CTC 169 OnScreenDisplay Problem

[Matt Baum]

The ProScan 27" set with CTC 169 chassis is over ten years old.
Recently onscreen display started tearing; after an hour or so of
"warmup" it would be OK.
Now it never displays properly. Video modulation comes through.
Horizontal sync is the problem; vertical is OK.
I have the Field Service manual, which says "The OSD horizontal position
is phase-locked with the H-SYNC signal at Pin 23. . . . Components
external to the micro at Pins 25 and 26 set up the characteristics of
the OSD PLL."
Pins 25 and 26 go to 2 resistors and one cap to ground.
This set is a mess to work on. If I am sure that it's one of these
three parts, I'll do it. (Otherwise I'll just forget about the OSD!)

Any suggestions?

Thanks -
Matt Baum
Expert in the obsolete!

 

[Jason D.]

On Tue, 11 Nov 2003 18:17:03 GMT, Matt Baum <mmbaum@optonline.net>
wrote:

The ProScan 27" set with CTC 169 chassis is over ten years old.
Recently onscreen display started tearing; after an hour or so of
"warmup" it would be OK.
Now it never displays properly. Video modulation comes through.
Horizontal sync is the problem; vertical is OK.
I have the Field Service manual, which says "The OSD horizontal position
is phase-locked with the H-SYNC signal at Pin 23. . . . Components
external to the micro at Pins 25 and 26 set up the characteristics of
the OSD PLL."
Pins 25 and 26 go to 2 resistors and one cap to ground.
This set is a mess to work on. If I am sure that it's one of these
three parts, I'll do it. (Otherwise I'll just forget about the OSD!)

Keep tracing back to the source, this H-pulses is used by many items
including syncing PSU to horizontal rate. Somewhere there's a bad
part or bad glue under a SMD device developed leakage.

Good for you to have real RCA schematics for CTC169 on a CD disc, I'm
still trying to order it from RCA without success.

Cheers,

Wizard

Any suggestions?

Thanks -
Matt Baum
Expert in the obsolete!

 

[Matt Baum]

Thanks Jason for the hint!

I see where the H-SYNC comes from Q4402 INTO the Sysem Control U3101 at
Pin 23.
However, I couldn't believe that U3101 doesn't use it for anything else.
(No other problems that I notice.)
If so, then Q4402 my be the culprit.

Has anyone else seen this kind of problem before?

Thanks -
Matt

Jason D. wrote:

On Tue, 11 Nov 2003 18:17:03 GMT, Matt Baum <mmbaum@optonline.net
wrote:


The ProScan 27" set with CTC 169 chassis is over ten years old.
Recently onscreen display started tearing; after an hour or so of
"warmup" it would be OK.
Now it never displays properly. Video modulation comes through.
Horizontal sync is the problem; vertical is OK.
I have the Field Service manual, which says "The OSD horizontal position
is phase-locked with the H-SYNC signal at Pin 23. . . . Components
external to the micro at Pins 25 and 26 set up the characteristics of
the OSD PLL."
Pins 25 and 26 go to 2 resistors and one cap to ground.
This set is a mess to work on. If I am sure that it's one of these
three parts, I'll do it. (Otherwise I'll just forget about the OSD!)


Keep tracing back to the source, this H-pulses is used by many items
including syncing PSU to horizontal rate. Somewhere there's a bad
part or bad glue under a SMD device developed leakage.

Good for you to have real RCA schematics for CTC169 on a CD disc, I'm
still trying to order it from RCA without success.

Cheers,

Wizard


Any suggestions?

Thanks -
Matt Baum
Expert in the obsolete!

 

[Jason D.]

On Wed, 12 Nov 2003 02:26:00 GMT, Matt Baum <mmbaum@optonline.net>
wrote:

Thanks Jason for the hint!

I see where the H-SYNC comes from Q4402 INTO the Sysem Control U3101 at
Pin 23.
However, I couldn't believe that U3101 doesn't use it for anything else.
(No other problems that I notice.)
If so, then Q4402 my be the culprit.

Has anyone else seen this kind of problem before?

Thanks -
Matt

Actually, this signal looks like a rounded off tall pulses from
flyback and get massaged lot by many components into nice square
topped h-sync pulses for the micro, mid way this pulse processing it
is sent on the way to other circuits that uses it.

Look again at your schematic from the flyback and trace it all the way
to the micro, also trace from fly to the power suplly, etc.

You do need scope to view the quality of waveforms because these
timing pulses that drives other devices are phase sensitive hence the
messed up text etc.

Also this is also monitored, if no horizontal pulses micro goes into 3
strikes and out mode. I have this projector waiting for a customer's
okay for estimate that is doing this three strikes & out thing I think
it lost a signal somewhere in this customer's tv.

Cheers,

Wizard

Jason D. wrote:
On Tue, 11 Nov 2003 18:17:03 GMT, Matt Baum <mmbaum@optonline.net
wrote:

 

[James Sweet]

"Matt Baum" <mmbaum@optonline.net> wrote in message
news:YSgsb.9995$B9.4014364@news4.srv.hcvlny.cv.net...

Thanks Jason for the hint!

I see where the H-SYNC comes from Q4402 INTO the Sysem Control U3101 at
Pin 23.
However, I couldn't believe that U3101 doesn't use it for anything else.
(No other problems that I notice.)
If so, then Q4402 my be the culprit.

Has anyone else seen this kind of problem before?

Thanks -
Matt

I would bet the problem is an electrolytic capacitor since it used to
improve as it warmed up.