[TechAssist] Re: CTC 169 TUNER , SAVE INFO
- From: "MONTE MONCRIEF" <DOCVIDEO.1@xxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>, <electronicrepair@xxxxxxxx>
- Date: Tue, 17 Jul 2001 17:06:05 -0700
TEC's
Here is the text for System Control, Micro Reset, RF AGC Alignment and Tuning
for
CTC169.
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------------------------------------------
System Control
The micro controller [ U3101 ] controls all functions of the Chassis. It
interprets
commands from the front control panel keyboard [ as well as remote control ] and
sends appropriate commands to various circuits of the chassis. Functions
preformed
within the micro controller are : D/A control, OSD generation, IR signal
processing,
sync presence detection, and AFT A/D conversion. Timing of communications is
controlled by a 4MHz clock internal to the micro.
The micro is responsible for channel tuning, band switching, on screen display
generation, and quasi-digital control over video and audio setup
parameters [ brightness, contrast, color, tint and volume ]. Video and audio
parameters are controlled by varying the digital outputs of the micro, which
are then
filtered to produce DC control voltages for the video and audio circuits.
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Micro Reset
The Micro Reset circuit controls pin # 1 of the micro. It consists of
resistor
R3114 , R3115 and zener diode CR 3101 with the +15V regulated source as
input
signal. The +5V standby source is derived from the +15V regulated source.
The
value of CR3101 [ 5.6V ] allows the +5V standby source to be established
before
Pin # 1 of micro becomes high. Likewise, during AC dropout, pin # 1 will go
low
before the +5V stanby source begins to drop. The purpose of R3116 and CR 3102,
connected between the reset circuit and the 4MHz oscillator, is to stop the
oscillator when the reset line voltage drops. This is to conserve the charge on
C4612 . The discharge time of C4612 is the memory retention time which is
specified
as a MINIMUM of 10 secinds. Typically the memory retention time is a few
minutes.
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RF AGC ALIGNMENT [ R2311 ]
The RF AGC control R2311 has been aligned for optimum performance over a wide
range
of Rf signal conditions. READJUSTMENT OF R2311 SHOULD NOT BE NESSESSARY
UNLESS........
1. Tuner has been replaced.
2. CTV IC U1001 has been replaced.
3. R2311 has been replaced or ADJUSTED
4. Unusual signal conditions exsit, such as cable TV adjacent
channel interference, picture bending, CHANNEL 6 color beats,
broadcast noise or weak signal conditions.
Cable TV adjacent channel interference, picture bending , and Channel 6 color
beats
are usually a result of excessive signal level, and may be improved by adjusting
R2311 to lower the gain of tuner ; however, this may result in a reduction in
S/N
ratio [ noise due to weak signal].
broadcast noise and weak signal may be improved by adjusting to increase the
gain of
tuner , however, this may result in a degradation of overload capabilities [
interference or distortion due to excessive signal ].
If the RF AGC control must be adjusted USE THE WEAKEST LOCAL BROADCAST CHANNEL
as a
signal source. After adjusting the control, check performance on all AVAILABLE
channels .
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TUNING SYSTEM
The tuning system used in this chassis is similar to the FS4 tuning system
used in
previous chassis. However, the phase-lock-loop [ PLL ] portion of the system is
now
an integral part ot the tuner SIP. Tuner band switching and tuning frequency
commands
are sent to the tuner SIP via the micro's clock and data lines and the tuner
responds
accordingly.
The AFT signal is input to the micro's internal A/D convertor [ the AFT signal
has a
negative slope ]. Tuning sync is also input to the micro and periodically
sampled
using a special sync presence detection algorithm.
The output od the sync separator is coupled with the KD3 line input at PIN # 12
of
micro in time-sharing fashion.
The first step in the tuning of AIR CHANNELS begins at nominal +156kHz. If an
AFT
voltage of less than 2V is measured, nominal -156kHz is synthesized. If the
AFT
voltage is now greater then 3V, an AFT crossover has been detected and the
nominal
frequency is synthesized.
During the SECOND step, if the less than 12V and greater than 3V criteria is
not met,
the system will sythesize nominal +3.0MHz. AT this time the system will begin
decrementing in 0.5MHz steps until an AFT crossover is detected. Once
detected, the
system checks for valid sync. After seeing valid sync, the AFT signal is
successivly
sampled to fine tune the channel. If an AFT crossover is never detected, the
system
will default to synthesizing the nominal frequency.
Tunning in the CABLE MODE is similar to AIR channel tuning with the following
exceptions.....
As in AIR channel tuning, the first step is to Synthesize nominal + 156kHz.
If the
AFT voltage is less than 2V, the nominal - 156kHz is synthesized.
If the AFT voltage is greater than 3V, a sync check is done. If sync is
present, the
nominal frequency is synthesized.
If an AFT crossover was not detected or sync was not valid, the system will
proceed
to step two in the tuning process. At this time the system will synthesize HRC
+156kHz, looking for the HRC frequency of -1.25MHz . Again, the AFT voltage
is
checked. If it is less than 3V, HRC
-156kHz is synthesized. If the AFT voltage is now greater than 3V, a crossover
is
detected and the sync is checked. If sync is valid, the nominal HRC frequency
is
synthesized. If an AFT crossover was not detected during STEP TWO, or sync was
not
valid, then the system will begin decrementing in - .5MHz steps until an AFT
crossover is detected. Once found, fine tuning is preformed similar to AIR
Tuning.
AFT is checked, at each of the 0.5MHz steps, whether sync is detected or not.
If an
AFT crossover was detected BUT no sync was, that step will be remembered. Then
at
end of SEARCH, the step where the AFT crossover was detected will be
synthesized.
This gives the system the capability to tune both offset music channels and
offset
scrambled channels which NORMALLY do not have valid video with the CARRIER.
This algorithm allows a +2.3 to - 1.9MHz offset signal without valid video to
be
tuned.
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AUTOPROGRAMMING
Autoprogramming is a feature which automatically programs the SCAN LIST by
progressively searching for channels at the ANTENNA INPUT. Autoprogramming
starts by
determining wheather the TV is connected to a CABLE SYSTEM or an " OFF-THE-AIR
"
antenna. This
ELIMINATES the need for a manual " cable/air " switch.
NOTE:
Because the system is LOOKING for valid sync, weak OFF-AIR signals
may not
be programmed. These channels can , however, be manually programmed by
selecting the
CHANNEL MEMORY feature in the SETUP MENUE.
Hope this will help ......
MONTE MONCRIEF
BAKERSFIELD , CA. 93304-3946
DOCVIDEO.1@xxxxxxxxxxxxxxxx
TEL# 10-10-811-1-661-398-1057
----- Original Message -----
From: "TechAssist Admin." <techassist@xxxxxxxxxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Tuesday, July 17, 2001 6:37 AM
Subject: [TechAssist] Re: RCA(F27201GG)CTC169CA
(Name?) Replace R3325, Possibly CR4712, U1001, & try and
adjust/re-align the AFT coil L2303. I also have a note to
check pin 36 of the "micro", it must be exactly 2.5vdc. I
assume that is after adjusting the AFT coil.
(may want to turn your CAPS LOCK off).
-Clint
http://computerhardware-consumerelectronics.com
http://orpheuscomputing.com/domain-names.html
http://orpheuscomputing.com
Clint Hamilton, Owner
Orpheus Audio/Video & Computing
Tech-Assist Administration
http://tech-assist.org
sales@xxxxxxxxxxxxxxxxxxxx
support@xxxxxxxxxxxxxxxxxxxx
purchasing@xxxxxxxxxxxxxxxxxxxx
repair@xxxxxxxxxxxxxxxxxxxx
4orpheus@xxxxxxxxxxxxx (alternates)
orpheuscomputing@xxxxxxxxx
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(PLEASE include previous correspondence
if replying to this email!!)
----- Original Message -----
From: <electronicrepair@xxxxxxxx>
To: <SERVICETALK@xxxxxxxxxxxxxxxx>
Cc: <TECHASSIST@xxxxxxxxxxxxx>
Sent: Tuesday, July 17, 2001 8:17
Subject: [TechAssist] RCA(F27201GG)CTC169CA
WILL NOT AUTO PROGRAM ALL STATIONS, EVEN IF CLEAR RECEIPTION.
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