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  #31  
Old 02-22-2020, 07:22 PM
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Is your circuit board designation marked as 8GC7? If not it's possible the previous owner was following the wrong schematic. I have two 1077 schematics here and on the 8GC7 version it does not use the JK flip flop. There's a possibility that there are revisions of this devise we're not aware of. Otherwise for loss of vertical check the 50uf cap on the cathode of V1B vertical output. Other than that you pretty much have to get in there with a scope and see where you're loosing your vertical waveform amplitude.

Last edited by Kevin Kuehn; 02-22-2020 at 07:33 PM.
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  #32  
Old 02-22-2020, 09:00 PM
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The label that shows the tube placements has it as a 8FQ7/8GC7. The voltage on the cathode of V1B is correct and flat on an oscilloscope, though the vertical disappeared after I replaced the the electrolytic can with new electrolytics. Basically I’ve checked a bunch of voltages and resistor values. I’m trying to get my hands on the voltage specs for a 1077B. They are different than the 1077, so until I get the right ones I’m not going to spend any more time on it, unless the OP chimes in with what happened with their unit.
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Last edited by judge; 02-22-2020 at 09:06 PM.
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  #33  
Old 02-23-2020, 08:22 PM
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The 8FQ7 and 6FQ7 are the same exact tube with the exception of heater voltage. The 6FQ version probably has a 6V heater transformer with parallel wired heaters and the 8FQ is probably a series wired heater unit. If the heaters are the only circuit difference and they are lighting properly then you can use the voltage chart and just ignore the heater pins...
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  #34  
Old 02-24-2020, 10:00 AM
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Hi Tom,

The schematics with the 8FQ7 and the 6FQ7 both have them series wired. Makes me wonder if the designation is an error in the schematic. It would be interesting to hear from someone else with a 1077B what tube is actually installed.
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  #35  
Old 02-25-2020, 06:53 PM
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Not getting anywhere with this. I’ve replaced the 8FQ7, which has no effect. Test point 17 shows a good waveform. At test point 3, it also looks good until I move the switch from stby to on, then the peak to peak voltage drops from 12 to 7.6. At test point 5 the peak to peak voltage is around 90, it should be 120. I’ve tested all the resistors around Q1 and Q2 and they appear fine. In my version the B-13 rail also powers Q4 and the J/K flipflops. Other than that I can’t find anywhere else it is used. I also checked the resistors that are used to form the negative rails, they are all fine too and I replaced those capacitors.

Just in case I tried a different cap to pin 3 of the 13GF7A, it made no difference, and anyway voltage on that pin is fine.
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  #36  
Old 02-25-2020, 11:03 PM
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I wound up finding a modern Philips device with similar functions so I put the 1077 to the side while I work on the pile of TVs I have.
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  #37  
Old 03-02-2020, 09:26 AM
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If anyone has a working 1077B with the J/K flipflops, could you test the B-13 rail when the unit switch is 'on' (not 'stand by')? It would help me rule out a whole section of the circuit, or narrow the problem down to precisely that part of the circuit.
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  #38  
Old 03-28-2022, 08:53 AM
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Hey everyone, remember this? I pulled it back out to continue working on it and have replaced a couple more electrolytics that were shorted and had related open resistors.

Only one problem now...when I put it in storage it had a raster, more or less, but only have about 1cm of vertical sweep. The entire vertical circuit is working OK but no sweep. One of the vertical deflection coils measures 34Ω, the other measures 156K. So, it's not exactly open, and I have never had occasion to measure the dc resistance of a yoke before so I'm not sure, but it seems to me that this is likely my problem.

Any opinions on why it failed and if it might be fixable? I'm pretty sure I'll never find a replacement. An additional challenge is that I'll probably also never get it off the crt; the base is already slightly bigger around than the neck of the tube, and the plastic of the yoke has shrunk so that it is very tight on there.

ETA: came across an old Shango video where he repairs a yoke with the same problem and says it's common on the 1077s. It looks like quite a job.

Last edited by AlanInSitges; 03-28-2022 at 09:16 AM.
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  #39  
Old 03-28-2022, 05:27 PM
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OK, I got the yoke off and managed to get it apart following the old Shango video. He says that he's repaired 3 1077s with bad vertical windings, and says you have to look for the "green", where there is a little spot of corrosion. The one he repairs in the video has a clearly broken wire right under the spot. Wire reattached, and the device works again.

My yoke had an identical green corrosion spot in exactly the same place as the Shango video, but the wire is intact. In fact I've spent the last hour with my 3.5x goggles going over every part of this yoke and can't find any broken/corroded wire. Verified that the winding measures 1.2M.

A couple of questions: first, shouldn't it measure open? What's going on there?

And second, how does one go about finding the point of failure? I'm pretty sure it's not on the surface. Are yoke windings interchangeable to the point that I might be able to pull one (either a yoke or another winding) off of another set? I guess it would have to be one with a really narrow deflection angle...

Thanks everyone.
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  #40  
Old 03-31-2022, 09:25 PM
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Maybe it will be worthwhile to get a yoke from a USA 1077, but I do not know if it will be different due to the line and frame rate differences.
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  #41  
Old 03-31-2022, 10:19 PM
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I think the yokes are very likely identical.
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  #42  
Old 04-07-2022, 10:51 AM
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Yeah I suspect they are the same yoke. Even the values of the R/C in the sweep circuits are the same between the two.

That said, getting my hands on one of those is going to be complicated; I would really like to try to figure out the one I have.

I spent another hour poring over this thing with a magnifying glass last night, millimeter by millimeter, and I can't see anything broken. But those wires are quite thick and heavy. It seems unlikely one would just open up on it own. And that brings me to the tests I did with an ohmmeter. The other coil measures 32 ohms, which seems about right. This one doesn't measure open; it measures 1.5M. And I noticed last night that if I leave the ohmmeter connected, this happens:



Why does this measure 1.7M instead of open? And why, if it's open, does it increase in resistance (repeated with two different meters)? And if it's not open, why does it measure so high?

Anyone?
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  #43  
Old 04-07-2022, 03:27 PM
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I really have no idea, but could it be that it shorted and then burned open and left a carbon track that is what you are measuring? Is the winding completely visible or are there some buried layers?
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  #44  
Old 04-08-2022, 06:23 AM
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There are a lot of buried layers, and of course unwinding this thing would be complete madness because it would never go back together. I'm sure you're right about what must have happened. It's just that the wire is so heavy, the enamel is not delicate at all, and there is such relatively small current flowing through the yoke that it seems unlikely. But in the absence of a better answer, this has to be the right one.



Photo shows the winding, along with the little green corrosion spot. Both the corrosion and black adhesive have since been removed and the wire beneath appears pristine.
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