I remember replacing these quite often many years ago and I still have
a few around here. They are pn. 22-7505, .015uf/1600V. These have four
leads. The two ends read continuity so as we'll probably never again
see the chassis these went into can they be used simply as a .015uf
1600V cap if I need one. What was "safety" about these? Lenny Stein,
Barlen Electronics.

If you watch how this type of cap goes open, it comes clear.

The two plates of the cap would very rarely if ever seperate, if a
problem happens there they generally short out. When they open it is
generally the connection to the plates. They are rolled up offset a
bit so the leads can attach.

The four lead cap actually uses two connections to each plate, so if
it opens up, there is no high voltage. The connection either to the
emitter or collector of the HOT is broken. If not, the high voltage
would rise quite a bit. It would cause Xrays and most likely blow
something out, but if it didn't you might have a nasty situation.

The Zenith EC series used to use multiple caps for this, and sometimes
one or more of them would open up causing an insidious excess of high
voltage, because there was no shutdown circuit at all. Thus they
needed the "4 lead capacitor modification". IIRC they came with a
sticker for the back of the set, but newer ones might not.

What to do with them now is anyone's guess.

JURB

On Sep 25, 8:42 am, wrote:
If you watch how this type of cap goes open, it comes clear.

The two plates of the cap would very rarely if ever seperate, if a
problem happens there they generally short out. When they open it is
generally the connection to the plates. They are rolled up offset a
bit so the leads can attach.

The four lead cap actually uses two connections to each plate, so if
it opens up, there is no high voltage. The connection either to the
emitter or collector of the HOT is broken. If not, the high voltage
would rise quite a bit. It would cause Xrays and most likely blow
something out, but if it didn't you might have a nasty situation.

The Zenith EC series used to use multiple caps for this, and sometimes
one or more of them would open up causing an insidious excess of high
voltage, because there was no shutdown circuit at all. Thus they
needed the "4 lead capacitor modification". IIRC they came with a
sticker for the back of the set, but newer ones might not.

What to do with them now is anyone's guess.

JURB

Thanks for the explanation. I never really understood the internals of
those things until now. Now, yes what to do with them......Lenny.

If you have ever torn down a paper / mylar / poly capacitor to view its internal infrastructure, you would see the offsetting of the dielectric foil upon the dielectric separator and the clustering of the mass at both ends . That then needs to be collectively interfaced to the two wire connector leads. That is usually accomplished by a pressure compression of lots of surface contacting area or a enclosed crimping action and the other means being via a large molten solder "blob" which will properly meld with the tinnable copper wire lead and be dependent upon the other contact aspect to be the extensive area of foil that has solder interspersed within it.

Now getting to your special feature of the "safety capacitor".
You will be finding it placed in the collector / to / flyback primary winding where it is resonating
along with the primary of that transformer, as that transformer action certainly is more efficient operating as handling a pseudo-sine wave versus a positive polarity sawtooth waveform.
With that resonance established between the two components of that tuned circuit , there will be
quite a degree of flywheel energy present and an actual lowered degree of required power required
as compared to a circuit with out that aspect being present.

Now lets look at that repetitive 15,734 ~ signal that is continually hitting that current loop in the hoz output stage, much in the order of an instantaneous power impact effect of a jackhammer.
If all is well in the hoz circuit, fine, no problems will be had.......but lets move back to the described capacitors internal structuring , if those high current pulse might find a weak / marginal contact area within that cap, expect it to arc over, vaporize metal and open a portion of a previously contacting area. That then leaves progressively less area to be carrying and sharing the current requirement.

A daisy chain or domino effect is then possible with the eventual loss of all contact area made to the foil and either arc over or loss of internal contact completely and the loss of connection and capacitance transfer.
Now IF that cap is effectively out of the circuit, by virtue of that opened internal connection.
Expect that previous effect of drawing less current while being in coincident or close to resonance state to the frequency that the hoz power circuitry was operating at, to no longer be valid.
The power consumption...i.e. current passing through that loop should increase, along with a shooting up of the high voltage level being produced at the fly /IHVT output by virtue of being hit by the sharp peak of a sawtooth waveform now.
That would be limit taxing on the HV components as well as possibly getting up into the X-ray level from picture tubes, or even up to the ultimate threshold of actually breaking the kine via a circular ring fracture about the yoke mounting area.
That is where the safety aspect of the mentioned capacitor comes into play.
In examining the circuitry, you will find that the caps dual leads are dependent upon completing specific interconnections.
That being in the closed loop from the B+ supply to the collector circuit of the Hoz output transistor. Within those capacitors, there are internal fusible links between adjunct leads, such that when operated beyond their current passage design center, an opening will occur internally, opening their circuit, such that the sweep circuit then becomes disabled.
Therefore being dubbed "safety capacitors", so that extreme condition never occurs, or merely rising upon that threshold for an instant.

Regards..... Edd

On Sep 25, 2:50 pm, Edd Whatley
wrote:
If you have ever torn down a paper / mylar / poly capacitor to view its
internal infrastructure, you would see the offsetting of the dielectric
foil upon the dielectric separator and the clustering of the mass at
both ends . That then needs to be collectively interfaced to the two
wire connector leads. That is usually accomplished by a pressure
compression of lots of surface contacting area or a enclosed crimping
action and the other means being via a large molten solder "blob" which
will properly meld with the tinnable copper wire lead and be dependent
upon the other contact aspect to be the extensive area of foil that has
solder interspersed within it.

Now getting to your special feature of the "safety capacitor".
You will be finding it placed in the collector / to / flyback primary
winding where it is resonating
along with the primary of that transformer, as that transformer action
certainly is more efficient operating as handling a pseudo-sine wave
versus a positive polarity sawtooth waveform.
With that resonance established between the two components of that
tuned circuit , there will be
quite a degree of flywheel energy present and an actual lowered degree
of required power required
as compared to a circuit with out that aspect being present.

Now lets look at that repetitive 15,734 ~ signal that is continually
hitting that current loop in the hoz output stage, much in the order of
an instantaneous power impact effect of a jackhammer.
If all is well in the hoz circuit, fine, no problems will be
had.......but lets move back to the described capacitors internal
structuring , if those high current pulse might find a weak / marginal
contact area within that cap, expect it to arc over, vaporize metal
and open a portion of a previously contacting area. That then leaves
progressively less area to be carrying and sharing the current
requirement.

A daisy chain or domino effect is then possible with the eventual loss
of all contact area made to the foil and either arc over or loss of
internal contact completely and the loss of connection and capacitance
transfer.
Now IF that cap is effectively out of the circuit, by virtue of that
opened internal connection.
Expect that previous effect of drawing less current while being in
coincident or close to resonance state to the frequency that the hoz
power circuitry was operating at, to no longer be valid.
The power consumption...i.e. current passing through that loop should
increase, along with a shooting up of the high voltage level being
produced at the fly /IHVT output by virtue of being hit by the sharp
peak of a sawtooth waveform now.
That would be limit taxing on the HV components as well as possibly
getting up into the X-ray level from picture tubes, or even up to the
ultimate threshold of actually breaking the kine via a circular ring
fracture about the yoke mounting area.
That is where the safety aspect of the mentioned capacitor comes into
play.
In examining the circuitry, you will find that the caps dual leads are
dependent upon completing specific interconnections.
That being in the closed loop from the B+ supply to the collector
circuit of the Hoz output transistor. Within those capacitors, there
are internal fusible links between adjunct leads, such that when
operated beyond their current passage design center, an opening will
occur internally, opening their circuit, such that the sweep circuit
then becomes disabled.
Therefore being dubbed "safety capacitors", so that extreme condition
never occurs, or merely rising upon that threshold for an instant.

Regards..... Edd

--
Edd Whatley

That is really an interesting discussion of how these things work. But
it begs the question of why didn't they simply put some type of fuse
or fusible link in the circuit? Lenny

A fuse won't work because current drain does not increase, in fact it
goes down.

When what I call the damper cap opens up, the HV produced is softer,
not as much current behind it, but at zero beam current rises quite a
bit.

Interestingly something very similar happens if the core of the
flyback cracks. I had one a long time ago, the damper caps were
checked, the picture was narrow and the tech was scratching his head.
He had the B+ turned down but couln't turn it up to normal because it
would shut down. As usual in such a case, I wound up with it.

I took a screwdriver handle and pushed down hard on the flyback core
and the picture widemed.

That's when it really pays to understand reactive scanning, although
these modern pincushion circuits befuddle me. Even a CTC169, my logic
says when the .056uF opens the picture should be too narrow. Then you
got Sonys doing the opposite of what you think a given bad component
should cause because of feedback. Then you have coils with magnets in
them, geez ! See my thread about a new profession lol.

JURB

wrote:
That's when it really pays to understand reactive scanning, although
these modern pincushion circuits befuddle me. Even a CTC169, my logic
says when the .056uF opens the picture should be too narrow. Then you
got Sonys doing the opposite of what you think a given bad component
should cause because of feedback. Then you have coils with magnets in
them, geez ! See my thread about a new profession lol.

If circuits always failed in ways you'd expect them to fail, then it
wouldn't be any fun any more, would it?

--
If you really believe carbon dioxide causes global warming,
you should stop exhaling.

" wrote:

On Sep 25, 2:50 pm, Edd Whatley
wrote:
If you have ever torn down a paper / mylar / poly capacitor to view its
internal infrastructure, you would see the offsetting of the dielectric
foil upon the dielectric separator and the clustering of the mass at
both ends . That then needs to be collectively interfaced to the two
wire connector leads. That is usually accomplished by a pressure
compression of lots of surface contacting area or a enclosed crimping
action and the other means being via a large molten solder "blob" which
will properly meld with the tinnable copper wire lead and be dependent
upon the other contact aspect to be the extensive area of foil that has
solder interspersed within it.

Now getting to your special feature of the "safety capacitor".
You will be finding it placed in the collector / to / flyback primary
winding where it is resonating
along with the primary of that transformer, as that transformer action
certainly is more efficient operating as handling a pseudo-sine wave
versus a positive polarity sawtooth waveform.
With that resonance established between the two components of that
tuned circuit , there will be
quite a degree of flywheel energy present and an actual lowered degree
of required power required
as compared to a circuit with out that aspect being present.

Now lets look at that repetitive 15,734 ~ signal that is continually
hitting that current loop in the hoz output stage, much in the order of
an instantaneous power impact effect of a jackhammer.
If all is well in the hoz circuit, fine, no problems will be
had.......but lets move back to the described capacitors internal
structuring , if those high current pulse might find a weak / marginal
contact area within that cap, expect it to arc over, vaporize metal
and open a portion of a previously contacting area. That then leaves
progressively less area to be carrying and sharing the current
requirement.

A daisy chain or domino effect is then possible with the eventual loss
of all contact area made to the foil and either arc over or loss of
internal contact completely and the loss of connection and capacitance
transfer.
Now IF that cap is effectively out of the circuit, by virtue of that
opened internal connection.
Expect that previous effect of drawing less current while being in
coincident or close to resonance state to the frequency that the hoz
power circuitry was operating at, to no longer be valid.
The power consumption...i.e. current passing through that loop should
increase, along with a shooting up of the high voltage level being
produced at the fly /IHVT output by virtue of being hit by the sharp
peak of a sawtooth waveform now.
That would be limit taxing on the HV components as well as possibly
getting up into the X-ray level from picture tubes, or even up to the
ultimate threshold of actually breaking the kine via a circular ring
fracture about the yoke mounting area.
That is where the safety aspect of the mentioned capacitor comes into
play.
In examining the circuitry, you will find that the caps dual leads are
dependent upon completing specific interconnections.
That being in the closed loop from the B+ supply to the collector
circuit of the Hoz output transistor. Within those capacitors, there
are internal fusible links between adjunct leads, such that when
operated beyond their current passage design center, an opening will
occur internally, opening their circuit, such that the sweep circuit
then becomes disabled.
Therefore being dubbed "safety capacitors", so that extreme condition
never occurs, or merely rising upon that threshold for an instant.

Regards..... Edd

--
Edd Whatley

That is really an interesting discussion of how these things work. But
it begs the question of why didn't they simply put some type of fuse
or fusible link in the circuit? Lenny


Have you ever seen the original three lead safety capacitor Zenith
used? When they failed, a high DC current flowed in the yoke, which
caused the neck of the CRT to crack. Plastic Capacitor Corp. made the
defective three lead parts, and went out of business. I was working for
a shop that sold Zenith, and went to the factory school on those sets.
As soon as the problem surfaced, a mad rush was on to find every Zenith
TV with the defective caps, and modify them to the new design, and apply
the modification sticker to the back of the cabinet. They showed a 16
mm film of a CRT self destructing.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida