9″ / 12″ CRT High-Voltage Safety & The Infamous PET "Killer Poke" Warning!

Unlike ordinary monitors that include an internal horizontal oscillator (555 / TDA1180), the built-in 9-inch and 12-inch monochrome CRTs in the Commodore PET are direct-drive monitors: the horizontal output transistor (BU406D / 2SD234) and flyback transformer are driven directly by the TTL HORIZ DRIVE pulse (J7 Pin 5) from the PET motherboard! This creates two critical hazards: (1) Inside the monitor housing sits ~10 kV–13 kV of lethal anode voltage (plus un-isolated mains or +18 V/+55 V B+ rails), and (2) running early PET 2001 POKE 59458,62 fast-print software on a 12-inch CRTC-equipped 4000/8000 ("Fat-40" / 8032) alters the horizontal drive timing and can physically overheat and destroy the CRT flyback transformer and horizontal output transistor!

1 What Is the PET "Killer Poke"?

How It Started on Non-CRTC PETs (2001 / 3032 / Early 4032): On early 9″ PETs without a 6845 CRTC chip, VIA CB2 (59458 decimal, $E842 bit 5) controlled a blanking wait-state line. Programmers discovered that executing POKE 59458,PEEK(59458) OR 32 (or POKE 59458,62) disabled vertical-blank wait states and sped up screen printing by 4×!
Why It Kills 12″ CRTC PETs (Fat-40 4032 & 8032): When Commodore redesigned the 12″ 4032 ("Fat-40") and 8032 around the MC6845 CRTC, they repurposed that exact VIA pin (59458 bit 5) to control character line height / vertical timing! On early 12″ analog monitor boards without protection diodes, executing POKE 59458,62 collapses vertical sweep or shifts horizontal drive duty cycle, burning out resistor R752, the 7812/7818 regulator, or the flyback stage!
Rule: Never run POKE 59458,62 on any PET that plays a piezo "chirp-chirp-chirp" beep on power-up (all chirping PETs have a 6845 CRTC chip!).

2 CRT Anode Discharge & Recapping

Unplug mains power and prop open the heavy hinged steel top hood using its built-in support rod (just like a car bonnet!).
To work on the 9″ (white/green P4/P31) or 12″ (green P31) CRT board, clip a heavy jumper wire to the bare metal CRT chassis frame and slide an insulated flathead screwdriver under the rubber anode suction cup until it clicks against the spring clip (hold 5 seconds, repeat after 1 minute).
Monitor Board Recapping Priorities:
- Replace the non-polarised (Bipolar) horizontal coupling capacitor (4.7 μF or 10 μF 50V NP) — when it dries out, the raster shrinks horizontally or loses linearity!
- Replace all electrolytic caps around the vertical deflection IC/transistors (10 μF–1000 μF 35V) to prevent vertical collapse (a bright horizontal line across the middle of the screen).
- Reflow cracked solder joints on the 7-pin J7 video header and flyback transformer pins!

3 Geometry, Width & Focus Controls

Control	Location & Adjustment Tip
BRIGHTNESS	Rear of monitor shell (or sub-pot on CRT PCB). Set so black background raster is just invisible.
V-HEIGHT & V-LIN	Trimpots on CRT PCB. Adjusts vertical height and top-vs-bottom character row symmetry.
H-WIDTH Coil	Hex ferrite slug on CRT PCB. Use a plastic hex alignment tool ONLY (a metal Allen key cracks the ferrite slug!).
FOCUS	Pot on CRT neck board or flyback. Adjusts character sharpness across all 40/80 columns.

PET Hardware Generations & Motherboard Selector

Compare the four distinct motherboard architectures spanning the 1977 PET 2001 through the 80-column CBM 8032 / 8096 / SuperPET.

Original PET 2001-4 & 2001-8 1977–1978 • ASSY 320008 • Chiclet Keyboard & Built-in Datasette

Designed by Chuck Peddle and Bill Seiler in 1977 as the world's first all-in-one personal computer (forming the "1977 Trinity" alongside the Apple II and TRS-80 Model I). Identifiable by its folded sheet-steel case, 9″ blue-or-black bezel CRT, built-in Sanyo/Commodore cassette deck on the left, and small calculator-style "chiclet" keyboard on the right. Internally, the original ASSY 320008 motherboard uses 100% Static RAM — assembled in four permutations of proprietary MOS 6540/6550 or industry-standard 2316B/2114 chips!

Key ICs & Architecture (`ASSY 320008`)

CPU (C4): MOS 6502 @ 1.00 MHz
PIA #1 (G8 — $E810): MOS 6520 — Keyboard row scanner (PA0–PA3 via 74LS145), Cassette #1 Sense, and Vertical Blank (SYNC) input
PIA #2 (B8 — $E820): MOS 6520 — 8-bit bi-directional IEEE-488 data bus (PA0–PA7 In, PB0–PB7 Out) and NDAC/DAV handshakes
VIA (A5 — $E840): MOS 6522 — User Port (PA0–PA7), Cassette motor control, CB2 audio/shift-register output, and IEEE-488 NRFD/ATN
Video Timing: Discrete 74LS TTL counters (NO 6845 CRTC chip!) reading 1 KB of dedicated Video SRAM ($8000–$83FF at C3 & C4)
Four Onboard 7805 / LM340T5 Regulators (VR1–VR4): Instead of one large 5 V supply, the 2001 board distributes heat across four separate TO-220 7805 regulators bolted to heatsinks right on the PCB!

The 4 Factory Combinations of 2001 RAM (`6550` vs `2114`) & ROM (`6540` vs `2316B`)

Check the white IC sockets on your ASSY 320008 board — Commodore produced four versions of this board depending on whether it used 28-pin MOS 6540 ROMs / 22-pin MOS 6550 SRAMs or 24-pin 2316B ROMs / 18-pin 2114 SRAMs:

Board Variant	ROM Sockets (`H1–H7`)	SRAM Sockets (`I1–J8` & Video `C3/C4`)
Type A (Earliest 1977)	7× MOS 6540 (28-pin, 2 KB clocked ROM)	16× MOS 6550 (22-pin, 1K×4 clocked SRAM)
Type B	7× MOS 6540 (28-pin)	16× 2114 (18-pin, 1K×4 standard SRAM)
Type C	7× 2316B (24-pin, 2 KB)	16× MOS 6550 (22-pin)
Type D (Easiest to Service)	7× 2316B (24-pin)	16× 2114 (18-pin standard SRAM)

Never Discard a Working 6540 ROM or 6550 SRAM! The 28-pin MOS 6540 and 22-pin MOS 6550 were only ever used in the 1977 PET 2001 and fail frequently. If any fail, plug in a modern 6540-to-2716 ROM adapter or 6550-to-2114/6116 SRAM adapter (or a single-socket ROMulan / PETvet / 6502 RAM+ROM replacement board under the CPU)!

PET 2001-N / CBM 3008 / 3016 / 3032 1979–1980 • ASSY 320351 • Full-Travel Keyboard & 4116 DRAM

In 1979 Commodore removed the internal cassette deck to make room for a full-size mechanical calculator-layout (or business-layout B) keyboard, upgraded the firmware to BASIC 2.0 (### COMMODORE BASIC ###), and replaced the hot static RAM array with sixteen 4116 (16K×1) dynamic RAMs (32KB) plus standard 24-pin 2332 (4 KB) ROMs! Sold as the 2001-16N/2001-32N in North America and the CBM 3016/3032 in Europe.

Key Architectural Highlights (`ASSY 320351`)

No 6845 CRTC Chip (Hardware 40×25 Video): Video timing is still generated by discrete 74LS counters reading 2× 2114 Video SRAMs (UF7 & UF8, $8000–$83FF) — meaning the video display starts up instantly even if the 6502 CPU or ROMs are completely dead!
Main RAM (UI2–UI9 & UJ2–UJ9): 8× or 16× 4116 DRAMs (requiring +5 V, +12 V, and −5 V!).
24-Pin 4KB ROM Sockets (UD6–UD9 + UF10 Char ROM): Uses standard 24-pin 2332 (4 KB) mask ROMs — meaning industry-standard 2532 UV EPROMs drop straight in with zero adapters!

Why `ASSY 320351` ("Dynamic PET") Is the Best Game Machine

Because ASSY 320351 has a full-travel keyboard, up to 32 KB of RAM, and retains the original non-CRTC 9″ video hardware (and doesn't suffer from the CRTC "Killer Poke"), it runs nearly 100% of classic 40-column PET games (Space Invaders, Petgalaga, Microchess, Dungeon). Many owners install a 3-way ROM switcher to toggle between BASIC 1.0, BASIC 2.0, and BASIC 4.0!

CBM 4016 / 4032 ("Thin-40" vs. "Fat-40" Universal CRTC Board) 1980–1982 • ASSY 8032080 • BASIC 4.0

Introduced Commodore BASIC 4.0 (*** COMMODORE BASIC 4.0 ***) with built-in disk commands (DIRECTORY, DLOAD, DSAVE, HEADER, COPY), a hardware piezo "chirp" speaker on CB2, and the Motorola MC6845 / MOS 6545 CRTC video controller! Early "Thin-40" 4032s used a 9″ CRT, while later "Fat-40" 4032s used the wider 12″ green-phosphor CRT cabinet and the Universal Dynamic Motherboard (ASSY 8032080 / 8032089) (which is actually an 8032 motherboard configured via jumpers for 40 columns!).

Crucial Diagnostic Difference on CRTC PETs (4032 / 8032)

No "Garbage Screen" If the CPU/ROM Fails Before Initialising the 6845 CRTC! Unlike the 2001/3032 (where discrete TTL counters always scan the screen), on a CRTC-based 4032 or 8032 the 6845 CRTC (UB13) outputs ZERO Horizontal or Vertical drive pulses until the 6502 CPU executes the Editor ROM ($E000) and writes the 18 CRTC timing registers!
Listen for the Power-On Piezo Chirp ("Bleep-bleep-bleep"): The Editor ROM (UD7) plays the 3-tone piezo chirp immediately after programming the 6845 CRTC registers!
- Chirp Heard + Black Screen: CPU, Kernal ($F000), Editor ($E000), and CRTC init succeeded! Check the 12″ CRT monitor, J7 video cable, or 74LS video output gates.
- NO Chirp + Black Screen: CPU never reached the Editor ROM! Check power rails, 6502 reset/clock, Kernal ROM (UD6), Editor ROM (UD7), or shorted low 4116 DRAM!

Converting a Universal Board (`8032080`) Between 40 and 80 Columns

The late "Fat-40" 4032 and the 8032 share the exact same ASSY 8032080 PCB — the 4032 simply leaves the second bank of two 2114 Odd-Column Video SRAMs (UC6/UC7) unpopulated, sets jumpers for 1 KB VRAM instead of 2 KB, and fits the 40-column Editor ROM (901498-01 / 901499-01)!

CBM 8032 / 8096 / 8296 & SuperPET (SP9000) 1980–1984 • 80×25 Green CRT • Business Keyboard

Commodore's flagship 80-column office and university computers. To double horizontal bandwidth from 40 to 80 characters per line without requiring double-speed SRAMs, the 8032 splits its 2 KB of Video RAM ($8000–$87FF) into two parallel 1 KB banks fetched simultaneously on every character clock: Even Columns (0, 2, 4…) live in UC4 & UC5 (2114) and Odd Columns (1, 3, 5…) live in UC6 & UC7 (2114)!

8000 Series Variants

CBM 8032 (ASSY 8032080): 32 KB Main RAM (16× 4116) + 2 KB Video RAM (4× 2114) + BASIC 4.0 + Business Keyboard (B).
CBM 8096: An 8032 factory-fitted with the 64 KB Memory Expansion Daughterboard (ASSY 8032096) (populated with 8× 4164 DRAMs) sitting over the 6502 socket (96KB total RAM for LOS-96 / WordPro!).
CBM 8296 / 8296-D: Sleek rounded cream Porsche-styled case with 128 KB onboard RAM (16× 4164), PLA logic (UE5/UE6), and optional internal dual 8250LP floppy drives.
SuperPET (MMF 9000): Developed with the University of Waterloo — adds a secondary motherboard with a Motorola MC6809 CPU, 64 KB banked RAM, RS-232 serial port, and three side toggle switches (6502 / 6809 / PROG) to run Waterloo APL, Pascal, Fortran, Cobol, and 6809 Macro Assembler!

8032 Even vs Odd Video RAM (`UC4–UC7`) Fault Decoder

2114 SRAM Chip	Columns & Bits Controlled	Visual Screen Symptom
UC4 (2114)	EVEN Columns (`0, 2, 4…`) Low Nibble (`ESD0–ESD3`)	Every 2nd character column (0, 2, 4…) shows wrong ASCII characters!
UC5 (2114)	EVEN Columns (`0, 2, 4…`) High Nibble (`ESD4–ESD7`)	Every 2nd character column (0, 2, 4…) is stuck in inverse video or wrong case!
UC6 (2114)	ODD Columns (`1, 3, 5…`) Low Nibble (`OSD0–OSD3`)	Every alternating odd column (1, 3, 5…) shows wrong characters!
UC7 (2114)	ODD Columns (`1, 3, 5…`) High Nibble (`OSD4–OSD7`)	Every alternating odd column (1, 3, 5…) is stuck in inverse video!

Diagnostic Checklist: "Garbage Screen", White Sockets & IEEE-488

Step-by-step bench troubleshooting for the classic PET "Random Character Garbage Screen", notorious white IC sockets, and dead disk drives.

▦

The Classic PET "Random Garbage Character Screen" Tree

On non-CRTC PETs (2001, 2001N, 30xx, early 40xx), powering on to a full screen of random, steady PETSCII characters (which never clears to *** COMMODORE BASIC ***) is the single most common fault!

1. What a Steady Garbage Screen Proves:
- Your 9″ CRT monitor, master crystal oscillator, video timing counters, Character ROM (UF10 / A2), and 2114 / 6550 Video SRAMs ($8000) are WORKING!
- The screen is simply displaying the random power-on contents of Video SRAM because the 6502 CPU never executed the Kernal/Editor screen-clear loop!
2. Check the Notorious White IC Sockets First:
- Early 1977–1979 PETs used cheap white single-wipe plastic IC sockets that lose contact pressure and tarnish heavily. Gently rock/reseat the 6502 CPU, Kernal ROM ($F000), and Editor ROM ($E000) — or replace degraded white sockets with turned-pin / dual-wipe sockets!
3. Check 6502 Reset (Pin 40), Clock (Pin 37), and Ready (Pin 2):
- Pin 40 (/RES) is driven by a 555 timer (NE555) through an open-collector inverter. If the timing capacitor on the 555 is leaky, /RES stays stuck low (0 V)!
4. Check Zero-Page / Stack RAM ($0000–$01FF) & Kernal ROM ($F000):
- If the 6502 cannot read the reset vector ($FFFC/$FFFD) from the Kernal ROM (H4/H7 on 2001; UD9 on 3032) or cannot push a return address onto the 6502 Stack in Low RAM (I1/J1 on 2001; UI2–UI9 4116 DRAM on 3032), it halts on the garbage screen!
- Plug a Romulan PET RAM/ROM / Tynemouth PET Diagnostic board into the 40-pin 6502 CPU socket to bypass all onboard RAM and ROMs in 30 seconds!

⚙

IEEE-488 Bus Troubleshooting (`DEVICE NOT PRESENT` / Hanging `LOAD`)

PET boots fine, but LOAD"$",8 or DIRECTORY hangs on SEARCHING FOR $ or immediately prints ?DEVICE NOT PRESENT ERROR with a 2031, 4040, 8050, or PETdisk MAX / SD2PET.

Suspect #1 — The Three MC3446N / MC3446AP IEEE-488 Bus Transceivers (UA7, UA8, UA9 / B9, A9, A10):
- Three 16-pin Motorola MC3446 quad bus transceivers sit directly between the rear IEEE-488 edge connector and the internal 6520 PIA / 6522 VIA!
- Static electricity or hot-plugging an IEEE-488 drive cable frequently kills one channel inside an MC3446, holding DAV, NRFD, NDAC, ATN, or one data bit (DIO1–DIO8) stuck high or low.
Quick BASIC IEEE-488 Loopback Self-Test (No Drive Connected!):
- With nothing plugged into the rear IEEE-488 port, run this 1-line check in BASIC to verify that PIA #2 (59424 = Data In, 59426 = Data Out) and both data MC3446 buffers can drive and read back all 8 data bits (0 to 255):
```
FOR I=0 TO 255:POKE 59426,I:IF PEEK(59424)<>I THEN PRINT "BAD BIT:";I XOR PEEK(59424)
NEXT:POKE 59426,255
```
- If any bit fails, either the corresponding MC3446 data transceiver (UA7/UA8) or 6520 PIA #2 (UB16/G8) is faulty!

Internal Linear Power Supply & J7 CRT Monitor Pinouts

Checking the PET's heavy internal transformer, multiple onboard +5V/+12V/−5V regulators, and the 7-pin J7 motherboard-to-CRT video connector.

Internal PSU Transformer & Multi-Regulator Architecture

Located in the rear-left base of the cabinet sits a massive mains transformer and an external/chassis-mounted 23,000 μF 15 V computer-grade screw-terminal filter capacitor. Raw ~8–9 V DC (plus 16 V AC center-tapped on dynamic boards) enters the motherboard on connector J8 (J10/J11), where multiple local TO-220 / TO-3 voltage regulators regulate each section of the board:

Motherboard Family	Regulators on PCB	Target Voltage & Role
PET 2001 Static (`ASSY 320008`)	4× `LM340T5` / `7805` (`VR1, VR2, VR3, VR4`)	+5.00 V DC (±5%) on EACH of the 4 regulators! Each 7805 powers a separate quadrant of the 6550/2114 SRAM and 6540/2316 ROM array. If just one of the four 7805s fails, a quarter of your RAM/ROM dies!
Dynamic PETs (3032 / 4032 / 8032)	2× `LM323K` / `7805` (+5V) 1× `7812` (+12V) 1× `7905` (−5V)	• +5.0 V DC: CPU, ROMs, 2114 VRAM, 4116 Pin 9 (`V_CC`) • +12.0 V DC: 4116 DRAM Pin 8 (`V_DD`) • −5.0 V DC: 4116 DRAM Pin 1 (`V_BB` — if −5V is missing, all sixteen 4116 DRAMs will burn up!)

Internal `J7` Motherboard-to-CRT Video Header 7-Pin Inline Molex (`0.156″`)

Carries separate TTL-level Video, Vertical Drive, and Horizontal Drive (plus raw AC power for the monitor on pins 6/7 on some models, or via a separate 2-pin/3-pin AC monitor power plug). You can also tap J7 into an RGBtoHDMI (TTL board) or a 3-resistor composite mixer to test a PET motherboard on an external monitor without the internal CRT!

J7 Pin	Signal	Level & Timing Notes
Pin 1	VIDEO DATA (TTL Pixel Stream)	5 V TTL (Active-low on 2001/3032/4032; check polarity jumper on universal boards)
Pin 2	GND (0 V)	Video Return Ground
Pin 3	VERT DRIVE (Vertical Sync)	5 V TTL Vertical Drive (60 Hz on Non-CRTC & NTSC; 50/60 Hz on CRTC)
Pin 4	GND (0 V)	Vertical Return Ground
Pin 5	HORIZ DRIVE (Horizontal Sync)	5 V TTL Horizontal Drive (15.625 kHz on 9″ Non-CRTC; ~20.0 kHz on 12″ CRTC 4032/8032!)
Pin 6	KEYWAY (Empty Pin)	Polarising keyway slot
Pin 7	GND (0 V)	Horizontal Return Ground

15.6kHz (9″) vs 20kHz (12″ CRTC) Horizontal Scan Rate Warning: Notice that 12″ CRTC PETs (Fat-40 4032 and 8032) run their CRT at a 20 kHz horizontal scan rate (not standard 15.6 kHz TV rate)! An RGBtoHDMI captures both 15.6 kHz and 20 kHz PET video effortlessly.

IEEE-488 (`J1`), User Port (`J2`) & Datasette (`J3`/`J6`) Pinouts

Rear PCB card-edge connector pinouts (0.156″ pitch) for connecting disk drives, PETdisk MAX / SD2PET, and CB2 sound amplifiers.

`J1` — IEEE-488 (GPIB) Bus Edge Connector 2×12 (24-Contact) • Rear Left

Connects Commodore 2040, 3040, 4040, 8050, 8250, SFD-1001, and 2031 disk drives, 4022/8023 printers, and modern PETdisk MAX / SD2PET SD-card drives. Top row = Pins 1–12 (Left-to-Right viewing rear of PET); Bottom row = Letters A–N (excluding G, I):

Top Pin (1–12)	IEEE-488 Signal	Bottom Pin (A–N)	IEEE-488 Signal
1	DIO1 (Data Bit 0)	A	DIO5 (Data Bit 4)
2	DIO2 (Data Bit 1)	B	DIO6 (Data Bit 5)
3	DIO3 (Data Bit 2)	C	DIO7 (Data Bit 6)
4	DIO4 (Data Bit 3)	D	DIO8 (Data Bit 7)
5	/EOI (End Or Identify)	E	/REN (Remote Enable — GND)
6	/DAV (Data Valid)	F	GND (Logic Ground)
7	/NRFD (Not Ready For Data)	H	GND (/DAV Return)
8	/NDAC (No Data Accepted)	J	GND (/NRFD Return)
9	/IFC (Interface Clear / Reset)	K	GND (/NDAC Return)
10	/SRQ (Service Request)	L	GND (/IFC Return)
11	/ATN (Attention Mode)	M	GND (/ATN Return)
12	Chassis Shield GND	N	GND (/SRQ Return)

`J2` — Parallel User Port & `CB2` Audio Out 2×12 Edge • Center

Driven by the 6522 VIA (PA0–PA7 & CA1/CB1/CB2). See also our dedicated PET IEEE-488 (J1) Bus, PET J7 7-Pin Video Header, and Datasette (J3/J6) pinout pages. Because early PETs (2001/3032) have no internal speaker, all PET game sound is output as a pulse-width / square-wave stream on User Port Pin M (CB2)!

Top Pin	Signal	Bottom Pin	Signal & Bench Role
1	GND (0 V)	A	GND (0 V)
2	TV Video Out	B	CA1 (Handshake Input)
3	/SRQ IN	C – L	PA0 – PA7 (8-Bit Parallel User I/O + Stupid PET Tricks Dual Joystick!)
4	/EOI	M	CB2 (PET SOUND OUTPUT!)
5	DIAG (Pull to GND for Monitor!)	N	GND (0 V Audio Return)
12	GND (0 V)	Note: Keyway slot between Pins 1/2 and 9/10.

2-Minute PET Sound Amplifier Mod: Wire User Port Pin M (CB2) through a 10 kΩ resistor + 0.1 μF capacitor in series to the input of any powered desktop speaker (with Pin N = GND) for instant PET game audio! Also note: grounding Top Pin 5 (DIAG) at power-on boots straight into the built-in TIM Machine Language Monitor (B*)!

`J3` (Rear) & `J6` (Internal) Datasette Ports (`2×6` Edge)

Identical to the C64 and VIC-20 Datasette connector (Pin A/1 = GND, Pin B/2 = +5V, Pin C/3 = +6V Motor, Pin D/4 = Read, Pin E/5 = Write, Pin F/6 = Sense). Uniquely, every PET has two independent tape ports (Device 1 and Device 2)!

Chip & 2532 / 2716 EPROM Reference

Interactive IC Pinout Finder cards for every major chip in the PET plus BASIC 1.0 / 2.0 / 4.0 ROM part numbers and EPROM rules.

DIP-40

MOS 6502 CPU

1.00 MHz 8-bit microprocessor driving every PET from the 1977 2001 to the 8296.

View Pinout →

DIP-40

MOS 6520 / 6821 PIA (×2)

Two 40-pin PIAs ($E810 Keyboard/Tape/VBlank & $E820 IEEE-488 Data Bus). Motorola MC6821P is a 100% drop-in substitute!

View Pinout →

DIP-40

MOS 6522 VIA

Mapped at $E840 — User Port, CB2 Sound shift register, Cassette motor control, and IEEE-488 handshake lines.

View Pinout →

DIP-40

MOS 6545 / MC6845 CRTC

Fitted to 12″ Fat-40 (4032) and 80-column (8032/8096/8296) PETs to generate programmable 20 kHz CRT timing.

View Pinout →

DIP-18

2114 SRAM (1K×4)

Used for Video RAM across all PETs (2× 2114 on 40-col; 4× 2114 on 80-col) and Main RAM on 2001 Type B/D boards.

View Pinout →

DIP-16

4116 DRAM (16K×1)

Triple-rail (−5 V, +12 V, +5 V) dynamic RAM (16× 4116 = 32 KB) on 2001N, 3032, 4032, and 8032 boards.

View Pinout →

PET BASIC 2.0 & BASIC 4.0 ROM Map (`2332` / `2316B` → `2532` / `2716` EPROMs)

On all dynamic PET motherboards (2001N, 3032, 4032, 8032), the 4 KB ROM sockets ($B000, $C000, $D000, $F000) use the 24-pin 2332 mask ROM pinout (where Pin 21 = +5V and Pin 18 = A11) — which means Texas Instruments TMS2532 / 2532A (4 KB) UV EPROMs are a 100% DIRECT DROP-IN with zero adapters, whereas the 2 KB Editor ROM ($E000) and Character ROM accept a standard 2716 (2 KB) EPROM directly!

Address Range	Role	BASIC 2.0 Part # (3032)	BASIC 4.0 Part # (4032 / 8032)	Direct EPROM Drop-In
`$B000–$BFFF` (Socket `UD9` / `UD12`)	BASIC 4.0 Disk/Extra Commands (Empty on BASIC 2.0!)	Empty Socket	`901465-23` (or `-19`)	`2532` (4 KB, 24-Pin) direct drop-in! (Or `2732` via a 2332-to-2732 adapter).
`$C000–$CFFF` (Socket `UD8` / `UD11`)	BASIC Interpreter Low	`901465-01`	`901465-20`	`2532` (4 KB, 24-Pin) direct drop-in!
`$D000–$DFFF` (Socket `UD7` / `UD10`)	BASIC Interpreter High	`901465-02`	`901465-21`	`2532` (4 KB, 24-Pin) direct drop-in!
`$E000–$E7FF` (Socket `UD6` / `UD7`)	Screen Editor & Keyboard + CRTC Init (`2KB`!)	`901447-24` (Normal Keybd) `901474-01` (Business Keybd)	`901498-01` (40-Col CRTC 50Hz) `901499-01` (40-Col CRTC 60Hz) `901474-04` (80-Col 8032)	`2716` (2 KB, 24-Pin) is a 100% Direct Drop-In! (Best socket for PETTESTER V4 by Dave Roberts!).
`$F000–$FFFF` (Socket `UD5` / `UD6`)	Kernal OS & IEEE-488	`901465-03`	`901465-22`	`2532` (4 KB, 24-Pin) direct drop-in!
Character Generator (Socket `UF10` / `UA3`)	2 KB / 4 KB Font ROM	`901447-10` (`2KB`)	`901447-10` (`2KB`)	`2716` (2 KB, 24-Pin) direct drop-in!

Ultimate Diagnostic Tool — Burning PETTESTER V4 into a 2716 EPROM for the $E000 Editor Socket: Because the $E000 Editor ROM is almost always in a socket and accepts a standard 2716 EPROM, plugging a 2716 burned with Dave Roberts's PETTESTER (Eudi's PET Tester) into the Editor socket requires zero working RAM to run: it initializes the CRTC, tests Video SRAM, tests Zero-Page/Stack RAM, checksums all ROMs, scans the keyboard, and loops a complete March-C test on all 16K/32K of 4116 DRAM!

Resources & Further Reading

Blog posts, interactive bench tools, and essential Commodore PET schematics & communities.

Smiggy's Commodore Posts

Bench Tools & Machine Hubs

Retro File Utilities (Rust/Wasm) — 6502 disassembler, .D64/.PRG extractor & PETTESTER/BASIC .BIN ROM CRC32 verifier
IC Pinout Finder — 6502, 6520/6821, 6522, 6845, 2114, 4116 & more
Connector Pinout Directory — IEEE-488 (GPIB) Bus, 24-Pin User Port, Datasette Edge, PET J7 Video Header
Recap & Repair Reference — capacitor replacement guide
Ohm's Law Calculator
C64 Machine Hub — Commodore 64 reference
VIC-20 Machine Hub — Commodore VIC-20 reference
C128 Machine Hub — C128, C128D & DCR reference
SX-64 Machine Hub — Executive Portable C64 reference
Amiga Machine Hub — A500/A600/A1200 reference
Big-Box Amiga Hub — A1000, A2000, A3000 & A4000 reference
Atari ST Hub — 520ST, 1040STFM & STE reference
Atari 8-Bit Hub — 400/800, 800XL & 130XE reference
Apple IIe Hub — Unenhanced, Enhanced & Platinum reference
BBC Micro Hub — Model B, B+ & Master 128 reference
Acorn Atom & Electron Hub — Atom & Electron reference
ZX Spectrum Hub — 16K/48K & +2/+3 reference
Sinclair QL Hub — 68008, Microdrive & ULA reference
Dragon 32/64 Hub — Dragon 32 & 64 reference
Oric-1 & Atmos Hub — Oric 6502A & ULA reference
Amstrad CPC 464 Hub — CPC 464 & Datacorder reference
Amstrad CPC 6128 Hub — 128K & 3″ disc reference
MSX Machine Hub — MSX1, MSX2, MSX2+ & Turbo R reference
Osborne 1 & Kaypro II Hub — CP/M luggable reference
Plus/4 & C16 (TED) Hub — 264 series reference
TRS-80 & CoCo Hub — Model I/III/4 & CoCo 1/2/3 reference
TI-99/4A Machine Hub — 16-bit TMS9900 & PEB reference

External Commodore PET Resources

Zimmers.net PET Schematics & ROMs — complete Commodore factory schematics and ROM images for every PET/CBM board
Andre Fachat's PET Index — deep-dive architectural analysis of static, dynamic, CRTC, and 8296 PET boards
PETTESTER V4 (GitHub) — Dave Roberts's essential $E000 diagnostic ROM and manual
PETdisk MAX (Bitfixer) — modern IEEE-488 SD card & Wi-Fi drive emulator for all Commodore PETs

Capacitor & Power Stage Reference

Commodore PET Series — Capacitor & Recap Reference

Board revisions, electrolytic capacitor lists, voltage/farad ratings, and Through-Hole servicing notes.

Commodore PET Series — Printable Board Recap & Capacitor BOM ReferenceFormat this system's capacitor replacement list, diagnostic flowchart, and IC pinouts into a high-contrast bench PDF.

Commodore PET Series — PET 2001N (320351) & 4032 / 8032 (8032080)

Dynamic RAM 40-column & 80-column Universal CRTC mainboards • Mount: Through-hole • Difficulty: Beginner friendly

Full Printable Recap Sheet →

PET 2001N / 4032 / 8032 Mainboard (8 Capacitors)

Ref	Capacitance	Voltage	Package / Type	Circuit Location & Bench Notes
`C1 (Chassis)`	22000 uF	16 V	Screw-Terminal / Axial	Original is 23,000 uF 15V Mallory screw-terminal can mounted by the transformer.
`C61`	470 uF	35 V	Axial
`C62`	10 uF	25 V	Axial
`C63`	470 uF	25 V	Axial
`C64`	10 uF	25 V	Axial
`C65`	22 uF	16 V	Axial
`C66`	22 uF	16 V	Axial
`C67`	1 uF	35 V	Radial

Printable Diagnostic Flowchart & Voltage CheckpointsFormat this step-by-step fault isolation tree into a high-contrast bench reference sheet.

Commodore PET Series — Interactive Diagnostic Flowchart & Voltage Checkpoints

Enable JavaScript to run the client-side interactive fault-isolation flowchart engine.

Complete Diagnostic Flowchart: Capacitive Load, ESR & Power Rail Ripple Diagnostic Tree (Universal Retro Mainboards (C64, Amiga, ZX Spectrum, Game Gear, Consoles))

STEP 1: Measure 100Hz/120Hz Peak-to-Peak AC Ripple on the +5V / +12V Bulk Filter Cap [node-1]

Set your oscilloscope to AC Coupling, 200 mV/div, and 2.5 ms/div (20 MHz bandwidth limit ON). Probe directly across the main bulk filter capacitor (e.g. C19 2200µF / C88 1000µF on C64, or C303/C304 on Amiga) under full system load. Measure the peak-to-peak sawtooth ripple amplitude (mVpp).

Expected Reading: < 50 mVpp clean regulated rail (post-regulator) or < 350 mVpp on raw unregulated bulk DC before the 7805/7812.

STEP 2: Check Linear Regulator (7805 / 7812) Input-to-Output Dropout Margin [node-2]

Switch oscilloscope or multimeter to DC Volts and measure Pin 1 (Input) of the 7805 (+5V) or 7812 (+12V) regulator at the bottom of the ripple trough. Verify that Input Voltage remains at least 2.0V above the regulated output (e.g. ≥7.2V into a 7805, ≥14.2V into a 7812).

Expected Reading: 7805 Input ≥ 7.2V DC; 7812 Input ≥ 14.2V DC. Below this dropout threshold, ripple punches straight through to the logic rail.

STEP 3: Check Local IC Decoupling & Audio/Video AC Coupling Capacitors [node-3]

Probe audio output coupling caps (e.g. C91 100µF on C64 SID Pin 27, or C324/C334 22µF SMD on Amiga Paula) — compare upstream vs. downstream signal amplitude. Inspect SMD electrolytic pads (Amiga 600/1200, Game Gear, DMG-01) under magnification for fishy odor, dull grey solder corrosion, or lifted copper traces.

Expected Reading: Full audio/video swing across the coupling capacitor with zero DC leakage on the output side and clean, shiny solder pads.

[ISOLATED FAULT: RES-BULK-CAP] Fault Isolated: High-ESR Bulk Filter Capacitor (>100 mVpp Rail Ripple) VERDICT

Excessive 100/120Hz sawtooth ripple on the DC rail confirms that the primary reservoir/filter electrolytics have dried out and lost effective capacitance.

[ISOLATED FAULT: RES-REG-DROPOUT] Fault Isolated: Linear Regulator Dropout / Bridge Rectifier Diode Open VERDICT

The pre-regulator DC rail is sagging below the minimum 2V dropout headroom required by the 7805/7812 regulator.

[ISOLATED FAULT: RES-COUPLING-CAP] Fault Isolated: Open/Leaky Audio or Video Coupling Capacitor & Trace Corrosion VERDICT

Signal attenuation, muffled audio, or DC offset hum across the coupling stage indicates dried-out or leaking coupling capacitors.

[ISOLATED FAULT: RES-RAILS-HEALTHY] Verification Passed: Power Rails, Ripple & Coupling Capacitors Within Spec VERDICT

All measured DC supply rails, AC ripple levels (<50 mVpp), and coupling stages pass bench specification. If performing a preventive recap, use the verified board BOM below.

Interactive Pinouts, Visualizers & Disassemblers

Commodore PET Series — System Bench Tools & IC Pinouts

Click any chip below to open its interactive DIP/PLCC pinout diagram, pin-by-pin signal table, and oscilloscope test waveforms.

Commodore PET Series — Printable IC Pinout & Chipset SummaryPrint this system's custom IC pinout summary or open any chip card below for its full DIP/PLCC pinout sheet.

DIP-14 74-Series Gates

74LS00

SN74LS00N / DM74LS00N

Quad 2-input NAND gate — the most common glue-logic part in retro computers.

Commodore PET Series Machine Hub

9″ / 12″ CRT High-Voltage Safety & The Infamous PET "Killer Poke" Warning!

1 What Is the PET "Killer Poke"?

2 CRT Anode Discharge & Recapping

3 Geometry, Width & Focus Controls

PET Hardware Generations & Motherboard Selector

Original PET 2001-4 & 2001-8 1977–1978 • ASSY 320008 • Chiclet Keyboard & Built-in Datasette

Key ICs & Architecture (ASSY 320008)

The 4 Factory Combinations of 2001 RAM (6550 vs 2114) & ROM (6540 vs 2316B)

PET 2001-N / CBM 3008 / 3016 / 3032 1979–1980 • ASSY 320351 • Full-Travel Keyboard & 4116 DRAM

Key Architectural Highlights (ASSY 320351)

Why ASSY 320351 ("Dynamic PET") Is the Best Game Machine

CBM 4016 / 4032 ("Thin-40" vs. "Fat-40" Universal CRTC Board) 1980–1982 • ASSY 8032080 • BASIC 4.0

Crucial Diagnostic Difference on CRTC PETs (4032 / 8032)

Converting a Universal Board (8032080) Between 40 and 80 Columns

CBM 8032 / 8096 / 8296 & SuperPET (SP9000) 1980–1984 • 80×25 Green CRT • Business Keyboard

8000 Series Variants

8032 Even vs Odd Video RAM (UC4–UC7) Fault Decoder

Diagnostic Checklist: "Garbage Screen", White Sockets & IEEE-488

The Classic PET "Random Garbage Character Screen" Tree

IEEE-488 Bus Troubleshooting (DEVICE NOT PRESENT / Hanging LOAD)

Internal Linear Power Supply & J7 CRT Monitor Pinouts

Internal PSU Transformer & Multi-Regulator Architecture

Internal J7 Motherboard-to-CRT Video Header 7-Pin Inline Molex (0.156″)

IEEE-488 (J1), User Port (J2) & Datasette (J3/J6) Pinouts

J1 — IEEE-488 (GPIB) Bus Edge Connector 2×12 (24-Contact) • Rear Left

J2 — Parallel User Port & CB2 Audio Out 2×12 Edge • Center

J3 (Rear) & J6 (Internal) Datasette Ports (2×6 Edge)

Chip & 2532 / 2716 EPROM Reference

MOS 6502 CPU

MOS 6520 / 6821 PIA (×2)

MOS 6522 VIA

MOS 6545 / MC6845 CRTC

2114 SRAM (1K×4)

4116 DRAM (16K×1)

PET BASIC 2.0 & BASIC 4.0 ROM Map (2332 / 2316B → 2532 / 2716 EPROMs)

Resources & Further Reading

Smiggy's Commodore Posts

Bench Tools & Machine Hubs

External Commodore PET Resources

Commodore PET (2001 / 4000 / 8000) — Unified Workbench Reference

Commodore PET Series — Capacitor & Recap Reference

Commodore PET Series — PET 2001N (320351) & 4032 / 8032 (8032080)

PET 2001N / 4032 / 8032 Mainboard (8 Capacitors)

Complete Diagnostic Flowchart: Capacitive Load, ESR & Power Rail Ripple Diagnostic Tree (Universal Retro Mainboards (C64, Amiga, ZX Spectrum, Game Gear, Consoles))

Commodore PET Series — System Bench Tools & IC Pinouts

74LS00

74LS02

74LS04

74LS08

74LS14

74LS244

MOS 6502

Motorola MC6809

WDC W65C02S

MOS 6522 VIA

Motorola MC6821 PIA

Signetics 82S100 FPLA

Motorola MC6845 CRTC

2114 1K x 4 SRAM

4116 16K x 1 DRAM

NE555

Signal & Trace Visualizer (Scope)

Retro File Utilities (Rust/Wasm)

Connector & Port Pinout Reference

Logic & RAM Substitution Guide

Theme Palette

Audio & Display

System Info

Key ICs & Architecture (`ASSY 320008`)

The 4 Factory Combinations of 2001 RAM (`6550` vs `2114`) & ROM (`6540` vs `2316B`)

Key Architectural Highlights (`ASSY 320351`)

Why `ASSY 320351` ("Dynamic PET") Is the Best Game Machine

Converting a Universal Board (`8032080`) Between 40 and 80 Columns

8032 Even vs Odd Video RAM (`UC4–UC7`) Fault Decoder

IEEE-488 Bus Troubleshooting (`DEVICE NOT PRESENT` / Hanging `LOAD`)

Internal `J7` Motherboard-to-CRT Video Header 7-Pin Inline Molex (`0.156″`)

IEEE-488 (`J1`), User Port (`J2`) & Datasette (`J3`/`J6`) Pinouts

`J1` — IEEE-488 (GPIB) Bus Edge Connector 2×12 (24-Contact) • Rear Left

`J2` — Parallel User Port & `CB2` Audio Out 2×12 Edge • Center

`J3` (Rear) & `J6` (Internal) Datasette Ports (`2×6` Edge)

PET BASIC 2.0 & BASIC 4.0 ROM Map (`2332` / `2316B` → `2532` / `2716` EPROMs)