restoring an emerson antique tv

ive been trying to restore an emerson model 663B.

i found out the weakness of the picture was the ion trap being on wrong.

the picture is now bright sharp and crisp.

everything works now, except for 2 problems. the horizontal is VERY touchy,
and the sound is weak, but i think i know whats wrong with the sound.

here is what i want to try to solve.

i got the set to work fine, but the horizontal wouldnt lock when turning the
hold control.

i went to the back and adjusted the horiz. freq. adjustment and it showed up
as multiple images on the screen, and i adjusted the hold control to get the
picture to lock into place. but here comes the problem:

the control is very touchy, you have to have it dead on to lock. and the
main problem is, lets say its on a scene from a program, and the picture is
locked in place. well, if the scene changes, like if it gets darker or
brighter, or if the scene moves, the horizontal is out again.

i readjust and get it to lock, and when the scene changes back, its gone
again.

but if i leave the lock alone, it will lose horizontal, and when it comes to
a scene similar to the one i adjusted it on, it slows down to a stop and
locks again, until the brightness, or the scene changes in any way, and the
horizontal jumps all over the place.

I dont have any trouble with the vertical, its as stable as can be,
although,
there are retrace and forground dashed lines that change at different scenes
that drive me nuts, but ive heard thats from too strong of signal.

Any ideas would be appriciated.

 

Have you replaced all the paper caps in the horizontal section, and checked
or subbed the oscillator tube?

jak

 

Good point! These days whenever I get into *anything* that has those old
paper caps in there they _ALL_ get replaced. No point in screwing around
with those, if they're not a problem now they will be later on.

Also, in something of that vintage there will be a separate sync separator
stage. This will possibly be tied in with or even combined with AGC
functions, and a mis-adjustment of the AGC control might produce the
symptoms described. I'd also check out any high-value resistors in that
area, I've seen ones (<=1M) that have drastically increased in value from
age. (Whoops! Dating myself here...

 

Maybe the set has one of those
Double Diodes that was common
back then,some were soldered in
and some plugged in.
Look in and around the Hor/Sync
section and see if it uses one of them.

kip

 

It has been over a 35 years since I have worked on these types of sets! I
cannot remember details, or have any service information about them.

Try the horiz oscillator tube, sync separator, sync amp, and video amp
tubes. Also, at the same time, check all the capacitors, and high omage
resistors involved. The combination of all of this mentioned will be the
fault area to fix the set. Considering the age of the set, you can repair
the rest of the faults if you take the time, and have the skills. If you
have a scope you can trace the sync signals to see if they are correct in
specs. Take care that in the horiz sync area, the sync reference feedback
can trigger the scope, and give a signal that looks like the proper sync
signal. This can fool you.

For the horiz sync lock, there is a feedback from the horiz output stage to
the sync control, which is part of the sync detector, and or the oscillator.
The feedback pulse is compared with the sync pulses coming in. They make a
type of servo DC correction to guide or hold the oscillator in place or
phase locked.

The AGC is also an area of problems with these sets. Improper AGC operation
will make the picture bend, have poor phase lock, be over contrast
(depending on how it is not working), and also may introduce buzz in the
audio.

When you fix the set, you will have a very good set!

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


ive been trying to restore an emerson model 663B.

i found out the weakness of the picture was the ion trap being on wrong.

the picture is now bright sharp and crisp.

everything works now, except for 2 problems. the horizontal is VERY touchy,
and the sound is weak, but i think i know whats wrong with the sound.

here is what i want to try to solve.

i got the set to work fine, but the horizontal wouldnt lock when turning the
hold control.

i went to the back and adjusted the horiz. freq. adjustment and it showed up
as multiple images on the screen, and i adjusted the hold control to get the
picture to lock into place. but here comes the problem:

the control is very touchy, you have to have it dead on to lock. and the
main problem is, lets say its on a scene from a program, and the picture is
locked in place. well, if the scene changes, like if it gets darker or
brighter, or if the scene moves, the horizontal is out again.

i readjust and get it to lock, and when the scene changes back, its gone
again.

but if i leave the lock alone, it will lose horizontal, and when it comes to
a scene similar to the one i adjusted it on, it slows down to a stop and
locks again, until the brightness, or the scene changes in any way, and the
horizontal jumps all over the place.

I dont have any trouble with the vertical, its as stable as can be,
although,
there are retrace and forground dashed lines that change at different scenes
that drive me nuts, but ive heard thats from too strong of signal.

Any ideas would be appriciated.

 

i will provide you with all the information:


i bought this set on ebay, and it was freight damaged. i replaced the
shattered picture tube, and replaced ALL paper and electrolytic caps.

i had to replace some tubes due to weak emission, and replace the choke, as
it was open when someone in the past tried to power it up with bad 'lytics.
i also found open and replaced the only ballast resistor, and i replaced the
focus resistor as it went from 1 megohm to like 5 megohms. I have the sams
to the set, and absolutly no diodes whatsoever. i believe the set was made
in '51

thanks for your input, and if someone would lead me in the right direction,
id appriciate it.

 

I can't really give you anything detailed, just some theory.

The AGC will control the overall amplitude of the video signal. Depending on
the polarity of the video detector, the sync pulse level will either be a
positive voltage or a negative one, and the peak white level will be the
opposite. For now, let's just assume that sync is negative and peak white is
positive. The NTSC standard would allow for 140 IRE units from sync tip to
white level, with sync at 0, black level at 40, and peak white 100 units
higher at 140. The DC levels must be maintained so the sync separator can
detect the difference between black and sync tips. As you noted, when the
picture has more white in it, the DC level is probably shifting, so the sync
sampling point shifts, and you lose sync lock.

There could be a DC restoration circuit in there that will attempt to
maintain the DC level for black. But if the AGC circuit isn't working
properly, or isn't adjusted the way it should be, then the amplitude of the
signal could be way off or even vary with picture content.

It's also been a long time since I fixed a tube set (over 35 years) so I'm
going on a lot of recall here. Hope this helps a bit.

Bob M.
======

 

Are you sure there are no diodes in the horz. afc circuit? Many of these sets had a set of two selenium diodes molded into a plastic assembly with three leads on it. There were several configurations including common anode, common cathode, and series connected. These often failed resulting in very poor or no horizontal sync.
Dave

 

I fixed it. stupid me, i had the caps backwards in the sync seperator. the
sync seperator tube 6au6, the coupling cap was accidently grounded, instead
of coupled into the sync amp tube. so, there was the problem.

the sync both vertical and horizontal is locked on tight. no drifting, but
there is a problem in the AGC. because when the scenes get brighter, the
picture begins to tear and notch horizontally, like your watching
macrovision, or a scrambled cable channel. but it only does it on bright
scenes. it works perfect on normal to darker scenes.

any ideas will help.







Are you sure there are no diodes in the horz. afc circuit? Many of these
sets had a set of two selenium diodes molded into a plastic assembly with
three leads on it. There were several configurations including common anode,
common cathode, and series connected. These often failed resulting in very
poor or no horizontal sync.
Dave

 

Never seen a TV yet that has NO diodes.

kip


Are you sure there are no diodes in the horz. afc circuit? Many of these
sets had a set of two selenium diodes molded into a plastic assembly with
three leads on it. There were several configurations including common anode,
common cathode, and series connected. These often failed resulting in very
poor or no horizontal sync.
Dave


no diodes whatsoever. i believe the set was made

 

nope, none. absolutely zero.

i have the sams sitting right in front of me.

 

Well I can name you 2 diodes in there without even looking at the schematic.
One begins with D and the other begins with S.

kip

 

sorry, dude. there is NONE.

the only thing diode-like are 2 rectifier tubes. 2 rectifiers each tube.

one is in the sound circuit, the other is in the IF circuit.

otherwise, NO DIODES.

 

Now you are getting close,what is a rectifier ?

kip

 

When you finally understood, that is excellent.

Rectifier, Hahaha... I wasn't from that era (born 1972) but I read
about old stuff and have yet to work on tube based TV set. Mind you,
I took apart several of them including one with 200+ colored pots with
triple convergence coils for the CRT when I was young.

Now about that one, rectifier yes I know what it is. Diode word &
symbol wasn't there back then. Think about it, Hot filment emitter &
cold plate all in a hard vacuum, what happens to those electrons flow?

Now read about why diode was called solid-state rectifier (another old
name.). A tiny slab of silicon doped with two types of dopants too
full of electrons atoms and holes where atoms had lost several
electons seperated by a "line" as junction. Again, find out why this
works this way.

Oh, the oddly shaped tube is still here and it's staring right in your
face is it too!

Cheers,

Wizard

 

The first diode; a vacuum tube diode was developed by J. Ambrose Fleming in
1902.



Just for reference..



kip

 

"Mike" bravely wrote to "All" (25 Oct 03 15:30:23)
--- on the heady topic of "Re: restoring an emerson antique tv"

The ACG action was "keyed" and required a properly timed pulse from the
horizontal section. The coupling cap would often open up due to the
higher voltages found there.

Aside from that, if the AGC voltage is 0, could be the tuner AGC bypass
feedthrough is shorted out. That used to happen from time to time and I
don't know why. Just reroute the wire with a 1nF (or so) cap to ground.
I replaced one once but it was a lot of trouble.


Mi> From: "Mike" <>

Mi> I fixed it. stupid me, i had the caps backwards in the sync seperator.
Mi> the sync seperator tube 6au6, the coupling cap was accidently grounded,
Mi> instead of coupled into the sync amp tube. so, there was the problem.

Mi> the sync both vertical and horizontal is locked on tight. no drifting,
Mi> but there is a problem in the AGC. because when the scenes get
Mi> brighter, the picture begins to tear and notch horizontally, like your
Mi> watching macrovision, or a scrambled cable channel. but it only does it
Mi> on bright scenes. it works perfect on normal to darker scenes.

Mi> any ideas will help.

.... I worked hard to attach the electrodes to it.

 

These TV sets were renowned for using variable resistor pots that do have tracks
in the pot that break. Check that the track is not broken and second has someone
replaced the pot at some time with a value that is to high. Try a pot with a
lower value. Do this in steps if it seems to help. Next check the resistors that
will be in series with the pot, they may have gone high in value. Lastly don't
look for the difficult solutions look simple it usually is. all the very best
Peta***

 

would a weak horiz ocillator tube cause AGC problems?

i put the 6sn7 on the tube tester, and out of a scale of 100% emission, its
reading 30. hmmmm.

 

Yes it would. AGC in lots and lots (most?) of tv sets is _keyed_ by a
horizontal pulse. Often this comes off the flyback, but not always.