Introduction
Background:
The original 9V AC power supply bricks required for these drives are slowly vanishing from the surface of the planet. They are bulky and heavy, not easy to transport, and ever harder to find.
It's about time for a definitive conversion of your drive so it can operate with a more convenient, lightweight and readily available / standard 12V DC power supply of your choice.
What is this modification about:
It consists of simply adding two jumper wires that will disable both the rectifying circuit and the voltage doubler. This will allow the drive to work with 12v DC, while working safely within similar (even lower) voltage and temperature ranges.
Why this mod:
- This is a very simple mod in concept. But it will require a steady pulse on your end and a soldering station. I prefer to do this mod on the soldering side of the board, but I made this guide with a top-board approach so you don't have to disassemble any further than strictly necessary.
- It is easily reversible if you ever want to have your drive back to its factory settings.
- It allows your drive to work well within noise and temperature parameters. Your drive should work and be healthy for years.
- Other mods disable the power switch. With this mod the switch works just as intended.
- It is safe (not foolproof though): If you ever plug one of the old 9V AC power supply by accident, it may damage the voltage regulators (which are easy to find and replace), but the rest of your drive has little chances of being damaged. There is an option if you want protection against that scenario though. Read for more...
About me: I am not an electronics professional, but I do have formal studies in electronics and I have repaired and tinkered with Atari gear for decades.
What you need
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What you will need:
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A 12volt, 2Amp DC capable power supply with a center positive 2.5mm barrel connector plug at the end. You can either go for switching (lightweight) power supply or the linear (heavy) type. It's your choice.
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A labeler machine or printer (for the warning sticker). This is important, I'll tell you about that later.
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Hemostats. These are a must because you will have to solder in places that are not easy to reach.
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A soldering station capable of 330°C. This temperature setting is relevant because you will solder on elements capable of dissipating heat.
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A small screwdriver for calibrating the motor speed.
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A copy of 1050 disk drive diagnostics diskette for final tests and calibration. Find the software here and have it ready before beginning: https://archive.org/details/a8b_1050_Dis...
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Take a look at the diagram: You are about to add the two jumper wires highlighted in red.
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Prepare your Atari 1050 on a clean surface. Put a towel on top of the table to prevent scratches to the unit.
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Remove all 6 philips screws on the underside of the unit
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Flip the unit back on its feet and carefully remove both the top and front cover as if they were one single piece. Be gentle: This plastic is over 40 years old.
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Preferably, use 20 AWG wire for the connections.
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Solder the first bridge on top of the CR19, which is one of the 4 large diodes (the one at the bottom left with the face of the drive pointing at you and the SIO connectors pointing away from you)
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You may skip this step if you use a higher voltage (14v or 15v) for your power supply. But if you use a 12v one, adding this jumper is required to minimize the voltage drop.
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With the help of pliers or hemostats, grab and pull the J14 connector out, which is the first on the row. This step is not required, but recommended.
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Since you will solder right next to this connector, removing it is a cautionary measure so you have more room and you don't melt this connector by accident.
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Get the wire jumper ready but stripping and tinning the tips with solder. Estimate the proper length. Also, pre-tin the pads where you will solder.
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One end of this jumper wire will be soldered to one of the two pads that are underneath the power jack. You will use the one that is closest to the SIO port and NOT the one below the center of the connector.
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Pass the jumper wire below the aluminum plate (heat dissipator). There is right about 1mm of room for you to do so.
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The other end of the jumper wire, will go to the input of the 12v regulator. See the picture for reference, it's the one below the tip of the screwdriver. There is a pad right next to it you can use.
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Alternate reality: If you use a good quality, regulated 12v power supply, you can actually solder this end of the wire to the OUTPUT of the 12V regulator for lower thermal operation however,
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by using the input pin instead, the 12v regulator will serve as protection in case anything goes wrong with your power supply.
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After finishing with the soldering, re-connect J14 right where it belongs.
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Chances are your drive is in working condition by now, ready to take the new 12v power supply. So, plug it in and give it a go!
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At this point, the speed of the spinning motor may be slightly altered. So we take care of that and fix it in this step.
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Locate the adjusting trimpot. There is a chance it comes with silicon coating on top. Break it off gently with your hemostats until you can access the small brass screw with a flat screwdriver.
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Load your 1050 diagnostic diskette and adjust the trimpot to the desired speed.
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You are almost finished. Reassemble the case and put the screws back on.
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Print a label that clearly states that your drive now takes 12V DC center positive. Don't call this project finished without this step.
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You want to avoid any confusion or someone plugging in an old AC power supply to this modified drive.
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For DC, you can actually go higher in voltage, all the way to 15v, even 18v. The drive will overheat, but it will work regardless, with minimal risk.
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Still, you want to stick to DC, not AC so the label is a MUST.
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For the electronics enthusiasts, I took some measurements so you don't have to. Here are the facts:
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12v rail voltage: The 12v regulator will read close to 12v at the input, and close to 10.6v at the output. This is OK for the drive. You will compensate for the slight drop in speed with the trim pot adjustment.
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5v rail voltage: The 5v regulator will read close to 11.2v at the input and 5.0v at the output. This is OK and the stock heat dissipator will take care of the heat.
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Temperature: At 22°C ambient temp and after 20 minutes of operation, the 12v regulator reads 40°C and the 5v regulator reads 47°C . This is all well within operating range.
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Current: After switching on, the current drawn from the new power supply reads 630mA (which is normal since it feeds all the electronics circuits and the chips). When the motors are in operation, the total current reads 1,170mA (~1.2 Amps).
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Heat: Your unit will now produce less heat: Since you disabled the voltage doubler, the 12v reg has very little work to do now, and thus, less heat to dissipate. The 5v reg has to drop 0.3v more than before, so almost no change on that front.
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These current readings mean that any nominal 12v/2A or 2.5A DC power supply will be powerful enough. If you only have a 1500mA power supply, no worries: you should still be fine, but in this case higher is better.
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Equipment used: Fluke 87V multimeter, Rigol DS 1054Z scope, HTI thermal camera.
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Enjoy your modernized floppy drive, feel free to contact me and contribute to make this tutorial better or clearer.
Enjoy your modernized floppy drive, feel free to contact me and contribute to make this tutorial better or clearer.
