Apple II Plus Last Remaining Roadblock

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Joined: Sep 21 2008
Posts: 61

I've have made a lot of progress in fixing my Apple II Plus, but now I'm stumped in what is blocking my progress at the current moment. I have replaced every last chip including CPU and ROM chips. Well every chip but the two 555 ICs, the Special ROM (Character ROM) (which seams to be in working order), and 741 IC. All chips where replaced with known good chips. Maybe one of the other components need replacing. When I start it now it displays this perfectly with no random characters appearing:

??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@

All the @@ are inverted. At the same time it displays that it beeps once. If I have the keyboard plugged in, and I hit reset it will reset to the same screen text and beep. If I go control-G it will trigger the bell now (it never did before (in the previous state)). Any suggestions would be helpful.

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Joined: Jun 5 2008
Posts: 380
Diagnosing one of these machi

Diagnosing one of these machines through these forums is usually pretty difficult. I have some ideas though.

I'm assuming that you have pulled out all expansion cards.

Based on the display it appears that your video section and DRAM are working ok.

Since contrl-G rings a bell, it is possible that the processor is actually working, but clearing and writing to the wrong memory block when it clears and writes to video or that the video reads are accessing the wrong block. Try some other commands that affect graphics mode and see what happens. For instance try typing GR (CR) and see if graphics mode kicks in. Or try contrl-B (CR) followed by GR (CR) just in case the machine booted into monitor. Also you might try TEXT (CR) or try HGR (CR) to see if either of those commands has an effect.

If these commands, then check high address decode for DRAM. ROM appears working, so the 6502 and bus drivers should be ok. Check address decode logic that includes 74LS257 at J1, 74LS153 at C1, 74LS139s at E2 and F2. Also the graphics mode decoder at C11 (74LS04) and C12(74LS257) - you can swap the 74LS257s and 74LS139s and see what affect it has Also make sure that memory jumper blocks are good.

It also could be in the DRAM address mux E11-E14 and C11,C12, but I think that is less likely, since the video display looks good.

You might have a bad socket or broken trace on the motherboard, so changing chips will not help. Get your self a logic probe or oscilloscope and schematics and make sure that signals are actually being driven on inputs to these chips.

Regards,
Mike Willegal

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Joined: Sep 21 2008
Posts: 61
All the expansion cards have

All the expansion cards have been removed so they don't interfere.

I'll try those commands to see if they work and I'll get back to you.

I'll try swapping the chips out later on today. As I said before they have all been replaced with known working chips (even RAM, ROMs, and CPU [All the socketed chips (3 aren't socketed]). This is the later model boards without the memory jumper blocks, and the one 8304 IC instead of the two 8T28s.

Since this was a once functional Apple II+ around 6 years ago I'm sure it's not a trace. A socket gone bad maybe. But since it was a card that shifted slightly out of it's slot that killed it I'm thinking it has to be one of the transistors or non electrolytic capacitors. I shut the power off immediately. There was no bang and all the electrolytic capacitors check out so I'm sure they are fine. I have the schematics for the II+ but not a logic probe or an oscilloscope (but I can get one). The problem is know where to start (as in terms of using them what pins on the chips should I start to probe and what signal should I receive). I know how to use and logic probe, and I never got around to using an oscilloscope.

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Joined: Sep 21 2008
Posts: 61
I type GR nothing happens on

I type GR nothing happens on screen but when I type return it then beeps. Control-B then GR is followed by the same thing. From fresh state (power off, power on) Reset followed by return = beep, and any command (control-G, control-B, etc) or input (any button but return) followed by return receives a beep. If you press return after that there is no beep. Keys on there own typed do not receive a beep.

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Joined: Sep 21 2008
Posts: 61
I've just changed out the key

I've just changed out the keyboard encoder if I type GR then return it will beep, then I type GR again then hit return and it will break the screen up so there is whatever is left of the text and a graphic area with white bars. These bars are opposite of the inverted text. It's as if they text was removed from that area so only the back and white bars remained then inverse that area only.

It still does the beeping thing with return. Shift -> return does not cause it to beep.

How do you return it back to text mode. I want to see if I can get the text to change back. TEXT? Um I'll try...

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Joined: Sep 21 2008
Posts: 61
It will not change back it wi

It will not change back it will only beep at me. I tried it in an emulator and that is the right command. It looks like it will not except any further commands from this point.

A2forever's picture
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Joined: Dec 20 2003
Posts: 226
II+ Motherobards.

I have several II+ motherboards , they are used , but have no clue if they work , but if you switch out the roms and rams and what not , it can't hurt , and it may get one of them up and running , if you want them , their yours... Just let me know... I will even put in an updated SPECIAL ROM , which will be the Pig-Font rom , it will have all Upper/Lowercase Characters + Extras...

Just let me know...

Patrick A.
Las Vegas, NV.

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Long Live The Apple ][

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Joined: Sep 21 2008
Posts: 61
Thanks it's worth a shot.

Thanks it's worth a shot.

BTW I changed back the keyboard encoder after the reset died on the new one. The original keyboard encoder works. I typed GR and hit returned and it when to the graphics mode. I type text and hit return and it goes back to the text mode. It still displays the same thing, though.

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Joined: Sep 21 2008
Posts: 61
I received the motherboard fr

I received the motherboard from A2forever today. At first it didn't seam to work either. So I started checking the ROMs out, I noticed that F8 was labeled as 341-0036 which struck me as odd so I looked it up on the list I have and it's the character ROM. So I switched it out with a F8 ROM and then move that ROM to the character ROM socket. It boot up perfectly. I then did a once over the board checking everything out. I noticed 3 74S components then I check it on mine, and 1 was an 74S and the others I accidentally replaced with 74LS which is a bit slower. I looked up what they did and since it's close to the timing circuit at the bottom left corner they are apart of it. Since the timing seams to be okay I assume the 74LS was good enough. I then continued checking and every chip seams to be in the right socket. I then started swapping chips (I guess I thought since I have a board with chips that are all working why not try to find the problem in the other board). I didn't get far before I had found the problem with my board. Since I was going top to bottom, left to right the first chip I pulled out was the problem chip. 74LS257 from socket J1 had pin 11 bent over in such a way that if you looked at it while socketed you'd never know. I was careful when putting the chips in but I guess with 80 of them there was a chance for at least one mishap like this. I replaced the chip with a new one and it to booted perfectly.

I also got a Apple II 5.25" interface card from A2forever as well. When my Disk II is connected to it, it still spins forever like mine does [the card] when it's connected to it [the drive]. Looks like I got more work to do on the drive though. Maybe the last IC I can't find a replacement for locally, or one of the other components, or maybe just needs some adjustments of the pots.

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Joined: Sep 21 2008
Posts: 61
Does anyone know what the App

Does anyone know what the Apple II case is 'exactly' made out of. I would like to glue my things for keeping the lid in place back on to the case. I think I might of found the right stuff to do it but I didn't buy it because it doesn't stick to one type of plastic. It will adhere to almost every other kind of plastic imaginable.

pmjett's picture
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Joined: Sep 5 2005
Posts: 181
plastic

I'm pretty sure that your glue probably said it won't adhere to polyethylene. Nothing seems to glue that (I think they usually heat-weld it). My best guess is something like ABS, but someone correct me. I imagine that whatever glue you found will probably work, just be careful not to use too much. If you are using one of the solvent based "plastic welders" trying to get the excess off to make a pretty glue line is a real pain.

Glad to hear your Plus is working!

mike

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128K, 512K, Mac Plus, Classic, SE/30, Indigo iMac, B&W, Sawtooth, iBook G4, Mini. Numerous SGI and Sun boxen.

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Joined: Sep 21 2008
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Yes the adhesive I was lookin

Yes the adhesive I was looking at wouldn't adhere to polyethylene and another poly something product which I think was polyethylene terephthalate. I found one place that said how the case was made. The case was made by a process know as reaction injection molding which the plastic used was polyurethane. I guess the glue would work. I never thought it would be ABS or PVC plastic, but there is so many to choose from it could of been any number of things really.

http://www.alanadams.net/legacy/senior_thesis/Section_4/side_notes/Apple_II_plastic_case.htm

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Joined: Sep 21 2008
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I take that back it is ABS pl

I take that back it is ABS plastic. Still doesn't look like it is [ABS plastic] to me. Whatever cases made in the time frame of just before April 1977 to the retooling in December 1977 are made out of polyurethane. These can be identified by their flaking paint. But from December 1977 on they used acrylonitrile-butadiene-styrene (ABS) which didn't need to be painted and could be made in larger volumes. Either way I can go back and buy the adhesive I was looking at.

http://www.landsnail.com/apple/local/design/apple2.html

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Joined: Sep 5 2005
Posts: 181
Cool.

Yeah, I'm afraid that I might fall into the hoarding category from the "thoughts on vintage Macs collection" thread. To that end, I've got lots of machines that have plastic cases that need mending. Particularly the skins on several of my SGI boxes. All their machines are skinned in ABS, and it figures (to me) that Apple would have done the same thing. Maybe ABS resin is cheap, has ok characteristics- and obviously can come in any color. It does look a little different when extruded into drain pipe!

Good luck glueing.
mike

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128K, 512K, Mac Plus, Classic, SE/30, Indigo iMac, B&W, Sawtooth, iBook G4, Mini. Numerous SGI and Sun boxen.

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Joined: Sep 21 2008
Posts: 61
Yah. The ABS in looks differ

Yah. The ABS used in the Apple II case looks different to me than anything else I seen made from it. From other computer cases, to chairs, to [yes] pipes. lol.