Tandy 1400FD PSUs

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The Tandy 1400FD had an external 12V 1.2A DC 'power brick', and an internal PSU that combined the PSU for the various voltages required by the computer and a battery charging circuit for the internal 4.8V NiCd battery pack in one internal unit. The unit has many electrolytic capacitors and is therefore very vulnerable to ageing.

External PSU

1400fd-230v-external-psu.jpg

The external PSU provides 12V DC regulated output at 1.2A.

It is a simple design: a stepdown transformer full-wave rectified with four diodes and a couple of smoothing capacitors feed an STR9012 12V voltage regulator.

The internal fuse is 3.15A.

Internal PSU

Outputs

15-pin Connector Pinouts (P1)
Pin Colour Voltage/Purpose Comments
1 White 5V -
2 Dark Blue - Reset? Jumps to 5V when machine is powered on, then declines to 0v quickly
3 Brown 5V -
4 Grey 5V -
5 Blue - 5V when on mains; 0V when on battery
6 Red 12V -
7 Purple -12V -
8 Orange -22V -
9 Black GND -
10 Black GND -
11 Black GND -
12 Black GND Feed to P2 (no feed from PSU)
13 n/c (key) - -
14 Green 5V Feed to P2 (no feed from PSU)
15 Pink 5V Maintained when on battery or mains


2-pin Connector Pinouts (P2) Fed from P1
Pin Colour Voltage/Purpose Comments
1 Black GND -
2 Green 5V -


2-pin Connector Pinouts (P3)
Pin Colour Voltage/Purpose Comments
1 Black GND -
2 Yellow 5V -


See Also