Partially failing 6561-101

[mrr19121970]

At 1st I suspected the CHAR rom.



Turned out to be a partially failing VIC-I

[eslapion]

AFAIK, there is no such thing as a partially failing 6561 or any other chip for that matter.

The MOS 6502 contains 3510 transistors and I suspect the works of lance.ewing will show the total count of transistors for the 6560/61 to be in the same range. If a single one of these transistors has been destroyed by overheating or static electricity then it's gone for good.

The effects of a single dead transistors usually makes the whole IC unusable and nothing* can fix it.

That's why I was surprised at your persistence to keep the half-dead 6522 you were mentioning in another thread.

* Nothing is a relative word here. Technically it is possible to dissolve the package of the chip and using a microscopic scale intervention system you could then - in theory - fix the die and repackage the IC. NASA sometimes does this sort of thing for unique components and it costs nearly a million dollars to do it.

[mrr19121970]

The idea of the post was to provide a pictorial summary of the symptoms. Clearly the VIC-I is working to some extent. The damage here is not sufficient to stop the chip from working. Therefore my choice to use the phrase partial failure.

In my other post there is one small part of the VIA chip that prevents certain key combinations. This is a symptom that I am aware of and can live with. Similarly if I go to a doctor with shoulder pain and the only option is invasive surgery.

[eslapion]

Similarly if I go to a doctor with shoulder pain and the only option is invasive surgery.

If I have an accident and a bit of one of my fingers gets cut off then at first it will bleed and if I go to a doctor, I'll get stitches and I'll get disinfectant, the bleeding will stop and all of my other internal organs should be fine.

Heck, I might even be able to get the piece of finger cut-off stitched back on my hand and it will heal.

It may hurt but even if I don't get my bit of finger back, I can still do 99.9% of what I did before I got hurt.

A single dead transistor never heals and is usually enough to prevent the chip from doing 99.9% of what you did with it before.

Of course the other side of this story is that a circuit will never grow old and if undamaged, it has (in theory) no lifespan limit.

Just like a precious vase, fragile and vulnerable but immortal.