Colecovision Game Consoles

[channelmaniac]

Symptom: Controller is not working.

Problem stays with board & doesn't follow controller. Replaced a bad 74LS541 IC to fix. (There are 2 on the board, one for each controller.)

[channelmaniac]

Symptom: Random Resets, Garbage on screen on power up

If the problem does not go away with turning the power off and on repeatedly then replace a bad 4116 DRAM IC.

If the problem goes away with turning power off & on repeatedly or occurs when the console is bumped then disassemble and clean the power switch. This is a common problem with the Colecovision.

[channelmaniac]

Symptom: Black and white bars on screen. Rumble in audio. No discernable video.

Since there was no discernable video the first thing to check was the power to the motherboard. It was missing the 5v line and the 12v was low.

The Colecovision power supply is old, very special (+/-5v and +12v), and hard to find. If you do find one then it's a crapshoot as to whether or not it works. The power supply housing is made of 2 pieces of welded plastic. It *is* possible to repair these if you are careful.

*WARNING* - do this at your own risk. Do not mess around with the fuse. If it's blown, fix the power supply and replace the fuse with the proper type. DO NOT bypass the fuse. You really don't want to start a fire by overloading a bad circuit.

The housing of the power supply can be opened by repeated firm raps with a hammer. Smack it on the short side of the seam as that short side fits under the long side and makes for a cleaner separation with a joint that is easier to repair. Once it's open check for and fix any problems found. On the one I repaired there were 4 bad solder joints with pins of components that were sliding in & out of the joint. I took 4 minutes to resolder the whole circuit board to repair this power supply.

Once you repair the power supply the supply can be epoxied back together. Use a clamp to hold the two halves together until it cures.

[channelmaniac]

Symptom: No audio

Replaced the SN75489 sound IC and tested.

[channelmaniac]

Symptom: Constant tone

Replaced the SN76489 sound chip and tested

[channelmaniac]

Tip: Modifying the Colecovision to use 4516 or 4164 DRAM

The Colecovision's power supply is finicky and the 4116 DRAM is just as finicky. To make the system run cooler and more reliably take out the 4116 DRAM which requires +5v, -5v, and +12v to run and replace it with 5v only 4516 or 4164 DRAM ICs.

The modification is as follows:

WARNING: Do this at your own risk. Only you are responsible for any damage to your system. These notes were created by me when modifying a Colecovision console.

Disassemble the Colecovision

Take 8 screws from the bottom. Carefully peel the silver & black Colecovision sticker from the front panel to reveal 3 more screws. Remove those and the front panel will come off. The expansion module door will fall out as well. It's only held in by the front panel's pressure against the case.

Take the 3 screws out of the RF shield then use a hot soldering iron to melt the solder by the epansion bay connector holding the shield in place. Remove the shield and remove the last screw in the middle of the board holding it in place.

Remove the 8 DRAM chips from U10 through U17 (4116 DRAM ICs)

Next, remove L2 (-5v filter for DRAM) and L3 (+12v filter for DRAM) This will remove the -5v and +12v voltage sources from the DRAM. The 4116 DRAM needs this but the 4516 and 4164 DRAM ICs do not.

On the 4516/4164 DRAMs, pin 1 is RFSH* while on the 4116 DRAMs, pin 1 is -5v. By taking the -5v off pin 1 and NOT connecting anything to that line it will float. Per Mostek's 4516/4164 datasheets this is OK to do if it is not being used.

Pin 9 of the 4116 is +5v while on the 4516/4164 this is NC (Not connected). Pin 8 of the 4116 is +12v while it is +5v on the 4516/4164 chips. A source of +5v needs to be connected to pin 8 of the DRAM chips. It does not matter if +5v is on pin 9 as it is NC on the 4516 and 4164 DRAMs.

Look at the L3 location - there are 2 solder points. Above the right hand solder point is capacitor C42. The solder point CLOSEST to the L3 for C42 is a source for +5v. Solder a jumper wire from C42 to the RIGHT SIDE PAD (Left side when working on the bottom of the board) for L3, this will be the pad closest to the DRAM.

Be careful! If you connect it to the left side pad by mistake you will be bridging +12v and +5v lines which will not only damage the Colecovision power supply but will most likey damage your gameboard beyond repair. Double check your work!

Double check your connections. Do this with the power switch ON, but the power brick NOT PLUGGED IN. This way you can check at the 4 power wires for any shorts between them.

The DRAM chips should now be wired as this:
Pin 1 = no connection to any power source.
Pin 16 = ground
Pin 8 & 9 = +5v

If all looks well, solder in the sockets, plug in the DRAM, and give it a smoke test! If nothing smokes, then turn it off, and try a cartridge, you should have the Colecovision splash screen. Congrats!

Reassemble the system. Don't forget to put the solder blob back on the RF shield to keep your picture looking nice. If you forget it you may find strange interference on the TV screen.

[channelmaniac]

TIP: Installing a "no title delay" BIOS

One of the popular mods for a Colecovision system is to replace the 4764 type BIOS chip with a replacement EPROM programmed with the "no title delay" custom BIOS chip. This can be done one of 2 ways.

1. Use a 24 pin 8k x 8 replacement EPROM such as a Motorola 68764 or 68766. This is a difficult to find and expensive chip.
2. Use a 2764 EPROM, a JEDEC standard EPROM which is cheap and easy to find.

Option 1 gives a direct drop in replacement while Option 2 requires some modifications to be done to the board.

The Colecovision board has a 24 pin BIOS chip in place but has holes for the standard 28 pin chip. The problem is that the 28 pin jack isn't wired properly. To use the 2764 chip a bit of board modification will have to be done.

First, desolder and remove the old BIOS chip. Next, desolder the holes for jumpers WJ4 and WJ5. These jumpers are located right next to the BIOS chip. Flip the board over and look at the desoldered holes for WJ5. Off each end of the jumper location (which is empty by default) WJ5 are little round cut-out pads connecting to other solder points. Cut these out. There's one between one end of WJ4 and WJ5 jumpers and another one that comes off of WJ4 and connects to pin 2 of the 28 pin socket location (Just left of pin 1 of the 4764 BIOS chip.)

With those 2 pads cut the next step is to solder in jumpers at location WJ4 and WJ5. The board is now wired for a 2764 EPROM.

Solder in a socket, program the proper code into the EPROM and insert it. Give the board a smoke test. If it's not working, trace the signals and double check your work.

Pin 2 is A12
Pin 23 is A11
Pin 20 is CE*

If A12 and A11 are shorted then you didn't cut the circular pad off one end of WJ4.

If A11 and CE* are shorted then you didn't cut the circular pad between WJ4 and WJ5

Once working... Congrats!

[channelmaniac]

TIP: Installing a Combo BIOS

Parts needed:

1. Colecovision BIOS and No Title Delay BIOS ROM images. These are available on the internet from various ROM download sites.
2. A 27128 EPROM
3. SPDT switch
4. Small gauge stranded wire
5. 2x 220 ohm 1/4 watt resistors

The standard BIOS has a 12 second title screen delay before allowing you to select and play a game. This is irritating but someone has created a custom BIOS to get around this problem. This BIOS can be installed by itself or a Combo BIOS using a larger ROM chip that has multiple images of the Colecovision BIOS code can be installed. A switch is used to flip between the versions of code to run to allow the system to run games that aren't compatible with the No Title Delay BIOS. To install a combination BIOS on the Coleco the board has to be modified to support a 2764 EPROM version of the BIOS. Do this first.

The code for both versions of the BIOS ROM must be combined into one file. The easiest way to do this is by using the MS-DOS Command Prompt in Windows.

(These commands were all tested under Windows XP, your mileage may vary)

Rename the files to "OldBIOS.rom" and "NewBIOS.rom" then save the files in the C:\Temp directory. Click Start > Run, type in CMD, and click OK.

Switch to the C:\Temp directory by typing: cd c:\temp <ENTER> (In other words, press the Enter key!)

Type in DIR <ENTER> and you will see the 2 files in the directory, each with a size of 8,192

To combine them type in: copy OldBIOS.rom /B + NewBIOS.rom /B ComboBIOS.rom <ENTER>

Type in DIR <ENTER> and you will see the 2 files in the directory, each with a size of 8,192 AND you'll see the ComboBIOS.rom file with a size of 16,384.

Now write that file into a 27128 EPROM with your EPROM programmer, plug it in, and give it a test. With a game cartridge installed it should immedately jump to the select screen. The EPROM has the lower half programmed with the standard BIOS and the upper half programmed with the No Title Delay BIOS. The upper address line on the EPROM is tied high when it is in the socket. This is why the No Title Delay BIOS is being run when the EPROM is inserted.

The next step is to wire up a switch to select between the high and low banks.

Drill a hole in the rear case of the Colecovision to mount the switch. Be careful on this step! Test fit the switch with the shield to ensure it will fit where you want to locate it. Also ensure you can put the board back! If it's a tight fit you can trim the solder lugs on the switch or trim the RF shield. Fold back the edges on the shield if you cut it to keep the sharp edges from cutting the wires.

Remove the 27128 EPROM from its socket and bend pin 26 up enough to stick straight out to the side of the chip. Cut the narrow part of the pin off of the chip then reinsert it into the socket. Run a wire from this pin to the center pin of the SPDT switch. Connect a wire from the upper pin of the switch to ground through a 220 ohm resistor then connect a wire from the lower pin to +5v through the other 220 ohm resistor. Try not to use any existing grounds for other mods such as Audio/Video to avoid noise. The front facing pin C7 is ground, rear facing is +5v and is a good one to use for this mod.

Reconnect the system and test. With the switch up the No Title Delay BIOS will run and with it in the down position the regular Colecovision BIOS will run. Congrats!

Keep in mind the system may crash if the switch is flipped while power is on. Simply press the reset button to recover.

[channelmaniac]

Symptom: Won't read cartridges

The Colecovision game console has its own BIOS chip and will tell you to insert a cartridge if one is not in it. If the cartridge or the slot is dirty you'll get this message.

To clean the cartridge slot:

First, shine a flashlight down into the cartridge slot and look for wires, paper clips, staples, or other things that could cause problems. Next, take a piece of heavy white poster board and fold it over a couple of times until it's about the thickness of the circuit board in the cartridge. Wet it lightly with some alcohol and insert & remove it from the cartridge slot repeatedly. You'll be surprised at the gunk that it will remove from the cartridge slot.

To clean the cartridges:

Take a Q-Tip and soak it in alcohol. Scrub it across the edge of the circuit board in the cartridge. Be sure to do both sides. It may take several Q-Tips to get all the gunk off.

If that doesn't do it then you'll need to disassemble the cartridge and clean the edge connection on it with a pink pencil eraser. The downside is that you'll have to damage the labels on the cartridges to get the screws out to take them apart.

[channelmaniac]

Model: Colecovision
Symptom: Power switch issues

Power switch is dirty and causing the system to not boot properly. Disassembled and cleaned the power switch. Repacked it with dielectric grease and reinstalled it.

Per customer instructions, installed an A/V kit and +5v only memory kit. Tested system. Replaced power-on reset capacitor and retested.

[channelmaniac]

Model: Colecovision
Symptom: Dead. Will not work with carts.

Replaced 2 x 74LS541 ICs, Z80 CPU, and disassembled/cleaned/lubed the power switch. Tested with multiple carts.