Toshiba FT 8908 Service Manual

FILE NO. 2B0-9806

SERVICE MANUAL

CORDLESS TELEPHONE

FT-8908

PUBLISHED IN JAPAN, Oct., 1998

CONTENTS

SAFETY PRECAUTIONS ......................................................................................................................1

OPERATING CONTROLS.....................................................................................................................2

ALIGNMENT PROCEDURE..................................................................................................................3

BLOCK DIAGRAMS...............................................................................................................................9

SCHEMATIC DIAGRAMS....................................................................................................................14

TROUBLESHOOTING HINTS.............................................................................................................26

IC AND TRANSISTOR VOLTAGE CHART ......................................................................................... 33

SEMICONDUCTOR LEAD IDENTIFICATION.....................................................................................40

ELECTRICAL PARTS LOCATION ......................................................................................................46

WIRING DIAGRAMS ...........................................................................................................................52

EXPLODED VIEW AND MECHANICAL PARTS LIST ........................................................................54

PARTS LIST ........................................................................................................................................58

ASSEMBLY PARTS LIST ....................................................................................................................80

SPECIFICATIONS ...............................................................................................................................81

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 ‚Å in the schematic diagram and the parts list. Before replacing 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.

— 1 —

HANDSET CONTROLS

TALK/BATT LOW LED (Red)

Standby status : OFF

•

Lights ON during a phone

conversation using the handset.

Blinks when a channel is changed,

•

and during the low battery status.

TALK button

TONE button MEM (Memory) but ton

OPERATING CONTROLS

Antenna

RDL (Redial) butt on FLASH button

SPEED DIAL INDEX (back)

Dialpad (0~9, and # buttons)

CH (Channel) button

PAUSE button

BASE UNIT CONTROLS

DC IN 9V jack TEL LINE jack

Speaker LED display

OGM button ANSWER button

REPEAT button PIN button

IN USE LED CHARGE LED

POWER LED

Lights in different colors dependi ng on the operation status as follows:

•Orange: AC adaptor operation with the base battery.

•Red: AC adaptor operation without the base battery.

•Green: Base battery operation during a power failure.

Charging Contacts

Battery compartment (back)

Microphone

VOL/RING button

Tone/Pulse switch RINGER ON/OFF switch

VOLUME button DELETE button PLAY/STOP button

REC TIME switch (ANN/4/1) RING TIME switch (2/4/TS)

Antenna

MEMO 2WAY REC button SKIP button CLOCK button

PAGE button

— 2 —

ALIGNMENT PROCEDURE

Test Mode For Base Unit

Press the “PAGE” key about 1.5 seconds while turning the power on.

1. To change the TEST mode: Press the “PAGE” key with T/P switch to PULSE position.

2. To change channel: Press the “PAGE” key with T/P switch to TONE position. 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 START CH TX CONT TX MUTE RX MUTE RL CONT REMARKS

1 VCO/TX FRQ. ADJ 19 L L L L 2 TX MODE CHECK 19 L H L H 3TX DATA 19LLLL*1 4 RX SENS. 19 H L H H 5 SQ SENS. 19 L L *A H 6 SINGLE TONE CHECK 19 H L L L 7 DUAL TONE CHECK 19 H L L H 8 DATA IN CHECK 19 L L L H 9 CHANNEL DATA CHECK 19 H L L L

10 DUPLEX 19 L H H H

*A : CHARGE LED is ON when SQ ON, CHARGE LED is OFF when SQ OFF. *1 : “0000...” (250Hz) will be fed out continuously as transmitting data. *2 : CHARGE LED lights when the received data are “0000...” .

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

*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

BASE RF PCB

RF Test Point

BASE MAIN PCB

DC IN

9V Jack

TEL Line

Jack

DC 9V

AF GEN.

1kHz 77.5mV

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

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 on 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 “PAGE” 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 77.5 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 120 60Hz

Alignment Point Location on Base Main PCB and Base RF PCB

Base Main PC B

RT2

Base RF PCB

CT201

— 5 —

J201

VR202

J1 TEL LINE Ja c k

J3 DC IN 9V Jack

S1 T/P Switch

RF TEST POINT

Receiver Section

Connection

RF SG

AC 120V

60Hz

BASE RF PCB

−

Test Point

Adapter

DC 9V

BASE MAIN PCB

DC IN

9V Jack

TEL Line

−

Jack

J2 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.

Alignme nt Procedure

Step Preset to Adjustment Remarks

Connect the RF Signal Generator t o the RF t est poi nt on t he Base RF PCB. Make sure that t he f requency 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 t o the RF t est poi nt on t he Base RF PCB.

Make sure that t he f requency is 902.984676 MHz. Connect the AC Voltmeter across a 600-ohm dummy to the Telephone Line Jack. Adjust RT1 f or a 218 mV reading on the AC voltmeter.

Press the “5” key to enter the T EST Mode 5. Make sure that the frequency of RF SG output is 902. 984676 MHz. Adjust VR201 to t urn t o t he poi nt where the b el l rings.

SG: 1 mV

No modulati on

SG: 1 mV

1 kHz ±8kHz

deviation

SG:

No modulati on

−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

J201

AF TEST POINT

J202

VR201

L212

— 6 —

J1 TEL LINE Jack

J3 DC IN 9V Jack

S1 T/P Switch

RF TEST POINT

Handset Unit

Transmitter Section

Connection

Power

Meter

Frequency

Counter

Deviation

Meter

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

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 tha t the 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

−

VR601

RF PCB

CT501

VR502

— 7 —

RF TEST POINT

J501

Receiver Section

Connection

RF SG

HANDSET RF PCB

−

Test Point

DC Power Supply

HANDSET MAIN PCB

DC 3.8V

Battery

Terminals

J602

Connector

J601 AF Terminal

− +

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.

Alignme nt Procedure

Step Preset to Adjustment Remarks

Connect the RF Signal Generator t o the RF test point on the handset RF PCB. Make sure that t he frequency is 926.994344 MHz. Connect the DC Voltmeter to the J601 AF test point . Adjust L512 t o indicate DC 0.95 V.

Connect the RF Signal Generator t o the RF test point on the handset RF PCB. Make sure that t he frequency is 926.994344 MHz. Connect the AC Voltmeter across a 150-ohm dummy to the SP Connector. Adjust VR602 for a 60 mV (Normal) reading on the AC Voltmeter.

Press the “5” key to enter the T EST Mode 5. Make sure that the frequency of RF SG output is 926. 994344 MHz. Adjust VR501 to t urn t o t he poi nt where the b el l rings.

SG: 1 mV

No modulati on

SG: 1 mV

1 kHz ±8 kHz

deviation

SG:

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

−

VR602

RF PCB

J502

VR501

L512

— 8 —

RF TEST POINT

J501

J602 SP Connector

BLOCK DIAGRAMS

— 9 — — 10 —

Base, Main

Base, RF

— 11 —

Handset, Main

— 12 —

Handset, RF

— 13 —

SCHEMATIC DIAGRAMS

Base, Main

— 14 — — 15 —

Base, RF

— 16 — — 17 —

Base, Key

— 18 — — 19 —

Base, DSP

— 20 — — 21 —

Handset, Main

— 22 — — 23 —

Handset, RF

— 24 — — 25 —

TROUBLESHOOTING HINTS

1. The bell does not ring.

When the PAGE key of the base is pressed, does the ringer on the handset ring?

When the TEL SG is joined with the base to make bell signal, is there pulse wave at Pin 4 of IC7?

Is there pulse wave at Pin 21 of IC22?

Check IC22 and its peripheral circuit.

See 2. The bell does not ring & page does not ring.

Check IC7 and TEL network circuit.

Check R61, R82, R83 and C53.

If you want to reset the unit to the factory settings

You can cancel the OGM, PIN, and the clock settings by the following process. 1 Disconnect the AC adapter and telephone line cord from the base. Also remove the battery pack from the base

unit. Keep the AC adaptor connected to the wall outlet. Make sure that the telephone line cord remains disconnected during this procedure.

2 While pressing the DELETE button, plug the AC power adaptor into the base. Keep pressing the DELETE

button for more than 4 seconds. A beep sounds and “88” blinks in the LED display.

To resume using the unit, connect the telephone line cord and place the handset on the base.

Note: If you turn on the unit again, “88” may flash.

— 26 —

2. The bell does not ring & page does not ring.

Can the base and handset be connected?

Press handset DIAL key while in TA LK MODE. Can key touch sound be heard from the ringer?

When the PAGE key of the base is pressed, does Pin 24 of IC22 change from high to low?

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?

At the Q606 collector, can the pulse wave be seen?

Check RINGER Y601.

Check DSP unit.

Check IC603.

Check R627, R629, Q605 and Q606.

Check IC22 and its peripheral circuit.

— 27 —

3. The base and handset cannot be connected.

Check whether the base is able to set in the test mode 1.

Check the TX POWER and the TX FREQUENCY on the base unit.

Set the base in the test mode 3, check whether deviation of the TX data is app. 7 kHz Dev.

Set the base in the test mode 8, 902.984676 MHz (250 Hz ±7 kHz Dev.) 1 mV output sig nal from RF jack is applied. Does the bell ring?

Check IC22 and its peripheral circuit.

Check base RF unit.

Check whether there is a 250 Hz data waveform at Pin 9 of J2.

Check base RF unit.

Check whether there is a 250 Hz data waveform at Pin 1 of J2.

Check whether there is a 250 Hz data waveform at the Q1 collector.

Check R37, R38, R39 R68, R69 and C27.

Check base RF unit.

Check RT1, Q1 and their peripheral circuits.

Check whether the handset is able to set in the test mode 1.

Check the TX POWER and the TX FREQUENCY on the handset unit.

Check whether there is a 250 Hz data waveform at Pin 38 of IC22.

Check IC22 and its peripheral circuit.

Check IC603 and its peripheral circuit.

Check handset RF unit.

Check Q9, Q10 and their peripheral circuits.

— 28 —

Set the handset in the test mode 3, check whether deviation of the TX data is app. 7 kHz Dev.

Check whether there is a 250Hz data waveform at Pin 9 of J601.

Check handset RF unit.

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.

Place the handset on the base to charge about 5 seconds, then connect again.

Check whether the 250 Hz data wareform from Pin 1 of J601 is fed.

Check whether there is a 250 Hz data waveform at the Q601 collector.

Check whether there is a 250 Hz data waveform at Pin 40 of IC603.

Check IC603 and its peripheral circuit.

Check handset RF unit.

Check VR602, Q601 and their peripheral circuits .

Check Q602, Q604 and their peripheral circuits .

— 29 —

4. Cannot make a phone call (pulse).

Can the base and handset be connected?

While in TALK MODE, press dial key of the handset. Check whether squar e waveform from pin 13 of IC22 is fed.

Check Q5, RL1 and their peripheral circuits.

See 3. The base and handset cannot be connected.

Check IC22.

5. Cannot make a phone call (tone).

Can the base and handset be connected?

While in TALK MODE, press dial key of the handset. Can tone waveform from pin 1of IC22 be fed?

Can tone signal be heard from the handset speaker?

Check the base TEL-line circuit and RELAY control circuit.

See 3. The base and handset be cannot be connected.

Check IC22.

Check IC6, Q2 and their peripheral circuits.

— 30 —

+ 55 hidden pages