Commodore Plus/4 strange display issue

[dslawton]

Hi all,

I've been like a kid with a new toy since recently acquiring a CPlus/4 - I always wanted one of these when I was a young lad, dunno why, but now I got one some 35 years later.

Anyway, looking for advice as I have a strange issue. Check out the screenshot below... I have rogue characters (double quotes) appearing in two locations on the screen. Always the same location, but can be different characters depending on what program is being run.

It's not the end of the world, everything else seems to work OK, but it's annoying more than anything.

Any Commodore gurus out there got any ideas?

Any help appreciated...thanks a lot.
Dean

 

[ddni]

The Plus/4 was the first official NSA computer. They had issues and sometimes the eyes of the internal secret agents become visible.

Shouldn't cause any harm, just don't let on that you have noticed or the agents will be horribly embarrassed.

 

[dslawton]

 

[Bryce]

The Plus/4 uses the main memory (&8000 to &87FF) for display RAM (ie: it doesn't have separate screen RAM), so I would guess that you have a few dodgy bits in one of the RAM ICs. Unfortunately, the Plus 4 has 8x 1bit RAM ICs, and it's difficult to tell (from the picture at least) which bits are actually flipped. You may be able to test this with some software tests, if not you may have to replace all 8 RAM ICs to repair this. Luckily it uses 4164 RAMs, which are still very easy to find.

Bryce.

 

[protek]

There was a similar issue here regarding a C64, if I remember correctly.

 

[TheCorfiot]

I would be very happy to repair this for you...

TC

 

[dslawton]

Err... Declaring interest? :blased: