IBM 2140, 2142 manual Diagnostic Aids, Using

Using

the

Check

Procedures

Failing

Parts

or

Assemblies:

The

check procedures generally help you

trace a problem to one part or assembly. The last step of

the

specific check

procedure you are using indicates that a

part

or

assembly

is

failing. You

should

inspect

the

part or

assembly

before

you

decide

to

replace

it. It

might

be loose, dirty, or in need

of

a

small

repair. The

check

procedures

might

lead you to two, or even

three, possible failing

parts

or

assemblies.

The

parts that might be failing

are listed in order of the most

probable

failure.

Measuring

Voltages:

Many

check

procedure steps instruct you to

measure

voltages

on

cable

plugs

and

electronic

board

connectors. If

you

are

asked

to measure

voltage

at

several places

on

a

plug

or

connector,

a

chart

next

to

or near the instruction indicates the number

of

the

plug

or

connector,

the

pin

numbers

you

should

measure,

the

signal

name,

and

the

correct

voltage

for

the

condition

you

are

measuring. Measure

the

voltage

only

at

the

pins

listed

in the chart. Remember to

set the meter on the correct scale

and

to

put

the

meter

leads

in

the

correct

position

for

the

voltage

you

are

asked

to

measure.

Note:

Use

frame

ground

for

the ground reference. Attach the

black

meter

(ground)

lead

to

frame

ground,

except

where

specified

otherwise.

Diagnostic Aids

This

chapter contains information outside the check procedures to help you

diagnose

a

failure

of

a

specific

part. Some

diagnostic

aids

are

resident in

the

machine, such as the Power-On Self Test (POST). The machine

performs the POST each time it is powered on. Use this information

throughout

the diagnostic

procedures. You

should become

familiar

with

the

POST

and

be

able

to

determine

if

the

machine performed

all

the

steps.

POST:

The

normal

POST

is

initiated

automatically

each time

the

system

unit

is

powered

on (when Power Management is

enabled, a

shorter

version

of

POST

is

initiated—see

“Power

Management”

on

page 1-21). The

POST

is

a series of system checks and initializations that verify the correct

operation of the base system. Two classifications of malfunctions might be

detected during the POST: critical and noncritical.

Critical malfunctionsprevent the system from operating at all, or

could

cause

incorrect

results

that are apparent

to

the

user. Examples of

critical

errors

include processor or interrupt controller malfunctions. If a critical error is detected during the POST, an attempt is made to indicate the error, and all testing halts.

General Information1-3