Teac CTM6845, Service Manual

. 

3

1.SAFETY PRECAUTIONS 

1.

The design of this product contains special hardware, many 
circuits and components specially for safety purposes. For 
continued protection, no changes should be made to the 
original design unless authorized in writing by the 
manufacturer. Replacement parts must be identical to those 
used in the original circuits. Service should be performed by 
qualified personnel only. 

 
2.

Alterations of the design or circuitry of the products should 
not be made. 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. 

 
3.

  Many electrical and mechanical parts in the products have 
special safety-related characteristics. These characteristics are 
often not evident from visual inspection nor can the protection 
afforded by them necessarily be obtained by using 
replacement components rated for higher voltage, wattage, etc. 
Replacement parts which have these special safety 
characteristics are identified in the parts list of Service 
manual. 

Electrical components having such features are identified 

by shading on the schematics and by ( 

！

    ) on the parts list in 

Service manual.

 The use of a substitute replacement which does 

not have the same safety characteristics as the recommended 
replacement part shown in the parts list of Service manual 
may cause shock, fire, or other hazards 

 
4.

Don’t short between the LIVE side ground and ISOLATED 
(NEUTRAL) side ground or EARTH side ground when repairing.

Some model’s power circuit is partly different in the GND. 
The difference of the GND is shown by the LIVE: (      ) side 
GND, ISOLATED (NEUTRAL) : (   ) side GND and 
EARTH : (    ) side GND. Don’t short between the LIVE 
side GND and ISOLATED (NEUTRAL) side GND or EARTH 
side GND and never measure with a measuring apparatus 
(oscilloscope etc.) the LIVE side GND and ISOLATED 
(NEUTRAL) side GND or EARTH side GND at the same time. 
If above note will not be kept, a fuse or any parts will be 
broken. 

 
5.

If any repair has been made to the chassis, it is recommended 
that the B1 setting should be checked or adjusted (See 
ADJUSTMENT OF B1 POWER SUPPLY). 

 
6.

The high voltage applied to the picture tube must conform 
with that specified in Service manual. Excessive high voltage 
can cause an increase in X-Ray emission, arcing and possible 
component damage, therefore operation under excessive high 
voltage conditions should be kept to a minimum, or should be 
prevented. If severe arcing occurs, remove the AC power 
immediately and determine the cause by visual inspection 
(incorrect installation, cracked or melted high voltage harness, 
poor soldering, etc.). To maintain the proper minimum level of 
soft X-Ray emission, components in the high voltage circuitry 
including the picture tube must be the exact replacements or 
alternatives approved by the manufacturer of the complete 
product. 

 
7.

Do not check high voltage by drawing an arc. Use a high 
voltage meter or a high voltage probe with a VTVM. 
Discharge the picture tube before attempting meter 
connection, by connecting a clip lead to the ground frame and 

connecting the other end of the lead through a 10k

Ω

 2W 

resitor to the anode button. 

 
8.

When service is required, observe the original lead dress. 
Extra precaution should be given to assure correct lead dress 
in the high voltage circuit area. Where a short circuit has 
occurred, those components that indicate evidence of 
overheating should be replaced. Always use the   

9.

manufacturer’s replacement components. 

10.

Isolation Check 
(Safety for Electrical Shock Hazard)

After re-assembling the product, always perform an isolation 
check on the exposed metal parts of the cabinet (antenna 
terminals, video/audio input and output terminals, Control 
knobs, metal cabinet, screwheads, earphone jack, control 
shafts, etc.) to be sure the product is safe to operate without 
danger of electrical shock. 

11.  

The surface of the TV screen is coated with a thin film which 

can easily be damaged. Be very careful with it when handle the 
TV.

Should the TV screen become soiled, wipe it with a soft 

dry cloth. Never rub it forcefully. Never use any cleaner or 
detergent on it.

 
(1)

Dielectric Strength Test 

The isolation between the AC primary circuit and all metal 
parts exposed to the user, particularly any exposed metal part 
having a return path to the chassis should withstand a voltage 
of 3000V AC (r.m.s.) for a period of one second. 
(…Withstand a voltage of 1100V AC (r.m.s.) to an appliance 
rated up to 120V, and 3000V AC (r.m.s.) to an appliance rated 
200V or more, for a periode of one second.) 
This method of test requires a test equipment not generally 
found in the service trade. 

(2)

Leakage Current Check 

Plug the AC line cord directly into the AC outlet (do not use a 
line isolation transformer during this check.). Using a 
“Leakage Current Tester”, measure the leakage current from 
each exposed metal part of the cabinet, particularly any 
exposed metal part having a return path to the chassis, to a 
known good earth ground (water pipe, etc.). Any leakage 
current must not exceed 0.5mA AC (r.m.s.). 
However, in tropical area, this must not exceed 0.2mA AC 
(r.m.s.). 

●

Alternate Check Method 

Plug the AC line cord directly into the AC outlet ( do not use a 
line isolation transformer during this check.). Use an AC 
voltmeter having 1000 ohms per volt or more sensitivity in the 

following manner. Connect a 1500

Ω

 10W resistor paralleled 

by a 0.15

μ

F AC-type capacitor between an exposed metal part 

and a known good earth ground (water pipe, etc.). Measure 
the AC voltage across the resistor with the AC voltmeter. Move 
the resistor connection to each exposed metal part, 
particularly any exposed metal part having a return path to 
the chassis, and measure the AC voltage across the resistor. 
Now, reverse the plug in the AC outlet and repeat each 
measurement. Any voltage measured must not exceed 0.75V 
AC (r.m.s.). This corresponds to 0.5mA AC (r.m.s.). 
However, in tropical area, this must not exceed 0.3V AC 
(r.m.s.). 
This corresponds to 0.2mA AC (r.m.s.)