exxos's Atari, Amiga & retro forum

OK so yes I _am_ being stupid - I connected my ground lead to the terminal marked ground rather than -ve. Turns out the GND terminal is for an earth strap. Not quite sure why there would be AC across there and the supply positive though.

I bought 10 IC's from a Chinese eBay seller last month, they were due to land any time in the next week or so and have been marked as shipped.

Out of the blue I received a full refund yesterday, with no other communication and no status change on the order.

I guess this means I'm not going to receive the IC's that I ordered, which tbh is pretty annoying as it's a month lost on the project I'm working on.

Is this common behaviour? It's the first time I've experienced it.

Sometimes. If packages hasn't arrived in set time (or sent), you get your money back. I think AliExpress has some of this per automation.

DoG wrote: 10 Apr 2022 12:24 Sometimes. If packages hasn't arrived in set time (or sent), you get your money back. I think AliExpress has some of this per automation.

I wondered about that but the item shows the following in my order list: "Estimated delivery Mon 11 Apr - Thu 28 Apr"

I just want the parts tbh :D

Well, I guess I know why I got refunded now. The package arrived empty :lol:

BennehBoy wrote: 14 Apr 2022 10:52 Well, I guess I know why I got refunded now. The package arrived empty :lol:

Ouch! So pretty much all the carbon footprint for no delivered parts. No wonder the planet is in the state it is :(

So I did some tweaking on my Master-41 drive yesterday. The Master-41 is a 1541 floppy clone, it's essentially identical to the Excelerator+ / Oceanic OC-118-N. This drive went through a number of transformations owing to legal action from Commodore, so the name changes and some hardware hacks were used to confound the litigation.

One of those hardware tweaks was to bit swap the ROM. The drive uses an exact copy of Commodores 1541 2x8KB ROMs concatenated into a single 16KB ROM (exactly how the 1541-II ROM is laid out, but older code minus the track zero sensor handling). Pins 15 & 16 of the ROM are physically swapped on the drive, these equate to D3&D4 on the chip which means that when the content of the ROM is dumped it is not the same as the standard rom due to the bit swapping, a simple but clever obfuscation technique.

The downside of this is that if you wish to burn custom firmware to replacement ROMs then you have to muck about bit swapping the files, not to mention also concatenating the new firmware with the CBM base ROM.

So to get around this I decided to 'unswap' the data lines physically on the hardware so I would not have to jump through this hoop every time I wanted to try a new firmware. I know not everyone will agree with physically modifying hardware but this is a very easily undone mod.

Step one was to cut the tracks for pin 15 & 16 of the rom socket on the board:


Then 2 bodge wires could be added to reroute and undo the bitswap:


Now I could burn any rom that I wished to, my first test was to burn an unbitswapped version of JiffyDOS to the drive (I have already purchased a licensed bitswapped version for this drive). SUCCESS, so I didn't break anything!

Because I only had 27C256 EPROMs available it seemed like a waste to burn a dual image of the 16KB of firmware, so I decided I would also like to be able to swap between 2 different firmware images with a switch.

The simplest solution for this would be to bend A14 (pin 27) of the EPROM up, and use this as the center tap of a 3 leg switch, the other two legs being connected to ground and VCC respectively. I'm sure there are more elegant solutions but this is what came to mind:


I had burned SpeedDOS 2.7 to the upper half of the 27C256 that I was using, SpeedDOS is a parallel speeder for the 1541, which massively increases throughput by sending all bits of each byte read simultaneously from the VIA of the drive to the user port of the C64. A nice side effect of this is that ZoomFloppy and similar tools can be used on the PC to make fast copies of disks to file, or dump files to fresh floppies.

Space in the Master-41 case is extremely limited compared to a 1541, they are much more compact, so I decided to use the piggyback method & some adapter PCBs that I have lying around...


I'm waiting for a 24 pin PCB edge connector to arrive so I can fab up a cable to connect the adapter to the C64. I'll also need to drill the case for the rom switch, and to pass the ribbon cable for the parallel connection out so I'll post an update when that's done.

I bought a kit to build a 1581 disk drive replica - via a German forum. Pretty reasonable compared to the cost of buying a used original.

I already owned a suitable PSU and a spare Amiga 3.5" floppy mechanism to use with the kit.

Anyway, the kit arrived on Friday and I set about building it on Sunday evening, it took a few hours and was quite straightforward.

I did some simple checks to make sure I hadn't dead shorted anything before powering it up.

It worked first time - amazed that I didn't mess anything up.

There's probably very little reason to own a 1581 these days, my 1541 U II+ can emulate one and mount .d81 disk images, but I just 'wanted' to do this as I remember dreaming about owning one when I was a kid.

Some kind souls out on the internet have converted a lot of multi-disk games to .d81 format, this means that there's no need to do any disk swapping, even if it would be just virtual disk images.

The first thing I tried with the drive was one of these images of Turrican II - I used an old amiga floppy with greaseweazle V4 to write the image out.

The built drive...


The drive electronics responding to a status command


Turrican II disk directory


Next job is to get a 3D printed case made by a friend.

Oh and my Edge connectors turned up so I can complete the parallel interface on my Master-41.

Looks good. I take it that you'll stay with the 3.5" drive rather than trying to find a 5.25" one?

I've already got 5 5.25" drives for the 64 :lol: