Re: R-DOS (REX DOS??) on an oceanic 1541 clone drive

From: Julian Perry <>
Date: Wed, 8 Oct 2014 08:58:08 +1100
Message-ID: <>

Wednesday, October 8, 2014, 2:18:50 AM, you wrote:

> On 10/06/2014 11:58 PM, Julian Perry wrote:
>> It's very definitely a KU board - pictures of the worklog can be found
>> at

> Ok, C107 and C108 on your board are not the dangerous kind. Feel free to
> replace them, but you don't have to.
I probably will - they will be cooked, at best. I plan to measure a
couple of the remainder, and if they're significantly out, replace
them too.

> Also, check the 7812, on my KU, one of the pins was almost broken, 
> probably from the thermal stress of heating up and cooling down over the
> years. If the middle pin of an 78xx-regulator loses connection to GND,
> the output voltage will go up.
Thanks for the tip. Will do.

>> As an aside - KU boards seem to have a bad reputation for edgy
>> timing glitches, but this one seems OK. It runs an Easyflash3 quite
>> happily, even in kernel replacement mode, and handles VSP without
>> memory corruptons - I guess I just got lucky.

> VSP problems have been linked to the VIC. So maybe your old 6569R1 is 
> not affected by it?
Not sure. I DO know that I fixed VSP problems in my main 250407
machine by replacing the RAM.

> And yes, the KU has a lot of ground issues. If you have an oscilloscope,
> check what happens if you hook up GND of a probe to GND and one side of
> the board and the probe itself to GND on the other side.

>> I'm still puzzled that a schematic for this rather quirky board seems
>> to be MIA.

> I think you can use the schematics for the 250407 instead...
There are a few differences I've noted, but that's what I resorted to
doing. Schematics aren't always the gospel truth against the physical
board, either: particularly in the Commodore world :)

On another topic - Silver:
I can confirm that the $C000-$FFFF ROM of that Oceanic drive is
mirrored from $8000, so it looks like the upper 32K region is not
completely decoded.
I noticed this when poking around inside it, when dumping out the ROM.


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Received on 2014-10-07 22:00:07

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