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#1
05-30-2023, 09:11 PM
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C3 replaced
http://suzaku.live-evil.org/0530232043.jpg http://suzaku.live-evil.org/0530232044.jpg C2 is next. one thing i noticed most of the time when the set is turned on, there is no luminance at all, brightness cont has no effect, but if I switch it in and out of service mode several times, it will suddenly start working. weird. all it does it cut power to IF 1&2 and the pincushion amp. still waiting for new tubes
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#2
05-30-2023, 09:54 PM
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"all it does it cut power to IF 1&2 and the pincushion amp."
Are you sure? I thought the service switch usually defeats the brightness adjustment also.
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#3
05-30-2023, 10:35 PM
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Quote:
http://suzaku.live-evil.org/servi1.jpg and that one line down goes to power the 12AX7 VIA L48 http://suzaku.live-evil.org/servi2.jpg
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#4
05-31-2023, 07:44 AM
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First step in greyscale setup is to set brightness, CRT bias & screens full CCW, so it's clear that brightness defeat was left out for some reason.
I just know that for now, it has this odd behavior which may or may no be tied to old tubes, hopefully new IF and 6GH8As, 6LM8 will be here by the weekend w/o a detour across the country like the 6MD8 did. Will just have to see if they make any change, otherwise there is something very weird going on that I have not seen before. Symptoms are as mentioned above, MOST of the time, not always. First cold turn on, no luminance , very dark screen, brightness has no effect at all, but some chroma seen faintly on screen, sound OK. After about 60-90 sec. Flip service switch in and out about 5 times a BOOM! Luminance comes to life, and brightness cont now works, however does not have the full contrast it should have. Weird.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#5
05-31-2023, 11:05 AM
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So, you're saying S9 has only the two sections, A and B. Hard to see how it can kill luma without also killing chroma. Definitely weird.
Regarding low contrast, tube color sets rely heavily on adequate gain of the video output tube. For the old Magnavox I had, I bought 5 or 6 video output tubes and swapped them out until I found the highest gain one. It made a big difference.
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#6
05-31-2023, 11:33 AM
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Quote:
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=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#7
05-31-2023, 08:29 PM
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c2 Replaced!
 http://suzaku.live-evil.org/0531232009.jpg it WAS borderline bad. i could not cram any more under there if I wanted! powered up OK, with horz disabled, no smoke! will have to get some silicone this weekend to tack it all down neatly. hopefully I can get away with leaving C1 as is, cause i just cant get to it. 
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=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#8
06-01-2023, 01:12 PM
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This maggie seems to have borrowed a bit from the RCA CTC-20 when it comes to the video amps and brightness control, including the cathode follower/ chroma sync amp and what looks like negative feedback loop circuit, where the Hoffman Colorcaster looked closer to a RCA CTC-16 (17 perhaps?)
Can't say which method is better. :/ Will post more schematics tonight. More tubes are due by the weekend, in the meantime, will check peaking coils, seriously doubt any will be bad.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#9
06-01-2023, 08:11 PM
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OK, the brightness control of this TV, something a bit new to me. :P
http://suzaku.live-evil.org/bright-1.jpg The POT seems to adjust the bias of the grid on the video output V6, this is nothing new, seen it before, but what is new to me is trace 30, http://suzaku.live-evil.org/bright-2.jpg which feeds in right after the detector and before the delay line line and first video amp and cathode follower, and seems to be some kind of negative feedback circuit i have not seen before in a tube set in the video area. granted, I have worked mostly with RCA stuff. on a lighter note one more tube came today, a NOS 100% tested 6GH8A, for the V19 blanker/ banbpass http://suzaku.live-evil.org/0601231819.jpg just got my nails done today! more tubes will come over the next 2 days, hopefully 
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=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#10
06-02-2023, 11:19 PM
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Quote:
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#11
06-02-2023, 08:35 AM
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2 more NOS tubes due today 1st & 2nd IF, (6GM6 6JH6), 3rd tomorrow, or so says USPS, as well as the 3 tested “good” used RCA 6GH8As, Tested At 88/88 Or Better, however the NOS 6LM8 won't show till next week.
 But everything I'm seeing, says that the 6GH8A is a drop in compatible sub for 6LM8, so, since I do now have the one NOS 6GH8A in place at V19 blanker/banpass, new IF tubes, (hopefully), and 3 good tested 6GH8As to try in the meantime while I wait for the NOS 6LM8 cathode follower's place, I should hope to see some improvement I would guess.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#12
06-03-2023, 04:54 PM
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__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#13
06-03-2023, 07:29 PM
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I may have gotten a flaky or bad NOS 12GN7A video output tube, it's that, or there is something off, in that circuit, cause when I put the old tube back, the odd bit about no luminance when first turned on seems to have gone away, not sure, still waiting for the new 6lm8 and ordered yet another 12GN7A.
did have a bit of an accident today  when trying the tube wiggle test, got my finger caught on the flange on the Drive control PCB, SHOCKING!  http://suzaku.live-evil.org/0603231855.jpg I'm literally putting my blood sweat and tears into this set! It's not really THAT bad, it's gonna hurt later, but i have it sealed with Cyanoacrylate, cheap and easy something an ER room would charge $300+ to do.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#14
06-03-2023, 10:13 PM
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best result yet!
https://www.youtube.com/watch?v=kIqNFMaDMAE Still have hum bar problem may have to cut out and replace C1 after all, and it still had the odd problem of no luminance when first turned on, but after fiddling with it pops on, not sure why it does this yet.
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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#15
06-04-2023, 10:28 PM
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the 6LM8 NOS it still on track to show up on Monday, will have to see if it fixes the strange brightness control problem.
still at a loss at what to do about C1, as replacing C2 & C3 did not get rid of the hum bars. but as mentioned, there is just no room I may try the unspeakable and do what many say not to do and tack in new caps in parallel to it, and hope it never shorts. http://suzaku.live-evil.org/magg1-cap.jpg R219 is very easy to reach and add a cap to, however the point of L56 and the bridge wont be so easy to reach, I have 82uf 500v caps now, but I think that will be a little too much to add in parallel to the existing C1, i was thinking of using 33uF 500v caps. sound reasonable?
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために
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