Mitsubishi V20, V21 Service Manual

V20 Chassis

VS-A50 WS-A48 WS-A65 VS-50111 WS-48311 WS-65311 VS-60111 WS-A55 WS-65411

WS-55311 WS-73411 WS-55411

V21 Chassis

WS-48511	WS-65511	WS-73711
WS-B55	WS-65611
WS-55511	WS-65711
WS-55711	WS-65712

Down To 1 - High Speed Troubleshooting

	CONTENTS
INTRODUCTION	3
SAFETY PRECAUTIONS	4
	V20 CHASSIS
PCB FUNCTIONS AND LOCATIONS	6
TROUBLESHOOTING CHARTS
Audio	7
Video	8
Power	10
Convergence	12
ADJUSTMENT DATA
Convergence Master	13
PARTS LIST	14
	V21 CHASSIS
PCB FUNCTIONS AND LOCATIONS	15
TROUBLESHOOTING CHARTS
Audio	16
Video	17
Power	19
Convergence	21
ADJUSTMENT DATA
Convergence Master	22
PARTS LIST	23

1

2

INTRODUCTION

DOWN to 1 Goal:	Isolate the faulty component 9 out of 10 times.
Required tools:	Signal Generator such as Sencore VP300 or VP301

DOWN to 1™ High Speed Troubleshooting

The troubleshooting of any PTV chassis involves one of two methods. The first involves an exhaustive checking of all suspect DC and AC voltages, waveforms, and the like. This is all possible given the necessary time and equipment. The second occurs most frequently in field service, where time is often insufficient and equipment unavailable or impractical. It is then that all of a technician’s practical experience must be brought to bear in order to make an educated guess as to where the product failure or difficulty may lie.

This second method is the focus of this publication and the DOWN to 1 discipline.

Color, Pattern and Perception

Observation is key to an overall evaluation strategy. The details gathered from a precise observation can go a long way toward arriving at a repair solution in a timely and efficient manner. With this understanding, MDEA has brought the combined technical expertise of its years to bear in creation of the DOWN to 1™ method. For simplicity and easy memorization, color, pattern and perception are employed as the primary tools.

Color

∙Each component has its corresponding unique color.

Pattern

∙For each troubleshooting case, the component to replace is identified by an oval color pad at the terminating end of its path.

Perception

∙A perceived problem provides deductive reasoning clues to its solution.

Main

Power

Signal

Terminal

2HDW

3DYC

Jungle Conv-Gen DM Assembly CRT(s)

3

SAFETY PRECAUTIONS

NOTICE: Observe all cautions and safety related notes located inside the receiver cabinet and on the receiver chassis.

WARNING:

1.Operation of this receiver outside the cabinet or with the cover removed presents a shock hazard from the receiver's power supplies.

	Work on the receiver should not be attempted by anyone who is not thoroughly familiar with the precautions necessary when working
on	high voltage equipment.

2.Do not install, remove or handle the picture tubes in any manner unless shatterproof goggles are worn. People not so equipped should be kept away while the picture tube is being handled. Keep the picture tube away from the body while handling.

3.When service is required, observe the original lead dress. Extra precaution should be taken to assure correct lead dress in the high

voltage

area. Where a short-circuit has occurred, replace those components that indicate evidence of overheating.

X-Radiation warning

The surface of the cathode ray tubes (CRTs) may generate X-Radiation, so take proper precautions when servicing. It is recommended that a lead apron be used for shielding while handling the CRT. Use this method if possible.

When replacing the CRTs, use only the designated replacement part since it is a critical component with regard to X-Radiation. High voltage must be set as prescribed in the V21 Service Manual under the section titled Electrical Adjustments.

Leakage current check

Before returning the receiver to the customer, it is recommended that leakage current be measured according to the following methods.

1.Cold Check

With the alternating current (AC) plug removed from the AC source, place a jumper across the two AC plug prongs. Connect one lead of an ohm meter

to the AC plug and touch the other lead to each exposed metal part (i.e. antennas, handle bracket, metal cabinet, screw heads, metal overlay, control shafts, ( etc.), particularly any exposed metal part that has a return path to the chassis. The resistance of the exposed metal parts having a return path to the chassis should be a minimum of 1Mega Ohm. Any resistance below this value indicates an abnormal condition and requires corrective action.

(continued next page)

4

SAFETY PRECAUTIONS (continued from preceding page)

2.Hot Check ...Use the circuit shown below to perform the hot check test.

1.Keep switch S1 open and connect the receiver to the measuring circuit. Immediately after connection, and with the switching devices of the receiver in their operating positions, measure the leakage current for both positions of switch S2.

2.Close switch S1, energizing the receiver. Immediately after closing switch S1, and with the switching devices of the receiver in their operating positions, measure the leakage current for both positions of switch S2. Repeat the current measurements of items 1 and 2 after the receiver has reached thermal stabilization. The leakage current must not exceed 0.5 milliampere (mA).

5

V20 Chassis - PCB Functions and Locations

PCB-Terminal

PCB-Signal

PCB-Doubler

PCB-Main

PCB-Power

A/V Inputs

Control uPC

PIP-POP

Horizontal Defl.

Power Supplies

A/V Selection

Tuning

Picture Format

Vertical Defl.

High Voltage

3D-Y/C

VCJ

3:2 Pull Down

Audio Amp.

SVM

NTSC Video

Convergence

Line Double

Convergence Amps.

Decoders

Generator

480i to 480p

DBF

6

			V20 Chassis - Audio Problem
			Supply				Supply
						NO	signal to
			signal to	Check Monitor					Have audio
	Audio						different
			antenna	Output. Good					to speakers?
	problem any						line
Audio problem			input.		audio?
	or all NTSC						inputs
	sources							NO
				YES
					PWB-Main			PWB-Terminal
									YES
									PWB-Signal
Main	Power	Signal	Terminal	2HDW	3DYC	Jungle	Conv-Gen	DM Assembly	CRT(s)
					7