My First Predicta

[Chris K]

I've successfully restored 2 Seventeeners that have similar guts but this is my first purchase of a Predicta. They don't come up for sale too often in my area. Holiday model in mahogany. Cabinet looks in good shape but the safety "plastic" looks pretty cigarette tar stained. I'll be picking it up this Saturday. I don't know the status of the CRT but that doesn't matter to me. I'll get a decent one from somewhere.

[Chris K]

First hurdle. 21EAP4 tests strong at 2.4 volts with good cutoff. Happiness!

[old_coot88]

Could the seller have rejuvvied it before selling the set? Finding one of those jugs that's not flat is a rarity.

[Chris K]

I don’t think so. He was not an electronics guy. Had the tv for a month after finding it cleaning out a house.

[Chris K]

Flyback looks to be in good shape. Chassis is almost all factory except for a capacitor on the main circuit board and the fusible resistor has been bypassed. Pretty clean and looks like it's had modestly light use. If Bob A is out there, do you know of a resistor substitute for the fuse plugin?

[Electronic M]

I typically sub a fuse of the same current rating and a resistor the same or higher resistance and power.
You can still sometimes find NOS fusistors. I've found if the one in the set is good it'll typically stay good unless I mess something up, so if I find a bad one and I have a good replacement NOS I'll use the NOS.

[bandersen]

Ah, but what is the current rating of the original? It's not in the service info.

The only thing I've ever found is this which rates them in wattage - not current. I assume 5.6 ohms at 5.6 watts translates to 1A. I've measured the B+ current in a few sets and it's slightly over 1A.

Watch this for suggestions on replacing them: https://youtu.be/hYDJZvHPM1A

[Chris K]

Got it...thanks Bob and Tom. I can't find the startup thermistor on this one though. They're usually on the bottom of the chassis right? Hmmmmm.

[bandersen]

Probably fell out. It happens a lot

[Chris K]

You gotta hand it to Mr Rigotti. These are fantastic and a wonderful timesaver.

[Chris K]

Got the shell and safety plastic off the CRT. I think the condition of the yoke provides more evidence this is a low hour TV. Nothing looking burned or full of dust...electrical tape still soft and adhered...plastic cover on the back of the yoke still pliable and no heat damage etc. Even though the glue on the label failed, the label itself is perfect and still glossy. The dag is perfect. I'm starting to believe more and more the CRT test on the Sencore showing strong emission with good cutoff is real.

At this point, there's no HV so the next step is to investigate that.

Chris

[Chris K]

Some photos of the neck and its insides.

[Electronic M]

For no HV check power supply is good, H osc is working (look for sufficient negative grid bias on the output), make sure the paper caps in the horizontal are changed and that the width pot isn't open (or dirty enough to act open), and make sure the damper tube is okay. Once those are checked good if still no HV lift the HV rect top cap and try to draw an arc from it....If you get a healthy arc then the rect tube is bad, it's heater winding/heater limiting resistor is bad (open or shorted to ground) or the wire from the HV rect socket to the CRT is open or unplugged.

If no arc anywhere after all that report the control and screen grid voltages on the H output tube vs schematic. Screen grid voltage will tell you if the flyback is drawing power from the flyback and if it's got a partial short or open.

[Chris K]

Thank you Tom! Will investigate as per your flow chart this evening and will report back!

[bandersen]

What about the rest of the set? Are you getting anything out of the speaker? Can you tune a station in?