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  #61  
Old 10-02-2014, 11:51 PM
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MIPS MIPS is offline
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I kept poking at the set and fiddling with the knobs but then decided to hang the pattern generator off it. Sure enough an RF signal (at least we know channels 3 and 4 work) and a bit more fiddling resulted in a good image aside form the bottom 1-2 inches not being used.




I'm calling it a night but there was a lot of progress today. Got any pointers where I should start looking next? I know I shouldn't be fine tuning the focus and ion trap until the controls are all working properly.

Oh yeah, one last thing. When I was fiddling with the controls I grabbed part of a metal rack behind me and received a light shock. The chassis seems to have 67V AC coming from somewhere.

Last edited by MIPS; 10-03-2014 at 12:46 AM.
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  #62  
Old 10-03-2014, 01:22 PM
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The yoke needed adjustment. After some more work we gained an odd bending on some of the patterns but otherwise we got a nice picture.






There's ghosting as well but that might be more the cabling I'm using to connect the set to the pattern generator and my videodisc player. We should be able to fine tune the picture once it's off the bench and in the cabinet upstairs. The controls continued to clean up as I adjusted the yoke as well however the height control is also still an all-or-nothing ordeal. The indian head pattern indicates I'm getting horizontal stretching but I'm not sure how to adjust that as there is no horizontal controls outside of hold. The VBI has also decided to slip down form its place at the top of the picture. The vertical hold can push it back to the top but any large scene changes and the image starts to roll. Any ideas?


Last edited by MIPS; 10-03-2014 at 05:30 PM.
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  #63  
Old 10-05-2014, 11:24 PM
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Started with tracing down the lack of width adjustment and came across a silver banded 2.2k that had drifted off to 3.5K (probably not my issue here but it wouldn't hurt to replace since it's almost doubled in value). At this point I realized I only stock 1/4 watt metal film resistors for digital electronics projects and that I have no way to figure out what the wattage is of these old carbon resistors. Is there a handy guide somewhere? Something like this?

Last edited by MIPS; 10-05-2014 at 11:42 PM.
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  #64  
Old 10-06-2014, 11:30 AM
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1/2 watt are by the most common types used in vintage TV and that guide you linked to shows the size.
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  #65  
Old 10-07-2014, 12:05 AM
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It appears that the 2.5 meg pot for height is bad. Twisting one way yields a good slider until 3/4 of a turn, then it ramps off to infinity (and the image collapses). Testing the other side I can at best get up to 200k after 1/4 rotation before it too ramps off to infinity. Now the challenge to find a replacement.

Last edited by MIPS; 10-07-2014 at 12:12 AM.
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  #66  
Old 10-09-2014, 10:57 AM
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A new pot and replacing a pile of resistors I was finding out of tolerance removed the VBI oddity and the lack of height control.




The width control however is still completely dead. I've replaced or verified all the resistors immediately adjacent to it in the circuit and I know that any capacitors in the area that aren't mica are good because they've all been replaced. Both parts of the width coil have continuity so at the least it's not gone open but there's no spec on what resistance if any it should have. Any ideas? Anyone? Anyone??


Last edited by MIPS; 10-09-2014 at 11:00 AM.
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  #67  
Old 10-09-2014, 12:30 PM
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Is there in fact a movable slug still inside the width coil, or has it possibly been broken and is now stuck at the far end, or fallen out?

I'm not familiar with this set's operation, but random picture bending can sometimes be caused by too strong of a signal overloading the circuit. You might try adjusting the video out level on your pattern generator.
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  #68  
Old 10-09-2014, 05:01 PM
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Pattern generator doesn't have an amplitude control for RF out but I can work around that.

I can see the slug inside and it moves when you spin the tuning screw so that's okay at least.

Edited: I setup a small test circuit on the bench with the scope and signal generator and I can definately see amplitude change when the slug is moved so the coil is behaving okay.

Last edited by MIPS; 10-09-2014 at 05:37 PM.
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  #69  
Old 10-12-2014, 10:12 AM
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Finally found something that was more than a resistor out of value. I swear I verified the two test points around the AGC/AFC tube but on checking again I appear to of been wrong.



(probe ground was chassis during testing)

Both waveforms are nowhere near what they should be and are oscillating. Well we have already replaced all the resistors around this tube and the tube itself was checked again for good health and swapped for the 6U8A that was being used for sync sep./ noise limiter with no changes being observed. All I can assume at this point is that a ceramic or mica capacitor has failed somewhere close and it's wreaking havoc. Does this sound correct?

Edited: I missed the noise limiter/sync separator circuit as well. Both of its waveforms are also not correct and there is glytchyness on the test point for the 12BY7 but everything else is either spot-on or close enough.

Last edited by MIPS; 10-12-2014 at 10:54 PM.
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  #70  
Old 10-27-2014, 03:13 AM
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Tried asking around at shops here in town and Vancouver and everyone was a little stumped. Best recommendation I got was to swap out the 6CU6 and 12BH7A. Found that one of my 6CU6's had gone south. Unfortunately in doing so no real change happened so I went back to fiddling with the controls. At this point I discovered that if I looked closely and twisted the width control from end to end there was something like 8mm of movement so it's less that the width is not working at all but more that it's really weak.
Further testing quickly halted when I cranked the vertical linearity and C-434 burst into flame. Looks like an arc popped through the casing and went into the ground clip that it was resting against. Set still seems to behave but I'll have to swap the disc cap out anyways.
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  #71  
Old 10-31-2014, 07:19 AM
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Hey MIPS ...perhaps your got the scope horz frequency set wrong?
those waveforms on the scope look like vert waveforms(fields) instead of horz waveforms (scan lines)that your diagram shows? iirc-your scope horz frequency should be set to microseconds(u) instead of milli seconds(m)? might be my old eyes-lol! great progress so far! pls keep at it.
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  #72  
Old 11-01-2014, 04:07 PM
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Quote:
Originally Posted by ronl View Post
Hey MIPS ...perhaps your got the scope horz frequency set wrong?
those waveforms on the scope look like vert waveforms(fields) instead of horz waveforms (scan lines)that your diagram shows? ...
Yes, they do look like what I'd expect for a trace showing the horiz over the time period of a vertical sweep (and then some). Showing that some vertical deflection energy getting into the horiz (usually not a problem).

The 2nd picture also looks like the scope ground had gotten poor, letting ground loop hum get into the trace.
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  #73  
Old 11-01-2014, 08:24 PM
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My probe ground has always been the TV's chassis which I've always been concerned about since it always has something like 60v running through it regardless of the set being on or off. I've tested everything on the primary side. Even disconnected everything form the terminals of the plug on the back. It's almost like the socket itself has a leak but if you check there's no resistance under 20 megaohms.



It's always entirely possible the bekelite insulator on the socket has broken down with time but god knows what adding 60v AC to the chassis has done.

Last edited by MIPS; 11-01-2014 at 10:16 PM.
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  #74  
Old 11-02-2014, 07:42 AM
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Hi Mips.
from what i gather without reading the schematic( gotta dig it out), most readings/waveforms use the chassis as ground for the test equipment with gear this vintage.check the footnotes on the schematic-it should say if the voltages/waveforms are taken with repect to chassis ground.

from what i have seen from your pictures-the last problem is width...tv width looks acceptable-some of these vintage sets never had perfect width or control of width.

i would try retaking those waveforms with the scope set in the "u" (horz)range?
might see they match the expexcted waveform? iirc,1 horz scan line is aprox 63.5 us or microseconds or 1/15750

not sure at this point without looking at the schematic why you are getting 60 vac with respect to ground-i suspect you are using a isolation transformer while working on this set so should be safe but will get back to you once i dig schematic out.
is picture good at this point other than width being a little wide?
just some thoughts.
RonL
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  #75  
Old 11-02-2014, 09:05 AM
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The picture at this point is excellent aside from some ghosting (and that I can tell it is not from an excessively strong signal). The concern is that there is little to no width control and even on the pattern generator I can't make things fit so we're looking at an image that is around two inches too wide. I don't recall moving the yoke that far when I reinstalled the tube. Just a light adjustment to center the picture again.

I'm not running with an isolation transformer. With my knowledge of bakelite we should not be seeing a voltage being passed through the insulated socket at all (especially with these "low" voltages). If I knew where to source a replacement I'd try swapping it out. I've already zapped myself on this set several times because of it but nothing ever warned that this was a hot chassis. It raises a flag IMHO.

I'm not hanging my scopes off this until we sort this voltage issue out. If you want to look at the schematics yourself I posted them back on the first or second page but here's a high-res version if you want to be able to read anything.
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