Commodore PET 4000 Series

Commodore PET 4000 Series

Commodore PET 4032 with the 12-inch monitor
Specifications
Manufacturer	Commodore Business Machines
Type	Personal computer
Released	1980
CPU	MOS Technology 6502 at 1 MHz
Memory	16 KB or 32 KB dynamic RAM, by model
Storage	IEEE-488 disk drives; two external cassette ports
Display	Built-in 9-inch or 12-inch monochrome CRT, 40 × 25 text
Sound	Piezo transducer MT1 on 12-inch models
Power	Internal linear supply: transformer, 23,000 µF filter capacitor, 1.6 A slow-blow fuse
OS / Firmware	Commodore BASIC 4.0
Predecessor	Commodore PET 2001
Successor	CBM 8000 series
Model no.	4016, 4032

The Commodore PET 4000 Series was introduced in 1980, replacing the PET 2001 and 3000 machines, and brought Commodore BASIC 4.0 with its disk commands. It is built on the universal dynamic PET board, a different design from the static board in the original Commodore PET 2001, with different rails, regulators and crystal.

Commodore's PET 4000 Series Technical Manual, P/N 990438, is hosted here and is the source for the hardware figures below.

Architecture and processor

The CPU is a MOS Technology 6502 at 1 MHz. The crystal Y1 is 16 MHz on this board, against 8 MHz on the PET 2001, which is a quick way to tell the two board generations apart.

Commodore BASIC 4.0 adds disk commands such as DLOAD, DSAVE, CATALOG and SCRATCH.

Power and rails

The supply chassis contains no regulator. Commodore's Power Supply Assy drawing 8032051 lists a transformer, one filter capacitor, a fuse, a fuse holder and a rocker switch.

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 stores real energy. Bleed it through a resistor before working near the chassis. Mains is present at the switch, fuse and transformer primary whenever the machine is plugged in.

The regulation is on the logic board:

Regulators on the universal dynamic PET board, drawing 8032090

Ref	Device	Output	Commodore part no.
VR1	7905, TO-220	−5 V, 1.5 A	901527-03
VR2	7812, TO-3	+12 V, 1 A	901528-04
VR4	LM323	+5 V	901528-01
VR5, VR6	7.5 V zener diodes		900941-01

The +5 V regulator is an LM323, not a 7805. In the board photo below, VR2 and VR4 are the two TO-3 cans on the heatsink along the top edge.

The −5 V rail is a real difference from the PET 2001, whose static board has no −5 V regulator. Check all three rails, +5 V, +12 V and −5 V, on this board.

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.

Storage and I/O

There is no internal cassette deck on a 4000-series machine. Storage is:

• IEEE-488 (GPIB) disk drives and printers
• Two cassette ports for external Datassettes
• The user port and the memory expansion connector

Video and sound

The display is character-based, 40 columns by 25 rows, on a built-in 9-inch or 12-inch monochrome CRT. The technical manual has waveform sets for both displays: drawing 321450 for the 12-inch and 321447 for the 9-inch.

The board has a piezo transducer, MT1 (Commodore part 907300-02). André Fachat notes that the 12-inch models have the beeper and, from BASIC 4, "chirp" at reset; a 12-inch machine that stays silent at reset points at the beeper signal or the VIA.

Electrolytics on the logic board

Commodore's list for the universal dynamic PET board gives these electrolytics and tantalums; the rest of the C1-C97 range is ceramics and mica.

Universal dynamic PET board, drawing 8032090

Ref	Value	Type	Commodore part no.
C1, C16, C17, C23, C24	10 µF 25 V	Low-leakage electrolytic	900109-03
C2	470 µF 16 V	Electrolytic	900100-44
C5	4700 µF 25 V	Electrolytic	900100-45
C7, C11	47 µF 16 V	Electrolytic	900101-37
C6, C51	1 µF 35 V	Tantalum	900402-13

Commodore lists C1, C16, C17, C23 and C24 as low-leakage electrolytics, with a reference to note 4 on the drawing; fit low-leakage parts there. Fit tantalums at C6 and C51.

Logic board

Logic board
Universal dynamic PET logic board, with the two TO-3 regulators on the heatsink at the top

Common faults

• Boot failures: ROM or dynamic RAM, or a rail that is out. Check +5 V, +12 V and −5 V before condemning a chip.
• A machine that shows nothing may still be running. On this board the CPU has to program the CRT controller (UB13) before there is any picture, so a blank screen does not separate a dead CPU from a dead video path the way garbage does on a PET 2001.
• Keyboard: worn contacts and debris in the full-travel switches.

For fault-finding see Commodore PET 4000 Series Troubleshooting Guide; for routine care see Commodore PET 4000 Series Maintenance Guide.

Documentation hosted here

• Commodore PET 4000 Series Technical Manual: Commodore's drawing set, P/N 990438
• Commodore PET 2001 Service Documentation: the earlier static board

Gallery

• 
  Side view of a PET 4032
• 
  A PET 4032 with the top lifted

Related pages

• Commodore PET 2001
• Commodore PET 4000 Series Maintenance Guide
• Commodore PET 4000 Series Troubleshooting Guide
• CRT Discharge Procedure