General

The North * Star MDS is beautifully illustrated in the following advertisement. The MDS consists of the disk controller (here single-density MDC-A), the blue housing with a Shugart SA400 or 400L, the charcteristic red cable and the corresponding software (not shown here).

Pictures

Power Supply Unit

I will replace some parts on the rectifier board . I assume that the transformer is still working perfectly; this component is not actually defective.

• D1, D1: MR501 (100 V, 3 A)
• D3, D4: 1N4002 (100 V, 1 A)

Update 12/12/2023: I resoldered a few solder joints, replaced the two large capacitors, as well as the 7805 regulator ... and ... the power supply is working perfectly again. The heating of the components is minimal. Since I could not buy the capacitors with the original values, they are slightly oversized in voltage and capacity.

• 5 V rail
• old: 3600 MFD, 1? V (the 2nd digit is not readable)
• new: 4700 MFD, 35 V
• 12 V rail
• old: 3100 MFD, 30 V
• new: 4700 MFD, 35 V

Mains voltage: The transformer is designed for 115 VAC, 60 Hz. If I apply this input voltage with my variable transformer, I end up with 11 and 22 VDC. Much too high. Therefore, as with my N* Horizon or IMSAI, it is sufficient to operate the transformer at 95 VAC and 50 Hz.

• 115 VAC
• 11,03 VDC -> 7805 ->  5,05 VDC
• 21,98 VDC -> 7812 -> 11,83 VDC
• 95 VAC
•  8,91 VDC -> 7805 ->  5,05 VDC
• 17,75 VDC -> 7812 -> 11,83 VDC

• ...

1. (↑) Byte, January 1975, page 15