This was picked up from another site
some very useful info .
You will need Chipper Checker for this..

CTC203
#1

*IIC "Run" Bus Servicing Strategies
This Phrase means, I squared C
Preface

This chassis incorporates 3 two wire IIC system control buses. They are;
Standby, Run, and Gemstar. This article only addresses the Run Bus issue.
There is no reason why the same approach cannot be used to isolate troubles
in either Standby or Gemstar IIC Buses. However the Run Bus occupies far
more landscape in this chassis making it harder to analyze and isolate.

It is assumed by this writer that the technician using this information
possesses a reasonable & fundamental knowledge on usage of the Chipper
Checker, IIC bus system controlling, and logical troubleshooting skills.

The following is a strategy to help the technician troubleshoot of the "Run"
Data or Clock Bus in the new Thomson CTC203 consumer television chassis. My
findings so far have found the Thomson's Chipper Checker has helped to
diagnose several intermittent, and "Hard" failures in this chassis. Chipper
Checker is not the cure-all, Tell All instrument in the case of this IIC
problem. It was instrumental in indicating an error code of "16". This
error code indicated the Run Bus was being held to a Logic "0". The
following text and an antidote might be help tech localize and isolate the
device responsible for this condition.

The next step after using the Chipper Checker, is to measure the "Run" IIC
buses on U13101(3 & 4) at the instant the power is applied. There should be
communications sustained for at least 45 Milliseconds on each IIC bus. At
turn on there will be continuos activity on the RUN/CLK bus. These
communication signals will be 5 volts peak to peak. If you discover either
one of these are stuck low proceed with the following steps.

Some precautions before starting.....

Loose the solder wick. Please! In order for solder wick to be effective the
iron temperature must be very hot between 700~800 degrees. The practice of
using high soldering temperatures and the solder wick tends to retain too
much heat.. These high temperatures are too high and will break down the
adhesive used on the copper traces. Once the adhesive is broken down the
trace lifts off the board and then your are left with mess.

The Hakko 471 is an excellent choice for desoldering the components on this
board. Just keep the temperature between 600 ~ 625 degrees and avoid
prolonged contact to the traces. If wick must be used, use only thin stuff,
and keep it trimmed back so only fresh braid contacts the trace the needs to
be desoldered.

OK..... Here's the Strategy for Isolating Error "16"

Place a short between the Q14104(C & E) located @ Q7 of main CBA. This
turns "ON" the necessary B+ to all the peripheral IC's in the chassis. It
must be done otherwise the "Run" Data and Clock buses will be loaded down
because all of the peripheral IC's are are loading them down.
Next float U13101 (3 & 4) these are the "RUN" data and clock pins from the
U13101 CPU.
Next apply power to the set. No need to turn on the television.
Next measure the solder foils or lands where U13101 (3 & 4) were connected.
The buses are supposed to be pulled high by one external pull up resistor
R13166 and R13169 on the each line. They both lines should measure between 5
~ 5.3 volts. If not, you will need to find out why. It has been my
experience that one or the other is low. It is possible both may be low too
but if so you will probably find as common reason. I.E. cracked board, board
contamination, missing B+ to a peripheral.
Finding the load can be tricky. On two out of five occasions these lines did
not measure a low resistance to ground. Instead they measured about 13K each
using a Fluke 78 meter. But an analogue meter gave different readings on the
bad line, 3K on the bad compared to 10K on the good line. The other two
televisions had solder bridges in the tuner assembly that caused the lines
to be held to ground, and the last Television had a defective Audio MTS
decoder IC U11601. Apparently on the last chassis the Stereo decoder did not
send an acknowledgment to the CPU after the first polling of the
peripherals. Note: If this chassis does not receive a ACK from each
peripheral the set will not turn on and it will log an error relative to the
defective peripheral.
Once it has been determined which bus is low, locate jumper wires that
relate to the appropriate bus and desolder them one at a time. Always
checking the condition on the land of U13101. The best way is to attack this
problem is to "half" the circuit. This means measure one side, and break the
line somewhere in the middle of the circuit between the CPU and the
furthest point away. Obviously always monitor the line that's in trouble.
Disconnecting the jumpers will make it easier in the localize the branch &
isolation the peripheral or passive component responsible for the defect. Be
careful to limit movement the free end of these jumpers it may weaken the
foil on the soldered end and the pad will tear from the board.

Begin As soon as you see the troubled line go high (5.0 ~ 5.2) volts you
have found the branch. At this point you will need to follow the schematic
and isolate the active components i.e. F2PIP module, T-4 chip, Stereo
decoder. If all else fails then you may have a passive components. Chip
capacitors should not be ruled out as potential suspects.

Jumpers related to "Run" Data are JW13122, JW13124, JW13128, and JW12112
Jumper related to "Run" Clock are JW13120, JW13123, JW13127, **JC12103

** A "JC" is a Jumper Component. It may look like a small chip resistor with
the number "0" printed on it. Some manufactures call them zero ohm
resistors.




Example of a Logic "0" Data Bus Problem

I was recently involved in troubleshooting a model F36445 CTC203 where it
was determined the IIC bus was held to logic "0". After lifting jumper wire
JW12112 on the data line, the load on U13101 (4) climbed from 1.9 to 5.2
volts. This jumper coupled the data line to several passive components, in
the tuner and Stereo decoder circuit, along with active components U16601(
9) MTS decoder, and the U17401(19) tuner PLL controller. A decision had to
be made to cut a trace ( see silk screen) located adjacent to the tuner
shield, in order to isolate the short. If you have the Thomson ESI schematic
locate the tuner section. The short was located along the data bus that
controls the tuner PLL. Capacitor C17416 in the silk screen was the
culprit. Removing the capacitor and reconnecting the cut trace allowed the
data line to finally go high and the set was operating again.. Capacitor was
replaced wit part# 214029 a 43 pf surface mounted capacitor.




Clipped from another source..

#2

Place a jumper between Q14104(E & C) This will turn on the Switched 12
volts and apply power to the all the peripherals. Next, carefully remove the
pins of U13101(3 &4) and apply power to the set. Both traces on the data and
clock must be 5 volts. If it is 5 volts then no excessive loads on the Data
or clock lines exist. In this case U13101(3) was 1.9 volts. This indicated
that something that connected to the Data line was loading it down. All ICs
were isolated by removal of the data and clock pins. It was discovered that
once capacitor C17416 part # 214029 was removed the load went away. It is a
43 pf capacitor. The mystery is this capacitor did not measure leaky. It is
believed the glue that held the device in place became conductive and causes
the trouble.



Good luck

kip