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!

On Tue, 11 Nov 2003 18:17:03 GMT, Matt Baum
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!

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
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!

On Wed, 12 Nov 2003 02:26:00 GMT, Matt Baum
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
wrote:

I finally got the transistor for Q4402, & replaced it.
Results same as before - OnScreenDisplay doesn't sync horizontally;
all else seems OK.

Since I now have the set apart, I checked the waveforms.
H pulses OK at base and emitter of Q4402 look just like what the manual
shows. Also waveform right at pin 23 of the micro is OK.

Micro pins 25 &26 (the passive components of the PLL) don't look so
great, but there are no manual waveforms to compare them with.
Any ideas - anybody??

Reply

"Matt Baum" wrote in message
...
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.

Double check the area around the crystal (the 503); there's an electrolytic cap
near it that leaks, causing all sorts of horiz and sync problems