Commodore Plus 4 Uživatelský manuál stáhnout pdf (Strana 20)

Issue 6, 1984 : Computer 3

.. commodore

Model: PLUS 4

1980 COMMODORE BUSINESS MACHINES INC.

Troubleshooting Aides

NOTE: Visual inspection is critical in this unit!

•

The upright position of many of the components used on the

board can create problems. It is possible for them to be

shorted to the shield or to each other. Make sure they are

evenly spaced and do not contact the shield.

Areas of the PCB particularly vulnerable to this

problem are:

Bottom right corner - caps

Bottom center - Jl-J6

Bottom left - Q3 shorted to FB57

Top left - ferrite beads

Center - Twisted caps (just outside of RF can)

1) NO VIDEO - Absolutely no video on screen

A) Check for 5 volts

O.K. If not: 1) Check fuse

2) Check for twisted or bent caps

+ (

5 V. short to ground)

3) Check Ll

B) Check for oscillation at pin 14 of Ul

O.K. If not: 1) Check for good connection at

pin 14 of Ul

2) Check for good connection at

Rl thru R7

C) Check for LUM signal at pin 23 of Ul, at pin 4 of

the modulator, at pin 8 of the modulator, at FB3

and at pinl of CN7

O.K. If not: 1) Check for LUM signal shorted

to ground

2) Check for open traces

3) Check modulator

D) Check for reset

O.K.

E) Check for control signals:

Signal

I.C.

Signal

I.C.

AEC

R/W

AEC

CAS

MUX

Ul 9

CSI

IRQ

CSl

U20

RDY

CSO

U20

RAS

1 2 ... 15 16 17 18 19 20 21 22 23 24 25

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