Commodore Plus 4 Uživatelský manuál stáhnout pdf (Strana 21)

PLUS 4 Troubleshooting Page 2

2) BAD VIDEO - Scrolling lines on screen - Random

blocks on screen - Blurred display

A) Check JI-J6 for shorts to ground or each other

O.K.

•

B) Check reset for correct operation

O.K.

•

C) Check Ul for proper operation

O.K. If not: 1) Check socket for good solder

• 2) Check for bad Ul

D) Check U2 for proper operation

O.K. If not: 1) Check socket

2) Check for bad U2

E) Check RAM data lines for correct amplitude

O.K. If not: 1) Check for hot surface of RAM

• 2) Jump out RAM to verify

F) Check multiplexers U9, UIO - signals at RP3

and RP4 should be similar in frequency and

amplitude

O.K. If not: 1) Suspect U9 or U10

G) Check ROM for chip select signal at p.in 22 of

U23 and U24

O.K. If not: 1) Check for signal generation

• at U20

H) Check that all ROM addresses are present and

correct amplitude

O.K. If not: 1) Trace problem address AO-A15

I) Check U19, U23, U24 by replacement with known

good

3) NO POWER

A) Verify voltage +5 and +9 volts

1) Check for shorts to ground

2) Check switch

3) Check power supply

4) BAD BASIC - Random characters on screen - Random

colors - Power-up message is missing

A) Check Basic ROM U23

B) Check B thru I above (Bad Video)

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Commodore Plus 4 Uživatelský manuál Strana 21