Video Board Schematic
Schematic, Service, Display Circuit — Commodore Business Machines, Inc.'s service schematic for the Commodore PET 2001 display assembly. One large sheet, scanned at 400 dpi.
"Video board" is this wiki's word, not Commodore's. Commodore calls it the display assembly, and it is the machine's power supply as well as its monitor.
 | The display assembly is the PET's power supply as well as its monitor. Mains voltage is present on it whenever the machine is plugged in, the CRT anode runs at roughly +10 kV from flyback T2, and C1 is a 4700 µF reservoir that stores real energy. Read CRT Discharge Procedure before working on this board. |
What is on the sheet
editThe full component-level circuit of the display assembly: the mains transformer T1, the CR19–CR22 bridge, the 4700 µF reservoir C1, regulator VR1 producing +12 V, the −30 V rail, the +85 V boost rail, the horizontal output stage around Q14 and flyback T2, and the CRT anode supply of roughly +10 kV. Values are printed against components on the drawing.
Fourteen oscilloscope waveform photographs are printed on the sheet at their test points. The vertical and timebase setting for each is not on this drawing — it is on a separate supplement, held here as Schematic Notes for Video Board. The two documents are useless apart.
The five service notes printed on the drawing
edit1. Adjust for best focus; voltage is selectable. 2. R20 is mounted perpendicular to the board for screwdriver adjustment. 3. R9 is at the rear of the PCB, on a 1/4-inch shaft about 2 inches long. 4. Board connectors are Molex 09-64-1021 and 09-64-1061. 5. On the flyback terminals and C25, the numbers in parentheses are for the DOK version — the alternative flyback, Commodore 902475.
The sheet marks flyback T2 as GI 294-7746.
What it does not contain
editNo parts list — for reference designators, values and Commodore part numbers see Video Board Parts List (1 of 3). No physical placement — for that see Video Board Parts Layout. Nothing about the main logic board, which is a separate set of drawings.
Two other revisions of this drawing are held here
edit| Page | Drawing number in the title block | Title as printed | Dates on the sheet |
|---|---|---|---|
| This page | not numbered in the title block | Schematic, Service, Display Circuit | — |
| Video Board Schematic (Rev 2, 320032) | 320032, rev A | Display Schematic | drawn 3-9-76; revised 3-17-77, 4-11-77, 6-15-77 |
| Video Board Schematic (Rev 3, 320033) | 320033, size D, rev P | Schematic, Display Circuit | drawn 5/78, engineered 6-29-78; next assembly 320012 |
The "Rev 2" and "Rev 3" in those page titles are this wiki's numbering, not Commodore's. The drawings' own revision marks are A and P respectively, and they are two different drawing numbers, not two revisions of one. Check the number in the title block against your own board before working from either.
Related pages
edit- Schematic Notes for Video Board — the oscilloscope settings for this sheet's 14 waveform photographs
- Video Board Parts Layout · Video Board Parts List (1 of 3)
- Commodore PET 2001 Service Documentation · Commodore PET 2001 Capacitor Replacement Guide · CRT Discharge Procedure
Download: video-1.gif