Philips EM5A NTSC Service Manual page 29

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3. Via the 'SUP-ENABLE' signal, the Main Supply is switched
"on" and will deliver the VBAT to the Line deflection stage
[2].
4. EHT generation is now started.
5. The OTC will un-blank the picture.
6. When you switch the set "off," this is performed in a
controlled way via the POR signal [3].
5.8.3 ComPair
This chassis does not have an IR transmitting LED (as in MG
sets.) Therefore, a "Service" (ComPair) connector which is
directly accessible, is located on the rear side of the set,. (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 (see the 'Stepwise Start-up /
Shutdown' section.)
5.8.4 Protections
There are "service pads" located on the SSB (items 9005 and
9006, outside the shielding), to force the set into SAM or SDM
(see the figure "SSB removal (part 3)" in the 'Disassembly'
section.) This will override the processor-controlled
protections, but not the hardware protections. This means that
the A/D-input protections (5 V and 8 V) and the I
acknowledging" info of the feature box (FBX) and of the Tuner
are overruled.
Caution: When doing this, the service technician must know
what he is doing and be careful, since a mistake could damage
the set.
The ARC protection and/or BRIDGECOIL protection are very
rarely 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 is needed!)
When you suspect the BRIDGECOIL protection, which can
also be due to an overly wide picture amplitude, short G and S
of the E/W MOSFET 7480. This will disable the protection. You
will now have minimal horizontal amplitude. Realign the
horizontal amplitude in the SAM menu and remove the G/S
short of TS7480.
5.8.5 Main Supply
The simplest way to repair the main supply is to check and
replace if necessary the gray marked components on the Main
Supply.
This is the more detailed method:
1. Replace FET 7504 and zener 6505.
2. Remove the SSB panel.
3. Short B and E of TS7529, in order to put the Main Supply
in "on" mode (TS7529 is then blocking.)
Caution: To prevent R3403 and TS7443 from damage,
disable the HW-protection of the deflection circuit first. To
do this, short circuit C2642 on the LSP (diagram A4.)
4. Attach a load of 500 Ω to VBAT capacitor C2515 (the
supply can not work without a minimum load.)
5. Use a variac, and slowly increase the VMAINS. Measure
over sensing resistors R3514/3515 if a steady sawtooth
voltage develops.
6. Also measure the VBAT. This should never exceed +141
V. If it does, there is something wrong in the feedback
circuitry (for example, regulator 7506.)
Service Modes, Error Codes and Fault Finding
2
C "not-
EM5A NTSC
Note: Be careful when measuring the gate of FET TS7504.
This circuitry is very high ohmic and can be damaged easily
(first connect ground to measuring equipment, than measure
the gate.)
5.8.6 Standby Supply
The simplest way to repair the standby supply is to check and
replace if necessary the gray marked components on Standby
Supply.
5.8.7 Line Deflection
The simplest way to repair the line deflection is to check and
replace if necessary the gray marked components on Line
Deflection circuitry.
5.8.8 Frame Deflection
Caution: When the Frame Deflection circuitry is suspected, one
must be careful. Because there is a DC voltage on the frame
deflection, the beam current could damage the CRT neck,
leading to a defective CRT.
The best thing to do is:
Interrupt resistors 3403 and 3404 on the CRT panel (diagram
F1), in order to remove the "filament" voltage from the tube
(there is no beam current, so there is no chance of destroying
the CRT.)
Interrupt resistor 3403 on the LSP (diagram A4) to disable the
'SUP-ENABLE' line.
Measure the functionality of the Frame stage with a multimeter
or with an oscilloscope.
After you have found the cause, exchange the defective
component (for example, TDA8177), and resolder the
interrupted resistors.
5. EN 29