Issue: Colecovision loads BIOS screen but won't play games

[Living Dead]

So my wife just acquired her childhood ColecoVision, and it's in really nice shape with the steering wheel, the super action controllers, tons of carts with overlays, you name it. When I turn it on, the screen displaying COLECOVISION loads just fine and is crystal clear with a modern A/V cable. However, any game I put into the cartridge slot just loads a black screen.

 

I know the games are good... I have another working Colecovision and I tested them in that machine. So my question for folks more skilled than myself is where do you start in diagnosing and fixing an issue like this? Can the cartridge slot go bad while everything else remains functional?

 

Most the tutorials I've seen for black screens just show that the system doesn't power on at all, but that is not the case here. I am a total amateur when it comes to these things... all I've ever done is replace capacitors in a Sega Master System. Any advice would be appreciated. If this issue is discussed elsewhere, I apologize for overlooking it.

[+nanochess]

Clean the inside of your cartridge slot with isopropyl alcohol and cotton swabs, make sure it is dry before turning on your Colecovision.

 

Use a magnifying glass to give a look to the cartridge internal pins for too open connections, you can adjust them carefully using a needle.

 

If the internal pins are broken then you need to replace the complete cartridge connector.

 

Edited September 25, 2020 by nanochess

[Ikrananka]

I'd also suggest trying the power supply from your working ColecoVision with the non-working one.

[digress]

Try one of the smaller games as i've heard say an 8 kb game may run whereas a 24kb game might not.

 

This has happened to a few people. One of  The traces from the cart port becomes broken or dirty so it can only read the lower part of the max rom size.

 

Qbert is 8kb. Try that if you have it.

 

burgertime or smurf is 16kb of a max 32kb standard cart.

Edited September 25, 2020 by digress

[ChildOfCv]

The confusing part is that if the cartridge is not responding at all, or responds with the wrong signature, you should still get the "Please insert cartridge before turning on the system" message.  In this case, the cartridge must be actively interfering with the system, which means the ROM chip(s) think they are being accessed even if they are not.  I have to wonder if U5 is constantly outputting an active select on one of the cartridge lines.

[Living Dead]

2 hours ago, ChildOfCv said:

The confusing part is that if the cartridge is not responding at all, or responds with the wrong signature, you should still get the "Please insert cartridge before turning on the system" message.  In this case, the cartridge must be actively interfering with the system, which means the ROM chip(s) think they are being accessed even if they are not.  I have to wonder if U5 is constantly outputting an active select on one of the cartridge lines.

It definitely recognizes that a cartridge has been inserted, because it loads a black screen every time. Take it out and the BIOS screen comes right back. Something I didn't think to do was to try to start a game even though the screen is black, like maybe it has music but no video. Regarding your comment, how could I determine if "U5 is constantly outputting an active select on one of the cartridge lines?"

 

Thank you for the suggestions so far. I will try them. I already tried cleaning the cartridge slot, but I only used canned air to blast it out. I'll try alcohol next.

Edited September 25, 2020 by Living Dead

[ChildOfCv]

 

With the CV on but no cartridge in, push the cartridge door out of the way and you should see this connector.

 

The red circles are the select lines.  The green circle is ground.  Put a meter in volts mode and place the black probe on the green circle.  I suggest using the back side of each contact, to keep from shorting across to the other side.  It is especially bad to do that on the ground, because across from it is +5V.

Measure the voltage with the red probe at each red circle.  Each one should be close to 5V.  If you read close to 0V (it won't be exact, so if you're reading exactly 0V or otherwise showing no difference in reading touching vs not, it's probably because you didn't make good contact, and that may also be the problem, BTW).