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Odd Question

robert_sissco

robert_sissco

Experienced Member
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Oct 12, 2021
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343
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Midwest U.S.A.
The hits just keep on giving. On the board I had with the bar RAM from earlier, been putting it through its paces, but I have a new issue.

When I boot with a cartridge (In this case both Epyx FastLoad and Mach5) I get no cursor. Remove the cartridge and it boots and runs just fine.

Diagnostics runs (a bit surprised) and it says the CIAs are bad.

This sounds like it, but I also know that these are getting a bit on the expensive side to find nowaways, and I was wondering if anyone had any other ideas before I open the wallet and put more money into this one (Not against it, just kinda wishin on a star that I won't have to).

The only other thing the Diag says is failing is the SID on screen, but the sounds plays just fine. But it has passed on the screen before, so I am not sure if the timing of the CIA's failing could be the cause of this as well, but right now the SID works as far as I can tell.
 
NM, after I had posted this I remembered I has a spare 6526 in my chip bin, and researching further inline it was likely U1, and when I swapped it out, I was back up and running with carts in.

Still, with prices going up I may order another just to have on hand in case again
 
OK, maybe I do have a question. The CIA in U1 died again. I have ordered some CIA savers to try and keep this from happening, and I will need to order some new CIA's now since my last one was in it, but any idea what I could look at to see what is killing the CIA in U1? Same symptoms as well. No cart and it works, insert a cart that and no cursor.
 
OK NEW NEW FRIGGIN UPDATE. When I disconnect the keyboard or use a different keyboard, it works no problem, apparently the issue is with the keyboard. It is an Aldi C64 keyboard, but when I use any other keyboard, the cursor works just fine. When I attach the Aldi 64 keyboard, no cursor with the keyboard attached and a cart in.

I did order new CIA's just in case these are just going flaky, but it seems that the issue with the keyboard mechanism. Any one have any ideas, this is just odd.
 
The only thing I can imagine that something is shorting the line of the RESTORE key. That will cause a continuous NMI. You could start with measuring the resistance between pin 3 and GND. Otherwise just remove the backplane, inspect it and if nothing found, connect it to your C64. If things work fine now, you have stuck keys.

Good luck!
 
Ruud said:
The only thing I can imagine that something is shorting the line of the RESTORE key. That will cause a continuous NMI. You could start with measuring the resistance between pin 3 and GND. Otherwise just remove the backplane, inspect it and if nothing found, connect it to your C64. If things work fine now, you have stuck keys.

Good luck!
Click to expand...
I will need to check the resistance. First thing I always do when I get a keyboard is disassemble it to clean the board and keycaps, so unless something fell in there when I was putting it back together, I do not think it is that.
 
Did you forget to put a spring back in for one of the keys? Maybe a key is stuck down.
 
A stuck key, any other than the Restore key, would produce a character on the screen. But IMHO it would not stop the IRQ interrupt because the routine for that interrupt is the one that creates the flashing cursor. No IRQ means no cursor. And a continuous NMI is the only signal that would cause that. (Or in the back of my hat: isn't the NMI edge triggered? If so, my theory won't stand either.)
But anyway, the remark about a forgotten spring is a good one!
 
There are no stuck keys and no missing springs. When I reassemble I do it one spring and cap at a time rather than putting all the springs on and then adding the caps so I don't accidently knock one off and miss it. I even removed the restore key an the spring was there.

And since it only happens with this one specific keyboard, I do not thing it is anything with the system. I may disassemble the keyboard again and see if there are somehow a shorted trace or anything on the restore key that is sending the signals.
 
Well, it isn't the keyboard. The system after three days of no issues has started showing the same issue with a different keyboard, or now even with no keyboard.

I did a bit more testing, and it seems that if I let it run for a few minutes it will sometimes work, but not always.

I am thinking that it is starting to look more and more like the CIA's. I may pickup a bit of Deoxit to see if that has any effect since the CIA's are in there pretty tight. They are also factory single wipe and I may try to remove and replace with doubles to see if that helps.

Next paycheck I am looking at picking up a harness to go with the diag cart to see if that can give me more insight.
 
You know... reading back through the comment history, something just popped into my mind. You said that it magically started working again when you changed keyboards, and now poof it's messing up again.

There's a lot of flexin and movin goin on when you remove and plug in a keyboard. You ~Might~ have a cold solder joint, cracked trace, or as you already mentioned.... dirty contacts or bad socket.
 
br44 said:
There's a lot of flexin and movin goin on when you remove and plug in a keyboard. You ~Might~ have a cold solder joint, cracked trace, or as you already mentioned.... dirty contacts or bad socket.
Click to expand...
That was my thought as well when this popped back up, that when I switched out the keyboard the first time, I might have put pressure on that U1 CIA chip and resat it enough to put contact back.

The CIA's are already socket in Commodore factory crappy ones like I noted, and I have a desolding gun anyways and I know I have the double wipes to fit them on hand so I think it might be best to just start there.

Once I have them re-socketed I'll give the multimeter a workout and check the traces to and from U1 just to confirm
 
If possible, replace the socket. Sockets can worn out as well. And by replacing it, make sure the pins are soldered well to the board.

Almost forgot, what happens if you swap the CIAs?
 
Ruud said:
If possible, replace the socket. Sockets can worn out as well. And by replacing it, make sure the pins are soldered well to the board.

Almost forgot, what happens if you swap the CIAs?
Click to expand...
I plan on replacing the sockets as a first step.

And I get the same behavior if I swat U1 and U2 around or replace either with a new CIA chip.

Like I said before it was only happening with a particular keyboard everytime before, but now it is occurring randomly with other keyboards as well
 
robert_sissco said:
I plan on replacing the sockets as a first step.

And I get the same behavior if I swat U1 and U2 around or replace either with a new CIA chip.

Like I said before it was only happening with a particular keyboard everytime before, but now it is occurring randomly with other keyboards as well
Click to expand...
If you're swapping chips and the issue is staying in the same spot, that means the issue isn't the chips. So yeah, it's either a bad/dirty socket or some sort of break down the line. It's highly unlikely to have multiple chips break in the exact same way.
 
br44 said:
If you're swapping chips and the issue is staying in the same spot, that means the issue isn't the chips. So yeah, it's either a bad/dirty socket or some sort of break down the line. It's highly unlikely to have multiple chips break in the exact same way.
Click to expand...
Yea, it was just so weird that when I swapped to a different keyboard, the issue worked everytime for about three days then returned. The board looked clean and I didn't see any traces that were bad and the CIA's had not been reworked in the past so I don't think they were previously damaged, but I have a new avenue to check.
 
OK, lifted the sockets, and it is a mess under them, I am seeing a lot of damaged traces. Looks like someone who may have been skilled gave this board some extra life, but when I came in the worked on it, the traces may have finally broken completely. At this point the board has given me so many issues I just think that I am going to get a sixty clone board and move the chips over. This is the same board that has the broken expansion port so I am starting to wonder if this didn't sustain some damage on that corner that caused all of this.
 
robert_sissco said:
OK, lifted the sockets, and it is a mess under them, I am seeing a lot of damaged traces. Looks like someone who may have been skilled gave this board some extra life, but when I came in the worked on it, the traces may have finally broken completely. At this point the board has given me so many issues I just think that I am going to get a sixty clone board and move the chips over. This is the same board that has the broken expansion port so I am starting to wonder if this didn't sustain some damage on that corner that caused all of this.
Click to expand...
What board revision do you have?
 
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