In 1980s, aluminum electrolytic capacitors with quaternary salt were used. It was said high performance and long life. Many companies made them. But about 5 years goes, they started leaking solutions that was high pH (having strong alkalinity). It was found that quaternary salt became alkaline belong long time use. That problems was not found in condensed test in labs. As a result, almost high performance caps in 1980 leaks in about 10 years. High pH caps not only leaks but makes short circuit. Then one day, PSU fires.
To prevent break down,we must need to renew all caps. But now, it is too late. Almost PSU is broken,isn't it?
We must replace not only caps but zener-diodes, photo couplers, some transistors, resistors, and so on. Ideally, all pars to be replaced but some parts was discontinued.
I researched succeeding parts, but it is imperfect. Any advices is welcome.
p.s. Original X68000 PSU seems not to use quaternary salt. But they are too old, so they should be replaced.
It has the same design as the PSU of Expert but features lower rated capacitors. It is recommended to use use the capacitor ratings which are mentioned in the Expert section.
Almost all info taken from: http://x68k.net/x68dengen/
All X68000 power supplies fail because of the capacitors. Here are a few common symptoms and solutions:
|Part number||Part description||Notes|
|F1||125V 4A fuse||(MZ) small type|
|ZD31||RD6.8EB||6.8V 1/2W Zener diode|
|ZD32||RD4.3EB||4.3V 1/2W Zener diode|
|ZD51||RD15EB||15V 1/2W Zener diode|
|PC31, PC51||PC8170, TLP521-1||Photocoupler|
|Q31||2SC2333 / 2SC2335||Transistor|
|Q32, Q33, Q53||2SC1815Y||Transistor|
|C9||200V 470μF||Original: 180V 470μF. Height must not exceed 41mm and diameter 25.8mm.|
|C25||16V 1000μF||Original: 16V 680μF (25V can also be used)|
|C27||25V 220μF||Original: 25V 120μF|
|C31||16V 100μF||Original: 10V 100μF|
|C33||16V 220μF||Optional: 25V can also be used|
|C34||10V 100μF||Original: 6.3V 100μF|
|C35||50V 10μF||Original: 25V 10μF|
|C40, C41||16V 6800μF||Original: 10V 5600μF|
|C42||10V 2200μF||Original: 6.3V 2200μF|
|R33, R34||100Ω 1/6W|
|R35||3Ω 1/4W||Original: 3.3Ω|
|R98||2.2KΩ 1/4W||Original: 1/6W|
These are more tolerant. Their capacitors leak but usually do not kill anything and a simple recap is all that is needed.