Powering your Apple IIe - (1) A simple, affordable DIY alternative

If you are in need of a Power Supply Unit (PSU) to resurrect your beloved Apple IIe, your may want to share my experience here. Among my dormant Apple II collections, my trusty enhanced IIe, like many others, had its Astec PSU gone south years ago and was in storage since then. The coming back of “Retro Gaming & Computing” had me hooked and so I decided to bring it and my other "good-old-days" of personal computing back to life.

The Power Problem

Problems with PSU is common among vintage personal computers such as Amiga, Apple, Commodore, Tandy, etc. and clones alike. Many were caused by leaky or aging capacitors. The Astec and DynaComp units common among Apple II’s are no exception but they were manufactured over 30 years ago and are no longer available nowadays except on the used market with questionable reliability and at hefty prices.

Hobbyists have been looking into using PSU of desktop PCs and adapter to connect the PSU to the Apple II motherboard but in most cases the bulky PSU won’t fit inside the Apple II case. Even if it did, the Apple II’s require -5V in addition to +5V, ±12V from the PSU to run but ATX PSU manufacturers have started dropping -5V since ATX12V v1.2 (published in 2002) because it is there only for the older PC ISA peripherals. That means you’ll need an extra single output DC-to-DC voltage converter (Note 1), like a linear voltage regulator, and some soldering to make -5V available. Besides, the PSU's 3.3V source is literally wasted.

Others that want to preserve the original look and feel of the Apple II may repair the broken PSU by replacing the damaged capacitors, coils and/or other components but that would be for the technically skilled. If the PCB (Printed Circuit Board) is badly "burned" by the ugly capacitor you may as well forget about fixing it unless you are an expert. Sourcing the right component(s) could be another problem. Still, even if all went well, there is no guarantee how much longer the repaired PSU will last. And more, you are still stuck with your original PSU's wattage.

Modern technology is so amazing that now you could find open-frame switching PSUs so small that will fit nicely inside the original Apple II PSU's case, replacing the old PCB and circuit components alike, and with performance exceeding that of the original PSU in every respect. Of course you still want a quad voltage (±5V, ±12V specifically) unit to keeps things simple and reliable. Two examples are SDS60UQ02 (60 Watts) from XP Power and SBU60-401 (60 Watts) from Sinpro. They and others share a more-or-less common design known as the “SBU60” series. Other examples with bigger wattages are REL-70-4004 (70 Watts), GRN-80-4002 (80 Watts) and REL-110-4004 / GRN-110-4002 (110 Watts) from Integrated Power Designs; and VLT80-4000 (80 Watts), VLT100-4000 (100 Watts) from EOS Power. You’ll also want to buy the connection kit of these PSU (if there is any) or make your own connection assembly to bridge the motherboard and the power module. One advantage of these units is, externally, you will barely notice the difference after changing the PSU's innards. This makes it particularly suitable for the Apple IIgs because, to keep the computer size small, the PSU is mounted in a peculiar way above the motherboard. This means the physical shape of the PSU has to remain the same or else it won’t mount inside the IIgs case like the original. However, if you decided to go this route, some of these modern designs could be difficult to come by and will set you back roughly USD50 to USD100 (per unit) plus shipping. 

Note 1 - Regarding such converters, the picoPSU from Mini-Box is a compact solution that uses high efficiency DC-to-DC voltage converters to remove the multi-voltage requirement of mini-ITX PCs, ... and perhaps our vintage “toys” too. Imagine powering your IIe or IIgs with a 15V power brick just like a IIc. With the right electronic parts available today, building such a power module for the desktop Apple IIs could make a nice project … 

The Meanwell RQ-85B

The Apple IIe (and presumably also II and II+) with its spacious interior is definitely at an advantage compared to the Apple IIgs in this case. I found this enclosed PSU on the Internet purely by chance (other models may work too). The RQ-85B from Taiwan manufacturer Meanwell is an 85 Watt AC-to-DC quad-voltage (±5V, ±12V) general purpose switching PSU. It accepts 100~240V, 50~60Hz AC electricity as input so it will work most likely anywhere. The PSU's MTBF (Mean Time Between Failures) is over 20 years. It’s currently and readily available at Jameco at USD27 apiece.

 

The low profile unit is much shorter than the original Astec unit but it’s about 10mm wider. I was skeptical at first about its dimensions but after some measurements I found no problem fitting the unit inside the Apple IIe. A more powerful (125 Watts) model, the RQ-125B, is also available if you needed or felt more comfortable with that kind of power. It will also fit but, but being 40mm longer, the mounting could be a little trickier.

This general purpose PSU uses a terminal block with screw-on clamps to secure the wirings and that means NO SOLDERING is necessary. The unit has a pot for fine tuning the loaded voltage (+5V only). You will need to install a power on/off switch because there is none on the unit.  Its metal case also has plenty of venting holes compared to none on the original Astec unit which in many cases causes overheating problems.

Starting with a PC extension power cord (also known as IEC60320 C14 to C13 power cord), you need the male end (C14) with the inlet like the one on your original PSU. The female end (C13) could be salvaged and used as a regular power cord by installing a bare plug for local electricity.

A power switch rated at 250V, 10A with power on light will work nicely. Depending on your preference, you may want a solderless version.

Now carefully strip the outside insulation of the extension power cord near the male end to expose the Earth (yellow and green), Neutral (blue) and Live (brown) wires (or whatever colours they are in your region). Keep the Earth wire intact and cut the latter two to expose the copper. Then install the power switch as in its instructions.

After installing the power switch, cut the extension power cord at the desired length and again strip the insulations of the Earth, Neutral and Live wire at the cut end.

Then remove the power plug and wire assembly from the original PSU by cutting the wires near the PCB. You will need to open the PSU case to do this but this will keep the wires at their maximum lengths in case you’ll need them later. (Please remember there could be dangerous voltages inside the PSU so it is wise to discharge it before opening the case.) Or you could make your own with AMP part no. 1-640520-0 (housing), 641300-1 (contacts), some color 18 AWG silicone wires and a crimping tool. When your plug-and-wire assembly is ready, strip the wire insulations at the cut end for the next step.

I added a 60mm x 60mm x 25mm DC 12V fan for improved air circulation inside the Apple IIe. The fan will turn on whenever the PSU is on and it’s mounted on the bottom pan with double-side adhesive tape. The noise level is very acceptable.

After some fiddling, the unit is wired up and ready for mounting on the Apple IIe’s bottom pan. I also thread-locked the screws to prevent loosening due to thermal cycling. The wire-terminal connections are:

Wire Color (Connector Pin)	RQ-85B Terminal Symbol	Reference
For the power-supply-to-motherboard assembly
Orange (pin 3)	+5V	+5V
Black x 2 (pin 1, 2)	COM	Common
Yellow (pin 4)	+V2	+12V
Blue (pin 6)	V3	-5V
Green (pin 5)	-V4	-12V
For the C14-inlet-to-power-supply assembly
Yellow-and-green		Earth
Blue	N	Neutral
Brown	L	Live
For the cooling fan
Red	+V2	+12V
Black	COM	Common

The PSU is tied down to the Apple IIe’s bottom pan using four 2mm x 200mm nylon cable ties. The latches are on the underside of the pan while the flexible lengths go through the original mounting holes (for screws) and around the venting holes on top of the PSU as shown. Make sure the four cable ties are tightened evenly to hold the PSU tightly in place. I also checked that the metal bottom pan is in good electric contact with the PSU's bottom and so is earthed properly.

I kept some extra length of the extension power cord and cable-tied it to the side of the PSU (as a strain relief to make the terminal connections less likely being pull loose). The power switch went outside the case through the cutout at the back of the metal pan. The cooling fan was mounted before the same cutout using double-side adhesive tape to draw fresh air above the PSU and inside the Apple IIe.

It’s a good idea to seal the high voltage terminals (N and L) to prevent possible electric shock. I used big globs of hot glue to do the job.

A fan grill definitely improves the look and prevents the fan from being damaged by external objects.

The Apple IIe with the upper case back on. Plenty of space left for air circulation.

Don’t ask! I know you may have noticed. It’s not the original motherboard but from a platinum Apple IIe :-)

View from the back. The look may be somewhat different from the original but I wanted a “working” Apple IIe at minimal cost to start with. And after all it’s a clean and tidy solution for today's Apple IIes.

Here is what the computer bottom looks like after excess lengths of the cable ties are removed. Absolutely NO DRILLING here!

All the tools I have used were a screwdriver, a wire cutter and stripper, and a hobby knife. I believe this is as simple as it can be for an average Apple II hobbyist. Please enjoy!

Thank you for visiting my blog!


Some good information related to this project are:

1. "Upgrading Apple II Powersupplies", SpeedyG, 2005
2. "Replacement GS PowerSupply – Complete :-)", Drew ][, 2009
3. “Reviews - Pico PSU Round Up”, jonnyGURU, 2010
4. "Power Supply – Conversion", Lukazi, 2011
5. “Apple IIe (1983)”, Oldcomputr, 2015
6. "Universal PSU Kit", ReActiveMicro, 2016
7. "Apple IIGS ASTEC Power Supply Repair", Apple IIoz, 2017
8. “Replacing Line Filter Capacitors on an Apple IIGS or an Apple //e Power Supply”, Damn Technology, 2017
9. “LittlePower Flip v3.0”, UltimateApple2, 2017
10. “Commonly Failing Electronic Components (in vintage computers)”, Minus Zero Degrees