Sharp 76GF-63 (serv.man2) Service Manual ▷ View online
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 45 of 80
Faults in the Audio Circuit
Faults in the audio stage are normally caused by high HT (see power supply section for more details on this fault
scenario). When the HT become excessive, it is possible for one or all of the audio output IC’s to fail. Usually,
the feed coils L350 and L351 (for IC301) and L315 and L316 (for IC302) will go open circuit as the IC draws
excessive current. The part number for these coils is VP-CD3R3K0000. Remember to also check IC1302 on the
centre speaker PWB as this also fails. The feed coils are L1302 and L1303, which have the same part number as
the main channel feed coils.
If a whistling sound is heard from the centre speaker, it could be that it is beating with either of the main audio
channel amplifiers. In this case R1312 can be changed for an 8k2Ω resistor (Sharp part number VRS-
TV1JD822J). This will change the frequency of operation of the class D amplifier and stop the beat.
If the speakers are left disconnected (left, right and centre), it is possible for the protection circuit to operate.
This can be particularly frustrating when repairing a set. As the leads connecting the speakers to the PWB are
fairly long, they can be kept in situ, even when the chassis is tilted to provide ease of service.
IC1300 on the centre speaker PWB can run hot and result in a dead set (short circuit on +16 or - 16v rails). To
reduce the operating temperature of IC1300, add jumper wires JL2 and JL3 as shown in figure 41.
Check for and if necessary re-solder dry joints on C1306. Also check the condition of IC1300 and replace if
necessary. Note that if the track is cut below IC1300 and jumper link JL1 is fitted (as in figure 45) it is not
necessary to carry out the modification as detailed in figure 46. The parts required for this improvement are
listed in the table below.
scenario). When the HT become excessive, it is possible for one or all of the audio output IC’s to fail. Usually,
the feed coils L350 and L351 (for IC301) and L315 and L316 (for IC302) will go open circuit as the IC draws
excessive current. The part number for these coils is VP-CD3R3K0000. Remember to also check IC1302 on the
centre speaker PWB as this also fails. The feed coils are L1302 and L1303, which have the same part number as
the main channel feed coils.
If a whistling sound is heard from the centre speaker, it could be that it is beating with either of the main audio
channel amplifiers. In this case R1312 can be changed for an 8k2Ω resistor (Sharp part number VRS-
TV1JD822J). This will change the frequency of operation of the class D amplifier and stop the beat.
If the speakers are left disconnected (left, right and centre), it is possible for the protection circuit to operate.
This can be particularly frustrating when repairing a set. As the leads connecting the speakers to the PWB are
fairly long, they can be kept in situ, even when the chassis is tilted to provide ease of service.
IC1300 on the centre speaker PWB can run hot and result in a dead set (short circuit on +16 or - 16v rails). To
reduce the operating temperature of IC1300, add jumper wires JL2 and JL3 as shown in figure 41.
Check for and if necessary re-solder dry joints on C1306. Also check the condition of IC1300 and replace if
necessary. Note that if the track is cut below IC1300 and jumper link JL1 is fitted (as in figure 45) it is not
necessary to carry out the modification as detailed in figure 46. The parts required for this improvement are
listed in the table below.
Reference Description
Part
Number
JF2 Jumper
VRS-TV1JD000J
JF3 Jumper
VRS-TV1JD000J
IC1300 Op-amp
IC
VHIBA4558F/-1
In the case of a dead set, caused by short circuit IC1300, it is possible to run the set by completely
disconnecting the centre speaker PWB.
Figure 45: Centre Speaker Modification 1
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 46 of 80
Figure 46: Centre Speaker PWB Modification 2
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) Chassis – Article for Television Magazine
Dolby Pro-Logic Circuit Operation
Dolby Pro-Logic functions are provided by a separate PWB on the models ending with the number 4, i.e.
66GF64H. This panel contains all the power supply, processing IC’s and output devices required for
the Dolby Pro-Logic function. The PWB is virtually identical between models, except that the GF
models route the sub-woofer output onto the main PWB as it exits the DPL processor (IC1301). It
also uses a different output on IC1301 for the sub-woofer. This means that the FW and GF PWB’s are
not interchangeable.
The power supply is identical in operation to the main chassis, but only generates four supplies. +/-17V
supply for the output amplifiers, +8V for the Dolby Pro-Logic processor and a +5V supply used for the
muting circuits. This power supply is turned off during standby by IC702 on the main chassis in the
identical way to the main power supply
A stereo signal is fed into the Dolby Pro-Logic PWB from the MSP. This is either derived from the
off air NICAM source or an external AV source. This signal is converted into a Dolby Pro-Logic signal
by IC1301 from which it is outputted to the various channel amplifiers as listed in the table below.
66GF64H. This panel contains all the power supply, processing IC’s and output devices required for
the Dolby Pro-Logic function. The PWB is virtually identical between models, except that the GF
models route the sub-woofer output onto the main PWB as it exits the DPL processor (IC1301). It
also uses a different output on IC1301 for the sub-woofer. This means that the FW and GF PWB’s are
not interchangeable.
The power supply is identical in operation to the main chassis, but only generates four supplies. +/-17V
supply for the output amplifiers, +8V for the Dolby Pro-Logic processor and a +5V supply used for the
muting circuits. This power supply is turned off during standby by IC702 on the main chassis in the
identical way to the main power supply
A stereo signal is fed into the Dolby Pro-Logic PWB from the MSP. This is either derived from the
off air NICAM source or an external AV source. This signal is converted into a Dolby Pro-Logic signal
by IC1301 from which it is outputted to the various channel amplifiers as listed in the table below.
Speaker Output IC Number Impedance
IC1301 pin – FW IC1301 pin – GF
Left IC1302
8Ω
24 – DACC1_L
24 – DACC1_L
Right IC1303
8Ω
23 – DACC1_R
23 – DACC1_R
Surround IC1304
16Ω each speaker
27 – SC1_OUT_R
31 – SC1_OUT_L
Sub-Woofer IC1305 4Ω base reflex
21 – DACC2_R
MSP (IC305) pin 31
Note that the output from the surround amplifier is connected to two 16Ω speakers. Both speakers
are connected in parallel, but in anti-phase to each other. If the front speakers are connected to the
rear speaker output, IC1304 will eventually fail. Invariably the customer will complain that the rear
speakers did not have enough volume before the IC failed.
The power supply used on this PWB is similar in operation to the main chassis, but the heatsink
containing the chopper transistor gets very hot. Sometimes it is too hot to touch - this is normal.
Figure 47: Pro-Logic PWB
Page 47 of 80
Sharp Electronics (UK) Limited - March 2003
Revision 2
DA100 (50Hz) Chassis – Article for Television Magazine
Figure 48: Dolby Pro-Logic Circuit Diagram (66GF64H)
Page 48 of 80
Sharp Electronics (UK) Limited - March 2003
Revision 2
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