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Old 15 July 2019, 01:46   #1
Tony Gunk
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Amiga 500 Issues (Continued)

Hello, again


Well, after assuming that the issues with my Amiga 500 were due to an underperforming PSU, I purchased a new one, and had no change in behavior. So, the current issues still stand:


-Power/drive LEDs are always lit
-No click from disk drive
-Various colors appearing on the monitor:
Blue
Light Green
Dark grey
Light grey
White


Base off of the colors being shown on screen, I can assume there's issues with the OSC (Fat Agnus, Paula, Denise), One of the two CIA chips, and the CPU, which I've already had replaced.


As before, any help with my problem would be much appreciated.


Thanks.
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Old 15 July 2019, 02:03   #2
lesta_smsc
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Check the RAM expansion pins. I had the same errors but it was because 2 pins were accidentally touching after installing RAM.
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Old 15 July 2019, 02:49   #3
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A green screen signals a RAM error in the first 256K of chip ram. Grey and white signal certain stages of the boot process. I haven't found blue by quickly looking at a disassembly of exec 33.192.

Can you burn a diagnostic ROM? http://www.diagrom.com/

This might provide some further insight.
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Old 15 July 2019, 02:50   #4
Tony Gunk
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Quote:
Originally Posted by lesta_smsc View Post
Check the RAM expansion pins. I had the same errors but it was because 2 pins were accidentally touching after installing RAM.


None of these pins are touching, and I have tested the machine with and without an A501 ram expansion without change in behavior.
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Old 15 July 2019, 05:29   #5
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Quote:
Originally Posted by R4M View Post
A green screen signals a RAM error in the first 256K of chip ram. Grey and white signal certain stages of the boot process. I haven't found blue by quickly looking at a disassembly of exec 33.192.

Can you burn a diagnostic ROM? http://www.diagrom.com/

This might provide some further insight.


I don't have any means of burning a ROM chip. Also, a light green screen is different from a "normal" green screen, as it indicates a CIA chip error.
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Old 15 July 2019, 07:05   #6
Bruce Abbott
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Quote:
Originally Posted by Tony Gunk View Post
a light green screen is different from a "normal" green screen, as it indicates a CIA chip error.
Which may be relevant because :-

Quote:
Power/drive LEDs are always lit
The drive LED should not be lit unless the drive motor has been turned on, and definitely not during reset. Being permanently lit suggests the even CIA chip is fried. Similarly for the power LED. It should stay dim or off until the audio filter is enabled, which is controlled by the odd CIA chip.

What revision is your motherboard?
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Old 15 July 2019, 16:21   #7
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It's a revision 5 board. It seems that replacement CIA chips are something to consider. However, I also get error screens regarding the OCS, which could be Denise, Paula, or Fat Agnus. On that same note, my Paula chip broke one of it's legs while being extracted, warranting a replacement.


It baffles me that there are so many supposed issues with the boot process, OCS, CIA chips, etc. all at once. I was told on my pervious thread about this topic that a possible cause for these issues could be a bad PSU. I got a replacement, but with no change in behavior. Don't quote me on this, but is it possible that a bad PSU could have fried the chips, causing all my problems? And I know, these machines get older every day, but it seems odd that seemingly everything on the board is failing.
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Old 15 July 2019, 17:17   #8
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If the voltage level of your old PSU was lower than normal, it should not have damaged your computer.

If you have a problem with the lower 256K of chip ram, you can not trust any error messages after the memory test. Because once exec thinks that the memory is OK, it sets the stack pointer to $40000 and then all bets are off.

A problem with the CIAA can also cause memory problems in the lower 256k. On reset, the ROM is mapped there until the overlay is turned off, if everything work as it should.

Code:
FC00FE  move.b    #3,BFE201         Set low two bits for output. 
FC0106  move.b    #2,BFE001         Set boot ROM off, power light dim.
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Old 15 July 2019, 18:24   #9
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I've got a multimeter on me, but I'm not very acquainted with it. Could I use it to check the 512k ram for issues?

Also, if a CIA chip needs replacing, do you know any good sources for such? Ebay is always an option, but prices can get high, and most Amiga related peripherals come from the UK, or elsewhere in Europe
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Old 15 July 2019, 19:49   #10
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I would get a DiagRom V1.1 first. They are around 12 bucks on ebay with international shipping.
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Old 15 July 2019, 20:10   #11
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drive LEDs are always lit
This is may indicate the floppy cable is plugged backwards. We've all done it as the connectors are not keyed. Double check pin 1 on the motherboard goes to pin 1 on the floppy drive.
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Old 15 July 2019, 21:11   #12
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I've gone ahead and purchased a DiagROM 1.1 chip. I'm not sure how it works though. Any pointers? or is it relatively straight forward?
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Old 15 July 2019, 22:39   #13
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Open your Amiga. Replace the ROM chips (take care to insert them the right way). Turn on the computer.

That is, if you're somewhat lucky. If the damage is so serious that the graphics output won't work, you'll have to connect another computer to the serial interface an hope that that's still working.
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Old 16 July 2019, 00:35   #14
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Quote:
Originally Posted by R4M View Post
Open your Amiga. Replace the ROM chips (take care to insert them the right way). Turn on the computer.

That is, if you're somewhat lucky. If the damage is so serious that the graphics output won't work, you'll have to connect another computer to the serial interface an hope that that's still working.


I've seen videos of people having to make modified sockets for their DiagROM chip to work in some older revision motherboards, and mine is a revision 5 board. Assuming the DiagROM has been updated since then, will this be an issue ill have to deal with on my amiga?
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Old 16 July 2019, 01:42   #15
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Rev 5 damit... You will have to make or get an adaptor. Sorry, I forgot about that. I don't own an A500.

http://eab.abime.net/showthread.php?t=82824
https://amigastore.eu/en/599-amiga-5...m-adapter.html
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Old 16 July 2019, 02:18   #16
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A slightly different approach around minute 8.

[ Show youtube player ]
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Old 16 July 2019, 10:35   #17
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Originally Posted by nogginthenog View Post
This is may indicate the floppy cable is plugged backwards. We've all done it as the connectors are not keyed. Double check pin 1 on the motherboard goes to pin 1 on the floppy drive.
Indeed, and it appears many A500s shipped with the floppy cable backwards at both ends from the factory. Still works fine of course, but can be confusing if you only disconnect one end to remove the drive, for example. I think you would still get the Kickstart insert disk screen if this was the only issue though...
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Old 16 July 2019, 21:44   #18
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I'm not so sure about the insert disk screen, but at least it would always stop at a white screen. I had this problem once with a broken df0: cable.
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Old 01 August 2019, 20:14   #19
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Well, I acquired a DiagROM chip, and an EPROM adapter to make it work properly in my rev5 motherboard; it didn't help whatsoever. The machine never made it to the DiagROM menu, and instead only presented the same response I've been getting all summer:


-No click from floppy drive
-No caps-lock error
-Power/Drive LED's remain lit at all times
-Shows a number of colored screens
.Blue
.Light Green
.Dark Grey
.Light Grey
.White


I know there's got to be a way to get this thing working again, but as of now I'm completely inept to that solution.


As usual, any help on this matter would be greatly appreciated.
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Old 01 August 2019, 21:46   #20
nogginthenog
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Are you 100% sure the floppy isn't plugged in backwards? The Amiga will show the kickstart screen with the floppy unplugged but it takes a while.
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