Coleco Gemini General Maintenance
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Cleaning, power checks and care for the Coleco Gemini, Coleco's Atari 2600-compatible console of 1983. The Gemini is a simple single-sided board with three main chips, a 7805 regulator and an RF modulator, and its usual faults are mechanical: cracked solder joints at the sockets and dirty cartridge contacts.[1][2] Fault-finding is on Coleco Gemini Troubleshooting Guide.
Cleaning
[edit | edit source]- Switch off and unplug the adapter from the wall before cleaning. Wipe the console, controllers and cartridges with a soft, slightly damp cloth, and never immerse them.[3]
- Clean cartridge edge connectors with isopropyl alcohol. Leaded Solder's copy of Venture would only run when held at an angle until its edge connector was cleaned with alcohol and the cartridge was pushed in and out a few times.[1]
- Corrosion or residue in the controller sockets: Leaded Solder cleared a green deposit from a left-hand socket with a little vinegar followed by isopropyl alcohol, then stood the console to drain.[1]
- Always switch off before inserting or removing a cartridge, and do not force one in. It goes into the slot on the right with its front label facing the back of the console.[3]
Power
[edit | edit source]The Gemini runs from a 9 V DC adapter with a centre-positive plug, Coleco part 91617, which takes the same plug as the Atari 2600's.[1] On the board a 7805 regulator on a heatsink makes +5 V, with a 2200 µF 16 V axial electrolytic (C34) beside it.[4][1]
| Point | Expect | If not |
|---|---|---|
| Adapter plug, centre pin | About 9 V DC, centre positive | Replace or repair the adapter |
| Regulator U5, input pin (marked IN) | Adapter voltage, less any drop in the jack and switch | Check the DC jack's solder joints and the power switch |
| Regulator U5, output | +5 V | Replace the regulator; check for a short on the +5 V side first |
Adapter rating from Leaded Solder;[1] the regulator and its marked input pin from the board photograph.[4] The 7805's output is a fixed +5 V.
Coleco's manual warns against connecting the supply to anything but a 110/120 V outlet and tells owners to unplug it after play.[3] Outside North America use an adapter made for the local mains with the same 9 V DC centre-positive output.
Solder joints
[edit | edit source]The controller sockets and the DC jack take force every time something is plugged in. Leaded Solder found the most cracked joints its author had ever seen on the controller 1 socket, partly cracked joints on the controller 2 socket and a cracked joint on the DC jack. Each was fluxed and reflowed with fresh solder and checked under magnification.[1] The controller 2 joints had not yet failed, so reflow these joints whenever a Gemini is opened, whether or not they look cracked.
The same board had an underfilled factory joint on the TIA-compatible chip, U3.[1] Inspect the chip pins while the board is out.
Capacitors
[edit | edit source]No Coleco parts list for the Gemini has been published, so there is no confirmed list of values. The board photographed by Evan-Amos shows these:[4]
| Ref | Type | Value | Notes |
|---|---|---|---|
| C34 | Axial aluminium electrolytic | 2200 µF 16 V | Beside the 7805; the supply reservoir |
| C15 | Radial aluminium electrolytic | Not legible in the photograph | Beside the 6507 (U1); read the value from the part |
| C46, C47 | Clear cylindrical capacitors | Not legible in the photograph | Near the RF section |
Leaded Solder's Gemini has two polystyrene capacitors, and its photographs show one of them at C46.[1] Replace an electrolytic only with the same value and an equal or higher voltage rating, and see Capacitor Failure Symptoms for what a failed one looks like. The Coleco Gemini Capacitor Replacement Guide has close-ups of C34 and C15 and the replacement steps.
Controllers
[edit | edit source]The Gemini's own controllers combine an eight-direction joystick, a side fire button and a paddle knob. Paddle games need both controllers on a WYE connector in the left socket. Any controller that works on an Atari VCS works on the Gemini.[3] David Farquhar notes that the Gemini controllers are fine for one-player paddle games, but multiplayer paddle games need a set of Atari paddles.[2]
Other consoles' pads are not wired the same way. Leaded Solder found that a Mega Drive (Genesis) pad made the Gemini read a constant "up", while an Atari joystick worked correctly.[1]
Related pages
[edit | edit source]- Coleco Gemini
- Coleco Gemini Troubleshooting Guide
- Coleco Gemini Capacitor Replacement Guide
- Coleco Gemini Owners Manual
- Atari 2600 General Maintenance
- Capacitor Failure Symptoms
- Recommended Tools
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 "Space Walking with Gemini", Leaded Solder, 6 April 2020, leadedsolder.com (retrieved 2026-10-06). Restoration of a Canadian Gemini: board CPC-2 Rev F (1983); green deposit in a controller socket cleaned with vinegar and isopropyl alcohol; cracked joints on both controller sockets, an underfilled joint on the TIA clone and a cracked joint on the DC jack, all reflowed; two polystyrene capacitors; Coleco 91617 adapter, 9 V DC centre-positive; cartridge contacts cleaned with alcohol; a Mega Drive pad reading as constant up; a Combat cartridge whose dust cover would not slide back.
- ↑ 2.0 2.1 David L. Farquhar, "Coleco Gemini: An Atari 2600 clone from 1983", The Silicon Underground, 2017, updated 2025 (retrieved 2026-10-06): broken solder joints as the most likely fault; the controllers' limits with multiplayer paddle games.
- ↑ 3.0 3.1 3.2 3.3 Coleco Industries, Gemini Video Game System Owners Manual, model 2510, Guide No. 91783A, 1983: p. 7 (power off before inserting or removing a cartridge; cartridge orientation), p. 9 (controllers, WYE connector, Atari VCS controllers), pp. 10–11 (troubleshooting checklist), p. 12 (care, cleaning, 110/120 V only). Hosted here as File:Coleco Gemini Owners Manual Guide 91783A.pdf (see Coleco Gemini Owners Manual).
- ↑ 4.0 4.1 4.2 Evan-Amos, photograph of a Coleco Gemini main board, 2018, from Wikimedia Commons (public domain): U5 µA7805UC on a heatsink with "IN" marked at its input pin; C34 2200 µF 16 V axial; C15, a small radial electrolytic beside U1; C46 and C47, clear cylindrical capacitors near the RF section.
