[C64] A question about the CIAs

[Herbarius]

So, much to my dismay, the trouble I was having with the second joystick port on my C64 (didn't register pressing "UP" anymore) turned out to be a defective CIA chip - as I swapped them, and then both controller ports worked fine.

 

At least for the moment...

 

Because now, a week later, maybe 10 hours of actual operation of the machine (or less), suddenly the controller port acts up again - this time not registering "FIRE!". I opened it up again, and swapped them again, and confirmed: Yes, I can choose between either "UP" or "FIRE!" not functioning. So I confirmed not only one, but both CIAs are defective.

 

 

So, now as soon as I manage to get replacements - which may be soon - I'm going to replace them both with good working ones.

 

 

But I am wondering: Was it just coincidence the second CIA went bad such a relatively short time after swapping them? Or is it simply that having the defective CIA in the second port may have driven the first one into failing as well?

If the answer to any of those two questions were "yes", then everything would be fine as soon as I get the new chips.

 

But I've also considered the possibility of something else in the machine being wrong which would be a common cause for both CIA failures, and might then trash the new ones within weeks as well... Do you think such a scenario is possible or propable? If yes, what other components might that be that are responsible?

 

 

On a related note, I thought about some safety precautions I'm planning to adhere to with the new chips, such as don't swap any cables - not even joystick cables - while the machine is on. Before now I laughed about people being scared to do it, now I understand why [No, I never touched the cables in the back or the power cable while it was powered on, but occasionally I swapped controllers while it was on... like when I loaded up a game but then realized, I hadn't plugged in the controller I want to use for the game or noticed I plugged it into the wrong port]

A second thing I'm going to do is cover the unused Cartridge- and User-Ports at the back with some cardboard (fixing inside the case.) Any other hints in that department any of you could provide?

Edited March 23, 2010 by Herbarius

[Rybags]

Something else bad in the machine sounds plausible.

The ports are also used for the keyboard scan so a failing there can affect joysticks too.

 

But, fire button is bit 4 of the CIA input, up is bit 0.

 

To test if the CIA is actually bad, you should be able to temporarily ground the relevant pins while a test program is running, and see if it registers.

 

Also, any bad input should have an adverse affect on the keyboard, 8 rows * 8 columns = 64 keys, just about all of which are used.

[Herbarius]

Also, any bad input should have an adverse affect on the keyboard, 8 rows * 8 columns = 64 keys, just about all of which are used.

 

Any single key on the keyboard works fine.

 

 

How am I supposed to ground the relevant pins to try that? I thought given that swapping the CIAs changed the behavior, consistently, ruled out any other possible cause...

Edited March 23, 2010 by Herbarius

[zylon]

I'd also invest in a new power supply. If your old one is starting to fail, it can take a few chips with it.

[GroovyBee]

I hope you changed the chips with the power removed . Do you have a nylon carpet in the room where the C64 is? Where did you perform the repair?

[Herbarius]

Yes of course I changed the chips with the power removed

 

I don't think the carpet is nylon. I usually don't experience static discharges (that I can feel) in my room.

 

I performed the "repairs" right here, at my desk. Each time I touched the pipe of the radiator in my room (central heating) before I touched anything inside the C64. The radiator is at arms reach, so I didn't have to move to/from it.

Edited March 23, 2010 by Herbarius

[GroovyBee]

Personally I'd get an anti-static wrist strap that connects to the earth in a wall socket. You know its going to be a good earth when you do that.

[Mirage]

Get a high-quality servicable power supply if you don't already have one. The epoxy sealed stock ones are junk and will take out your machine probably sooner than later when it fails.

[Herbarius]

Also, any bad input should have an adverse affect on the keyboard, 8 rows * 8 columns = 64 keys, just about all of which are used.

 

Any single key on the keyboard works fine.

 

I have to take that back... or rather expand upon it. While every single key seems to work fine when pressed alone, I just noticed that when I try to type the character ">" (by pressing Shift and the "."-key) it doesn't always work... I have to press it multiple times until it finally reacts (on average I'd say two times). When that happens isn't enough to continue holding Shift down and just pressing "." again, I have to release Shift and press both again.

There may be other keys that don't work normally in unison with the Shift or C= key anymore, maybe later I'll try them all, but the great majority of keys seems to work properly. Oh, that behaviour, when trying to type ">", only happens with the right Shift key used, with the left one it works fine. (But even with the right Shift key most or all other keys work fine.) [EDIT: Just found out, trying to type "<" using the left Shift key has the same behavior, in that case working properly with the right Shift key.]

It's kinda like the thing when you try to use RUN/STOP+RESTORE. You have to invest some "effort" to make it work. I hope you know what I mean, I'm not sure if that beaviour is intended, however I've seen in videos of people pressing RUN/STOP+RESTORE that they seem to have the same issue, so I figured it might either be intentional, so you don't press it by accident, or the other possibility, the RUN/STOP key is just "worn out" from propably thousands and thousands of presses - which propably is a common condition among C64 keyboards if that theory is true.

 

 

 

About the power supply, I've got the stock "C64C" power supply. The one you see here in the second picture - not the first one. That propably is the power supply that originally came with the system, so it too is almost 25 years old, but I figure at least it's better than the one in the first picture ...

I'll have to look into the possibility to get a replacement power supply. Maybe the same online-shop I got my XM1541- and S-Video-cables from does have some.

Edited March 24, 2010 by Herbarius

[Mayhem]

You are using a proper Atari style joystick, and not a Megadrive pad or similar? Those have been known to burn out CIAs when used too much...

[Herbarius]

I've been using Atari 7800 joypads, a QuickShot II, and this one here.

 

At least the QuickShot and the Sigma were advertised as being C64-compatible. The 7800 pads most likely weren't but those shouldn't cause any trouble, should they?