Sidebar Sidebar
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.

Apple II - Possible PSU Issue

HunterCupp

HunterCupp

macrumors regular
Original poster
Feb 13, 2014
140
8
Columbus, OH
Hello, all.

I have recently acquired an Apple II and have been confused for days about a problem that may be just a simple as an off switch.

My Problem
-----------
Apple II does not respond to key presses other than 'RESET' button. The screen is NOT frozen.
-----------

As for the expansion slots, 1 and 2 are filled. 1, with a Language Card, and 2 with an Apple RAM Module. I have tried taking both out and re-attempting the process in hopes of a change, but there has been no success. Everything else seems to be in it's proper places.

I have tried troubleshooting over other parts of the web and have only found a source which said--
"Computer Does Not Respond to Key Presses
Make sure that the Caps Lock key is pressed."

I however believe that is meant for a later model, such as the Apple Plus, as there is no 'Caps Lock Key' on an original Apple II.

I have come across the thought of in order to use the command line, needing to have a Master System Disk booted upon start up, but I currently do not have one, nor a floppy disk drive, nor a Disk II controller card.

I hope that it is an easy fix that I have just overlooked.
Thanks in advance,
-Hunter
 
Last edited:
Remove the disk controller card. Turn on the computer.

It should be a blinking cursor at a prompt.

Can you type?
 
Phew - many causes so it' hard to say.

Firstly, does the power light on the keyboard work? If it does, this indicates that +5v is getting to the keyboard. If not, then it could be a blown globe so it doesn't exactly mean a problem elsewhere.

The rest of the possible causes are numerous.

I'll assume we're talking about the two piece keyboard.

Bad cable or bent/broken pin on the 16pin keyboard cable, Or incorrectly oriented cable.

On the keyboard encoder board:
Failed keyboard encoder chip (AY-5-3600)
Bad 7404 at U4 on the keyboard encoder board.
Bad 7400 at U3 and U2 (keyboard strobe)

On the motheroard:
B6 74LS257
B7 74LS257
B10-74LS74
C11-74LS04

Of course, there are passive components that may have failed, as well as the usual bad IC sockets problems.

A logic probe really helps with these old machines, but sometimes reseating the affected ICs can help (if only for a short time).
 
MacTech68 said:
Firstly, does the power light on the keyboard work? If it does, this indicates that +5v is getting to the keyboard. If not, then it could be a blown globe so it doesn't exactly mean a problem elsewhere.

The rest of the possible causes are numerous.

I'll assume we're talking about the two piece keyboard.

Bad cable or bent/broken pin on the 16pin keyboard cable, Or incorrectly oriented cable.
Click to expand...

MacTech68

The power light does in fact work. Although sometimes I have noticed that a start up doesn't always turn it on, but to activate it if that happens, just press any button on the keyboard and it's on. (I am speaking about the light, not the Apple II itself.)

I'm not entirely sure what you mean by "two piece keyboard" unless you are talking about the one with the numpad off to the side. I will check the keyboard plug/connecter as soon as I can.

I have attached a picture of my Apple II for reference.

Thanks,
-Hunter
 

Attachments

  • image.jpg
    image.jpg
    1.2 MB · Views: 392
I could be wrong here, but you may have Integer Basic ROMs without autostart.

If that is the case, you might find that holding "CTRL" and pressing "Reset" will drop you into a prompt, then try a "CTRL" and "B" to get into Integer Basic, where the keyboard works.

I'm a bit hazy on the detail but if you have a greater than sign for a prompt (which it looks like in your pic) then that's Integer Basic ROMS which lack the Auostart ROM and without a DISK II controller, the reset never gets triggered.

(I think...) :confused:

Keyboard revisions for the Apple II can be seen here (somewhat down the page).
http://www.willegal.net/appleii/early-a2-keyboards.htm
 
The rest of my question was still valid. So you don't have the card, you can skip the step of taking it out.. ;-)

Since I see a clear screen and just a > - that tells me it's got Integer ROMs with autostart. Otherwise you'd have a screen with several 'strips' of characters, and a blinking cursor at a * prompt, near the bottom.

The reset key does not use any of the encoder functions, and is basically a hard switch. There is a jumper/switch that sets it to require CTRL to be held down, or not. Sounds like it's set to not require it.

That may be a one piece keyboard with integrated encoder. The simplest way to check it is to swap with another one, of course. No keys working at all? I would find it very odd that every switch quit, but depending on environmental influences.. not specifically unheard of.

Using a meter, you can try switches individually from the bottom side of the PCB. If they're working, I'd suspect that the AY-3600 could be bad, which is somewhat common.
 
To all.

I have purchased an Apple Disk I/O Controller Card and a 5.25 (A9M0107) Floppy Drive, all supposedly working, from eBay.

I plan on testing the keys/switches with a multimeter within the week as well. If I do receive voltage, I will then attempt at replacing the 'AY-3600' chip that tdiaz mentioned in the previous post.

I will keep everyone updated as I go along. I am away from home this weekend so I won't be able to do any further testing until late Monday evening or in the afternoon on Tuesday.

Thanks,
-Hunter
 
To all.

Well, I'm not sure exactly what happened here, but listen.

I was taking apart the Apple II so I could use the multimeter to test the switches. As I was removing the Language Card, I heard a buzz of sorts, very quiet like. Me, being me, realized that the Apple II was still on from prior testing. I immediately became extremely worried and turned it off. I sat around for a few minutes and decided to make sure nothing happened and turned it on, this time I did NOT hear a startup beep or see anything on the screen. The 'POWER' key on the keyboard was lit, however.

I've just dug myself into a deeper hole.

I hope someone can help.

Thanks,
-Hunter
 
Did you put it back? .. and connect the cable back to the motherboard?

That you sometimes pressed a key to get the light to come on is already suspect.

The power supplies are known to pop a filter cap, pulling cards out while the power is on is known to blast other things, especially if the cards are pulled out "twisted" (leaning to the back) vs. yanked straight, and I mean -STRAIGHT- up.

Pulling straight generally will not cause anything. That you heard something tells me it was not, and the bus was probably shorted.

I might be passing Columbus sometime in late July .. ;) after stopping in Kansas City for a week.
 
Last edited:
tdiaz said:
Did you put it back? .. and connect the cable back to the motherboard?

That you sometimes pressed a key to get the light to come on is already suspect.

The power supplies are known to pop a filter cap, pulling cards out while the power is on is known to blast other things, especially if the cards are pulled out "twisted" (leaning to the back) vs. yanked straight, and I mean -STRAIGHT- up.

Pulling straight generally will not cause anything. That you heard something tells me it was not, and the bus was probably shorted.

I might be passing Columbus sometime in late July .. ;) after stopping in Kansas City for a week.
Click to expand...

tdiaz

Yes, I did later attempt at inserting the Language Card back into the Apple II. There was no change.

The light thing that I mentioned has not happened since the original post, but something new has started happening that I kind of just brushed off as something that happened with age; when powered on, a 'popping' noise would occur, one out of three times of being powered on.

So, basically, I've busted the power supply?

Are you stopping for a convention in Columbus or are you just generally passing by?

Thanks, Hunter.

EDIT!-
I'm not really sure how I could have given so much information here, but here is what actually happened. The Apple II was on as I was attempting to insert the Language Card, not remove it. As the bottom pieces touched the Apple II expansion slot pins, the buzz occurred. Everything else holds to the story.
------------------
 
Last edited:
To all.

Make sure to read the last part of the post above.

Thanks,
-Hunter

P.S.

tdiaz

Is there any easier way to contact you? Do you have a Skype account? It would make things a lot easier for me, having fast access to someone who seems to know what may or may not be wrong. I appreciate the help you have given, along with MacTech68. A form of instant messaging would be nice, considering that MacRumors seems to be a little slow with replies.

Thanks, again.
-Hunter
 
Ouch.

I doubt that the powersupply is damaged. Switch Mode Power Supplies are built to power down under a short condition. They'll cycle from power-up to power-down until the short is removed.

It's more likely that an IC has been zapped. I'm hoping it isn't, but my gut call is one of the 8T28 bus transceiver.
 
Yup... power-on card insertion .. is typically a bus killer, as most people will instinctively (for lack of a better word), put the card in and push it to the back of the slot.

Not all II's have the 8T28, but those that do, it's usually a good bet. It's to the right of the CPU..
 
tdiaz and MacTech68

Thanks for the info on the chips and busses! I would most likely need a kind of diagram/example of where the chip(s) possibly needing replacing may be. I have another Apple II (Board) that may or may not work for our cost, it's never been tested for functionality, but I have so far only used it for spare parts and they've seemed to work so far.

Also, is there any way to repair damaged pins on some of the Apple II's chips? Some have broken off throughout the years as they have come out and needed bent back into place, I've kept them just in case a repair is possible.

I will send pictures of my board(s) and damaged chips tomorrow afternoon.

Thanks,
-Hunter

P.S.
The keyboard encoder chip that tdiaz mentioned that may possibly need replaced would be one of the chips that I need the location of.
 
The two 8T28 chips are circled in red in the pic below. As tdiaz says, some boards use a different IC. If you have one larger chip there it's probably marked as an 8304.

As for the keyboard, have a look at the second pic. This is the more common keyboard, but yours may be the older type. A pic of yours from the same angle will let us know. Basically the revised keyboard has a second smaller board that plugs into the keyboard.
 

Attachments

  • Apple II MB 8T28.jpg
    Apple II MB 8T28.jpg
    39.9 KB · Views: 768
  • AppleII.jpg
    AppleII.jpg
    57.8 KB · Views: 479
Last edited:
To all.

I've replace the two chips and attempted a power up. Still no beep, or sign of improvement.

I've attached a picture of my Apple II's board.
I will later post a picture of the keyboard from an angle as seen in MacTech68's photo.

Thanks,
-Hunter

P.S.
The two missing ROM chips have been missing before this problem occurred.
 

Attachments

  • image.jpg
    image.jpg
    2 MB · Views: 473
BTW, I would suggest removing ALL 3 cards (returning the two RAM chips to their sockets) whilst you are trying to get the main board going.

Ahem, make sure the power cord is removed. ;) ;)
 
MacTech68 said:
BTW, I would suggest removing ALL 3 cards (returning the two RAM chips to their sockets) whilst you are trying to get the main board going.

Ahem, make sure the power cord is removed. ;) ;)
Click to expand...

MacTech68

I just attended what you recommended and there was no change, unfortunately.

Thanks,
-Hunter
 
If you look at the edges of the board, there is a grid with letters down one side (say the y axis) and numbers (1 thru 14) along the x axis.

This way, the ones you ALREADY swapped were H10 and H11.

Does that make sense?

EDIT: See attached pic
 

Attachments

  • Apple II H3-H5 B6-B7.jpg
    Apple II H3-H5 B6-B7.jpg
    133.6 KB · Views: 587
Last edited:
MacTech68 said:
If you look at the edges of the board, there is a grid with letters down one side (say the y axis) and numbers (1 thru 14) along the x axis.

This way, the ones you ALREADY swapped were H10 and H11.

Does that make sense?

EDIT: See attached pic
Click to expand...

MacTech68

Ah, I see now.
They've all been replaced (Including the H3,4, and 7.. Still no change.)

Thanks,
-Hunter
 
Shoot - from here I'd usually start with a logic probe.

Does the keyboard light still illuminate?

EDIT: Try the 6502 CPU (largest chip - 40pin)

EDIT 2: Also try 74LS194 @ B4 AND 74LS174 @ B5 (Kind of guessing now).
 
Last edited:
MacTech68 said:
Shoot - from here I'd usually start with a logic probe.

Does the keyboard light still illuminate?

EDIT: Try the 6502 CPU (largest chip - 40pin)

EDIT 2: Also try 74LS194 @ B4 AND 74LS174 @ B5 (Kind of guessing now).
Click to expand...

MacTech68

Yes, the light does still turn on when powered. I will replace the chips as soon as possible, as I am not home at the moment.

Thanks,
-Hunter
 
You must log in or register to reply here.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.
Top Bottom
Back