Help with Apple ][+ not working

[Wilm]

Hi all,

I'm not quite sure if this is the right place to ask, but I could use some help repairing an Apple ][+ (not an Europlus, but an European Version with 220 VAC).

Problem: The Board powers up and fills the screen with more or less random letters, some of which are blinking. I do not get a BASIC prompt, and the reset-key on the keyboard doesn't do anything. I bought this computer as "not working", therefore anything might be damaged.

The story so far: I replaced the X2-Cap in the power supply. It outputs the following voltages (unloaded): +11,84 VDC, +5,12 VDC, -10,83 VDC, -4,66 VDC.

When I connect the power supply to the mainboard an turn in on, I get +11,90 VDC, +4,95 VDC, -12,53 VDC, -5,42 VDC (measured at the expansion slots).

I re-seated all of the ICs on the board, even sanding down the most corroded ones, and user de-oxid/contact cleaner for the sockets that are suspect. I checked all the chips that I cloud, most of the TTLs in the miniPro, others (like the 6502 in the Chip Tester Pro (link). And no, I don't have a spare Apple ][+. :-(

I found two TTLs that needs to be replaced, and one 4116-RAM that I replaced. Having done that, I'm stuck right now. I checked the activity on the CPU and noticed

• occasionally, there is activity on all data- and address lines, but not on IRQ, RDY, NMI, and R/W, all of which are stuck high
• most of the times, it behaves as above, but with all address lines stuck high

Does the Apple ][+ need a working keyboard? Other than the glowing power light on the keyboard, I have no other way to check if it's working.
Apart from that, the 74LS195 and the 74LS175 on B13 and B14 get really hot, but test OK in the mini pro. The ROMs get hot es well.

Any help would be greatly appreciated. Thanks!

 

[retr01]

@jajan547!

 

[Wilm]

Forgot to mention: Reset-Signal on the CPU is fine

 

[jajan547]

This still looks like a bad RAM or ROM, have you gone through and verified all RAM is good aside from the one you’ve replaced? If not swap banks and see if characters change. Another thing I’d like to add is no the Apple ii doesn’t need the keyboard but it does if you plan to reset it or do anything/load in AppleSoft basic. If your reset key isn’t working take apart the keyboard and clean the contacts.

 

[Wilm]

Checked all the RAM-Chips with the Chip Tester Pro, and in fact 6 of them (Row E) tested bad. But that was probably because of corrosion, because sanding them als lots of contact cleaner later the all tested good, so I put them back in the board. NOS RAMs are on their way, because I don't have enough spares at hand.

However, powering up the Apple ][ did not produce any change. So I started interchanging the two lower rows of RAMs with the following results:

Row D empty:

Rows C and D interchanged:

Row C empty:

Row D empty, but with different RAMs in Row C (some characters are blinking):

I pulled every socketed chip (i.e. all of them) and used contact cleaner on all sockets and sandpaper (if needed) on the chips, but that didn't help.

By the way, this is a revision 820-0014-01 board.

It's getting late, but tomorrow I can continue working on the machine, if I can think of something to try ...

 

[jajan547]

Id say you have a bad RAM in ROW C because that's the only ROW that vastly changes the characters. Let me try this on my own Apple II Plus and I'll be back with my results so you can compare.

 

[jajan547]

So I tried with almost every chip and the closest I came to seeing what you have on your screen is when the 8304 or 9334 is removed.

 

[Wilm]

First of all, thanks for your effort - I know how much fun it is pulling a million of ICs out of sockets for testing ...

Is there a way to test the 8304 or the 9334 (via oscilloscope or whatever), before I try to order some? And would you try to get those chips from China, or is there a more reliable source in Europe that you know of?

 

[Wilm]

Out of curiosity: where on the board do I find those 8304 or 9334 ? On the board revision that I have, I couldn't find anything ...

 

[jajan547]

Out of curiosity: where on the board do I find those 8304 or 9334 ? On the board revision that I have, I couldn't find anything ...

I see what you mean I overlooked that, I have a US board so it’s different. One thing I’d try next is the chips near the CPU or the ROMs just pop one out and see if issues are the same. After that you can always go back and make sure there are no bent pins.

 

[Wilm]

Sorry, but I will have little time in the next few days working on that Apple ][+ ... :-(

I'm afraid I don't get it yet. By taking out one chip after another, the board will not start working again. So I look for changes or note when the board does not display anything at all? How can this be helpful? Sorry for asking, I just try to understand what I'm doing here ...

 

[skate323k137]

Sorry, but I will have little time in the next few days working on that Apple ][+ ... :-(

I'm afraid I don't get it yet. By taking out one chip after another, the board will not start working again. So I look for changes or note when the board does not display anything at all? How can this be helpful? Sorry for asking, I just try to understand what I'm doing here ...

The goal would be to hopefully find the IC which doesn't change the problem [much] while removed, and to rule that IC as faulty.

The folks on the AppleFritter forums have decades of experience on these, I would not be surprised to see someone there solve this nearly on sight, and I'd be shocked if they couldn't at least help.