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Old 12 October 2019, 06:08   #1
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Amiga 2000 - Recreation - some minor issues

Hi All,

Hoping someone with a bit more technical knowledge can give me some guidance.

I've assembled the first of 2 A2000 Recreation boards, but are having some minor issues. Its currently bare bones - no expansions just the standard R6 board with standard 1mb Chip and 68000

Issue 1 - unstable display with tick selected to VSYNC. With tick set to the A2000 power supply the system runs mostly fine, but when tick is set to VSYNC - the system boots to WB fine but the screen constantly turns on and off (I cant tell if there are further issues stemming from this). I don't think this is normal behavior? It is running on a Dell VGA monitor via
a Commodore VGA adapter. This monitor has functioned normally on every other Amiga I've ever had - unfortunately I haven't currently got another way to display this A2000. What generates the VSYNC tick (is it the monitor)?

Issue 2 - Floppy drive. Setup with an internal floppy drive and external Gotek. The external Gotek loads fine to WB3.1 (using 3.1 rom and latest stable Flash Floppy on the Gotek), but sometimes reports block errors. It also will not format the real drive on DF0 (reports write protected), nor will it allow writing to the Gotek. The apparent answer seems the CIA as the write protect line goes to the even CIA (I think) - but Diagrom reports the CIA as fine, and I've not had a problem with this particular Gotek ever.

Essentially the only non new parts in the system are the custom chips (of course), the crystal oscillator, and some of the Zorro connectors/external ports

Diagrom reports no issues with the system (I was suspect of the CIA's)

Any suggestions?
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Old 14 October 2019, 02:39   #2
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I found the issue with the floppy not writing/formatting.....the external drive (Gotek) is in a Power Computing housing, which has a couple of switches on it. One of the switches has an "Antivirus" feature which disables writing to the boot block of the disk. It must also prevent the same for the internal drive when selected. Flipped the switch and that parts all good now Strange I've never had this situation with this drive before, but I don't use floppies to write to much at all!

Unless I get some feedback here, I'm still googling to try understand the tick, or more importantly hows its generated outside the power supply and what effect it has on each system component
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Old 21 October 2019, 09:38   #3
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Recently had the same issue with losing sync on a Dell monitor while repairing a rev 4.4 B2000. Like yours, worked when using the power supply tick but not the Agnus generated VSync. Also, the problem was only there when using a 8371 agnus, was fine when using a 8372. I put it down to noise or an issue with the older Agnus driving the line (although the only thing extra it's driving is the CIA). Never looked at it with the scope as the problem went away with the 8372.

Have you got the C915 capacitor in? if not it may help if it is noise related.
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