Editing Commodore PET 4000 Series (section)

== Power and rails ==

'''The supply chassis contains no regulator.''' Commodore's ''Power Supply Assy, 8032'' drawing lists a transformer, one filter capacitor, a fuse, a fuse holder and a rocker switch — nothing else.<ref name="tm4k" />

{| class="wikitable styled-table" style="width:95%; text-align:left;"
|+'''Supply chassis, Commodore drawing 8032051'''
! Ref !! Part !! Commodore part no.
|-
| '''T1''' || Transformer, on the universal power chassis 8032043-02 || 320902-01
|-
| '''C1''' || Filter capacitor, '''23,000 µF''' || 900102-01
|-
| '''F1''' || Fuse, '''125 V slow-blow, 1.6 A''' || 903557-04
|-
| XF1, SW1 || Fuse holder and rocker switch || 903611-03, 904507-01
|-
| — || Dynamic PET power harness || 320289-01
|}

'''C1 is a 23,000 µF can and it stores real energy.''' Bleed it through a resistor before working near the chassis; do not short it with a screwdriver. Mains is present on the primary side of T1 whenever the machine is plugged in.

All the regulation happens '''on the logic board''':<ref name="tm4k" />

{| class="wikitable styled-table" style="width:95%; text-align:left;"
|+'''Regulators on the universal dynamic PET board, drawing 8032090'''
! Ref !! Device !! Output !! Commodore part no.
|-
| '''VR1''' || 7905 || '''−5 V''', 1.5 A || 901527-03
|-
| '''VR2''' || 7812 || '''+12 V''', 1 A || 901528-04
|-
| '''VR4''' || '''LM323''', TO-3 || +5 V || 901528-01
|-
| VR5, VR6 || 7.5 V zener diodes || — || 900941-01
|}

'''The +5 V regulator is an LM323, not a 7805.''' It is the same TO-3 5 A part Commodore used in the early [[Commodore VIC-20]], and it is not a drop-in swap for a 1 A TO-220 device.

'''There is a −5 V rail on this machine.''' That is a real difference from the PET 2001, which has none — so a rail list copied between the two will be wrong in one direction or the other.

Rectification on the board is by bridges CR2 and CR4 (4 A / 50 V) and diodes CR1, CR5 and CR7 (1N4005), with CR3 a 1N5402.<ref name="tm4k" />