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 Post subject: Re: 1077B schematic?
PostPosted: Mar Thu 05, 2020 3:10 pm 
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I don't see what foil you are talking about. There is none anywhere near the brown lead.

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 Post subject: Re: 1077B schematic?
PostPosted: Mar Thu 05, 2020 7:22 pm 
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Well, the brown lead has to be connected to the B+ somehow. See if you can verify that it is connected someway.

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 Post subject: Re: 1077B schematic?
PostPosted: Mar Thu 05, 2020 8:27 pm 
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I won't be able to measure the minus 13 volts until saturday. (overworked). I will check the waveforms on the verticl stage .........

I had made a drawing several years ago of the Flip-Flop section as I had the other schematic. I did note that the voltage at the - 13 point was - 7 volts at the 10K resistor ahead of the collector of Q4.

Not to force my opinion but . . . .

You have a purple horizontal line on the screen with little to no vertical sweep. This tells me the horizontal sweep section is essentially working. You have horizontal sweep, you have High Voltage, and you have some Boost voltage. The earlier version of these devices had a knob on the front panel to adjust horizontal frequency and it had a very broad range. This proovs to me the the H-sweep is not very touchy about frequency.

Do you have the waveform sheet that went with the manual? Thinking the waveforms may look OK but be very low.

I re-soldered all the tube sockets


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 Post subject: Re: 1077B schematic?
PostPosted: Mar Fri 06, 2020 4:31 am 
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Tom: Yes it is connected. I need to power it up and check that the B+ is getting to it though.

jimmc: Yes I have the waveform sheet. The waveforms look good - the frequencies are correct, but yes, the voltages of the waveforms are low. All the B+ Voltages are OK - they are a little high, as might be expected when running off today's voltage. It sounds like you see about the same voltage on B-13 as I do, so I can ignore that as an issue.

So at this point it sounds like the boost voltage may be off? I have already checked R59, R60, R61, C34 and C35. I replaced C36 (which made no difference).

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 Post subject: Re: 1077B schematic?
PostPosted: Mar Fri 06, 2020 6:15 am 
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Given that the horizontal deflection looks to be good, the raw boost should be close to the correct value. The decoupled boost could be low if too much current is being drawn.
Is the expected value of the boost listed somewhere?
The only place the boost is used in the vertical circuit is the plate supply of V!-A. Is the expected DC voltage for the plate of V!-A listed and if it is how does it compare to what you measure? But as your vertical deflection is only something like 10% of the correct amount, the plate voltage on V1-A would have to be extremely low for that to cause the problem.
The plate voltage on a tube can vary quite a lot without much affecting the gain of the tube.

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 Post subject: Re: 1077B schematic?
PostPosted: Mar Sat 07, 2020 4:12 pm 
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I measured the -13 volts this morning and it is -7.33 volts measured on the neg end of the little electrolytic cap on the sweep board c-64, with the unit in the full on mode.

Jim


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 Post subject: Re: 1077B schematic?
PostPosted: May Sat 09, 2020 8:47 pm 
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I shelved this project for a bit, but I find myself between other projects at the moment, so took another bash at this. I had the yoke apart and checked the continuity of the vertical coils. They are fine. The parallel resistors are fine too. I measured the waveform either side of the vertical output transformer. Results are below. Voltages are 10x those shown on the screen, so about 400V peak-to-peak input and 72V peak-to-peak across the coils. B+ is at 239V. I don't know what this shows me, I'm hoping someone will tell me if these waveforms are OK. Well, I'm hoping that they aren't OK and that something can be deduced from that!

Attachment:
File comment: The vertical output circuit, showing T1
IMG_4970.JPG
IMG_4970.JPG [ 398.87 KiB | Viewed 241 times ]


Attachment:
File comment: waveform across the vertical deflection coils.
IMG_4969.JPG
IMG_4969.JPG [ 507.74 KiB | Viewed 241 times ]


Attachment:
File comment: waveform from Pin 6 of the 13GF7A to B+225
IMG_4968.JPG
IMG_4968.JPG [ 547.65 KiB | Viewed 241 times ]

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 Post subject: Re: 1077B schematic?
PostPosted: May Mon 11, 2020 5:20 pm 
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I briefly got a full raster, not that I did anything to get it, and it wasn’t there after a power cycle. Then I released some magic smoke, so now I have some parts on order.

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 Post subject: Re: 1077B schematic?
PostPosted: May Mon 11, 2020 6:07 pm 
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sorry to see you having all this fun and magic smoke to boot.

I am wondering if your horizontal frequency is high, like maybe the divide by 12 chips are screwd up. You did say you have the chip version.

I have an empty bench and could take some measurements as I am home in quartine about one mor week.

My 1077B has the IC chips.

Jim


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 Post subject: Re: 1077B schematic?
PostPosted: May Mon 11, 2020 6:23 pm 
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jimmc wrote:
sorry to see you having all this fun and magic smoke to boot.

I am wondering if your horizontal frequency is high, like maybe the divide by 12 chips are screwd up. You did say you have the chip version.

I have an empty bench and could take some measurements as I am home in quartine about one mor week.

My 1077B has the IC chips.

Jim


Yes, I'm kind of hoping it is those ICs - they are the main thing I am replacing when I get the new parts. That and Q1, Q2 and Q4 if the problem is still apparent - I'm reluctant to just swap them out with new transistors, because exact replacements aren't available, plus when I finally fix this I want to know what the problem was. The only thing I can find on the web that shows the exact same symptom (narrow, distorted vertical, not completely collapsed) is also one with these ICs. Unfortunately, that guy never got around to fixing it.

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 Post subject: Re: 1077B schematic?
PostPosted: May Sun 17, 2020 2:35 am 
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It wasn’t the J/K flipflops. Replacing them got it back to the state it was in prior to the magic smoke, i.e. a collapsed and distorted raster.

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