I was reading some of the posts on this thread about various repairs, and noticed that there was something missing: Power Supplies. In seeing many “repair videos” on Youtube, one thing kept coming up: faulty power supplies that can sometimes destroy a computer. Some are fairly simple to deal with, others are not. Here I will list a few things that I seen and done, increasing in complexity.
 
Commodore C64:
This will include the Vic20, all using the 7 Pin DIN “Power Brick.” This Power Supply unit is known to short out and instead of 5 volts being delivered to the computer, the power increases to 15 or more volts, often causing damage to the computer. This Power Supply Unit is a Linear unit, taking 120/220 VAC from the wall and converting around 10VAC from a transformer and then through a simple filtering circuit gives 5VDC and 9VAC to be sent through the 7 Pin DIN and into the computer. It is the transformer that shorts out, creating an over voltage situation and flood the system more power that can (and will) damage the system.
 
Around 2005, somebody started selling a “System Saver” which goes between the computer and the Power Brick; it adds more power regulation and in case of overvoltage, blows a fuse and shuts down the system before the over voltage can cause problems. Since 2010, somebody else decided to create their own Linear power supply with modern parts, and is now selling them as replacements to the Commodore power brick. There are instructions and videos online to make your down.
 
One of the more famous videos of a Commodore Supply failing is from the 8Bit Guy. He was demonstrating how to interface an LCD Display Panel various devices to display text and graphics. This included interfacing it to a Commodore 64 through the Cartridge Port and the User Port. It is during this demonstration when the power supply began to fail and cause damage to the Commodore 64. 8Bit Guy’s LCD Experiment Leading to C64’s Destruction And Eventual Death:
Part 1: https://www.youtube.com/watch?v=hZRL8luuPb8
Part 2: https://www.youtube.com/watch?v=vV8FbwobrKY (where the issues begin to show)
Part 3: https://www.youtube.com/watch?v=pQk3XgpuaJ4
 
Apple II/II+/IIe/IIc
 
This includes some old Macintosh systems and even a few PC; as it involves that is known as “Rifa Caps.” A Rifa Cap is a filtering capacitor used in smoothing out the power from the wall from any power spikes and surges. They are made from polyester dielectric with aluminum or zinc and great in providing smooth clean power to the rest of the PSU to insure proper voltage conversion for the mother board and other devices connected to use. Thing is Rifa Caps have a limited life span of some 10 – 20 years, depending on the usage of the system. They are known to explode with a loud “bang!” and emit a strong offensive smell. The system will continue to run but there is a danger of the PSU shorting out.
 
The PSU can run without Rifa Caps but it will not provide protection and power smoothing for the power unit to work better with. But when they explode, they throw out the metal material inside the capacitor throughout the inside the PSU and can cause short circuits if not cleaned out.
 
Apple II series PSUs have anywhere between 2 and 4 Rifa Caps (and in rare cases as many as 8), one large one (around .1uf at 250V) and the other small ones (around .01uf at 250V); the original Rifa Caps are in a Clear Rectangular Prism with text printed on them, the clear plastic showing a gold color material inside the cap. Replacement Rifa caps are solid color in yellow or black. They are not polarized as they are dealing with AC Voltage.
 
Again, an Apple II Series PSU can run without the Rifa Caps, they are filtering the input voltage from the wall and removing them does not shut down the PSU. But the PSU will be introducing voltage spikes and surges to the mother board and connected devices.
 
The best option is to open the PSU, remove the PSU board and replace the Rifa Caps. They are only a couple dollars each at places like Jamesco, Mouser Electronics and Element 14.
 
Rifa caps are only used in the input power of the Power Supply, and thus some on other systems. On the Macintosh systems 128K to Plus they are found near the power input and On/Off Switch on the Analog Board; on the Mac SE, SE\30, Classic, Classic II and Color Classic series the Rifa Caps are in the PSU connected to the Analog board. Though not always true for all other Macs, if there are Rifa Caps , they are inside the PSU between the Power In and Power switch.
 
Macintosh LC Series
 
This one I personally know as I worked on many LC systems.
 
Symptom: You turn on the LC and nothing happens.
 
Issue/Problem: Dead Caps in the PSU’s Low Voltage Side.
 
Solution: Recap the PSU.
 
Though it is rare to find a Rifa Cap inside the LC’s PSU, the issue is one not thought of: the physical size of the cap interfering with the reassembly of the PSU. The caps being replaced are the one at the low voltage side. But when buying replacements, you have to measure the physical size of the cap and replace them with caps of the same value and physical size or the PSU Case will not close. I have run into this situation a few number of times. Making it more difficult, Apple hired TDK, Astek and Dyna to make the PSU for the LC Series and other Macintosh Systems, and each company used different sized and value caps, so you have to take note as to which PSU you are working on and get what parts are needed for that PSU.
 
One would not think that size matters. A .47uf @ 16v capacitor is a .47uf @ 16v capacitor regardless if it is a Ceramic Cap, a Polyester Cap, an Electrolytic Cap, a Tantalum cap, and so on, but this is not true as there are other things to consider as in the size and shape of the cap on top of its electric characteristics.
 
With the PSU recapped, it works as it should. LC PSUs are the easiest PSU to work on and recap but the only difficulty requiring that the caps to be replaced are to be similar in size or smaller. But at the same time the caps on the motherboard would need to be replaced as well. A motherboard in dire need of a recap may not turn on even if the PSU was recapped. The motherboard while it is populated with electrolytic caps (that leak after the passage of time, and the cause of the problem), can be replaced with various caps.  The best solution is to recap the motherboard with solid state caps, either in ceramic, tantalum or polyester. Solid State Caps have a 20 to 50 year life span. Macs using Solid State Caps are still useable today; many PCs were made with solid state caps, and they are still in use today though once in a while one will find a “dead board”. This “dead board” usually has a shorted out tantalum cap on the 12v rail. Once found and replaced, the board will come back to life.
 
IBM and Other PCs
 
If you have a X86 system from the original IBM PC to P4 that does not turn on even though you know that the PSU is in working order, this can be a simple repair if there is no damage to some of the custom chips. Most of the time it is a shorted out tantalum cap in the 5V or 12V rails. To test the rails, remove all the cards from the machine, then with the PSU disconnected from the motherboard use a multi-meter and with one lead to ground and the other lead to voltage rails to see if any of them are shorted. In finding the shorted rails, one can look at the board and trace out the rails. The 12V usually goes to the expansion slots on the older PCs, and 5V to the chips on the board.
 
Oddly, a motherboard can be resurrected when the cards are removed. This says that the problem is with the card taking down the system, and the usual suspect is either the 12v or 5V rail on the card. Test like stated above but instead of searching the motherboard, you have to search the card for the shorted cap. Once you find the cap, remove and replace it.
 
With the board(s) repairs and the caps replaced, chances are it will turn on and work flawlessly.
 
Other systems?
 
Again, the issue with many PSUs going bad brings down the whole system. For the DIY Hobbyist who made their PC, they are often swapping out their PSU. The Pi sector of SBC (Small Board Computers), bad or mis-wired power supplies to the unit, shorting out the unit and damaging chips on the board. Unlike large sized computer boards, once chips are damaged on the small board, repair would be nearly impossible.  
 
(Personal note: ) in a forum discussion with “Mr. Eton” Raspberry Pi founder, Director and CEO of Raspberry Inc and the Raspberry Foundation, I made the statement of “many people are frying their Raspberry Pies, and doing in an autopsy on some dead Raspberry Pi’s I had found, I found that other than a couple regulators, the main chips was fried. It would not take much to remove the old chip from the board, clean and recycle the board and put in a new chip. The Raspberry Pi can then be returned to the owner for a small service fee or sold as refurbished equipment.”
 
I was floored with his reply, “a Raspberry Pi is (at the time) $35 for a Model B and $25 for a Model A. They are low cost enough for anyone to buy another as a replacement. If they buy a Raspberry Pi and damage it then the only option they have is to trash the damaged unit and buy a new one.”
 
Considering that in my time I had in repairing Raspberry Pis and making discoveries in potential repairs. And with proper equipment (A Hot Air Soldering Station), if I had a supply of chips, I would be able to swap out chips on the Raspberry Pi Board and repair 90% or more of dead Raspberry Pies. Oddly, Atmel, makers of the Atmel Microcontrollers used in the Arduino and other DIY Microcontroller boards, sell their Atmel series Microcontroller chips, making the Arduino and other hobby boards easy to replace and repair. (Years later) Raspberry Pi in seeing this, when making their Raspberry Pi Pico Microcontroller Boards, also started to sell their 2040 microcontroller chips used on the Pico separately. Thus those who can, started to do their own repairs with chip replacements. But as far as their Raspberry Pi Computers are concerned, no such option is available.
 
Conclusion
Repairs to older 8Bit systems are doable; though some older systems using custom chips, many of these custom chips are obtainable or modern equivalents can be use in their place.  Capacitors are easily but time consuming to do and can bring back many dead systems. Power Supplies can be rebuilt (with recapping) or replaced with a modern equivalent. There are many Youtubers out there that specialize in older computer repairs, and often do advise many who want to venture on repairing their older machines. Jan Beta, Adrian Black of Adrian’s Digital Basement, Nolan of Nolan’s Retro Lab, Arctic Retro in Norway, and many others specialize in old system repairs and rebuilds.
 
A new breed of “hackers” is coming out with the various system communities are redesigning and reprinting old computer boards. One of the oldest of this is the Apple I board, which goes for around $50 to $100 for the board alone, and one has to get the chips, capacitors, resistors and other parts which would increase the price to around $250 - $500 to assemble. Newer system boards now include the Commodore 64, Vic20, Sinclair ZX80 (modifiable to a ZX81), Sinclair Spectrum, Amstrad C 464 and a couple MSX systems. More boards are being designed, redesigned and printed almost every day. Some online stores sell complete kits to build/rebuild older systems, like Tismouth of the UK who sell kits and parts to refurbish/repair Sinclair computers. They also sell basic parts to repair some other computers made for the UK/EU market.
 
Though some would say that it is a waste of time and money to repair or refurbish older system when a ‘new’ can do anything an old system can do. But there are those who are collectors, creating a mini museum for their entertainment and pleasure. Others want to be able to use bare metal hardware of the older systems. And lastly are owner who managed to hold onto their old systems in storage, and use them again like they did in their younger years. But all these older systems need a little maintenance, refurbishment and repairs to get them going again. Thus time and money are a well placed investment in bringing back an older machine.