20 July 2023, 05:48 | #1 |
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Amiga 1200 DRAM Signal Issues
Hey guys,
Doing a Reamiga 1.5 board and having issues with DRAM. Checked soldering, lines for shorts, bridges etc Basically I've found that the entire DRD 1-15 across the top of Budgie has a ocassional pulse signal - like its waiting (pic.2)- same as DRD 16-31 before Diagram seems to test this area of memory. DRD 1-15 just never seems to become engaged like DRD 16-31 does with proper high low activity (pic1) What would cause this? Some kind of address bus issue, bank select or something? |
03 August 2023, 03:18 | #2 |
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I'm fairly certain now its an address line issue, perhaps Alice or Gayle.
A12 on Alice just looks weird compared to its neighbours. Checking the A20 line to see if its actually selecting the upper or lower bank of memory Just hoping its not a dodgy Alice, bloody expensive chip |
03 August 2023, 11:35 | #3 |
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IMHO it could be better to use logic analyzer than scope, activity on one of lines doesn't need to be suspicious especially if you use digital oscilloscope that perform probably undersampling...
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09 August 2023, 04:51 | #4 |
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Any recommendations for a logic analyzer?
I've managed to burn diagrom 1.3 and run the better mem test. It confirms its not the address lines, but yes issues on DRD 0-15 regardless of which ram chip gets installed. Fastmem with accelator works perfectly. |
09 August 2023, 13:41 | #5 | |
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Quote:
Check if they are decoded correctly for byte, word, long word. Last edited by Lunda; 09 August 2023 at 13:48. |
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14 August 2023, 05:10 | #6 |
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I did and found a problem compared to a working 1200. The RAS/CAS on Alice seemed weird and I compared them. Image 1 from the non working, image 2 from working.
Thinking it must be a bad alice chip... |
14 August 2023, 05:22 | #7 |
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...unless Budgie is pulling the signal down..
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14 August 2023, 07:37 | #8 |
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Yes, possible Budgie pulling down on RAS/CAS inputs from Alice.
Lift pins on RAS/CAS input on Budgie and recheck? Images of RAS/CAS input into Budgie. Last edited by stormahead; 14 August 2023 at 07:44. |
21 November 2023, 07:30 | #9 |
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Just to go back and provide update for others..
It was a bad Paula connection causing the DRD signal issues which makes sense when DRD0:15 goes to Paula. Even though I had continuity and solder looked fine even under a micro- a full resolder did the job. Next mission is to find why only 1024kb is being detected by Diagrom - $0000400 to $00FFFF only, nothing found higher. Address and data lines look ok on the scope. |
23 November 2023, 03:29 | #10 |
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Resolved with a resolder of Budgie making painfully sure each pin was square on the pad and then a quick ultrasonic bath.
I did replace the Alice and Budgie in the end so its hard to pinpoint which was causing the addressing issues with whole chunks of mem missing. |
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