Philips A02U AA Скачать руководство пользователя страница 18

Страница: 18 / 118

Service Modes, Error Codes, and Fault Finding

EN 18

A02U AA

Figure 5-7 Flash Protection

5.7.5

Hardware Related Protections

Due to the architecture (read: "hot" deflection), some
protections cannot be sensed by the microprocessor. These
protections will lead to a protection on set level (Standby mode
and blinking LED).

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. This prevents further
arcing.

Vertical Protection
If the frame stage generates no pulses, TS7641 will block.
TS7443 is now switched "on", which will lead to Standby mode.
Therefore, in normal operation condition, TS7641 and TS7652
are conducting, while TS7443 is blocked.

EW protection
Several faults in the defection circuit can cause excessive
currents through MOSFET 7480. The temperature of this
device can become too high, causing an unsafe situation. The
power supply is shut down in the above-mentioned way.
Caution: All hardware deflection protections can be disabled
by interrupting R3403 on the LSP.
However, be careful: unsafe situations (heat) can occur or the
picture tube can be destroyed.

Bridge coil protection
According safety regulations, every coil may be short-circuited.
By doing this in the secondary winding of coil L5422, high
currents will flow in the winding. With no safety circuit, the coil
will begin to burn soon.
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.
Note: Maximum EW width settings can also cause a
protection.

5.8

Repair tips

5.8.1

Miscellaneous

The relay you hear when you switch the set "on" (from Standby
or via the AC power switch), is from the degaussing circuitry. It
is not used for switching the Power Supply (as done in the MG-
chassis).

•

Where the circuitry was too "crowded" for service printing,
you can find the correct location on the "test point
overviews" in this manual.

•

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/Shut-down Sequence

For a detailed description, see chapter 9 " Circuit Descriptions,
Abbreviation List, and IC Data Sheets".

5.8.3

ComPair

This chassis does not have an IR transmitting LED (as in MG-
sets). Therefore, a "Service" (ComPair) connector is
implemented at the rear side of the set, which is directly
accessible. In addition to this, there is also a blinking LED
procedure to show the contents of the error buffer.

When you use ComPair, you have the possibility to activate a
"stepwise start-up" mode. With this mode, you can initiate the
start-up sequence step by step. This also means that in certain
steps, some protections are not activated. This is sometimes
very convenient during repair.

5.8.4

Protections

Activating SDM via the "service pads" will overrule the
processor-controlled protections, but not the hardware
protections.
Caution: When doing this, the service technician must know
what he is doing, as it could lead to damaging the set.

The "ARC"- and/or "BRIDGECOIL" protection are hardly ever
triggered, however:

•

When you suspect the "ARC" protection, look for bad
solder joints and smell. By interrupting resistor 3497, this
protection is disabled (special attention needed!).

•

When you suspect the "BRIDGECOIL" protection, which
can also be due to a too wide picture amplitude, shorten G
and S of the E/W MOSFET 7480. This will disable the
protection. You will now have minimal horizontal amplitude.
Re-align the horizontal amplitude in the SAM menu and
remove the G/S short of TS7480.

FLASH

DOP

ADOC

BCL

NOHFB

XPROT

ADC
KEYBOARD

MPIF_IRQ

MIPS CORE

-Ve

Threshold

+Ve