Coleco Gemini Troubleshooting Guide
Fault-finding on the Coleco Gemini, Coleco's Atari 2600-compatible console. Coleco's owners manual has a troubleshooting checklist aimed at setting up the RF connection, reproduced below. Repairers report that the faults inside the console are mostly cracked solder joints at the controller sockets and the DC jack.[1][2][3] Cleaning and power checks are on Coleco Gemini General Maintenance.
Before you start
[edit | edit source]- Use a 9 V DC adapter with a centre-positive plug. Coleco's part is 91617, and it takes the same plug as the Atari 2600's.[2]
- Test with an Atari joystick or a Gemini controller. Any controller that works on an Atari VCS works on the Gemini;[1] a Mega Drive (Genesis) pad does not, and makes the console see a constant "up".[2]
- Set the TV to channel 3, or channel 2 if the switch at the back of the console is set to 2.[1]
Coleco's checklist
[edit | edit source]| Symptom | Remedy |
|---|---|
| No game picture; faint or blurred picture | Antenna switch box not fully at GAME, or the game cable not plugged in at the console or the switch box: slide the switch fully to GAME, back to TV, then to GAME again. Antenna leads not attached as instructed. Power switch off, adapter not fully in the outlet or power cable not connected. TV not on channel 3 (or 2). Cartridge not fully seated. Cartridge inserted with the power on: switch off, then on again. Some TVs have two fine-tuning points for one channel; tune for the best picture. TV volume turned down; fine tuning wrong. |
| Buzzing or distorted sound | Adjust the fine tuning. A strong local station on channel 3 or 2, or cable TV, can interfere: disconnect the aerial from the switch box while playing |
| No ordinary TV programmes | Switch box left at GAME; switch box or TV connections wrong |
| Stripes or heavy snow | Adjust horizontal hold; reduce colour; adjust fine tuning and contrast if the picture waves; coil the excess game cable and move the console away from the TV |
| Controller not working | Check the plug is fully in. Swap the controllers: if the working controller fails in the same socket, the console is at fault; if it works, the first controller is faulty |
| No colour on a colour TV | COLOR/B&W switch at B&W; adjust the TV's colour control |
Coleco's manual also says to switch off before inserting or removing a cartridge.[1]
Faults inside the console
[edit | edit source]| Symptom | Cause found | Action |
|---|---|---|
| Power unreliable | Cracked solder joint on the DC jack | Reflow the jack's joints[2] |
| One or both controller sockets not working; socket loose | Cracked joints on the controller socket pins | Flux and reflow every pin of both sockets[2] |
| Game runs only when the cartridge is held at an angle | Dirty cartridge edge connector | Clean the edge connector with isopropyl alcohol and reseat the cartridge a few times[2] |
| Cartridge will not go in | The cartridge's own dust cover does not slide back (seen on a Combat cartridge) | Hold the cover back and insert the cartridge; the fault is in the cartridge[2] |
| Player always moving up | A non-Atari controller (Mega Drive pad) | Use an Atari-compatible controller[2] |
| Green deposit in a controller socket | Corrosion or contamination | Clean with a little vinegar, then isopropyl alcohol, and let it drain[2] |
Leaded Solder's Gemini also had an underfilled factory joint on the TIA-compatible chip, U3; check its pins whenever the board is out.[2]
Supply checks
[edit | edit source]A 7805 regulator (U5) on the board makes +5 V from the adapter's 9 V, with a 2200 µF 16 V capacitor (C34) beside it.[4]
- Measure the adapter at its plug: about 9 V DC, centre positive.[2]
- Measure at the regulator's input pin, marked IN on the board, with the console switched on. No voltage here with a good adapter points at the DC jack joints or the power switch.[4][2]
- Measure the regulator's output: +5 V. If the input is good and the output is missing or low, disconnect the supply and check the +5 V side for a short before replacing the regulator.
Chips
[edit | edit source]| Position | Part | Notes |
|---|---|---|
| U1 | 6507 CPU (Synertek SY6507) | The same type as the Atari 2600's CPU[3] |
| U2 | 6532 RIOT (Synertek SY6532) | RAM, I/O ports and timer, the same type as the Atari 2600's[2] |
| U3 | TIA-compatible chip by VTI, marked "COLECO 73192 E4002" | Video and sound; not an Atari part[3][4] |
On the photographed board all three chips are soldered in, not socketed.[4] The 6507 and 6532 are standard parts that several companies made; the TIA-compatible chip was made by VTI for Coleco.[3]
Related pages
[edit | edit source]- Coleco Gemini
- Coleco Gemini General Maintenance
- Coleco Gemini Capacitor Replacement Guide
- Coleco Gemini Owners Manual
- Atari 2600 Troubleshooting Guide
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 Coleco Industries, Gemini Video Game System Owners Manual, model 2510, Guide No. 91783A, 1983: p. 6 (channel 2-3 switch), p. 7 (cartridge insertion with power off), p. 9 (controllers; WYE connector; Atari VCS controllers work), pp. 10–11 (troubleshooting checklist), p. 12 (care; no owner-serviceable parts). Hosted here as File:Coleco Gemini Owners Manual Guide 91783A.pdf (see Coleco Gemini Owners Manual).
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 "Space Walking with Gemini", Leaded Solder, 6 April 2020, leadedsolder.com (retrieved 2026-10-06). Restoration of a Gemini on board CPC-2 Rev F: unreliable power cured by reflowing the DC jack; dead controllers cured by reflowing both controller sockets; an underfilled joint on the TIA clone; cartridge contacts cleaned with alcohol; a Mega Drive pad reading as constant up; a Combat cartridge whose dust cover would not open; adapter Coleco 91617, 9 V DC centre-positive.
- ↑ 3.0 3.1 3.2 3.3 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 on a broken Gemini.
- ↑ 4.0 4.1 4.2 4.3 Evan-Amos, photograph of a Coleco Gemini main board, 2018, from Wikimedia Commons (public domain): U1 6507, U2 6532, U3 "COLECO 73192 E4002", U5 µA7805UC with "IN" marked at its input pin, C34 2200 µF 16 V, power switch among S1–S6, RF modulator can.
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