"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.

you would think so, but they seem to do things odd in this one,

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

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.

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.

The way they have the brightness control is a bit odd, at least I have not seen anything like it before, seems to be some odd feedback loop, it starts from point 30 on the linked schematic above, far side of the 2 peaking coils off the detector, and goes to the bottom of the brightness control pot, right before another peaking coil that feeds G1 of the video output.

c2 Replaced! :D

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. :sigh:

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.

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! :D

more tubes will come over the next 2 days, hopefully :yes:

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.

Brightness in the Magnavox T931 and T933 is just partial DC restoration where the brightness potentiometer controls how partial the DC restoration is. In more detail: the DC bias of the output of the video detector is the DC bias of the video signal, the actual brightness. The pot is used to create a new DC bias that is the average of the actual DC bias off the video detector and a constant DC bias of around 2.5 volts. You want to set cutoff of the CRT using the CRT G2 pots and CRT G1 pots so that you can dial the brightness pot as low as possible because that maximizes the amount of DC coupling of the original video signal’s DC bias, that is, this preserves the actual brightness information of the original video signal. The higher the brightness pot, the less brightness info you keep from the video signal.

slowly getting there

https://www.youtube.com/watch?v=Sd4y_47yX0o

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 :tears:
when trying the tube wiggle test, got my finger caught on the flange on the Drive control PCB, SHOCKING! :yikes:
http://suzaku.live-evil.org/0603231855.jpg

I'm literally putting my blood sweat and tears into this set! :D :yes:
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.

best result yet!
https://www.youtube.com/watch?v=kIqNFMaDMAE

Still have hum bar problem :tears:

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.

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?

So, for lack of any better idea to try, I will order 2 of these to put in parallel to C1A & C1B this weekend, 661-EKXJ501ELL330MK4.
And hope it helps with the hum bars, if it does not, then there is something else causing it, :(

Due to my unfortunate shocking adventure in protruding electrified edges this weekend, something I've not had the joy of experiencing since High School with a vicious Zenith hybrid, I won't be pulling the chassis for a while in this till it heals a bit. :/

“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”

Why not add the 82 uf caps downstream, at the circuits that are supplied by the 400 and 390 A sources? :scratch2:

jr

correction: C1 B is on the 270V source not the 390 A source.

yes, I do have access to R112, the only point that seems to be hooked to 400v can't find the 2nd that is mentioned on the distro chart, won't putting in the 82s w/o being able to reach in and unhook the old C1 cause undue stress on the diodes? or will the termistor dampen this? this was the only reason I was thinking of using 33uf.

“won't putting in the 82s w/o being able to reach in and unhook the old C1 cause undue stress on the diodes?”

I suspect C1 sections are now effectively much less than 80 uf, and wouldn’t worry about the diodes. Also, thermistor should limit inrush current.

jr

will try sat.

http://suzaku.live-evil.org/0605232106a.jpg

best pic so far!
6LM8 NOS did seem to help

found why I was getting such a snowy pic
I am missing a tuner bias!
http://suzaku.live-evil.org/tuner111.jpg
bias source 1 is not there, which powers the RF amp. problem with R240?
in the mean time till i can pull the chassis, i took a 18 ohm resistor and hooked it to the B source 2, and it now has a clear pic.

Have you tried substituting a 6GH8A for the 6LM8? I am curious to know which performs best.

did not like it at all :P

I found out why I lost B+ source #1 on the tuner. :(

when I was first poking around trying to reach in there to get to C1, I broke R240!

http://suzaku.live-evil.org/0609232225.jpg
it's just so dang packed in there!
it USED to go to that orange wire, you can see C! way down in there.

http://suzaku.live-evil.org/0609232243.jpg

the fix!
all tacked down with silicone

seeing a little bit of color echo/ ringing to the right, mostly on reds.
http://suzaku.live-evil.org/0610231942.jpg
can be seen on the V on their shirts.

have new V20 color demod, and V22 killer burst amp ordered, these are also old original tubes.

Replace that 6GH8 Video blanker tube. It's a common problem with dim pictures on this chassis and several relatives. It's not unusual to see these weak or bad. It makes a major difference in how the set functions. I always replaced weak/bad ones when I was a grunt technician in my younger years.

V19 blanker/ bandpass was replaced with a NOS early on when i had weak brightness, but it was the V5 6LM8 that mad a big difference as well.

now I wanna try and clean up the color echo a bit.

All I see is the L blue conv is way off. Otherwise it looks pretty normal
for an aged Maggy. On Maggys there is what we called a "Brownulator"
switch. Turn it OFF if its on. It gives the pix an overall brown to it.
Always turn off any auto color schemes while working on a set.
One last thing is ground lugs. Where the PCB's are soldered to the
steel frame resolder them. Can cause strange int problems on most
brands of TV.

73 Zeno:smoke:
LFOD !

I'm aware of the convergence issues, have not really tried to mess wit it yet, cause when I pull the CRT later this summer on a 100+ day to try and fix the cataract, the convergence will be messed up all over again! :tears:

Hopefully the new 6MK8 demod tube will clear up the slightly bleedy red, another symptom is, when color pot is turned up all the way, all color is lost, flashes to greenish tone for a bit, then BW. Backing off, color pops back on strong.

The 6MK8 is a selected 6HS8. I had a GE branded one that had the 6HS8 number sand blasted like GE was famous for, but had the 6MK8 number printed on like the logo. :scratch2:
The last Warwick Sears hybrid used a 5MK8.

New tubes did not help the color shadow much, it's still there, chroma bandpass may be slightly off alignment, not much I can do about it, as I don't have the rig to adjust it, fine tuning has no effect on the shadow.

V22 must have been weak, ( color killer/burst amp) 6KE8, because when the new one was put in, color intensity levels were MUCH lower then with the old OEM one, I thought this very strange at first, until I found that the color killer pot R10 had been turned up almost past 2/3s past max, turning it way down got strong colors back with the new tube.

As someone said before, this chassis is picky about tubes, especially the 6GH8As it seems. :O

Can you post a picture of the "color shadow?" I'm not picturing it in my mind.

I will try to get better examples tonight, but you can see it in the V on his vest, a bleed to the right with reds, its there on all colors, but seen most on red.
http://suzaku.live-evil.org/0610231942.jpg

What is the source? If it's a VCR, ignore it, as the poor bandwidth of the tape chroma can mask any effects of the TV alignment.

Source is a Sony DVPSR210P DVD Player, playing videos from blu-ray videos that were converted down to DVD format.

I just happen to like using Lost in Space because of the loud gaudy outfit colors, and it's period correct for the set! :)

pics of color echo

paused DVD lost in space

http://suzaku.live-evil.org/0616232041.jpg

color off
http://suzaku.live-evil.org/0616232042.jpg

pro DVD
Futurama paused
http://suzaku.live-evil.org/0616232047.jpg

http://suzaku.live-evil.org/0616232049.jpg

fine tuning has no effect

That indicates it's not due to IF misalignment.
So, it could be a misadjusted 4.5 MHz trap or the color bandpass alignment, etc. - something following the video detector.

That's what I thought, where I can adjust the 4.5 MHz trap by eye, but as of yet, I don't yet have the tools to adjust the color bandpass alignment, and I'm not foolish enough to try THAT by eye, cause it would only make it worse. :tears:

I have done all I can do with this Maggie pretty much chassis wise, next step would be CRT cataract repair, I'm still not sure what tube it even has yet, as the number is blocked by the x-ray shield, I just know it's a heat removal type, and it's risky with this tube. :(

All I can say is I like this chassis type the least so far, due to it being so finicky about the tubes you put in it, change any tubes in the color section, and you almost HAVE to go through the color AFC procedure for best results, or keep swapping tubes till you get optimum picture.
Not something I have seen with RCA and clones.

From everything I've seen, this CRT type has the most risk with cataract removal, due to the RCA type of bonded safety glass and the rectangle shape, hot wire method does not work, like on the green gooey Zenith type, unfortunately heat is one of the few things to get it to let go, but can also cause uneven stress on the tube.
It's not like there has not been a lack of very hot days to leave it out in direct sunlight to warm it up, but most likely to get it off a heatgun will be needed, and there is always risk with that no matter what especially with these rectangle tubes. :(