Toshiba FT 8508 Service Manual
FILE NO. 2B0-9804
SERVICE MANUAL
CORDLESS TELEPHONE
FT-8508
PUBLISHED IN JAPAN, Jun., 1998
CONTENTS
SAFETY PRECAUTIONS................................................................................................................... 1
OPERATING CONTROLS.................................................................................................................. 2
ALIGNMENT PROCEDURE............................................................................................................... 3
BLOCK DIAGRAMS ........................................................................................................................... 9
SCHEMATIC DIAGRAMS ................................................................................................................ 14
TROUBLESHOOTING HINTS .......................................................................................................... 24
IC AND TRANSISTOR VOLTAGE CHART....................................................................................... 31
SEMICONDUCTOR LEAD IDENTIFICATION .................................................................................. 36
ELECTRICAL PARTS LOCATION.................................................................................................... 41
WIRING DIAGRAMS ........................................................................................................................ 46
EXPLODED VIEW AND MECHANICAL PARTS LIST ...................................................................... 48
PARTS LIST ..................................................................................................................................... 52
ASSEMBLY PARTS LIST................................................................................................................. 71
SPECIFICATIONS............................................................................................................................ 72
SAFETY PRECAUTIONS
Before returning any models to the customer, a safety check of the entire instrument should be made.
The service technician must be sure that no protective device built into the instrument by the manufacturer
has become defective or inadvertently degraded during servicing.
1. WARNING:
Alterations of the design or circuitry of these models should not be made.
Any design changes or additions such as, but not limited to, circuit modifications, auxiliary speaker
jacks, switches, grounding, active or passive circuitry, etc. may alter the safety characteristics of these
models and potentially create a hazardous situation for the user.
Any design alterations or additions will void the manufacturer’s warranty and will further relieve the
manufacturer of responsibility for personal injury or property damage resulting therefrom.
2. PRODUCT SAFETY NOTICE
Many electrical and mechanical parts in this chassis have special characteristics. These characteristics
often pass unnoticed and the protection afforded by them cannot necessarily be obtained by using
replacement components rated for higher voltage, wattage, etc. Replacement parts that have these
special safety characteristics are identified in this manual and its supplements; electrical components
having such features are identified by a
any of these components, read the parts list in this manual carefully. The use of substitute replacement
parts that do not have the same safety characteristics as specified in the parts list may create shock, fire
or other hazards.
in the schematic diagram and the parts list. Before replacing
— 1 —
HANDSET CONTROLS
OPERATING CONTROLS
BASE UNIT CONTROLS
RS
YZ
— 2 —
1
2
ALIGNMENT PROCEDURE
Test Mode For Base Unit
Press the “ ” and “#” keys at the same time about 1.5 seconds while turning the power on, the confirmation beep
will sound to indicate that the unit is in the test mode.
1. To change the TEST mode: Press the number key for the corresponding TEST mode.
(Refer to the following table)
2. To change channel: Press the “RDL” key, but if changing the step, the channel returns to the start
channel.
3. To cancel Test mode: Bell rings, charge the Handset or Power off.
STEP FUNCTION KEY START CH TX CONT TX MUTE RX MUTE RL CONT REMARKS
1 VCO/TX FRQ. ADJ 1 19 L L L L
2 TX MODE CHECK 2 19 L H L H
3TX DATA 319LLLL*1
4 RX SENS. 4 19 H L H H
5 SQ SENS. 5 19 L L H/L H
6 RING CHECK 6 19 H L L L
7 DUAL TONE CHECK 7 19 H L L H
8 DATA IN CHECK 8 19 L L L H
9
CHANNEL DATA CHECK
10 DUPLEX 0 19 L H H H
11 INT' COM MEM 19 L H H L
919HLLL*5
*
2
*
3
*
4
*1 : “0000...” (250Hz) will be fed out continuously as transmitting data.
*2 : Bell rings when sensing SQ.
*3 : Every pushing of FLASH key makes tone change.(In the case of Dual Tone, changes as 1→ 2 → 3 → 4 →5
→ 6 →7 → 8 → 9 → 0 → * → # → 1.)
DTMF Frequency
ROW1 : 697 ROW2 : 770
ROW3 : 852 ROW4 : 941
COL1 : 1209 COL2 : 1336
COL3 : 1477
*4 : Bell rings when the received data are “0000...” (250Hz).
*5 : Charge LED lights when detecting Charge ON.
Channel rotation
19 → 20 → 21 → 40 → 1 → 2 → 3 → 4 → 5 . . . . . . . . 37 → 38 → 39 → 40
↑
— 3 —
Test Mode For Handset Unit
To perform the TEST mode, turn the power ON by pressing the “ ” and “#” buttons at the same time.
When entered the TEST mode, the bell rings and the unit enters TEST mode 1 . ( Refer to the following table. )
1. To change the TEST mode: Press the number key for the corresponding TEST mode.
(Refer to the following table)
2. To change channel: Press “CH” key.
( Note: If the step is changed, the channel returns to the start channel. )
3. To cancel the TEST mode: Turn the power OFF, charge the Handset, or press the “TALK” key.
STEP FUNCTION KEY START CH TX CONT SC TX MUTE RX MUTE CONV REMARKS
1 VCO/TX FREQ. ADJ 1 21 L H H L H
2 TX MOD. CHECK 2 21 L H L L L
3TX DATA 3 21 L H L L L
4 RX SENS 4 21 H H L H L
5SQ SENS 521LHL*AL
6 RECEIVE DATA CHECK 6 21 L H L L H
7 BELL 7 21 H L L L H
8 BATTERY LOW CHECK 8 21 H L L L H
9 CHARGE CHECK 9 21 H L L L H
10 DUPLEX 0 21 L H H H L
*
1
*
2
*
3
*
4
*
5
*A : Squelch ON is H, or Squelch OFF is L.
*1 : In the TEST mode 3, “0000...” will be fed out continuously as transmitting data.
*2 : In the TEST mode 6, bell (1kHz) rings when the data received is “0000...”.
*3 : In the TEST mode 7, bell rings with initial 2 tone (2kHz, 2.2kHz).
*4 : In the TEST mode 8, bell (1kHz) rings when P_BATLOW is “L”.
*5 : In the TEST mode 9, bell rings when P_CHRGIN is “L”.
Channel rotation
21 → 20 → 19 → 40 → 1 → 2 → 3 → 4 → 5 . . . . . . . . 37 → 38 → 39 → 40
↑
— 4 —
Base Unit
Transmitter Section
Connection
Power
Meter
Frequency
Counter
Deviation
Meter
RF
Test Point
RF
Test Point
BASE RF PCB
RF
Test Point
BASE MAIN PCB
J2
DC IN
9V Jack
TEL Line
J6
Jack
DC 9V
1kHz 61.0mV
AF GEN.
AC
Adapter
Preset
Place the Base Unit in VCO/TX FREQ ADJ mode in accordance with the procedure on page 3.
Alignment Procedure
Step Adjustment Remarks
1
2
3
VR202
(TX Power)
CT201
(TX Frequency)
RT2
(TX Modulation)
Connect the Power Meter to the RF test point on the Base RF PCB. Adjust
VR202 for a
−
6.5 dBm reading o n the Power Meter.
Connect the Frequency Counter to the RF test point on the Base RF PCB.
Adjust CT201 to make sure that the frequency is 926.893873 MHz.
Press the “2” key to enter the TEST Mode 2. Connect the AF Generator to
the TEL Line Jack on the Base Main PCB. Make sure that the output is 1
kHz 61.0 mV from the AF Generator.
Connect the Deviation Meter to the RF test point on the Base RF PCB.
Adjust RT2 to indicate
±
8 kHz Dev.
AC 120V
60Hz
Alignment Point Location on Base Main PCB and Base RF PCB
Base Main PCB
RT2
Base RF PCB
CT201
— 5 —
VR202
J201
J6
TEL LINE Jack
J2
DC IN 9V Jack
RF TEST POINT
Receiver Section
Connection
RF SG
AC 120V
60Hz
BASE RF PCB
−
RF
+
Test Point
AC
Adapter
DC 9V
BASE MAIN PCB
J2
DC IN
9V Jack
TEL Line
J6
−
Jack
+
J1
AF Terminal
Dummy Load
(600-ohm)
DC Voltmeter
Preset
Place the Base Unit in RX SENS mode (step 4) in accordance with the procedure on page 3.
Alignment Procedure
Step Preset to Adjustment Remarks
Connect the RF Signal Generator to the RF test point on the Base RF
PCB. Make sure that the frequency is 902.984676 MHz.
Connect the DC Voltmeter to the J1 AF test point. Adjust L212 to indicate
DC 0.95 V.
Connect the RF Signal Generator to the RF test point on the Base RF
PCB. Make sure that the frequency is 902.984676 MHz.
Connect the AC Voltmeter across a 600-ohm dummy to the Telephone
Line Jack. Adjust R T1 for a 218 mV reading on the AC voltmeter.
Press the “5” key to enter the TEST Mode 5. Make sure that the
frequency of RF SG output is 902.984676 MHz. Adjust VR201 to turn to
the point where the bell rings.
1
SG: 1mV
No modulation
SG: 1 mV
2
1 kHz ±8kHz
deviation
SG:
3
No modulation
−7
dBµV
L212
(Discriminator
Voltage)
RT1
(RX AF
Voltage)
VR201
(SQ Point)
AC Voltmeter
Alignment Point Location on Base Main PCB and Base RF PCB
Base Main PCB
RT1
Base RF PCB
J202
AF TEST POINT
VR201
L212
— 6 —
J201
J6
TEL LINE Jack
J2
DC IN 9V Jack
RF TEST POINT
Handset Unit
Transmitter Section
Connection
Power
Meter
Frequency
Counter
Deviation
Meter
RF
Test Point
RF
Test Point
HANDSET RF PCB
RF
Test Point
HANDSET MAIN PCB
Battery
Terminals
MIC + Pin
AF GEN.
1kHz 11.0mV
DC Power Supply
DC 3.8V
Preset
Place the Handset in VCO/TX FREQ. ADJ mode in accordance with the procedure on page 4.
Alignment Procedure
Step Adjustment Remarks
1
2
3
VR502
(TX Power)
CT501
(TX Frequency)
VR601
(TX Modulation)
Connect the RF power Meter to the RF test point on the handset RF PCB.
Adjust VR502 for a −7 dBm reading on the Power Meter.
Connect the Frequency Counter to the RF test point on the handset RF
PCB. Adjust CT 501 to make sure that t he frequency is 903.085147 MHz.
Press the “2” key to enter the TEST Mode 2. Connect the AF Generator to
the MIC Connector. Make sure th at the ou tput is 1 kHz 11.0 mV from the AF
Generator.
Connect the Deviation Meter to the RF test point on the handset RF PCB.
Adjust VR601 to indicate ± 8kHz Dev.
Alignment Point Location on Handset Main PCB and Handset RF PCB
Handset Main PCB
Battery Terminals
MIC + Pin
MC601
−
+
RF PCB
VR601
CT501
— 7 —
RF TEST POINT
J501
VR502
Receiver Section
Connection
RF SG
HANDSET RF PCB
−
RF
+
Test Point
DC Power Supply
HANDSET MAIN PCB
DC 3.8V
Battery
Terminals
J602
Connector
J601
AF Terminal
SP
−
+
Dummy Load
(150-ohm)
DC Voltmeter
AC Voltmeter
Preset
Place the Handset in RX SENS mode (step 4) in accordance with the procedure on page 4.
Alignment Procedure
Step Preset to Adjustment Remarks
Connect the RF Signal Generator to the RF test point on the handset RF
PCB. Make sure that the frequency is 926.994344 MHz.
Connect the DC Voltmeter to the J601 AF test point. Adjust L512 to
indicate DC 0.95 V.
Connect the RF Signal Generator to the RF test point on the handset RF
PCB. Make sure that the frequency is 926.994344 MHz.
Connect the AC Voltmeter across a 150-ohm dummy to the SP
Connector. Adjust VR602 for a 60 mV reading on the AC Voltmeter.
Press the “5” key to enter the TEST Mode 5. Make sure that the
frequency of RF SG output is 926.994344 MHz. Adjust VR501 to turn to
the point where the bell rings.
1
SG: 1 mV
No modulation
SG: 1 mV
2
1 kHz ±8 kHz
deviation
SG:
3
1 kHz ±8 kHz
deviation
−7 dBµV
L512
(Discriminator
Voltage)
VR602
(RX AF
Output)
VR501
(SQ Point)
Alignment Point Location on Handset Main PCB and Handset RF PCB
Handset Main PCB
−
Battery Terminals
+
AF TEST POINT
RF PCB
J502
VR602
VR501
L512
— 8 —
J501
RF TEST POINT
J602
SP
Connector
Handset, Main
BLOCK DIAGRAMS
—9 —
Handset, RF
—10 —
Base, RF
—11 —
— 13 —
Base, Main
— 12 —
SCHEMATIC DIAGRAMS
— 15 —
Base, Main
— 14 —
— 17 —
Base, RF
— 16 —
— 19 —
Base, Key
— 18 —
— 21 —
Handset, Main
— 20 —
— 23 —
Handset, RF
— 22 —
TROUBLESHOOTING HINTS
1. The bell does not ring.
When the INTCOM key of
the base is pressed, does
the ringer on the handset
ring?
OK
When the TEL SG is joined
with the base to make bell
signal, is there pulse wave
at Pin 4 of IC3?
OK
Is there pulse wave at
Pin 33?
OK
Check IC18 and its
peripheral circuit.
NG
NG
NG
See 2. The bell does not
ring & page does not ring.
Check IC3 and TEL network
circuit.
Check R42, R80, R107 and
C51.
— 24 —
2. The bell does not ring & page does not ring.
Can the base and handset
be connected?
OK
Press handset DIAL key
while in TALK MODE.
Can key touch sound be
heard from the ringer?
OK
When the INTCOM key of
the base is pressed, does
Pin 8 of J1 change from
high to low?
NG
NG
NG
See 3. The base and
handset cannot be
connected.
When the key of the
handset is pressed, can the
pulse output at pin 38 of
IC603 be seen?
OK
At the Q606 collector, can
the pulse wave be seen?
OK
Check RINGER Y601.
Check KEY RUBBER.
NG
NG
Check IC603.
Check R627, R629, Q605
and Q606.
OK
Check IC18 and its
peripheral circuit.
— 25 —
3. The base and handset cannot be connected.
Check whether the base is
able to set in the test
mode 1.
OK
Check the TX POWER and
the TX FREQUENCY on
the base unit.
OK
Set the base in the test
mode 3, check whether
deviation of the TX data is
app. 7 kHz Dev.
OK
Set the base in the test
mode 8, 902.984676 MHz
(250 Hz ±7 kHz Dev.) 1 mV
output signal from RF jack
is applied.
Does the bell ring?
OK
NG
NG
NG
NG
Check IC18 and its
peripheral circuit.
Check base RF unit.
Check whether there is a
250 Hz data waveform at
Pin 9 of J1.
OK
Check base RF unit.
Check whether there is a
250 Hz data waveform at
Pin 1 of J1.
OK
Check whether there is a
250 Hz data waveform at
the Q2 collector.
NG
NG
NG
Check RT2, R22, R56, R57
R58, R59 and C18.
Check base RF unit.
Check RT1, Q2 and their
peripheral circuits.
Check whether the
handset is able to set in the
test mode 1.
OK
Check the TX POWER and
the TX FREQUENCY on
the handset unit.
OK
NG
NG
OK
Check whether there is a
250 Hz data waveform at
Pin 48 of IC18.
OK
Check IC18 and its
peripheral circuit.
Check IC603 and its
peripheral circuit.
Check handset RF unit.
NG
Check Q5, Q6 and their
peripheral circuits.
— 26 —
Set the handset in the test
mode 3, check whether
deviation of the TX data is
app. 7 kHz Dev.
OK
NG
Check whether there is a
250Hz data waveform at
Pin 9 of J601.
OK
Check handset RF unit.
NG
Check VR601, R619, R632,
R634, R635, R636
and C611.
Set the handset in the test
mode 6, 926.893873 MHz
(250 Hz ±7 kHz Dev.) 1mV
output signal from RF jack
is applied. Check whether
the bell ring.
OK
Place the handset on the
base to charge about
5 seconds, then connect
again.
NG
Check whether the 250 Hz
data wareform from Pin 1
of J601 is fed.
OK
Check whether there is a
250 Hz data waveform at
the Q601 collector.
OK
Check whether there is a
250 Hz data waveform at
Pin 40 of IC603.
OK
Check IC603 and its
peripheral circuit.
NG
NG
NG
Check handset RF unit.
Check VR602, Q601 and
their peripheral circuits.
Check Q602, Q604 and
their peripheral circuits.
— 27 —
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