Service Modes, Error Codes and Fault Finding
EN 28 EM5A P/M5.
NVM, and Tuner are initialised again, to ensure the normal
picture and sound conditions of the set.
8 V and 5 V protection: The microprocessor senses the
presence of the 8 V and 5 V (via the '+5V_CON' and
'+8V_CON' lines). If one (or both) of these voltages is (are) not
present, an error code is stored in the error buffer of the NVM,
and the set is put in the protection mode.
5.7.4 HOP Related Protections
Every 200 ms, the status register of the HOP is read by the
OTC (via the I
2
C bus). If a protection signal is detected on one
of the inputs of the HOP, the relevant error bit in the HOP
register is set to “high”. If this error bit is still “high” after 1 s, the
OTC will store the error code in the error buffer of the NVM and,
depending on the relevancy of the error bit, the set will either
go into the protection mode or not.
The following protections are implemented:
• HFB (Horizontal Flyback): If the horizontal flyback is not
present, this is detected via the HOP (HFB_X-
RAY_PROT). One status bit is set to “high”. The error code
is stored in the error buffer and the set will go into the
protection mode.
• XPR (X-ray protection): If the HFB pulses are too low
(level detection), the HOP will detect this via the XPR-bit.
The error will be logged in the error buffer and the set will
go into protection mode.
Note: Both errors will be logged as HFB-failure.
5.7.5 Hardware Related Protections
Due to the architecture (“hot” deflection), some protections
cannot be sensed by the microprocessor. Three of these
protections will lead to a protection on set level (Standby mode
and blinking LED), while another will only lead to a circuit
protection.
TV-set Protection
The following fault conditions will lead to a “complete” set
protection:
• BRIDGECOIL protection: This is sensed via the 'EW'
signal going to the base of TS7652 (via R3495 and D6499).
In a normal situation, the voltage on C2498 (diagram A4) is
high and TS7652 is conducting. When bridge coil 5422
(diagram A3) is short circuited, the voltage on C2498
changes to low, which will block TS7652. In this case, also
TS7641 will block and the voltage on 2642 will rise until
TS7443 is forced in conduction. The 'SUP-ENABLE' signal
(in normal operating condition -20 V) is shorted now to
ground level, which will force the Main Power Supply to
Standby mode.
• ARC protection: If there are “open” connections (e.g. bad
solder joints) in the high-energy deflection circuitry, this can
lead to damaging effects (read: fire). For that reason, the E/
W current is sensed (via 3479//3480). If this current
becomes too high, the “thyristor” circuit (TS7653 and
TS7654) is triggered. TS7442 is switched “on” and TS7443
is forced into conduction. . The 'SUP-ENABLE' signal is
shorted now to ground level, which will force the Main
Power Supply to Standby mode.
• NON_VFB (No vertical Flyback) protection: If the frame
stage generates no pulses, TS7641 will block. TS7443 is
now switched “on”, which will lead to Standby mode. So, in
normal operation condition, TS7641 and TS7652 are
conducting, while TS7443 is blocked.
Circuit Protection
The following fault condition will lead to a “partly” set protection:
• PROT1 (DC) protection: When a DC-voltage (positive or
negative) is sensed on one of the loudspeaker outputs, the
protection circuit (TS7704, 7705, 7706 and 7707 in
diagram A6) will put the IC7700 in Standby mode (via tri-
state input pin 6).
5.8 Repair tips
5.8.1 Miscellaneous
The relay you hear when you switch the set “on” (from Standby
or via the mains switch), is from the degaussing circuitry. It is
not used for switching the Power Supply (as done in the MG-
chassis).
Take care not to touch the “hot” heatsink while disconnecting
the SSB, despite the fact that the mains cord is out of the mains
socket. There can still be an annoying rest-voltage on the
heatsink for a short while. Advice: when you remove the SSB,
disconnect the Mains cord, but keep the Mains Switch “on”.
Do not try to measure on the SSB side, which is facing the “hot”
heatsink. This is dangerous. Most service test points are
guided to the “tuner” side and are indicated by the “service”
printing. Where the circuitry was too “crowded” for this printing,
you can find the correct location on the “test point overviews”.
A very large part of the LSP is “hot”, such as:
– The primary part of the Standby Supply.
– The whole Main supply (except for the secondary Audio
supply).
– And the complete deflection circuitry (so notice that the
deflection coil is hot!!).
5.8.2 Start-up Sequence
Figure 5-3 Start-up circuitry
The start up sequence differs from other sets (e.g. MG-sets or
EM2E-sets, but is same as in EM3E-set):
1. When the set is switched “on”, the 5 and 8 V lines
(‘+5V_CON’ and ‘+8V_CON’) of the standby power supply
are activated.
2. After the OTC senses them, the µP will address the HOP
via the I
2
C-bus, to start the drive [1].
3. Via the ‘SUP-ENABLE’ signal, the Main Supply is switched
“on” and will deliver the V
BAT
to the Line deflection stage
[2].
4. EHT generation is now started.
5. The OTC will un-blank the picture.
RESET
5V
CON
8V
CON
8V
29
I
2
C BUS
5
17/39
OUT
HOP
CUTOFF
(from
CRT panel)
START/STOP
START/STOP
COLD
EHT-INFO
HOT
7131
7141
5V
8V
+11D
OTC
POR
POR
7445
106 105
99 104
STANDBY
low 7131/41 closed
high 7131/41 open
220 VAC
STBY
SUPPLY
Vbat
SUP-ENABLE
MAIN
SUPPLY
PROT-
SENSING
LINE DEFL.
(BRIDGECOIL
-PROT)
(ARC-PROT)
FRAME
DEFL
(NON-VFB)
CL16532044_023.eps
140501
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