- 1 Chips & ICs
- 2 Schematics
- 3 Common Problems
- 4 Technical Tips (From Service manual)
- 5 RF Adjustment / Alignment
- 6 +5 Volt RAM Modification
- 7 No-delay BIOS Modification
- 8 Opening the Power Supply
- 9 Capacitor List
Chips & ICs
- U1: CPU: NEC μPD780C-1 (Z80 clone)
- U2: BIOS: 313 10031-4005 73108A
- U3, U4: RAM: 2114
- U5: 74LS138
- U6: 74LS138
- U7: 74LS05
- U8: 74LS74
- U9: GPU: TMS9928A
- U10 - U17: VRAM: 4116
- U18, U19: Controller Input: 74LS541
- U20: Sound Generator: SN76489AN
- U21: TV Video Modulator: LM1889 (on RF modulator PCB)
- U22: 74LS04
- U23: HEF4066BP
- U24: 74LS00
- IC1: Voltage Regulator: CA723CE
- IC2: Voltage Regulator: CA723CE
- IC3: -5v Regulator: 7905C (with mica insulator)
- IC?: TIP41
- IC?: TIP41
These excellent schematics were drawn by Dan Boris
- Graphics are corrupted, text is unreadable. Random blocks appear and game characters can interact or be blocked by them.
- Dirty power switch. Switch must be disassembled, contacts cleaned / burnished, and reassembled.
- Defective power supply
- VRAM failure. All 8 VRAM chips use 3 voltage power and are known for running hot and developing issues over time. A +5v memory kit and replacement instructions are available.
- TMS9928 failure. These chips tend to run hot and if the heat sink has fallen off they may have become damaged over time. The 9928 was used in arcade hardware but in the Colecovision doesn't seem circulate air well OR they are prone to static damage.
Dysfunctional Controller Chips
If your Colecovision isn't behaving correctly, games start by themselves, or they behave as if one controller direction is pressed down constantly, the U18 / U19 74LS541 chips have probably been static fried. Purchase new controllers chips as a kit
Technical Tips (From Service manual)
- Black out on screen
- If the screen blacks out after the game has been played for a short interval, check C106 for proper polarity. If polarity is wrong, replace C106
- Purple Monkey
- In Donkey Kong, if the monkey, Mario, and the barrels are purple, rather than their normal colors, replace U9
- Joystick Game Selection
- If the keypad does not control the game selection, only the joystick can be used to select games, replace U6 (also see Common Problems section above)
- Channel 3 but not 4
- Channel 3 operates normally but channel 4 only works if the game is turned off and then turned back on again, (or vise versa) replace RF board.
- Not all cartridges function
- Game does not accept all and/or any cartridges. Examine C70 for mechanical obstructions. Is it flopped over flat on board? Replace U5.
- Vertical lines
- Vertical lines on background rather than solid blue background with no lines. Replace C106.
- Skips menu
- Menu is skipped. This is the blue screen with skill levels. Check pins 3-9 of U18 with DVM. If any pin is below 2.2VDC change U18. Check pins 2-8 of U19 with DVM. If any pin is below 2.2VDC change U19.
- No explosion
- If there is no explosion, a sound testing of the noise generator, on the final test, replace U20.
- 12 VDC is shorted to -5 VDC
- Examine WJ2 to see if it has shorted to adjacent test points.
- No RF voltage
- If there is no voltage on the RF board, check WJ2.
- No Color
- If color has disappeared, check frequency at J4 pin 6. Correct frequency is 3.57954 Mhz +/- 100 Hz. If the frequency is incorrect, check the clock circuit.
- Double images
- Replace U9 for double images.
- Wavey (sic) picture
- If picture is wavy, ensure that R62 is 270Ω and C90 is 120pF. If they are incorrect, replace them. Check Q2, if it is an ITT transistor, replace it.
- Incorrect scoring
- If scoring is not working properly, replace U3 and/or U4.
- Wrong frequency
- 3.579 Mhz clock is the wrong frequency. If U22 is a Texas Instruments IC, replace it.
- Bad spinner interface
- Spinner interface is not working. If U24 is a Texas Instruments IC, replace it.
- Slow game
- If game is running abnormally slow, replace U20.
RF Adjustment / Alignment
+5 Volt RAM Modification
No-delay BIOS Modification
Opening the Power Supply
It's not quite an easy job as the two case halves were glued / plastic welded when built.
Here are a few potential methods:
- Cut the case apart with a saw or Dremel tool. If you can place the supply in a vice, using a fine-tooth hacksaw right in the groove where the two halves meet should produce fairly clean results.
- Hit with a hammer around the perimeter to break the glue/welds. Probably not the most effective and risks a full fracture through the case.
- Use a hot-wire cutter and some wedges to separate the case. Cuts cleanly but a little challenging as the ABS tends to melt itself back together - creative use of wedges may help. Avoid penetrating further than 6-7mm or you may cut into the transformer case or transformer wires.
If you want to avoid cutting near the output wire, you really only need to separate the sides & top of the case. Once they are free you can pry the case open and snap the bottom fairly cleanly.
Look over the existing soldering for flaws. The few I've seen have had some sketchy looking solder joints, improper fills, things like that.
Revision J C3 1uF 50v C16 10uF 16v C34 10uF 16v C36 10uF 16v C68 10uF 16v C87 10uF 16v MOD 10uF 50v (on modulator PCB)
Remember to retain the mica insulator when replacing the 7905 regulator!
PC-016-1 C1 1000uF 25v C2 4700uF 16v C3 220uF 25v C4 1000uF 16v C7 22uF 50v C8 22uF 50v C9 22uF 50v