#1
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zenith porthole question
I picked up this h2439r with chassis 24h20 right before we moved. Removed crt and chassis on site to transport. Just got it together this weekend. Only got half a picture. Where to start, I'm assuming vertical section? Got 1 vertical half frame. Thought maybe it was yoke or crt was twisted up or down, but both the yoke and crt are in a fixed position. Vertical size adjustment does not stretch it all the way. Horz. and vertical do lock. I have not messed with any tv's for over 2 years and am rusty. Could use some help....
Last edited by stusnyder; 01-20-2015 at 04:15 AM. |
#2
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Has this set been restored? If not, then you should be thinking full restoration, and not of repairing the set. If you insist on operating the set as-is, keep close
tabs on the four filter cans. If any start getting hot, you had better shut it down in a hurry. Also, there is a picture control switch in the pencil box. You need to have it in full circle mode before you can make height + linearity adjustments. Looks more like the AGC is set too high. Do you need a channel knob for it? Last edited by John Marinello; 01-27-2015 at 09:45 PM. |
#3
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Looks like it may be running at twice normal vertical rate (120 Hz instead of 60).
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#4
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Quote:
Yes I have it set to full circle. I have the knobs for it in storage, just did not find them yet. Also all the tubes checked out ok. |
#5
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I read that in a book someplace. Only problem is the book did not say how to correct it...
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Audiokarma |
#6
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The image is stretched big time vertically.
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#7
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I would re-check values of all replaced parts in the vert section. A single misplaced decimal point can cause all kindza woes.
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#8
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Quote:
The problem with vertical running off frequency usually is a result of RC timing components in the feed back/feed forward loop of the vertical osc/multivibrator circuit having drifted off speck or being replaced by the wrong value due to human error. Check all resistors in the V osc/output stage for out of tolerance duds. Replace any original capacitors in that area, and make sure your replacements are of the correct capacitance. I don't know if Zenith portholes use vertical osc transformers or not, but if it does check the transformer too.
__________________
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 |
#9
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Riders list c37 4 section can with 2 20uf sections. Now I did not have any 20's that high of voltage, so I used 33uf....is that going to make a difference?
Also on c37 riders lists the unmarked terminal 80uf but the actual can is marked 20uf. So which to go by? |
#10
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checked the vertical output, vertical osc. and agc section. Did not find anything significant... But I did find a new problem. I decided to check voltages, and I started at the power supply. There are 3 tubes in the supply, a 5y3gt, 5u4g, and a 6bf5.
So here's what I found: 5y3gt pin 2 riders says 187 volts. I got 218 volts. 5u4g pin 2 riders - 382 volts. I got 415 6bf5 pin 6 riders - 97 volts. I got 137. My line voltage is 116 volts. Anyone have any ideas? |
Audiokarma |
#11
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If so , your readings look fine . If you have a good ol Simpson 260 or other such vintage meter around , I'll bet you find the readings will more closely resemble spec. Remember , our modern DVMs don't load the circuit they're measuring like the classic 260 would , and thus the higher readings . PS , what did the schematic call out for Input voltage ? If they listed 110 and your at 116 , that could also explain slightly higher readings ... |
#12
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Quote:
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#13
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Sorry to be a fuddyduddy, but the 260, with sensitivity of 20,000 ohms/volt, will impose a loading of 5 megohms when on the 250V scale (250X20,000=5 meg.).
The only time loading would be a problem with the 260 is in very high impedance circuitry. In the old days meters typically had sensitivity of 1000 ohms/V, 5000 ohms/V. etc. Those could cause signifigant loading errors. |
#14
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Ok got the simpson 260 out and checked.
5u4g pin 2 420v should be 382v 5y3 pin 2 220v should be 187 6bf5 pin 6 105v should be 97 The simpson says my line voltage is 125v Hooked up the variac and dialed in input voltage to 105 volts. At that voltage I get correct readings, but picture is about the same. The top half of the picture just fades away to nothing. Last edited by stusnyder; 02-01-2015 at 08:44 PM. Reason: more data |
#15
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Finally got some progress on this set. I injected a IF signal on the 4th IF tube and I got a decent test pattern. Backed up to the 3rd IF tube and got the half picture. So the problem is before the 4th IF stage. I checked the resistors in the whole IF stage and all the 470 ohms were way out of tolerance, some 200 ohms or more. Replaced them, but still no change.
I also injected a video signal at the video amp and got a decent pic. The IF section got lots of "dogbone" capacitors. Should I be looking at those, or do I have to search before the IF stage? Also my voltages are running 30 volts high on the IF stages. |
Audiokarma |
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