#16
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Alright, I just checked the pins on the base of the CRT while it was turned on and everything was plugged in. I removed the connector enough to wiggle a multimeter probe in there while maintaining electrical connection.
Most of the pins seem to check normal, but pin 3, which is listed as 260V boost, is showing closer to 90V. Could low boost voltage be causing my problem? I'm not actually sure what it does, but it doesn't seem like there should be that much variance. It looks like that's coming off of a lug on my flyback, and going through resistor R79. I suppose my next step is to verify that R79 hasn't drifted above tolerance. I remember hearing that, when testing a resistor, the correct procedure is to unsolder one of the leads and isolate it from the circuit. Would that be correct in this case?
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To keep your tubes running smoothly, make sure to dust underneath the glass as well. |
#17
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Time to back up a little...........
Remove the plate cap from the 1G3 & let it hang away from metal. Take a well insulated screw driver & get it near the cap ( wire end). You should get about a 1/2 inch arc, NOT just a spark if you touch it or get very close. Boost comes from the flyback. Its stacked on top of regular B+ voltage ( think of 2 batteries in series ) & filtered by C50 & C51. R79 must also be good. On your set if pin 3 of CRT goes to low it will kill the raster BUT not effect the HV. Next is to get good HV ( that nice arc ) you need the following stages running. 1) horz osc 2) horz output 3) damper Any defect will lower & or kill the HV & boost. Bottom line it nice big arc = good till that point Small arc = problem is before HV rect. 73 Zeno LFOD ! |
#18
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Gotcha. That's the first test I ran, so I can say with certainty that it was a very small spark. The screwdriver didn't have to quite touch the metal inside the cap, but it had to come very close to get a spark. I'd estimate a maybe 1/16" spark? Maybe less. So it sounds like my HV is low.
I keep thinking back to that Horizontal Hold control. It may be a red herring, but I was noticing some significant power supply defects when I adjusted that control before I recapped in. Specifically, a DTV converter box on the same outlet would actually reset itself as if the power were interrupted if I turned that control all the way up. Obviously I didn't repeat the test after I figured out what was happening, but I hope I didn't damage something doing it. A short somewhere, maybe? I checked the control, and it seemed to test fine, though I need to go back and make sure I'm testing the three leads correctly. I used to know how to do that, but it's been so long I've forgotten the specifics. I did notice that, at the extreme end, it drop from kohms down to ohms, which seemed extreme. I wonder if I've got a bad control, though that wouldn't explain the low voltage elsewhere. I think I'll still give R79 a looksee. Worst case, I've practiced testing a resistor, and I might find a problem.
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To keep your tubes running smoothly, make sure to dust underneath the glass as well. |
#19
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Resistors should be check with one leg lifted IF they check
bad in circuit. After a while you get the hang of which to do & speed things up. For now check pin 2 of the horz out tube & be sure its about -20 VDC. If not its a dead horz osc stage. Also check voltages on the 8FQ7 & 22JU6 & post them. 73 Zeno LFOD ! |
#20
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Quote:
If the boost voltage on the CRT is that low it probably would prevent the beam from lighting the screen. It also would suggest that your HV was low. If the horizontal frequency is far off it would decrease the HV. |
Audiokarma |
#21
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Quote:
Sorry for the late response, all. I was out of town over the weekend, but I'll run those voltage checks sometime today or, if not, Thursday and see where I am.
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To keep your tubes running smoothly, make sure to dust underneath the glass as well. |
#22
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Quote:
tone. A beap is 0 ohms. If you wiggle something like a connector with a rusty connector it will make the scratch sound. Many meters have range select & auto range also so watch for that when measuring, 73 Zeno LFOD ! |
#23
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Usually a continuity test is for things where you expect the resistance is very low, maybe no higher than 10 ohms. It is really for testing wire, contacts and switches. You can also use it on things like filaments and modern speakers. If it is a resistor use the ohms measurement, otherwise you will just confuse yourself.
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#24
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Okay, so I may have broken something, but it may not have been something I did.
I got the voltage measurements. For my 22JU6: 1: Unused 2: -20V 3: 0V 4: .3V 5: .15V 6: Unused 7: 120V 8: 37V 9: Unused For the 8FQ7 (I checked then all because it's easier to access the pins above the chassis): 1: 0V 2: 5V 3: 8.6V 4: 109V 5: .04V 6: .06V 7: 5V 8:2.3V Then, I measured Pin 9 on my 8FQ7, and the yoke started squealing and sparking. I see no indication that I shouldn't measure that pin on the schematic, and I fact, looking underneath, I don't even see anything hooked up to that pin, nor any mention of it at all on the schematic. It looks like a wire may have broken on my yoke. I'm attempting to attach a picture, but I'm on mobile so I may have to do a separate reply for that. So basically here's where I am: I don't think I should go any further without looking this yoke over. Is there a way to check if it's okay? If I do have a broken wire (it's accessible, but small) what are my repair options? If the yoke was having trouble, could that be causing my low high voltage problem? Also, from the schematic, should I be safe to measure pin 9 of my 8FQ7? How do my other voltages look? Some of them seemed off to me.
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To keep your tubes running smoothly, make sure to dust underneath the glass as well. |
#25
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Your 22JU6 voltages are fine except pin 8, you got 37V but it should be 25V.
You should measure on the other side of R77, the voltage should be near 145V. Also check the value of R77, should measure 47K. Your 8FQ7 are nearly all wrong! Did you measure the wrong tube? Yes, check out the yoke. Perhaps there is a short or maybe is arced because the voltage got too high somewhere. When you measure the filament pins you need to use the AC volt ranges. Last edited by Notimetolooz; 11-01-2018 at 08:00 PM. Reason: Typos |
Audiokarma |
#26
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Quote:
Quote:
While I'm at it, I suppose it would be a good idea to measure the resistance on the yoke. I imagine I can do that from the plug, but I'm not sure how to tell which lead is which. Any ideas?
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To keep your tubes running smoothly, make sure to dust underneath the glass as well. |
#27
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Maybe the arcing at the yoke when you were measuring pin 9 was a coincidence.
The yoke plug pin out and connection is shown on the schematic. The coil resistances also. Unplug the yoke to make the measurements. Make sure that the resistance between the horizontal and vertical coils is basically infinite. From your picture it is hard to tell whether there is a strand out of place that is causing a short or close gap that may have arced, or maybe a wire has opened. The filaments are fed AC, the rest of the tube pins should DC measurements. The filament string voltages are shown in the lower left corner of the schematic but are seldom the problem. |
#28
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If the yoke is open or shorted it will greatly reduce the HV and throw off everything else in the horizontal section...Ever pull the H yoke leads on a CTC-15 and power it up?..I have.
Check your yoke like tolooz sayz. That magnet wire is coated in lacquer or some such translucent insulator and you'll need to scrape, melt, or dissolve it off before you can solder it...A short jumper if a section burned off will be fine...Just don't make it longer than it needs to be and don't place it where it could arc to other things. It could be that pin 9 was being used as a terminal/tie point for other things in the horizontal osc or that it shorted to another pin...Sometimes if the osc is tuned close to the point where it screams adding a small bit of load to the circuit from a meter can push it over the edge in to the scream zone.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#29
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Looks like some carbon was created when the arc occured.make sure you scrape and or sand that black stuff off.its conductive.RonL
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#30
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You have -20 volts on the G-1 of the output so the osc
is running. Testing around the osc will often throw it off freq so that may be the scream you got. If yoke wire broken you may be able to patch it if you can dig out both ends. After that you are pretty much don to a bad flyback, yoke or damper tube. HINT ! When yokes get a shorted winding its usually on the inside windings. Pull the yoke back off the bell. That will give it air to burn better & you will see it often. Saves time ! If its not burning you may see on the CRT where it was burning. 73 Zeno LFOD ! |
Audiokarma |
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