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#31
04-28-2016, 11:07 AM
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Ok I went over everything can't find anything wrong so I think it's just low hv voltage . The screen is dark even on a second crt I have thats good. The b+ voltage is 130vdc with no diodes put on the 25z6 . Every cap was replaced and the only thing I'm coming up with is that on v17 pin 5 should be - 5.3 Vdc but I'm getting -125 Vdc I even tried another tube same thing and I went over the SAMs and the rider schematic to make sure it's wired right and can find nothing wrong there. A 39k to the 1b3 feedback and it's good there is an 82k also good and the 2 caps at the tube as well both good. There is a cap on the hv oscillator that's good. Tried a new 1b3 too. Strange thing is checking voltages around v17 the screen blanks out dark then comes back after removing the test probe. I do know there are 2 positive points and 2 negative points in this set and I went over the power supply and checked all of that and cannot find anything wrong there. If anyone knows where to go with this pilot at this point I'm all eyes because it looks like I am out of options.
Last edited by timmy; 04-28-2016 at 05:14 PM. 
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#32
04-28-2016, 04:43 PM
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Well the first thing that jumps off the page for me is why. V17 pin5 shows +117 when it should show -5 volts. There is something going on there for sure. When I get home I'll yank out my SAMs and have a look at that see if anything jumps to mind. But I do know that if a circuit is expecting negative potential and it's getting a huge positive there is something wrong in there.
George
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#33
04-28-2016, 05:13 PM
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Quote:
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#34
04-28-2016, 05:54 PM
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Aah.. Ok but still way off spec!
George
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#35
04-28-2016, 06:29 PM
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I'll tell you what I spent hours and hours going over the riders and SAMs and I must be missing something but now I am literally lost because I cannot find what's going on. If the hv is low the the vert and horiz plates won't work right and in this case the vert is missing on the bottom and the size pot is maxed and the picture is dim consistant with low hv.
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#39
04-29-2016, 05:07 PM
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Ok my mistake the SAMs didn't show to check that voltage,grid, cathode usually it's ground or otherwise specified. So that voltage is neg 3 volts and SAMs shows 5.6 I believe but rider shows neg 7- 12 volts so this is still low and if the hv was up where it should be then the cry would be much brighter then it is and there would be enough voltage to even out the verticle plates and it would be centered. Went over yet more and still cannot find any mistakes. This set was all redone by someone else and done a very neat job and replaced everything caps, resistors, Micas in the IF and RF but it does have good sound and nice picture but just Alittle more then half and dark so I do think is lacking hv. Even turning the hv adjust on the hv cage brightens Alittle but does nothing for the verticle. These sets have 2 different linearity setups to improve this, 1.2 and 5.6 Meg ohm resistors and using different values for both don't help and has the 2 1500 mmf caps also remove for the other setup still don't help. I guess nothing will unless I can get the correct hv.
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#41
04-29-2016, 08:53 PM
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Hi Timmy,
Having read through this thread so far, I have a few questions. Bear in mind I have never worked on a Pilot set. Does a Pilot have a crt/ neck shield? The Sylvania 400 scope I finished repairing last month needed one to help center the spot. It had to be properly rotated. You mentioned at the very beginning of the thread that the speaker had been changed. Where was the old field coil remounted? Improper shielding and odd magnetic fields can shift your whole image. With such a small crt image it is easy to deflect it without any noticable change in picture linearity. Just ideas,  Ed
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#43
04-29-2016, 10:25 PM
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Quote:
No it don't take a shield on the crt and the speaker field coil is still being used with the new permanent magnet speaker I just tack welded the field coil to the back of the new speaker and its in the same spot as befor but I can set in some type of shield to see if it makes any difference. And I subbed all the tubes mentioned. It really seems like low hv.
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#44
04-30-2016, 08:24 PM
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Well got a few more things to look at like the b+ I'm thinking maybe it's to high causing problems somewhere I just don't know. I have read 100 volts, 109 volts, but mine is up there over 125 volts being the line voltage is higher now then it was in 1948 although the pilot says 117- 120 volts but sometimes 122- 123 is the norm now. There is a 33 ohm resistor just after the ac plug that measures 28 ohms so I think I'm going to try a 50 ohm and see if anything improves. I read threads where some pilots were only giving 90 volts and they worked and then placing a diode across the positive tube to raise the b+ to Alittle over a 100 volts. The other day the b+ was 135 volts depending what comes down the line wire. I don't know if excessive voltage could do what this set is doing but it's worth a try. These sets are not bright to begin with but it would be nice to have a full screen. I got rid of the speaker field coil and replaced it with a 150 ohm resistor thinking as another member mentioned that it may be causing emf interference at the crt because the speaker is new but I thought I needed the coil and it was setting on top of the chassis so it's gone now.
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#45
04-30-2016, 08:47 PM
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Bear in mind this set isn't supposed to fill the entire face of the tube, there should be a blank space on top and bottom that's covered by the mask.
If you're trying to fill the entire tube face it might just bee too much for the circuitry to handle.
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