Dead Apple II+, good power on beep, but only ?'s displayed

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djw
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Dead Apple II+, good power on beep, but only ?'s displayed

Hi,

Longtime watcher, first time poster.  I recently got an Apple II+ from ebay and am trying to get it working.  Seller reported the power supply was dead, and that proved to be totally wrong.  I've gotton to the point where it will boot up to all question marks (common fault of course), but I do have a power on and reset key beep - so it seems it is kinda working.  I have not seen that scenario (beep with question marks) mentioned here - usually no beep when only question marks.  Any help on what to focus in on would be appreciated.

Here is the saga so far...

1) Power lamp was dim on keyboard.  Ribbon cable had been plugged in backwards, and a pin was broken.  Corrected, and power lamp now works.

2) Improper 5V RAM was fitted in E3 (4164) - burning hot.  Probably someone had a RAM expansion card at some point.  Replaced with correct 4116 RAM (12V).

3) Power on and reset beep, but no video displayed.  Isolated to dead D13 (74LS161).  Replaced all 4 video counter ICs, video now working.

4) Only question marks are displayed, with some random and flashing characters flashing in a few spots (changes with power cycle - not reset).  Computer seems to kinda start-up as beep is heard at both power up and reset button press.  Floppy drive seeks at startup, and stops when reset is pressed.

5) Typing on keyboard does nothing - screen unchanged and only shows full display of '?' (no Apple II text),  and does not echo keys.

All voltages test correct.  Problem persists with floppy card in Slot 6 or not (no other cards in computer).  With the exception of the 8304 IC (and 6802), I have removed and tested all logic IC's in a generic 74LS tester.  The IC's all auto-detect the proper type and test ok (except D13-74LS161 which I replaced to correct the video issue).  I made a 2716 adapter socket and dumped all 6 ROMs with a DataMan 48Pro programmer, comparing with posted files - all match perfectly.  Same for the character generator ROM.  I have removed extra RAM banks, leaving only 16KB in row C.  Same symptoms exist when all 3 banks are populated.  All RAM ICs have been tested in a RAM tester (Inquisitor), and I've tried various other RAM ICs as well (Motorola and MOS).  Removing one of the 8 RAM ICs does result in a no beep scenario, so it seems the RAM is being accessed ok - at least partially.

I ordered a 'new' 8304.  Changing it had no effect.  No way to know if the replacement is good, but having no IC present results in a no beep scenario so it seems like it is ok.  I have not purchased a 6802 as it seems to be working enough to get a beep, which means a fair amount of code is executing from what I understand.  So I'm guessing the CPU is ok and the fault lies elsewhere.

The board is emaculate with no mods top or bottom.  I'm suspecting some sort of marginal IC (one that tests ok in a tester but not when stressed in the computer), but I'm not sure what to target for replacement.  I only have this Apple II+ and no other computer to start swapping IC's, so any expert advise on what area to scope out would be welcome.

Thanks for any help!

Dave

 

 

 

 

 

 

 

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Sorry, did you mean 6502, or

Sorry, did you mean 6502, or are you trying to use a MC 6802 in this machine? If so, that is not going to work:

 

PinMC6802PinMOS6502

2

Halt2Ready
3∅1 (in)3∅1 (out)
5Valid memory address5N.C.
7Bus available7SYNC
36Data bus enable36N.C.
37∅2 (in)37∅0 (in)
38N.C.38Set overflow flag
39Three-state control39∅2 (out)
djw
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Yes, 6502.  Typo - correcting

Yes, 6502.  Typo.

Tried to go back and correct the original post, but apparently you can't go back and edit after a certain amount of time.

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Keyboard problem

Often when the keyboard cable is reversed, it damages the 74ls04 inverter on the encoder daughter board. On the units I've repaired, sometimes I've also needed to replace the 74ls00 as well. Tedious but not too dfficult to desolder and swap. You can check operation with a logic probe to confirm function. 

djw
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Thanks for the tip about the

Thanks for the tip about the keyboard IC(s) - I will check those.  But I'm assuming that if the 74ls04 (and 74ls00) on the keyboard daughterboard is damaged (possible) it would not cause the symptoms I'm seeing?  Or would a fault on that indeed cause the question marks, even though the computer is getting to the reset beep?  I've tried booting with and without the keyboard cable plugged in, but still have the same problem.

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If you get a "beep" then at

If you get a "beep" then at least the CPU is finding the F8 ROM and executing some code.

 

Try removing all the Applesoft ROMS but not the F8.  Doing so in a healthy machine will cause the machine to start up and drop into the monitor.

This might isolate some issues with poor sockets or a bad data or address line to some of the ROMs.

 

Also, after you get a screenful of question marks can you type in anything, press return and get another beep for a syntax error?  Does pressing control-G generate a beep?

 

 

djw
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Ok, some definate progress. 

Ok, some definate progress.  On advice by stanleyruppert and knowing that the keyboard cable had been plugged in backward previously, I checked all logic IC's on the keyboard encoder daughterboard.  Using a logic probe, U3 (74LS00) was clearly not behaving as a proper NAND gate.  This makes sense, as this IC would have been hit with the -12V rail with the prior cable reversal.  Desoldered the chip, tested bad in an IC tester.  I had a spare 74LS00 on hand, and installed (with a socket).  The other ICs on the daughterboard seemed fine - in cicuit anyway with using the logic probe.

After that U3 fix, there is a bit more functionality.  Cntrl-G now does the beep, and typing some things and Return also results in a beep.  However, typing valid basic commands also result in an error beep, and PR#6 does not start the floppy drive.  I'm doing this blind as the display is still showing only question marks.  I'm guessing the computer is dumped into the monitor function and not basic, based on the behaviour.  But I don't really know as I can't see what the computer thinks I'm typing - could be bad keys and not know.

Regarding ROMS, I did verify proper continuity on all pins back to the address and data lines at the related ICs, as well as chip selects.  So that I think verifies the sockets (and traces).  The ROMs were also removed and read out properly when using an EPROM reader, so I think the ROMS themselves are good.  Regarding removing some and trying to boot, are you saying to leave only F8 and remove all other 5?  I wasn't sure what was meant by removing 'all Applesoft ROMs'.  Is that everything except F8?

Thanks again for all the help so far.

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It's possible your screen is

It's possible your screen is showing Page 2 text. You should check F14 pin 6. If there ever was a Videx Softswitch installed there, the socket might be damaged.

 

Also, if you think you're in the monitor and PR#6 doesn't work, try 6 ctrl-P or C600G and see if the disk boots.

 

 

djw
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Thanks for the suggestions. 

Thanks for the suggestions.  F14 pin 6 is low - not sure if that is a good or bad thing.

Typing 6<cntrl>P does nothing immeadiately, and error beep when hitting return.  Same thing with C600G - nothing immeadiately, and error beep after hitting return.  So I guess I don't know where the code is.  And in all cases, the floppy doesn't access.

A couple other observations to try and figure out where the code might be (Basic, Monitor, or somewhere else).  No keystrokes are registered after boot until reset is pressed.  And then, pressing return results in no error beep (imagine a blank line).  I can press return all day with no error beep, as long as nothing else was input before.  However, if I press any other key (or keys) and then return, I get the error beep.  Cntrl-G works immeadiately on pressing.  Not sure if this is helpful, but it is all I can observe with the display only filled with '?' all the time.

djw
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OK, significant progress. 

OK, significant progress.  When testing a bit more with the keyboard, it was apparent that scan codes were not correct.  Certain keys weren't working, but other weird things like 'Shift 7' behaving like Cntrl G - immeadiate beep.  So even though the 74LS04 (U4) seemed ok with a logic probe, I desoldered it and replaced it.  The original was indeed bad (surely damaged by the ribbon cable reversal) - failed testing in the IC tester.

With the new IC in place, I steped through the key and return combinations, trying to see if each key was being read (syntax error beep).  "I , ;" were not working, nor with shift either.  Additional fault turned out to be a bent pin in the keyboard to daughterboard connector - pin 15 was not making connection.  I bent it back a bit and used some Deoxit, and those associated keys now are working.

With the keyboard seemingly outputting good data now, PR#6 causes the drive to work.  Properly formatted BASIC commands also cause no syntax error beep.  So safe to assume BASIC is running, and it just can't be seen with the question marks.

So, I tried the GR and HGR commands.  In both cases, the screen blanks.  Typing is still not displayed.  Exitting graphics mode by typing 'TEXT' (or hitting reset) returns  to the question mark screen.  But, if HGR was used, those question marks are now inverted @ symbols.

So it seems things are close - the keyboard issues were a nice diversion, but something still wrong about video content control.

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djw wrote:Thanks for the
djw wrote:

Thanks for the suggestions.  F14 pin 6 is low - not sure if that is a good or bad thing.

 That's correct. Now check the same signal at B1 pin 9 to see if it is also low.

 

But it sounds like you've got other issues as well.

djw
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B1 pin 9 is not low - it is

B1 pin 9 is not low - it is the 14MHz clock.  Looks ok.  Did you mean to check a different signal?

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djw wrote:B1 pin 9 is not low
djw wrote:

B1 pin 9 is not low - it is the 14MHz clock.  Looks ok.  Did you mean to check a different signal?

 Sorry, meant to write H1 pin 9.

djw
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H1 pin 9 measures low for

H1 pin 9 measures low for TEXT, GR, and HGR modes.

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Do you have anything in slot

Do you have anything in slot 0 right now? I have seen this issue with a bad language card or bad exp on slot 0. 

 

Please try pulling every card and the third RAM bank, droppng to 32K wth no cards installed, amd tell us if this changes aught. 

djw
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In order to rule out other

In order to rule out other problems, I'm currently setup for just RAM bank C (16K), and the disk controller in Slot 6.  Symptoms are the same without the disk controller, or with 32K or 48K of mainboard RAM.

Now that the keyboard input is working (albiet blindly) and confirmed to be in BASIC, I can enter commands (TEXT, GR, HGR, PEEK/POKE) and monitor signals on the board.  Thinking at this point that something in the video scanning is not reading the correct memory area (bad mux/counter/latch socket, etc).  Could be opposite problem also, where the computer is writing to the wrong RAM area and video reading is correct.

If anything is known to die when a 4164 RAM IC is placed in E3 instead of a 4116, that did happen on this board - not sure if that might point to some things to check.

 

 

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djw wrote:In order to rule
djw wrote:

In order to rule out other problems, I'm currently setup for just RAM bank C (16K), and the disk controller in Slot 6.  Symptoms are the same without the disk controller, or with 32K or 48K of mainboard RAM.

Now that the keyboard input is working (albiet blindly) and confirmed to be in BASIC, I can enter commands (TEXT, GR, HGR, PEEK/POKE) and monitor signals on the board.  Thinking at this point that something in the video scanning is not reading the correct memory area (bad mux/counter/latch socket, etc).  Could be opposite problem also, where the computer is writing to the wrong RAM area and video reading is correct.

If anything is known to die when a 4164 RAM IC is placed in E3 instead of a 4116, that did happen on this board - 

 

I think you're on the right track - the machine is clearly funcitonal except for video output.

I'd suspect some of your video shift registers now.  The monitor and BASIC are trying to write to the screen but since the screen is filled with garbage you're getting nothing seen.

Have you got any "cracked" game disks on hand that have a graphics splash screen?  See if one of them boots and it's able to "clear" the screen and switch to graphics mode.

(I suspect I already know the answer to this...)

 

djw
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I don't have any games

I don't have any games rounded up just yet (trying to get back into this after 40 years), but I can use BASIC and POKE to switch graphics modes to test.  If I go into GR, HGR, or HGR2, the ? marks go away and the screen is completely blank.  However, there is still no text displayed - even in mixed text/graphics modes.  I've confirmed that the soft-switch F14 is outputing the correct state for each mode.  I've also verified on the scope that the video modes seem to switch ok - with colorburst present in graphics modes, and not in text.

Is any of that helpful regarding next steps?

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Hi all

A good source for repairing an APPLE II is 

https://vintageapple.org/apple_ii/pdf/How_To_Repair_And_Maintain_Your_Apple_Computer_1985.pdf

 

Kind Regards

Michael

djw
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Thanks.  I didn't find that

Thanks.  I didn't find that book, but have been referring to the Robert Brenner Apple II / II+ Troubleshooting and Repair Guide, the Winston Gayler The Apple II Circuit Description, and the Apple II Serice manual.  All great references, but narrowing the fault is quite the challenge given the complexity (elegance?) of the Apple II video generation approach.

 

djw
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'?' marks solved, but another video issue / question.

So the '?' fault has been identified.  Swapped around the 74LS257's (there are 5) and normal text and the Apple II prompt appeared.  C12 was identified to be the problem - didn't work with a TI part in that spot - but did work with a Signetics (or SGS?) part.  Didn't make any sense that taking that IC and placing it elsewhere also worked - a different function did not become broken.  Also didn't make sense that all IC's tested good in the IC tester.  Kicker was also that if I put the other TI LS257 from elsewhere on the board into C12, the fault returned.  So any TI part would fail in that position.

Got to thinking it might be something else loading the chip differently, so I scoped all the pins.  Turned out the pin 11 was floating - should be ground.  Amazingly, the leads are just slightly different Signetics vs. TI, and the Signetics (SGS) part makes contact.  Conected a jumper to the IC lead, and the TI parts also worked (of course).  So, real fault is a bad socket pin - not the IC. 

I'll run some diagnostics and make sure nothing else shows up.  But one thing causing grief is the video and TV compatability.  The first TV I tried (a nothing special Westinghouse 42" LCD), text is ok but nothing is displayed in graphics mode.  TV also says 'no signal' occasionally.  The scope shows there is a signal ( a bit over 1V pk-pk at max), but the TV doesn't like it (in graphics modes).

With a cheap composite to VGA adapter, it has no signal at all in any video mode.  Works with other things (Nintendo), but not the Apple II.

The best I've been able to do so far is with my Samsung UHD TV.  Crisp picture and all video modes work - but none have color.  Again on the scope, the colorburst is there (for the graphics modes).

I know the Apple II+ takes shortcuts on the video generation and is not fully NTSC compliant.  Is the behaviour I'm seeing with 'modern' TVs typical, or do I  have a video output issue that needs fixing?

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This is indeed typical. Use a

This is indeed typical. Use a composite CRT or a CRT television on an RF mod, or a 90s CRT television with RCA in. 

djw
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Best composite to modern TV/monitor converter?

Unforetunately the last of my CRT TVs went to the e-waste center just before I decided to tackle this project.  Regarding using this with current displays, I have the cheap ebay composite to VGA adapter which is unworkable.  Is there a 'known good' recommended converter to VGA, DVI, or HDMI that is compatible with the Apple II+?  The 'good enough' type that would get stable picture and color, but not as fancy and low-lag as the more costly RetroTink and OSSC flavors?

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djw wrote:Unforetunately the
djw wrote:

Unforetunately the last of my CRT TVs went to the e-waste center just before I decided to tackle this project.  Regarding using this with current displays, I have the cheap ebay composite to VGA adapter which is unworkable.  Is there a 'known good' recommended converter to VGA, DVI, or HDMI that is compatible with the Apple II+?  The 'good enough' type that would get stable pictu

 The de-facto standard VGA converter for eht Apple II is the VGA Scaler from A2Heaven.com.

If all yo uhave is modern monitors this might work for you (although I have found that cheap VGA monitors sometimes don't like to sync up to it properly in 80-column mode) then this card is probably the best out there.  Also, the VidHD card from Blue Shift Inc's John Brooks.  I am unsure as to the availability of it right now, but here's some contact information:  https://www.facebook.com/groups/5251478676/permalink/10158076443038677/

Also, I've found that even composite monitors on some Apple II+ motherboards have trouble stabilizing a picture unless I turn up the brightness pot on the motherboard - the one at J-14 near the game port.  That might be what's causing your LCD television to kakk when you switch to graphics mode.

 

 

djw
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Thanks!

Thanks for the info.  Is there a recommeded voltage level (bottom of sync pulse to top of white video) to adjust the video gain pot for best compatability with current TV's (with composite)?

Yes, I've seen the a2heaven card - and a few others also.  I'm sure they have exellent output and work well, but quite expensive and somewhat scary internal hookups to get at the raw signals.  I was hoping for something where the computer would remain stock, and do this via native composite output - such as the Retrotink or OSSC does.   I imagine this is a common issue for most nowadays - is there a thread here that discusses options for video (Apple 2+ specific)?  I know this is venturing off the topic of this post - glad what I'm seeing is normal.

Thanks to everyone for all the tips in helping to make this repair possible.  I'm exicited to clean the floppy drive and see if my old discs work, and likely update to a modern SD storage method.

 

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