Daewoo DTC-20, DTC-21, DTY-21, DTY-25 Service Manual - Important Service Notes

1. X-ray Radiation Rrecaution

1)  Excessive high voltage can produce potentially hazardous X-RAY RADIA-

TION. To avoid such hazards, the high voltage must not be above the spec-

ified limit. The nominal value of the high voltage  of this receiver is

25.5kv(20”/21”) & 23.5kv(14”)at zero beam current (minimum brightness)

under a 120V/220V AC power source. The high voltage must not, under any

circumstances, exceed 28kv(20”/21”) & 26kv(14”). Each time a receiver

requires servicing, the high voltage should be checked following the HIGH

VOLTAGE CHECK procedure on page 10 of this manual. It is recom-

mended as a parts of the service record. It is important to use an accurate

and reliable high voltage meter.

2) This receiver is equipped with X-RADIATION PROTECTION circuit which

prevents the receiver from producing an excessively high voltage even if the

B+voltage increases abnormally. Each time the receiver is serviced, X-

RADIATION PROTECTION circuit must be checked to determine that the

circuit is properly functioning, following the X-RADIATION PROTECTION

CIRCUIT CHECK procedure on page 6 of this manual.

3) The only source of X-RAY RADIATION in this TV receiver is the picture tube.

For continued X-RAY RADIATION protection, the replacement tube must be

exactly the same type tube as specified in the parts list.

4)  Some parts in this receiver have special safety-related characteristics for X-

RAY RADIATION protection. For continued safety, parts replacement

should be undertaken only after referring to the PRODUCT SAFETY

NOTICE below.

2. Safety Precaution

WARNING: Service should not be attempted by anyone unfamiliar with the

necessary precaution on this receiver. The following are the necessary precau-

tion to be observed before servicing.

1) Since the chassis of this receiver has hazardous potential to ground when-

ever the receiver is plugged in (floating chassis), an isolation transformer

must be used during servicing to avoid shock hazard.

2) Always discharge the picture tube anode to the CRT conductive coating the

picture tube. The picture tube is highly evacuated and if broken, glass frag-

ments will be violently expelled. Use shatterproof goggles and keep picture

tube away from the body while handling.

3) When placing chassis in the cabinet, always be certain that all the protective

devices are put back in place, such   as; nonmetallic control knobs, insulat-

ing covers, shields, isolation resistor-capacitor network, etc.

4) Before returning the set to the customer, always perform an AC leakage cur-

rent check on the exposed metallic parts of the cabinet, such as antennas,

terminals, screw-heads, metal overlays, control shafts etc. to be sure the set

is safe to operate without  danger of electrical shock. Plug the AC line cord

directly into a 120V AC outlet (do not use a line isolation transformer during

this check). Use an  AC voltmeter having 5000 ohms per volt or more sensi-

tivi-ty in the following manner.

Connect at 1500 ohm 10 watt resistor, paralleled by a 0.15 mfd. AC type

capacitor, between a known good earth ground (water pipe, conduit etc.)

and the exposed metallic parts, one at a time. Measure the AC voltage

across the combination of 1500 ohm resistor and 0.15 mfd capacitor. Volt-

age measured must not exceed 0.3 volts RMS. This corresponds to 0.2 mill-

liamp. AC. Any value exceeding the limit constitutes a potential shock

hazard and must be corrected immediately.

3. Product Safety Notice

Many electrical and mechanical parts in this chassis have special safety-related

characteristics. These characteristics are often passed unnoticed by a visual

inspection and the protection afforded by them cannot necessarily be obtained

by using replacement components rated for higher voltage, wattage, etc.

Replacement parts which have these special safety characteristics are identi-

fied in this manual and its supplements; electrical components having such fea-

tures are identified by shading on 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 which do not have the same

safety characteristics as specified in the parts list may create X-ray radiation or

other hazards.

4. Service Notes

1) When replacing parts or circuit boards, clamp or bend the lead wires to termi-

nals before soldering.

2) When replacing a high wattage resistor (metal oxide film resistor) in the cir-

cuit board, keep the resistor min 1/2 inch away form circuit board.

3) Keep wires away from high voltage or high temperature components.

Important Service Notes

AC VOLT METER

Good earth ground

such as d water

pipe, conduit, etc.

Place this probe

on each exposed

metallic part.

0.15uF

1500   OHM

10WATT

DAEWOO ELECTRONICS CO., LTD.

C.P.OBOX8003 SEOUL, KOREA

Tel : 82-2-360-7798

Fax : 82-2-360-7877

E-mail : G7F00E@dwe.web.co.kr

Printed in Apr. 2000