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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Wed 18, 2021 12:58 am 
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Location: Dallas, TX
You are making good progress.
The last picture shows the vertical sweep not locked, but the horizontal on frequency at least.
The video signal is making it to the CRT.
Looks like too much width, possibly the control is bad or something else. There could be a sync separator problem. With good tubes, most caps and resistors checked or replaced that narrows things down.
Of course everyone makes a mistake for time to time so one of the replacements might be out of place.
Mica caps while less likely do show up bad from time to time. Something may have caused the alignment of a coil to be off. That may explain the sound problem.
Do you have an oscilloscope?

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Wed 18, 2021 2:16 am 
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Notimetolooz wrote:
You are making good progress.
The last picture shows the vertical sweep not locked, but the horizontal on frequency at least.
The video signal is making it to the CRT.
Looks like too much width, possibly the control is bad or something else. There could be a sync separator problem. With good tubes, most caps and resistors checked or replaced that narrows things down.
Of course everyone makes a mistake for time to time so one of the replacements might be out of place.
Mica caps while less likely do show up bad from time to time. Something may have caused the alignment of a coil to be off. That may explain the sound problem.
Do you have an oscilloscope?


Yes, I do have a scope and a signal generator (if need be). Not a TV alignment type with markers though - never thought I would need one... In regard to the vertical sweep - is this an outer ring adjustment on the leftmost control? I think me attempting to fiddle with it threw the whole thing off...

I will try a different signal source in the meantime - just to eliminate a possibility of it being the culprit...


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Wed 18, 2021 4:37 am 
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Fennec wrote:
Yes, I do have a scope and a signal generator (if need be). Not a TV alignment type with markers though - never thought I would need one... In regard to the vertical sweep - is this an outer ring adjustment on the leftmost control? I think me attempting to fiddle with it threw the whole thing off...

I will try a different signal source in the meantime - just to eliminate a possibility of it being the culprit...

Yes, I think the vertical hold is the outer knob on the left.
Give it another try. The control could be dirty or worn.
There is a adjustment called "Horizontal Drive" that could effect the width although it usually is adjusted for something else. Now that the horizontal is locked have you tried the width control?

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Wed 18, 2021 5:42 am 
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The width control from one extreme to the other is only going to affect the width maybe 1/4 to 1/2 of an inch. It's a coil in parallel with part of the flyback and is only mean for a minor tweak. It the width is way off, I'd look elsewhere. Like the voltage on the horizontal output tube and the drive level.

It really doesn't look that off to me though. Could use a little more height maybe.

As for sync. If they are both touchy, it's likely the sync separator circuit or lack of gain in the IF/video amp stages.


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Wed 18, 2021 7:11 pm 
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I think I would adjust the screen centering to better judge the width, etc. As Bob said maybe the width is fine. It does look like the vertical linearity is a bit off.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Thu 19, 2021 11:31 am 
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My tip: a wiring error in the sync separator. There is a high value resistor on G1 of the 1st stage. That could be O/C or miswired.

An open circuit / disconnected / wrongly connected AGC bypass cap also cause weak sync.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sat 21, 2021 10:52 pm 
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Thank you everyone for your suggestions so far. I have decided to put the absence of sound problem off for a while.

After a fair amount of mucking around with focus coil, and all available adjustments, switching progressively from prayers, to incantations, and finally to profanity, I think I am making a very slight progress - my picture now looks less like a work of Pablo Picasso, and more like that of Salvador Dali...

Granted, both vertical and horizontal linearity is horrible. However the biggest issue I have is that I cannot - no matter how hard I try, - to have the picture fill the screen properly from left to right edge...

Attachment:
01.jpg
01.jpg [ 606.07 KiB | Viewed 1206 times ]


It's as if the picture is "too wide" to fit in - I run out of Width adjustment range. Any attempts to "compress" the picture further results in it going out of sync. This is with the Width screw almost completely out, just a touch from breaking:

Attachment:
04.jpg
04.jpg [ 481.68 KiB | Viewed 1206 times ]


Another issue is the Horizontal Frequency adjustment - the manual says that once set by means of the "Horizontal Lock", it should remain stable within at least 3/4 of the "Horizontal" control range. I am getting barely 1/16 wiggle before the picture starts tearing up again...

So, I suppose in order of importance - unless these are all interconnected, - I need to:

1. Resolve the issue of picture being too wide for the screen - currently only 75% of it is fitting in
2. Stabilize Horizontal Frequency, so that it is not as sensitive to the Horizontal control
3. Stabilize Vertical - same problem with control sensitivity.

Anyone has encountered issues like these in the past? If so - where should I look/ what should I try? Could the problem be in the tuner section, or an IF alignment?


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sun 22, 2021 1:55 am 
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The video signal is a bit smeared perhaps but really not bad at this stage. That says good things about the tuner and IF sections. Again the HV for the CRT is fine and sometime that is a big problem.

It is not uncommon for the adjustments to interact with one another.
You might look into adjusting the horizontal drive cap. There is also a horizontal linearity adjustment.
Look on page 8 of the pdf for adjustment info.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sun 22, 2021 5:22 am 
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bandersen wrote:
As for sync. If they are both touchy, it's likely the sync separator circuit or lack of gain in the IF/video amp stages.
Amen. Have you checked the sync separator yet? When you have weak lock in both the vertical and horizontal, the separator is a logical place to look because it feeds both sweep sections.

Until you have a stable picture, it seems a little premature to get too picky about size and linearity.

Regards,

Phil Nelson


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Sun 22, 2021 7:33 am 
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A good starting point is to adjust the Horizontal Linearity for minimum cathode current on the Horizontal Output tube. Try not to deviate too far from this position.

Does the yoke have centering tabs?

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Mon 23, 2021 9:12 pm 
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Watching this thread with popcorn as I'm working on a 20x12 and have the same problem with excessive width. :lol:


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Tue 24, 2021 2:08 pm 
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FrankieKat wrote:
Watching this thread with popcorn as I'm working on a 20x12 and have the same problem with excessive width. :lol:


Ah! So I am not the only one with this idiosyncrasy then! Nice to know :) I am still trying to gather enough courage to flip the chassis back on its side - it's heavy, and I am deathly afraid of damaging the precious CRT... I did swap a couple of sync separator 6AU6's - just to see if perchance it's the tube. No cigar - the exact same issue. Next will be checking voltages - this should give (hopefully) some clues for the more knowledgeable folks here... For reference, this is what it's supposed to be:

Attachment:
6AU6_Sync_Sep_V.jpg
6AU6_Sync_Sep_V.jpg [ 64.08 KiB | Viewed 1088 times ]


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Tue 24, 2021 2:50 pm 
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Have you adjusted the horizontal drive control ? It has a profound effect on width and linearity. It's a variable capacitor you adjust with a flat bladed tool through a hold in the back of the chassis.

Other things to try are swap out the horizontal output and damper tubes.

irob2345 wrote:
Does the yoke have centering tabs?


No, the yoke assembly can be moved to center the picture.


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Tue 24, 2021 5:38 pm 
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Location: New York, NY
Fennec wrote:
FrankieKat wrote:
Watching this thread with popcorn as I'm working on a 20x12 and have the same problem with excessive width. :lol:


Ah! So I am not the only one with this idiosyncrasy then! Nice to know :) I am still trying to gather enough courage to flip the chassis back on its side - it's heavy, and I am deathly afraid of damaging the precious CRT... I did swap a couple of sync separator 6AU6's - just to see if perchance it's the tube. No cigar - the exact same issue. Next will be checking voltages - this should give (hopefully) some clues for the more knowledgeable folks here... For reference, this is what it's supposed to be:

Attachment:
6AU6_Sync_Sep_V.jpg


Fortunately the HV cage on the 20x1 makes a stable support for the chassis to be on it's side, not sure about the 20B1 though. Like you I've done a ton of checks, swaps and head scratching and haven't found the culprit yet. :roll:

FK


Last edited by FrankieKat on Aug Fri 27, 2021 6:43 pm, edited 1 time in total.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Aug Wed 25, 2021 12:50 am 
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The sync separator relies on running the tube with somewhat odd voltages. To do that some of the resistors are at somewhat odd values for a tube amplifier. So check all the resistors around the sync separator. Also, while mica caps generally do not fail, those in the sync and horizontal circuits do fail. And the failure will not show up on a capacitor tester. So, if you can not find anything else, replace the mica caps in these circuits. You should use mica caps to replace them.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Sep Thu 02, 2021 6:59 pm 
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Still did not do anything major, other than swapping out a Horizontal Output (6BG6) and a Damper (6W4GT) - no noticeable changes... Will try swapping a Horizontal Oscillator (6SN7) and Horizontal Sync. Disc. (6AL5) next...

Playing strictly with controls and adjustments, this is my best result so far (sorry, Harry Potter is the only 4:3 "professional" material I have on hand)... Linearity and width are still a problem. A thin band with some stripes on top - is this the NTSC signal carrier artifact?

Attachment:
Screen01.jpg
Screen01.jpg [ 470.36 KiB | Viewed 750 times ]

Attachment:
Screen02.jpg
Screen02.jpg [ 74.34 KiB | Viewed 750 times ]


Still no sound - just faint hissing from the speaker, which gets louder with the volume control...


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Sep Fri 03, 2021 12:03 am 
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The stripes on top are closed caption stripes. NTSC originally had 525 active horizontal video lines, but now has only 480. The top 45 are now used for closed captioning, teletext, VIR, and other things. IIRC LD and CED analog video disc players didn't support those systems because they placed a frame count on those lines to implement anti-skip and frame seek functions.


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Sep Fri 03, 2021 11:10 pm 
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...snip...
Electronic Memory wrote:
NTSC originally had 525 active horizontal video lines, but now has only 480.


NTSC never had 525 active lines; that was the total line count per frame. There were originally only 36 lines per frame devoted to blanking in the B&W specs (RS-170), for 489 active lines. Blanking time was increased in the color system (NTSC) to a minimum of 38 lines and a maximum of 42 lines (per FCC). However, broadcasters could pretty much do what they wanted with the unblanked (active) time, IIRC. Analog TVs tended to have enough overscan that the first (and last) few lines were not usually visible, so various signals were developed to fit into that overscan area: VITS (Vertical Interval Test Signals), closed captioning, Teletext, etc. Most viewers never saw them. The notion that NTSC has only 480 active lines is mostly due to computers adopting a 640x480 standard, in part so they could display TV-compatible video. It's close enough that no one complained.

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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Sep Sat 04, 2021 1:53 am 
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That last picture isn't vertical ghosting (there is no such thing) your vertical is out of sync or synced at some multiple of the frequency it should be.


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 Post subject: Re: Admiral 24C16, 20B1 chassis
PostPosted: Sep Sat 04, 2021 10:33 pm 
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That lack of sound may F.M.'s version of 'silver mica disease'. You might open the IF can and look. Craig


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