Discussion:
Apple IIgs boot problem - checkerboard pattern
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cb meeks
2017-07-30 15:25:52 UTC
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I have two Apple IIgs's. One is a ROM 3 that works great.

The other is either a ROM 0 or ROM 1 and when I power it on, I only get a checkerboard pattern on the screen. But it's not a perfect checkerboard. Sort of random but in B/W.

This board only has the one ROM chip and it's labeled "TC531000P-7095".

I've re-seated all of the chips that are in a socket. I've swapped out the CPU with a known, working one. I don't get any beeps either.

My suspicion is the ROM is bad. I get the exact same behavior when I power up the board with no ROM at all.

Any ideas what it could be? I could post pics if needed or any model numbers.

Thanks.
John Brooks
2017-07-30 15:52:00 UTC
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Post by cb meeks
I have two Apple IIgs's. One is a ROM 3 that works great.
The other is either a ROM 0 or ROM 1 and when I power it on, I only get a checkerboard pattern on the screen. But it's not a perfect checkerboard. Sort of random but in B/W.
This board only has the one ROM chip and it's labeled "TC531000P-7095".
I've re-seated all of the chips that are in a socket. I've swapped out the CPU with a known, working one. I don't get any beeps either.
My suspicion is the ROM is bad. I get the exact same behavior when I power up the board with no ROM at all.
Any ideas what it could be? I could post pics if needed or any model numbers.
Thanks.
I'd suspect the ROM too. I have a Woz GS that lost it's ROM a couple years ago.

Fixed it with an A2Heaven GS X ROM:

http://www.a2heaven.com/webshop/index.php?rt=product/product&path=75&product_id=137

-JB
@JBrooksBSI
cb meeks
2017-07-30 16:04:17 UTC
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Post by John Brooks
Post by cb meeks
I have two Apple IIgs's. One is a ROM 3 that works great.
The other is either a ROM 0 or ROM 1 and when I power it on, I only get a checkerboard pattern on the screen. But it's not a perfect checkerboard. Sort of random but in B/W.
This board only has the one ROM chip and it's labeled "TC531000P-7095".
I've re-seated all of the chips that are in a socket. I've swapped out the CPU with a known, working one. I don't get any beeps either.
My suspicion is the ROM is bad. I get the exact same behavior when I power up the board with no ROM at all.
Any ideas what it could be? I could post pics if needed or any model numbers.
Thanks.
I'd suspect the ROM too. I have a Woz GS that lost it's ROM a couple years ago.
http://www.a2heaven.com/webshop/index.php?rt=product/product&path=75&product_id=137
-JB
@JBrooksBSI
Thanks for the link!

So, a little update...

I put a logic probe on the RAM chips. They are all 41464C-12. One thing I noticed that all of the RAM chips except the "FAST RAM" pulse on the I/O (data) lines. The FAST RAM data lines are a constant LOW. I'm not sure if this is an issue but I noticed it was different.

All of the RAM chips are getting a solid 5V which tells me the PSU should be good.
Charlie
2017-07-30 17:49:52 UTC
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Post by cb meeks
Post by John Brooks
Post by cb meeks
I have two Apple IIgs's. One is a ROM 3 that works great.
The other is either a ROM 0 or ROM 1 and when I power it on, I only get a checkerboard pattern on the screen. But it's not a perfect checkerboard. Sort of random but in B/W.
This board only has the one ROM chip and it's labeled "TC531000P-7095".
I've re-seated all of the chips that are in a socket. I've swapped out the CPU with a known, working one. I don't get any beeps either.
My suspicion is the ROM is bad. I get the exact same behavior when I power up the board with no ROM at all.
Any ideas what it could be? I could post pics if needed or any model numbers.
Thanks.
I'd suspect the ROM too. I have a Woz GS that lost it's ROM a couple years ago.
http://www.a2heaven.com/webshop/index.php?rt=product/product&path=75&product_id=137
-JB
@JBrooksBSI
Thanks for the link!
So, a little update...
I put a logic probe on the RAM chips. They are all 41464C-12. One thing I noticed that all of the RAM chips except the "FAST RAM" pulse on the I/O (data) lines. The FAST RAM data lines are a constant LOW. I'm not sure if this is an issue but I noticed it was different.
All of the RAM chips are getting a solid 5V which tells me the PSU should be good.
You might want to check if the RESET line is being held low.
That gives a, sort of, checkerboard pattern on my ROM 01.

Charlie
John Brooks
2017-07-30 18:00:09 UTC
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Post by cb meeks
Post by John Brooks
Post by cb meeks
I have two Apple IIgs's. One is a ROM 3 that works great.
The other is either a ROM 0 or ROM 1 and when I power it on, I only get a checkerboard pattern on the screen. But it's not a perfect checkerboard. Sort of random but in B/W.
This board only has the one ROM chip and it's labeled "TC531000P-7095".
I've re-seated all of the chips that are in a socket. I've swapped out the CPU with a known, working one. I don't get any beeps either.
My suspicion is the ROM is bad. I get the exact same behavior when I power up the board with no ROM at all.
Any ideas what it could be? I could post pics if needed or any model numbers.
Thanks.
I'd suspect the ROM too. I have a Woz GS that lost it's ROM a couple years ago.
http://www.a2heaven.com/webshop/index.php?rt=product/product&path=75&product_id=137
-JB
@JBrooksBSI
Thanks for the link!
So, a little update...
I put a logic probe on the RAM chips. They are all 41464C-12. One thing I noticed that all of the RAM chips except the "FAST RAM" pulse on the I/O (data) lines. The FAST RAM data lines are a constant LOW. I'm not sure if this is an issue but I noticed it was different.
All of the RAM chips are getting a solid 5V which tells me the PSU should be good.
If you get a beep at power up, the ROM is good enough that you should be able to test the RAM via self test (open-apple + close-apple + ctrl + reset).

If you don't get a beep at power up, then the CPU or ROM (or clock, etc) is bad.

-JB
@JBrooksBSI
cb meeks
2017-07-30 20:12:37 UTC
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Post by John Brooks
Post by cb meeks
Post by John Brooks
Post by cb meeks
I have two Apple IIgs's. One is a ROM 3 that works great.
The other is either a ROM 0 or ROM 1 and when I power it on, I only get a checkerboard pattern on the screen. But it's not a perfect checkerboard. Sort of random but in B/W.
This board only has the one ROM chip and it's labeled "TC531000P-7095".
I've re-seated all of the chips that are in a socket. I've swapped out the CPU with a known, working one. I don't get any beeps either.
My suspicion is the ROM is bad. I get the exact same behavior when I power up the board with no ROM at all.
Any ideas what it could be? I could post pics if needed or any model numbers.
Thanks.
I'd suspect the ROM too. I have a Woz GS that lost it's ROM a couple years ago.
http://www.a2heaven.com/webshop/index.php?rt=product/product&path=75&product_id=137
-JB
@JBrooksBSI
Thanks for the link!
So, a little update...
I put a logic probe on the RAM chips. They are all 41464C-12. One thing I noticed that all of the RAM chips except the "FAST RAM" pulse on the I/O (data) lines. The FAST RAM data lines are a constant LOW. I'm not sure if this is an issue but I noticed it was different.
All of the RAM chips are getting a solid 5V which tells me the PSU should be good.
If you get a beep at power up, the ROM is good enough that you should be able to test the RAM via self test (open-apple + close-apple + ctrl + reset).
If you don't get a beep at power up, then the CPU or ROM (or clock, etc) is bad.
-JB
@JBrooksBSI
My Apple keyboard doesn't have a close-apple. But I get no beeps at all.

I'll check the reset line too.
g***@sasktel.net
2017-07-30 20:24:30 UTC
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Post by cb meeks
My Apple keyboard doesn't have a close-apple. But I get no beeps at all.
I'll check the reset line too.
Closed Apple is the same as the Option key on a Mac keyboard
cb meeks
2017-07-30 20:32:29 UTC
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Post by g***@sasktel.net
Post by cb meeks
My Apple keyboard doesn't have a close-apple. But I get no beeps at all.
I'll check the reset line too.
Closed Apple is the same as the Option key on a Mac keyboard
Ah cool.. Thanks.

FYI, the /RESET shows a solid 5V which should be correct.

Hmmm...not sure on this one. I may order some RAM chips and see if that helps. Is there a modern ROM replacement I can get? Or is that GS X ROM my best option?
barrym95838
2017-08-01 05:12:05 UTC
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On Sunday, July 30, 2017 at 1:32:31 PM UTC-7, cb meeks wrote:
Ah cool.. Thanks.
Post by cb meeks
FYI, the /RESET shows a solid 5V which should be correct.
...
Can you strobe it low for a few msec with something on-hand,
after the power supply and clock have had at least a few msec
to stabilize?

Mike B.
Michael J. Mahon
2017-08-01 18:59:58 UTC
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Post by cb meeks
Ah cool.. Thanks.
Post by cb meeks
FYI, the /RESET shows a solid 5V which should be correct.
...
Can you strobe it low for a few msec with something on-hand,
after the power supply and clock have had at least a few msec
to stabilize?
Mike B.
Pressing the Reset key (with Ctrl) does that. ;-)
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
barrym95838
2017-08-02 08:08:28 UTC
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Post by Michael J. Mahon
Pressing the Reset key (with Ctrl) does that. ;-)
I'm sure that you're describing the behavior of a properly functioning
device. Are we safe in assuming the same for a (clearly) broken one?

Mike B.
Michael J. Mahon
2017-08-02 15:10:58 UTC
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Post by barrym95838
Post by Michael J. Mahon
Pressing the Reset key (with Ctrl) does that. ;-)
I'm sure that you're describing the behavior of a properly functioning
device. Are we safe in assuming the same for a (clearly) broken one?
Mike B.
The /RESET circuit is pretty simple on 8-bit Apples, but may depend on the
keyboard controller for IIgs's.

It's easy to check in either: monitor the /RESET pin on the processor while
pressing the key(s).
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
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