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Old 28 February 2021, 13:12   #1
mathop
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A500(+) random lockups

Hi. This is more or less a sequel to my post about my A500 booting into a black screen.
Since then I mostly got it working again. The most obvious problems where: fat agnus socket pin bent - I fixed that by replacing the socket. Also the keyboard would randomly flash its caps lock led. After suggestions from this forum I re-soldered the keyboard controller IC and that seems to have fixed that.


Since then the board more or less works. I decided to invest a little. So I got an ACA500plus and a Gotek drive with adapter so I could plug it into the external floppy connector. (I originally had it mounted inside but the original floppy drive still worked so I put that one back.) I also got a new trapdoor RAM extension with RTC which acts as 512K slow ram. (I didn't do the A500+ 1MB onboard RAM mod yet.)



Now still every once in a while the Amiga will either not boot, or it will lock up at seemingly random places. Without the ACA500+ it does the grey flashes, then halts at a white screen (I guess right before it attempts to load from floppy.) With the ACA500+ it boots into the star-field but then freezes. The ACA500+ has a LED digit display. When it freezes the display is either at 96 or 97. (Normally it would proceed to FE and then turn off.)



I have also had lockups simply by inserting a floppy disk when using workbench. The display would remain visible but the mouse pointer no longer works, and caps lock light no longer toggles after about 16 presses.

So I suspect there is still some loose contact somewhere. How do I go about solving this? I guess I could re-solder all remaining chip sockets but what if that doesn't fix it?



The board is a Rev8A. I replaced all electrolytic caps. I either socketed or re-socketed all chips, except the CPU, Gary, Paula and Denise, which still have their original sockets. I also replaced the trapdoor connector, as the original had corrosion on it.



I also continuity-tested every IC pin as best as I could, and could not find anything wrong.


Looking to hear some insightful comments, or otherwise thankful that you listened to my slight rambling.
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Old 28 February 2021, 22:13   #2
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I would have a look at Gary and potentially Paula. Gary usually takes a massive hit in the A500+ when the battery farts. I would replace the socket and clean the IC. If you still have same problem I would do the same for Paula.

Last edited by mart1n; 28 February 2021 at 22:40.
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Old 01 March 2021, 20:17   #3
Toni Wilen
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Quote:
Originally Posted by mathop View Post
With the ACA500+ it boots into the star-field but then freezes. The ACA500+ has a LED digit display. When it freezes the display is either at 96 or 97. (Normally it would proceed to FE and then turn off.)
96 enables vblank interrupt. 97 waits for first vblank interrupt. Always getting stuck at 97 would mean interrupts are 100% not working but randomly getting stuck at 96 means it can't be 100% caused by missing interrupts.

Possibly Paula related problem.
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Old 02 March 2021, 23:48   #4
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I also find that the ACA500+ serial logging does not work if it boots into 96 or 97.
On normal boot I get serial output almost immediately.
Don't know if this rings any further bells.
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Old 03 March 2021, 13:38   #5
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Contact for pin 24 paula was bent back, I'll order a replacement socket and see if replacing the socket makes the problems go away.
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Old 03 March 2021, 17:35   #6
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It is now almost certainly Paula because it also handles serial port. Pin 24 = one of RGA address bus pins which tells Denise and Paula which register is being accessed.
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Old 03 March 2021, 21:17   #7
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Used the male end of a dupont cable as a stopgap so paula pin 24 would make contact.

(Marked with a circle - see picture.)


The amiga now boots. Also if I take it out it now never boots. Guess I ruined the socket even further. I ordered some turned pin sockets, since I was already using that for the other chips.
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Old 10 March 2021, 13:53   #8
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FYI - I replaced the Paula socket and it appears the random crashes are gone - knock wood.
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Old 18 March 2021, 17:24   #9
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Quote:
Originally Posted by mathop View Post

Since then the board more or less works. I decided to invest a little. So I got an ACA500plus and a Gotek drive with adapter so I could plug it into the external floppy connector. (I originally had it mounted inside but the original floppy drive still worked so I put that one back.) I also got a new trapdoor RAM extension with RTC which acts as 512K slow ram. (I didn't do the A500+ 1MB onboard RAM mod yet.)

Don´t do the chip ram mod!


Aca500plus does that for you.
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Old 18 March 2021, 19:22   #10
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Yes, I'm going to leave it alone now.
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