TOSHIBA ft8939 Service Manual

FILE NO. 2B0-9904

SERVICE MANUAL

CORDLESS TELEPHONE

FT-8939

PUBLISHED IN JAPAN, Sep., 1999

CONTENTS

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

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

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

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

SCHEMATIC DIAGRAMS..........................................................................................................12

TROUBLESHOOTING HINTS ................................................................................................... 18

IC AND TRANSISTOR VOLTAGE CHART ............................................................................... 25

SEMICONDUCTOR LEAD IDENTIFICATION........................................................................... 31

ELECTRICAL PARTS LOCATION............................................................................................. 34

WIRING DIAGRAMS .................................................................................................................37

EXPLODED VIEW AND MECHANICAL PARTS LIST............................................................... 40

PARTS LIST............................................................................................................................... 44

ASSEMBLY PARTS LIST .......................................................................................................... 60

SPECIFICATIONS ..................................................................................................................... 61

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 manufacture
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 indentified by a 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

OPERATING CONTROLS

HANDSET CONTROLS AND FUNCTIONS

Antenna

TALK/BATT.LOW LED

TALK Button

TONE Button

MEM (Memory) Button

PAUSE Buttons

One-touch dialing Button

( MEM1 - MEM3 )

Rechargeable Battery Pack
(back)

BASE UNIT CONTROLS AND FUNCTIONS

DC in 9V Jack

TEL LINE Jack

REDIAL Button

FLASH Button

Dialpad (0~9, ∗ and # buttons)
VOL/RING Button

CH Button
MUTE Button

Charging Contacts

T-P(TONE-PULSE) Switch
Ringer ON/OFF Switch

Speaker

OGM Button

ANSWER Button

REPEAT Button

PIN Button

IN USE LED

CHARGE LED

POWER LED

Antenna
LED Display
VOLUME Buttons

DELETE Button
MEMO / 2WAY REC Button

PLAY / STOP Button
PAGE Button

SKIP Button
Rec Time Switch (ANN/4/1)
CLOCK Button
Ring Time Switch (2/4/TS)

SPEAKER Button
Speaker LED

Microphone

2

ALIGNMENT PROCEDURE

Test Mode For Base Unit

Press the “PAGE” k ey about 3.0 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

1

VCO/TX FRQ. ADJ

2

TX MODE CHECK

3

TX DATA

4

RX SENS.

5

SQ SENS.

6

SINGLE TONE CHECK

7

DUAL T ONE CHECK

8

DATA IN CHECK

9

CHANNEL DATA CHECK

10

*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...”.

DUPLEX

FUNCTION

START CH

19
19
19
19
19
19
19
19
19
19

TX CONT

L
L
L

H

L
H
H

L
H

L

TX MUTE

L

H

L
L
L
L
L
L
L

H

Channel rotation

19ð20ð21ð40ð1ð25ð2ð3........24ð26........38ð39ð40

RX MUTE

L
L
L

H

*A

L
L
L
L

H

RL CONT

L

H

L
H
H
H
H

L

L
H

REMARKS

*1

*2

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 follwing table.)

1. To change the TEST mode: Press the number key for the corresponding TEST mode.
(Refer to the follo wing tab le)

2. To change channel: Press “CH” k ey.
(Note: If the step is changed, the channel return to the start channel.)

3. To cancel Test mode: Turn the power OFF, charge the Handset , or press the “TALK” key .

STEP

1
2
3
4
5
6
7
8
9

10

*A : Squelch ON is H, or Squelch OFF is L.
*1 : In the TEST mode 3, “0000...” will be f ed out contin uously as transmitting data.
*2 : In the TEST mode 6, bell (2kHz, 2.2kHz) 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 (2kHz, 2.2kHz) rings when P_BATLOW is “L”.
*5 : In the TEST mode 9, bell (2kHz, 2.2kHz) rings when P_CHRGIN is “L”

FUNCTION
VCO/TX FRQ. ADJ
TX MOD . CHECK
TX DATA
RX SENS
SQ SENS
RECEIVE DATA CHECK
BELL
BATTER Y LOW CHECK
CHARGE CHECK
DUPLEX

KEY

1
2
3
4
5
6
7
8
9
0

START CH

21
21
21
21
21
21
21
21
21
21

TX CONT

L
L
L

H

L

L
H
H
H

L

SC

H
H
H
H
H
H

L
L
L

H

TX MUTE

L

H

L
L
L
L
L
L
L

H

RX MUTE

*A

Channel rotation

21ð20ð19ð40ð1ð25ð2ð3........24ð26........38ð39ð40

CONV
L
L
L

H

L
L
L
L

H

H

L
L
L

L
H
H
H
H

L

REMARKS

*1

*2
*3
*4
*5

4

Base Unit

Transmitter Section

Connections

Preset

Place the Base Unit in VCO/TX FREQ.ADJ mode in accordance with the procedure on page 3.

Alignment Procedure

Power

Meter

Frequency

Counter

Deviation

Mater

RF
Test Point

RF
Test Point

BASE Unit

J4
DC IN
9V Jack

TEL Line

Jack

J1

1kHz 77.5mV

AF GEN.

AC

Adapter

AC 120V
60Hz

step

1

2

Adjustment

RT301

(TX P ower)

CT1

(TX Frequency)

Remarks

Connect the Power Meter to the RF test point on the Base MAIN PCB.
Adjust RT301 for a -6.0dBm reading on the Power Meter.

Connect the Frequency Counter to the RF test point on the Base MAIN
PCB. Adjust CT1 to make sure that the frequency is 926.897468 MHz.

Press the “PAGE” k e y to enter the TEST Mode 2. Connect the AF Generator

3

RT3

(TX Modulation)

to the TEL Line Jack on the Base Main PCB. Mak e 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 MAIN PCB .
Adjust RT3 to indicate ±8 kHz Dev.

Alignment Point Location on Base Main PCB and Base RF PCB

Base Main PCB

J1
TEL LINE Jack

J4
DC IN 9V Jack

T

S2
T/P Switch

P

CT1

RT3

Base RF PCB

RT301

RF Test Point

5

Receiver Section

Connections

RF SG

­+

RF
Test Point

TEL Line

Jack

J1

Dummy Load

(600-ohm)

­+

AC V oltmeterBASE Unit

AC 120V

60Hz

AC

Adapter

DC IN 9V Jack

J4

AF
Test Point

DC V oltmeter

Preset

Place the Base Unit in RX SENS mode (step 4) in accordance with the precedure on page 3.

Alignment Procedure

step

Preset to

1

SG: 1mV

No modulation

SG: 1mV

2

1 kHz ±8kHz

deviation

SG: -6.0 dB

3

1kHz ±8kHz

Deviation

Adjustment

(Discriminator

Voltage)

(RX AF

Voltage)

µµ

µV

µµ

(SQ Point)

L4

RT2

RT1

Remarks

Connect the RF Signal Generator to the RF test point on the Base MAIN
PCB. Make sure that the frequency is 902.952467 MHz.
Connect the DC Voltmeter to the AF test point. Adjust L4 to indicate DC

1.00 V .
Connect the AC Voltmeter across a 600-ohm dummy to the Telephone Line

Jack. Adjust RT2 for a 245 mV reading on the AC voltmeter.
Press the “PAGE” key to enter the TEST Mode 5. Make sure that the

frequency of RF SG output is 902.952467 MHz. Adjust RT1 to turn to the
point where the bell rings.

Alignment Point Location on Base Main PCB and Base RF PCB

Base Main PCB

RT2

RT1

L4

AF Test Point

RF Test Point

J1
TEL LINE Jack

J4
DC IN 9V Jack

T

S2
T/P Switch

P

6

Handset Unit

Transmitter Section

Connection

Power

Meter

Frequency

Counter

Deviation

Mater

RF
Test Point

RF
Test Point

HANDSET Unit

J401
Battery
Connector

MIC+Pin

DC 3.8V

AF GEN.

1kHz 9mV

DC Power Supply

Preset

Place the Handset in VCO/TX FREQ. ADJ mode in accordance with the procedure on page 4.

Alignment Procedure

step

1

2

3

Adjustment

RT501

(TX P ower)

CT401

(TX Frequency)

RT403

(TX Modulation)

Remarks

Connect the RF power Meter to the RF test point on the handset MAIN PCB.
Adjust RT501 for a -7.5dBm reading on the Power Meter.

Connect the Frequency Counter to the RF test point on the handset MAIN
PCB. Adjust CT401 to make sure that the frequency is 903.052467 MHz.

Press the “2” key to enter the TEST Mode 2. Connect the AF Generator to
the MIC Connector. Make sure that the output is 1kHz 9mV from the AF
Generator.
Connect the Deviation Meter to the RF test point on the handset MAIN PCB.
Adjust RT403 to indicate ±8 kHz De v.

Alignment Point Location on Handset Main PCB and Handset RF PCB

Handset PCB

MC401

J401

RT403

CT401

7

RF PCB

RT501

RF Test Point

Receiver Section

Connections

RF SG

DC Power Supply

­+

Battery

Connector

DC 3.8V

RF
Test Point

J603

Terminal

Dummy Load

SP

­+

AF
Test Point

(150-ohm)

DC V oltmeter

Preset

Place the Handset in RX SENS mode (step 4) in accordance with the procedure on page 4.

Alignment Procedure

step

Preset to

1

SG: 1mV

No modulation

SG: 1mV

2

1 kHz ±8kHz

deviation

Adjustment

L402

(Discriminator

Voltage)

RT402

(RX AF

Voltage)

Remarks

Connect the RF Singal Generator to the RF test point on the handset MAIN
PCB. Make sure that the frequency is 926.997467 MHz.
Connect the DC Voltmeter to the AF test point. Adjust L402 to indicate
DC 1.00 V.

Connect the RF Signal Generator to the RF test point on the handset MAIN
PCB. Make sure that the frequency is 926.997467 MHz.
Connect the AC Voltmeter across a 150-ohm dummy to the SP Connector.
Adjust RT402 for a 128 mV (Medium) reading on the AC Voltmeter.

AC V oltmeterHANDSET Unit

SG: -6.0 dB

3

1kHz ±8kHz

Deviation

µµ

µV

µµ

RT401

(SQ Point)

Press the “5” k e y to enter the TEST Mode 5. Make sure that the frequency
of RF SG output is 926.997467 MHz. Adjust RT401 to turn to the point
where the indication is just vibrated.

Alignment Point Location on Handset Main PCB and Handset RF PCB

Handset PCB

J401

L402

RT402

RT401

AF Test Point

RF Test Point

RF PCB

(-)

SP Terminal

(+)

8

Base Unit, Main

BLOCK DIAGRAMS

9

Base Unit, DSP

10

Handset

11

Base Unit, Main

SCHEMATIC DIAGRAMS

12

13

Base Unit, Key

14

15

Handset

16

17

TROUBLESHOOTING HINTS

1. The bell does not ring.

When the PAGE SW 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 IC2?

OK

Is there pulse wave at
pin 21 of IC11?

OK

Check IC11 and its
peripheral circuit.

NG

NG

NG

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

Check IC2 and TEL network
circuit.

Check R78,R82,R94 and
C76.

If you want to reset the unit to the factroy settings

You can cancel the OGM, PIN, and the clock settings by the following process.
1 Disconnect the AC adaptor and telephone line cord from the base. Keep the AC adaptor connected to the wall

outlet. Make sure that the telephone line cord remains disconnected furing 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 “ P” 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, “ P” may flash.

18

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 PAGE SW of the
base is pressed, does pin24
of IC11 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 IC404 be seen?

OK

At the Q408 collector, can the
pulse wave be seen?

OK

Check RINGER Y401.

Check DSP unit.

NG

NG

Check IC404.

Check R454, R457, Q409,
Q408 and D402.

OK

Check IC11 and its periph­eral circuit.

19

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. 8.5 kHz Dev.

OK

Set the base in the test
mode 8, 902.952467
MHz (250 Hz ±8 kHz
Dev.) 1mV output signal
from RF test point is
applied. Does the
CHARGE LED light?

OK

NGACheck IC11 and its

peripheral circuit.

NG

Check base RF unit.

Check whether there is a

NG

250 Hz data wavef orm at
“MOD” of RF unit.

OK

Check base RF unit.

NG Check whether there is a

250 Hz data wavef orm at
RT2 AF test point.

OK

Check whether there is a
250 Hz data wavef orm at
the Q2 collector.

OK

Check RT3, R30, R76,

NG

R77, R91, R49, C122,
C33 and C52.

Check IC3, Q1 and their

NG

peripheral circuit.

Check RT2, Q2 and their

NG

peripheral circuit.

OK

NG

Check base RF unit.

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

Check whether there is a
250 Hz data wavef orm at
pin 38 of IC11.

OK

Check IC11 and its
peripheral circuit.

NG Check IC404 and its

peripheral circuit.

NG

Check handset RF unit.

Check IC1 and its

NG

peripheral circuit.

20

A

Set the handset in the
test mode 3, check
whether deviation of the
TX data is app. 8.5 kHz
Dev.

OK

Set the handset in the
test mode 6, 926.997467
MHz (250 Hz ±8 kHz
Dev.) 1mV output signal
from RF test point 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 there is a

250 Hz data wav eform at
“MOD” of RF unit.

OK

Check handset RF unit.

Check whether the 250

NG

Hz data waveform from
pin 9 of IC401 is fed.

OK

Check whether there is a
250 Hz data wavef orm at
the Q402 collector.

OK

Check whether there is a
250 Hz data wavef orm at
pin 40 of IC404.

OK

Check RT403, R441,

NG

R442, R443, R444,
R445 and C453.

Check IC401, Q401 and

NG

their peripheral circuit.

Check RT402, Q402 and

NG

their peripheral circuit.

Check R428, R429,

NG

IC403 and their
peripheral circuit.

OK

NG

Check handset RF unit.

Check IC404 and its
peripheral circuit.

21