Apple II Plus No Cursor

It is a capacitor. .1uf is the value. 555 might be a reference to a 555 timer IC. The 555 timer IC is a small IC with 8 pins on it. B8 might refer to the location on the motherboard. There are letters and numbers on Apple ii motherboards used to locate components. You use them just like a multiplication table, which is commonly found on composition books for children at school.

There is another common reason to see no cursor. If you have a disk controller in slot 6 and no disk drive the same thing will happen. Check inside to see if the controller is there. If it's there, just remove it.

B3 is the location of the cursor 555 timer chip. The capacitor in question connects between pins 2 and 6 of the 555 on one lead and ground (pin 1) on the other. To replace it you will need to remove the motherboard from the chassis. You will also need some top notch soldering skills or there is a high risk of destroying the copper traces and lands associated with the capacitor.

Before you begin, check pin 3 of the 555 using an analog meter, scope or logic probe to ensure that it is indeed not working. If the 555 circuit is working correctly, pin 3 will toggle between 5V (1) and 0V (0) at the rate the cursor should flash. If it is doing this, then you have a problem other than the capacitor.

Once you are satisfied the 555 is not operating and the main board has been removed from the chassis, here is the process:

Items needed - Low wattage soldering iron (preferably heat controlled) with 1.5mm flattened (screw-driver style) tip. Fine (.6mm) resin core solder. High quality solder wick or solder sucker. Needle nose pliers. Flush cutting side cutter. Replacement capacitor.

1) Cut the leads of the capacitor as close to the capacitor as possible, leaving as much as you can to grasp with a needle nose pliers.

2) While grasping a remaining capacitor lead from the component side (top) of the board, gently use the soldering iron to melt the solder holding it in place from the bottom side of the bard. You may need to 'tin' the iron tip with a small amount of solder to make proper thermal contact. Be careful not to apply too much pressure to the board with the iron. Once the solder melts gingerly pull the lead out with the pliers. Repeat for the other lead. Clean the tip of the iron between Every operation.

3) Again using the iron with either the solder wick or the solder sucker, remove the remaining solder from the holes where the capacitor leads were. Remember to keep the iron tip clean and tinned.

4) Place the new capacitor into the holes from the component side and insert as close to the board as possible. It may be necessary to bend the leads of the capacitor to do this properly. Try to make it look like the capacitor you just removed. once in place bend the leads on the bottom of the board just enough to keep the capacitor from falling out and flip the board over so that the bottom side is up.

5) With a clean and freshly tinned iron solder the leads in place. Make sure you heat the lead/land junction properly before applying the solder, but no so much as to do damage. 2-3 seconds of heating should be enough. Again, do not use a lot of pressure, only enough to make sufficient contact. Apply a small amount of solder, just enough to fill in hole and adhere to the capacitor leads and keep the iron on the joint for another 2-3 seconds. The resulting joint should be shinny and climb in a concave fashion up the leads of the capacitor a tiny bit (1mm-2mm). Look at other joints already on the board to see how it should look.

6) Trim the leads with the cutters to within to about 1mm from the board. Do not trim too close.

If you are not really good at soldering, I would strongly advise you to take the board to an experienced technician to have the capacitor replaced. Remember, they are not making any more Apple II mother boards and it would be a shame to lose one.

Does the system otherwise work?

What you are discussing is the video flashing circuit. If you have a cursor, but it doesn't blink, and everything else works fine, then you might have an issue with the 555 timer or a couple of chips in the video circuit downstream from the 555 timer.

However, if you don't have a cursor at all, something else is wrong. The cursor is set up by software putting a character in a memory mapped video memory location. If software doesn't initialize screen memory and put the cursor in character video memory, you will not get any cursor, at all. Any number of processor, bus, and memory issues can cause this type of issue.

regards,
Mike W.