If you remember, I was having slow warm-up, focus, and black-level problems
with this set.

Over the past two months, the picture gradually stabilized, with these
problems fading away (for no obvious reason). Nevertheless, I thought it
would be a good idea to replace the caps on the video driver board, just to
be safe.

I hadn't ordered them from Digi-Key (or any other company), because those
that had the values I wanted required a $25 minimum order, and there was
nothing else that I needed. But I needed an RS-232 cable, and Fry's -- not
far from my home -- had the cable and all the caps (NTEs, if it's of any
interest).

Well, I replaced two of the three caps on the board -- the ones I'd replaced
10+ years ago -- and guess what -- the set is _worse_ than it was before I
replaced them.

The black level is unstable and "flickers" occasionally. The focus sometimes
jumps out of line. Warm-up (that is,, the first appearance of a picture) is
more or less normal, though it's sometimes darker than it should be.

I saved the existing caps, and am thinking about putting them back. (Here's
a case where I could really use an ESR meter!)

They are the correct values, except one is 350V when it should be 250V. (I
checked before buying the parts, and found that the 250V caps in the set had
200V across them. So I couldn't safely use the 160V cap.)

Assuming the replacement caps aren't bad (and they might very well be, as
they're probably five years old), does anyone have an idea of why "new"
parts should (apparently) degrade the set's performance?

Thanks.

William Sommerwerck wrote:
Assuming the replacement caps aren't bad (and they might very well be, as
they're probably five years old), does anyone have an idea of why "new"
parts should (apparently) degrade the set's performance?

Probably highlighting other problems.

--
Dec. 6 (Bloomberg) -- Government officials and activists flying to Bali,
Indonesia, for the United Nations meeting on climate change will cause
as much pollution as 20,000 cars in a year.

On Dec 25, 11:28*am, clifto wrote:
William Sommerwerck wrote:
Assuming the replacement caps aren't bad (and they might very well be, as
they're probably five years old), does anyone have an idea of why "new"
parts should (apparently) degrade the set's performance?

Probably highlighting other problems.

--
Dec. 6 (Bloomberg) -- Government officials and activists flying to Bali,
Indonesia, for the United Nations meeting on climate change will cause
as much pollution as 20,000 cars in a year.

Just physically moving the chassis may have aggravated some cold
solder joints into becoming more active again.

H. R. (Bob) Hofmann

"hr(bob) " wrote in message
...
On Dec 25, 11:28 am, clifto wrote:
William Sommerwerck wrote:

Assuming the replacement caps aren't bad (and they might
very well be, as they're probably five years old), does anyone
have an idea of why "new" parts should (apparently) degrade
the set's performance?

Probably highlighting other problems.

Just physically moving the chassis may have aggravated some
cold solder joints into becoming more active again.

I appreciate your comments, but the chassis was not moved. And the symptoms
are qualitatively no different than they were when the problems first
surfaced two or three months ago.

I wouldn't mind ripping into the set and replacing most of the electrolytic
caps in the video, horizontal, and HV sections. But this is not a set
designed to be easily serviced -- the main board is large and sits above a
wooden base.

I welcome further thoughts. I think later today I'll put the "old" caps back
and see what happens.

On Dec 26, 6:20*am, "William Sommerwerck"
wrote:
"hr(bob) " wrote in message

...
On Dec 25, 11:28 am, clifto wrote:

William Sommerwerck wrote:
Assuming the replacement caps aren't bad (and they might
very well be, as they're probably five years old), does anyone
have an idea of why "new" parts should (apparently) degrade
the set's performance?
Probably highlighting other problems.
Just physically moving the chassis may have aggravated some
cold solder joints into becoming more active again.

I appreciate your comments, but the chassis was not moved. And the symptoms
are qualitatively no different than they were when the problems first
surfaced two or three months ago.

I wouldn't mind ripping into the set and replacing most of the electrolytic
caps in the video, horizontal, and HV sections. But this is not a set
designed to be easily serviced -- the main board is large and sits above a
wooden base.

I welcome further thoughts. I think later today I'll put the "old" caps back
and see what happens.

I am a little confused. How did you replace the capacitors without
moving the chassis?

Anyway, I would monitor the power supply voltages with a voltmeter or
scope, if they are changing enough to produce the effects you
mentioned, you should be able to see some shifting of voltages, then
it's just a matter of tracing backwards. Do you have the schematic?
That would be a tremendous help?

H. R(Bob) Hofmann

On Dec 25, 10:04*am, "William Sommerwerck"
wrote:
If you remember, I was having slow warm-up, focus, and black-level problems
with this set.

Over the past two months, the picture gradually stabilized, with these
problems fading away (for no obvious reason). Nevertheless, I thought it
would be a good idea to replace the caps on the video driver board, just to
be safe.

I hadn't ordered them from Digi-Key (or any other company), because those
that had the values I wanted required a $25 minimum order, and there was
nothing else that I needed. But I needed an RS-232 cable, and Fry's -- not
far from my home -- had the cable and all the caps (NTEs, if it's of any
interest).

Well, I replaced two of the three caps on the board -- the ones I'd replaced
10+ years ago -- and guess what -- the set is _worse_ than it was before I
replaced them.

The black level is unstable and "flickers" occasionally. The focus sometimes
jumps out of line. Warm-up (that is,, the first appearance of a picture) is
more or less normal, though it's sometimes darker than it should be.

I saved the existing caps, and am thinking about putting them back. (Here's
a case where I could really use an ESR meter!)

They are the correct values, except one is 350V when it should be 250V. (I
checked before buying the parts, and found that the 250V caps in the set had
200V across them. So I couldn't safely use the 160V cap.)

Assuming the replacement caps aren't bad (and they might very well be, as
they're probably five years old), does anyone have an idea of why "new"
parts should (apparently) degrade the set's performance?

Thanks.

Is it possible that the tolerance of the new caps is way larger than
the originals?

I've measured many larger-value electrolytics and have had so many of
them
read way beyond their stated capacitance that I've begun to consider
the face
value as "minimum guaranteed capacitance."

Just a thought...

"hr(bob) " wrote in message
...

I am a little confused. How did you replace the capacitors without
moving the chassis?

Easy. They're on the video driver board, which pops right off the CRT. This
is a common (though not universal) arrangement.


Anyway, I would monitor the power supply voltages with a voltmeter or
scope, if they are changing enough to produce the effects you
mentioned, you should be able to see some shifting of voltages, then
it's just a matter of tracing backwards. Do you have the schematic?
That would be a tremendous help?

Yes, I have the schematic. I think. (It's disappeared at the moment.) The
problem is that the schematic doesn't give voltages. So you don't always
know for sure whether a fluctuation is a cause or effect, and are, to some
extent guessing.

"Mr. Land" wrote in message
...

Is it possible that the tolerance of the new caps is way larger than
the originals?

It's possible. As far as I can tell, tolerances have gotten tighter over the
years, with the errors leaning more in the direction of "too much" rather t
han too-little (as your observations suggest).

As electrolytics are most-often used for coupling, decoupling, bypassing,
and filtering -- all applications where "more" capacitance is not usually a
problem -- this seems to be the right way to spec them.

The set appears to be stabilizing; the problems aren't as severe as they
were two days ago.

"William Sommerwerck" wrote in
news
"Mr. Land" wrote in message
...

Is it possible that the tolerance of the new caps is way larger than
the originals?

It's possible. As far as I can tell, tolerances have gotten tighter over
the years, with the errors leaning more in the direction of "too much"
rather t han too-little (as your observations suggest).

As electrolytics are most-often used for coupling, decoupling,
bypassing, and filtering -- all applications where "more" capacitance is
not usually a problem -- this seems to be the right way to spec them.

The set appears to be stabilizing; the problems aren't as severe as they
were two days ago.


De-aging may be the cause.

Most ceramic capacitors [and perhaps some electrolytics] decrease in value
at a consistent aging rate.

A plot of cap vs natural log of time gives a straight line.
Let us say a particular cap ages 1% per decade. Its value will drop 1% in
the first hour, 1% in the next 10 hours, 1% in the next 100 hours, 1% in
the next 1000 hours, etc.

The STARTING point for aging is when the cap cools down after being heated
above the ceramic's curie point.

In other words, heating up the capacitor above a particular temperature
[that varies with the ceramic's formulation] "de-ages" the capacitor.

It is quite possible that soldering a part into a circuit can 'deage' it.

If HIGH cap at some point in the circuit is causing your problems, de-aging
may exacerbate the problem and aging may 'cure' it.


--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap