Scrambled Colecovision Graphics

[Emehr]

I'm on a quest to get my broken systems fixed. This time it's my Colecovision giving me trouble: the graphics are scrambled, including text. I did a search (here and on Google) for Colecovision troubleshooting and repair and the closest solution I get is from the Colecovision FAQ.

 

In some cases, sprite problems can be solved by cleaning the cartridge in question.  But if the startup screen has letters screwed up, such as CKHACK, you probably have a bad DRAM.  U10 is D7 and U17 is D0.  CKHACK indicates a bad D2 line, which would be U15.  General directions for replacing a bad chip can be found in Section 10.3. - 29

 

Just a note: there is no Section 10.3 in the FAQ(!)

 

All 4 of my Colecovision games exhibit the same behavior so I'm certain it isn't a problem with the cartridges. My test subject is Q*Bert and it has screwy letters on the startup screen (i.e. "P*BDRT, RDLDBT F@LD" instead of "Q*BERT, SELECT GAME") as well as disjointed graphics in-game.

 

I'm guessing (from the FAQ) that the problem lies with one (or more?) of the 8 Mostek 4116 chips on the board, but the FAQ is cryptic.

 

U10 is D7 and U17 is D0.

 

So...

D0 (U17)

D1 (U16)

D2 (U15)

D3 (U14)

D4 (U13)

D5 (U12)

D6 (U11)

D7 (U10)

 

...and each chip (U1x) is a 2K VRAM location? accessed by the appropriate data (Dx) pin from the video display processor?

 

CKHACK indicates a bad D2 line

 

It does? How is this figured? Or are all problems with scrambled text associated with D2? If not, how do I go about determining which line is bad on my system? Should I just replace them all (considering availability of these chips)?

 

Am I on the right track here?

 

Thanks!

 

- Jason

[joeybastard]

Just open up the CV and clean the power switch. It'll cure any graphic problems in CV games 90% of the time. On some CV's you'll have to desolder the metal cover to get to it, but once you open it up, you'll see what to do.

[Bruce Tomlin]

In some cases, sprite problems can be solved by cleaning the cartridge in question.  But if the startup screen has letters screwed up, such as CKHACK, you probably have a bad DRAM.  U10 is D7 and U17 is D0.  CKHACK indicates a bad D2 line, which would be U15.

I'm pretty sure I'm the one who wrote that. :-)

 

All 4 of my Colecovision games exhibit the same behavior so I'm certain it isn't a problem with the cartridges. My test subject is Q*Bert and it has screwy letters on the startup screen (i.e. "P*BDRT, RDLDBT F@LD" instead of "Q*BERT, SELECT GAME") as well as disjointed graphics in-game.

Q = 51 P = 50

E = 45 D = 44

A = 41 @ = 40

 

Your D0 chip is bad. U17 needs to be replaced. Be careful when desoldering, use a socket, and be warned that not all 16K DRAMs are identical. You need a "plain" 4116.

[Emehr]

Thanks for the tip. I just tried it. No luck, unfortunately. I desoldered the switch cover and cleaned the contacts. For grins I even jumped the connections and got the same scrambled result.

 

The power supply was obtained from eBay as the one that came with the system was used as someone's dog's chew toy. The one from eBay looked like it had never been used so I don't suspect it.

 

Jason

[joeybastard]

Oh well, it always worked on all 3 of my CV's. I guess you'll have to look into what Bruce is saying. I'm glad I didn't have to do what he talks about, I'm pretty sure I'd mess it up bad.

[Emehr]

I'm pretty sure I'm the one who wrote that. :-)

 

So _that's_ what the "- 29" after the snippet was: a reference to the original author! Sorry 'bout that! *smacks self in forehead for hastily skipping through the FAQ looking for a quick answer*

 

 

Your D0 chip is bad.  U17 needs to be replaced.  Be careful when desoldering, use a socket, and be warned that not all 16K DRAMs are identical.  You need a "plain" 4116.

 

Thanks! I just emailed Clay at Multigame.com about his 4116 chips (not sure if they're plain or not, I gave him the info printed on the chip). Do you know of any other sources for this chip. I've been Googling but not having much luck.

 

Also, how will I know a plain 4116 if I see one?

 

Thanks,

Jason

[Bruce Tomlin]

Also, how will I know a plain 4116 if I see one?

Uhhhh... it'll say "4116" on it? (as opposed to 8116 or some other number)

 

In particular, I know that ITT 4116 chips work, because I've found them in some CVs. I happened to have a few left over from way back when, so I grabbed one to fix mine. I'm pretty sure that was the unit that ended up being my "dev system", with about half the chips now socketed, especially the CPU (so I can plug in an In-Circuit Emulator).

[Emehr]

Also, how will I know a plain 4116 if I see one?

Uhhhh... it'll say "4116" on it? (as opposed to 8116 or some other number)

 

Oh, I thought you meant "plain" 4116 as opposed to some variant of the number (e.g. 4116-xx or whatever).

 

Thanks a lot for your help! My quest continues...

 

Jason