to the flyback, I think it's original. There's a story with it though. When flaking all the tar off to recoat it, I discovered a hair thin wire sticking out of the side of the over wind. It was near the inner core of the wind, next to where the wire from terminal D (HOT plate) comes in. I'm assuming I broke something when I removed the tar, and the logical place for this strand of wire to go was to the wire that comes in from D. So I connected it there, but who knows, I may have it wrong and be causing my own problems.

I'll look at subbing a yoke this weekend, but I'm suspicious of the flyback.

What was puzzling from the outset was that strange frequency disparity (where you said there was some sweep at 3X normal frequency, but lost it when returned to normal frequency).
it got to wondering at that point if the fly mighta been replaced and miswired. But evidently the fly is original.

[Down Under]

From my understanding, the frequency issue occurs because at lower frequencies the HOT is driven harder, as is the flyback. If anyone could enlighten me on this it would be appreciated. That's why I wondered if I had a partial short that wasn't making itself known at high frequencies because of lower stresses. I'm quite sure the fly is an original because everything looks untouched, and there was plenty of tar that had dribbled onto the chassis underneath.

When starting work on the chassis, I took the flyback out to clean it and disconnected all the wires from the terminal board. As far as I can tell I replaced them correctly, since I took pictures. I have checked them, but I'll do so again. I'd love it if the fix was as simple as that! I carefully rejoined that very fine wire and the resistances are back to normal. I think that I might have it as it should be, as it turns out.

I'll sub in a yoke from a Seventeener and report.

[Down Under]

Hi guys,

I know this is an old thread, but it may help someone.

I found my issue. Just a reminder, B+ was a bit low at around 235V, the width of the
picture was very reduced with a bit of foldover on the RHS and with severe blooming and associated loss of high voltage. When I adjusted the horiz hold, I could get a better HV with brighter picture, but the frequency was way off; too high.

Well, it turns out that I'm an idiot. When rechecking C45 (SAMs, 0.033 uF), it turned out that I had put in a 0.0033 uF. I only just discovered my mistake and after fitting the correct value, B+ is around 255V, same as my working Tandem. HV is where it should be, judging by no blooming, a bright picture, and a decent arc off the rectifier plate lead.

Very happy now!

Now to recoat the flyback properly.

Cheers,

Adam