Apple II plus

I wrote a little Applesoft BASIC program to simulate the pattern that appears on your Apple II plus's screen. Normally, the pattern is ??@@ (inverse at signs) which are FF FF 00 00 bytes in memory when you power on the Apple II+. It may be that the bytes are F7 F7 00 00 in your Apple II's memory which would appear as 77@@.

I know more about software than hardware, but my guess is that perhaps that out of the eight data lines, the data line that provides fifth bit for each byte is always zero. Here is a byte pattern for when seven bits are working indicated with an x, and the fifth bit is always zero: xxxx0xxx

If this is what is happening, it may be why the screen appears as it does, and why your Apple II plus would freeze. Perhaps, a trace line is broken, or as you mentioned a chip may have gone bad.

Thank you for your reaction. I added new photos of the ??@@ pattern which appears when the reset button is pressed. At release the ? turns into a 7 again. You say that if I repair the fifth data line the machine will probably work again. I don't know where the data lines are. Maybe you know where they are. The Apple II plus doesn't freeze completely because you can still press reset. If you press other keys the screen gets blurry and ? 's appear followed by numbers. The disk drive spins but won't load a program. Maybe you know more, or someone else does, and can help me out.
Yosha

Here are some comments on a similar thread that may help:

http://www.applefritter.com/node/18714

Kind of hard to tell from your photos, but what is the ribbon cable attached to one the right side of the motherboard? I would remove all the peripheral cards first. Make sure nothing foreign is in the computer, push down on all the chips, and try powering it on again.

Dave...

Hi,

Thank you all for your comments. I tried everything. I Removed all cables, reseated all chips. Finaly I got the board out and turned it upside down. As you can see on my pictures ( http://www.flickr.com/photos/24500646@N02/ ) there are 3 cables on the down side of the board. I don't think they are supposed to be there. 2 of them are unshielded. They might make contact with other things on the board. Can I simply remove them or should I let them in place because they don't have anything todo with the problem.

I followed every link on this forum. I read every issue about the Apple II plus on this forum. I also visited a google news group site.

I hope someone recognizes this and can help me out.

Yosha

Hi,

Thank you all for your comments. I tried everything. I Removed all cables, reseated all chips. Finaly I got the board out and turned it upside down. As you can see on my pictures ( http://www.flickr.com/photos/24500646@N02/ ) there are 3 cables on the down side of the board. I don't think they are supposed to be there. 2 of them are unshielded. They might make contact with other things on the board. Can I simply remove them or should I let them in place because they don't have anything to do with the problem.

I followed every link on this forum. I read every issue about the Apple II plus on this forum. I also visited a google news group site.

I hope someone recognizes this and can help me out.

Yosha

Hi,

Thank you all for your comments. I tried everything. I Removed all cables, reseated all chips. Finaly I got the board out and turned it upside down. As you can see on my pictures ( http://www.flickr.com/photos/24500646@N02/ ) there are 3 cables on the down side of the board. I don't think they are supposed to be there. 2 of them are unshielded. They might make contact with other things on the board. Can I simply remove them or should I let them in place because they don't have anything to do with the problem.

I followed every link on this forum. I read every issue about the Apple II plus on this forum. I also visited a google news group site.

I hope someone recognizes this and can help me out.

Yosha

It sounds like the reset line isn't doing its job. The wire traces are also suspicious, and I'd get rid of them. But a thread you'll want to read is here:
http://groups.google.com/group/comp.sys.apple2/browse_frm/thread/d373fe8be9141a72/3283054d45e0362c?lnk=gst&q=reset+line#3283054d45e0362c

At this point, it certainly couldn't hurt to remove those lines. I have never seen an Apple II with those. Make sure you record where they go in case they are supposed to fix some fried traces on the motherboard. Do you have a logic probe, or a voltmeter to use? As Dave mentions above, comp.sys.apple2 is the next place to ask for ideas.

Dave...

The 'WIRES' you are referring to, on the bottom of the board, are quite common on the Apple II line of computers. They are there to correct a bug found in the normal operation of the computer between board REV's.
The 'unshielded wires' are more likely wirewrap wires. It was cheaper to add these wires than to scrap all the motherboards and start over again. I have seen at least 2 dozen motherboards this way, and I even have a IIGS with a jumper on the bottom side.

Hi,

I allready removed them. Fortunately I took many pictures of the cables and there locations. The Apple II didn't react differnent without the shielded cable. With the other 2 the picture on the screen was stable. Probably because there are no unwanted contacts made.

I have a multimeter (Volt, Ohm and more) and I will check the reset line. Pressing reset sometimes changes the screen. However, I don't think the processor gets the reset. I am going to check that.

If anyone has a suggestion please post a comment, I will tell you if there is any progress.

Yosha

My Apple II plus is revision 4. It's hard to see because the expansion slot card holder is made over it. I think it sais rev. 4 or rev. A.

Yosha

The beep, screen clear, and appleII banner occur very early in the autostart PROM code. Something is preventing the code from executing properly. There is a fair amount of logic that needs to work just to get a beep. I had an issue like this on a TRS80 and it was a blown chip that was holding down 4 data lines. You may be able to debug this with an ohm meter but most likely you will need a oscilloscope and some schematics (which should be on-line). I just fixed a II+ that had a bad PROM where Applesoft is stored. In this case the computer basically worked but would not run Applesoft. It would drop into the monitor (*) prompt.

So to get a beep and banner, you need a handful of ICs (including PROMs) and about 30 address, data, and control signals working.

Mike

Hi Yosha
About a year and a half ago I started a thread since I had the same problem with my Apple II+. The thread is here: http://www.applefritter.com/node/18714

It turned out to be one faulty bus driver and two faulty RAM chips. What you could do is swapping each RAM chip one by one while checking for any change in the Apple's behaviour at power on, as I mentioned in my old thread.