C64 reapir. Scrambled characters in start screen. breadbox64.com

Assy 250407 Rev. C #1

This machine is an Assy No. 250425 long board.

C64 reapir. Scrambled characters in start screen. breadbox64.com

The startup screen was filled with scrambled characters.

C64 reapir. Scrambled characters in start screen. breadbox64.com

This particular fault has previously been related to a faulty CHARACTER ROM at U5 (MOS 901225-01 chip) on another long board (link).

C64 reapir. Scrambled characters in start screen. breadbox64.com

Changing the Character ROM did no cure the fault. I therefore tested the machine with Jupiter Lander on cartridge as this game will run even with a broken Character ROM.

C64 reapir. Scrambled characters in start screen. breadbox64.com

However, this caused a greyed out screen much like the one found in another machine (link).

C64 reapir. Scrambled characters in start screen. breadbox64.com

On that particular repair job, the problem was related to the PLA. I therefore changed the PLA (MOS 906114-01 chip) with a more modern version – the PLAnkton as described here in further details (link).

C64 reapir. Scrambled characters in start screen. breadbox64.com

C64 reapir. Scrambled characters in start screen. breadbox64.com

…and back came the sweet blue screen!

C64 reapir. Scrambled characters in start screen. breadbox64.com

The scrambled startup screen needed these two replacement ‘chips’ before it was back to normal operation! I guess the PLA can cause issues that seems like they come from other chips…

C64 reapir. Scrambled characters in start screen. breadbox64.com

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