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#241
06-23-2019, 10:35 PM
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Perhaps I should try 1 more time now to get color via the tuner/IF section, but from what I saw in the past, I won't get my hopes up.
 another thing noticed, when injecting video like I am now, I get retrace lines, that i'm pretty sure i did not see with input via the tuner. perhaps I need to tweak the input amp gain up a tad. IDK 
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#242
06-24-2019, 07:44 PM
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as expected, no color via the tuner/if. no surprise there .
and I did see things correctly, retrace lines much less notable with tuner input, so I will have to set the gain on the amp a wee bit higher I think.
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#243
06-26-2019, 08:54 PM
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I just tweaked the video amp a bit, replaced R7 with a 750 ohm trimpot, so i was able to up the gain a bit and it looks fantastic now, color is VERY stable, and black levels are OK.
next thing to work on is the damn cataract , I am also seeing the same problem with vert that Rocket described, so I guess I must replace some caps there to get full field, I also got to set up audio injection as well, but i do not see that being that hard. I am also seriously thinking of getting a solid state HV rectifier for it to lower the load on the FBT.
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#244
06-28-2019, 10:44 AM
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Just a wild guess, a good point for audio injection is point 30, V7 & V8 ,no longer needed, should probably remove C53, but not 100 % if that's needed .
I will also try to get full vert height this weekend, following in Rocket's footsteps. I'm still waiting for a really hot summer weekend, where I can have a friend help with the cataract repair, it's really too big / bulky for me to do on my own, and I do not want a repeat of the 25###22 incident when I was in electronics class, one second the CRT was there in front of me, the next, it was gone...
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#245
06-28-2019, 02:39 PM
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| Audiokarma |
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#246
06-28-2019, 10:58 PM
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https://imgur.com/GYwbedU
WOO-HOO!  I now have full screen!   Audio input DOES work at that point, but i have to boost the level way up to get any volume, gonna have to build a pre-amp for the audio i guess.
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#247
06-29-2019, 12:03 PM
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still got retrace lines, time to look at the blanking amp i guess, also, blue screel level is fluctuating slightly, bad cap or pot in screen grid circuit? R19 / C137 or something in B-Y amp affecting level?
CRT bias switch at lowest setting.
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#248
06-30-2019, 01:16 AM
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I think I see the problem with the retrace lines, the resistors on the blanking amp were never replaced, still all original. waveform on grid is perfect, @ 238v ptp, and at -82v R203 is old, measures 245k in circuit , plate is at 158v (too high should be 115v) suspect r204 bad measures too low in circuit, cathode voltage OK at 5.5v, should prob replace all (R203,204,205 206).
-EDIT, parts ordered, did not have any of the higher watt resisters on hand, will see if it works any better once they are replaced. Last edited by Yamamaya42; 06-30-2019 at 12:44 PM.
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#249
07-01-2019, 09:32 AM
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More luck, was able to track down a R-2AV2 (solid state) plug in replacement for the focus rectifier, in addition to SS HV rectifier coming today, so there will be even less stress on the flyback from heaters.
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#250
07-01-2019, 11:47 AM
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If I am seeing this right, once I get the resistors in the blanking amp replaced, & hopefully get the plate V to around 115v like it says in the SAMS, I should see an inverted wave of what is on the grid ( break out the 100x probe ) at C135 being fed to the cathodes of the G-Y / B-Y / R-Y amps if all is working as it should.
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| Audiokarma |
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#251
07-01-2019, 01:47 PM
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Note that the three amplifier cathodes are tied together on the right side of C135, to form the matrix from X and Z to R-Y, G-Y, and B-Y. Therefore, you have a mixed waveform at that point, which is not the opposite of the three different waveforms on the CRT grids. This is because each amplifier has a different waveform on its grid.
The waveform on the CRT grid will be approximately the opposite of the associated amplifier grid, but somewhat different due to the matrixing. The G-Y amp has only DC on its grid, and therefore the green CRT grid will be the same polarity as the voltage on the common amplifier cathodes (but amplified). So, what you will see on the right side of C135 is actually a G-Y signal. Note that there is a large negative blanking pulse connected to the amplifier cathodes, so this negative pulse appears on the CRT grids also. This is easiest to see on the green CRT grid.
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#252
07-01-2019, 02:40 PM
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Quote:
It is that large negative pulse that I'll scope out first , pin 1 v21, though i doubt it, c135 may be flaky.
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#253
07-01-2019, 06:49 PM
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Well that sucks, the SK3756/NTE508 lasted for 45 sec, then burned up.
 must have been bad or something cause the box it came in has an insert saying , replaces 3CA3. put old fashion one back for now. :/
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#254
07-02-2019, 10:54 AM
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Is it even worth trying again with another SK3756/NTE508 to save some the ma from the heater draw?
everything I have looked up says it should not have burned up like that :/ https://www.nteinc.com/specs/500to59...hru510_514.pdf http://www.tubebooks.org/tubedata/hb...art_1/3CA3.PDF
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#255
07-02-2019, 03:34 PM
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I have no experience making this replacement, but have to agree that the pinout and specs look right. NC on all the other pins means it should work even if this chassis used some of them as convenient soldering points.
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| Audiokarma |
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