ColecoVision Crisis!

[CV Gus]

Well, my CV is malfunctioning.

 

When you switch it on, all you get is a black screen and a sort of high-pitched hum. No COLECOVISION, and no message if you leave out the cartridge. It's the same either way.

 

However, the 2600 module works fine.

 

If anyone here can pinpoint the problem so I don't have to test anything, that would be a great timesaver.

 

Thanks.

[opcode]

Well, my CV is malfunctioning.

 

When you switch it on, all you get is a black screen and a sort of high-pitched hum. No COLECOVISION, and no message if you leave out the cartridge. It's the same either way.

 

However, the 2600 module works fine.

 

If anyone here can pinpoint the problem so I don't have to test anything, that would be a great timesaver.

 

Thanks.

 

My guess is that the CPU died, or perhaps the BIOS ROM...

2600 module is an almost standalone console, it uses the power supply and video output stuff, so we know for sure those are still working.

 

Eduardo

[NIAD]

Agree with Opcode that it's either the CPU chip, BIOS chip or it could be the DRAM chips... but usually they don't all go bad at once and you therefore would get funky graphic displays.

 

Will have to wait for the resident CV hardware guru, Yurkie, to chime in as he would be the best source for an answer.

[Murph74]

Have you repacked the power switch or had it refurbed?

[+Yurkie]

There are so many things that could cause a unit to do nothing, that it is a ridiculous thread to even start. CV Gus should have known better to even start such a thread. CV Gus, I have not seen a post from you in years, you should have just said "Hi, guys it's been awhile since I posted...How is everybody?" And then took the CV a part and fixed it.

[CV Gus]

There are so many things that could cause a unit to do nothing, that it is a ridiculous thread to even start. CV Gus should have known better to even start such a thread. CV Gus, I have not seen a post from you in years, you should have just said "Hi, guys it's been awhile since I posted...How is everybody?" And then took the CV a part and fixed it.

 

 

As I did with the Roller Controller.

 

But with the sort of equipment I have to test things with, it would take a long time- even with good schematics- to track down this particular problem.

 

It did not seem unreasonable to assume, like with the infamous "autostart" problem, that there would likely be a particular cause of this and someone could at least narrow it down ("it is probably the SN555-5555 chip").

[+Yurkie]

There are so many things that could cause a unit to do nothing, that it is a ridiculous thread to even start. CV Gus should have known better to even start such a thread. CV Gus, I have not seen a post from you in years, you should have just said "Hi, guys it's been awhile since I posted...How is everybody?" And then took the CV a part and fixed it.

 

 

As I did with the Roller Controller.

 

But with the sort of equipment I have to test things with, it would take a long time- even with good schematics- to track down this particular problem.

 

It did not seem unreasonable to assume, like with the infamous "autostart" problem, that there would likely be a particular cause of this and someone could at least narrow it down ("it is probably the SN555-5555 chip").

 

OK if I where going to gamble and not test anything......replace the VDP. No video.. dead VDP. Not necessarily the problem, but if you want down and dirty what is wrong, that's my guess.

[CV Gus]

I never said I wasn't going to test anything, just if someone could narrow it down for me. It took me some time to trace the circuits in the 5200 before I was able to guess what the problem was (turned out I was right).

 

Thanks. I'll check the schematics for it, and try it out.

[opcode]

OK if I where going to gamble and not test anything......replace the VDP. No video.. dead VDP. Not necessarily the problem, but if you want down and dirty what is wrong, that's my guess.

 

I don't think it is the VDP, otherwise he shouldn't be getting noise from the PSG. It seems to be CPU related to me (or BIOS/RAM). No CPU, no video (when the VDP resets, video output is disabled) and noise (the CV PSG doesn't have a RESET signal to disable sound).

 

[EDIT]: BTW, I think your first post was kind of rude to say at least.

CV Gus has been a CV enthusiast for a loooong time, I remember him from way before I released Space Invaders Collection (though from the DP boards). For many years he was very active and supported the CV scene in a big way, wrote many reviews about both new and old CV games, etc.

IFAIK he has been going through hard times for a while, and that surely gets in the way of hobbies, etc. Even if it wasn’t the case, we need to keep in mind this is an open forum, people are free to come here and post whenever they want. In fact we should welcome back those that have been away for a while, we are a small group, so the more the merrier.

Finally, I fail to see how this thread can be “ridiculous”. It is a fellow CV enthusiast asking for help to fix his CV. And we always have the option to ignore people we don't think deserve help.

 

Eduardo

Edited June 22, 2011 by opcode

[+Yurkie]

I have read all the old threads, and CV Gus used to post all the time and even talked about different mod ideas, someone with his degree of knowledge posting a question like he did seemed ridiculous to me, and I stand by my comment 100%. I didn't flame him, and I even played along and gave him my opinion.

[CV Gus]

First of all, much of my knowledge relates to the Atari 5200, oddly enough...

 

But I can't seem to find any actual schematics about the CPU chip- to test it, I need to know the logic gates of the Z80 CPU; anyone here know where to look? The ones for the CV Roller Controller were very clear, and so I was able to repair it (it was a gate that always stayed "on" instead of flickering when the roller was used).

 

My testing equipment is an ancient multitester and a weird red/green LED light tester built from wooden rods, nails, and old wire and LEDs from a 1970's broken VCR...

 

Thanks.

[+Yurkie]

First of all, much of my knowledge relates to the Atari 5200, oddly enough...

 

But I can't seem to find any actual schematics about the CPU chip- to test it, I need to know the logic gates of the Z80 CPU; anyone here know where to look? The ones for the CV Roller Controller were very clear, and so I was able to repair it (it was a gate that always stayed "on" instead of flickering when the roller was used).

 

My testing equipment is an ancient multitester and a weird red/green LED light tester built from wooden rods, nails, and old wire and LEDs from a 1970's broken VCR...

 

Thanks.

I think I have a .PDF for the z80 send me a pm and I will get it to you.

[russell56443]

OK if I where going to gamble and not test anything......replace the VDP. No video.. dead VDP. Not necessarily the problem, but if you want down and dirty what is wrong, that's my guess.

 

I don't think it is the VDP, otherwise he shouldn't be getting noise from the PSG. It seems to be CPU related to me (or BIOS/RAM). No CPU, no video (when the VDP resets, video output is disabled) and noise (the CV PSG doesn't have a RESET signal to disable sound).

 

[EDIT]: BTW, I think your first post was kind of rude to say at least.

CV Gus has been a CV enthusiast for a loooong time, I remember him from way before I released Space Invaders Collection (though from the DP boards). For many years he was very active and supported the CV scene in a big way, wrote many reviews about both new and old CV games, etc.

IFAIK he has been going through hard times for a while, and that surely gets in the way of hobbies, etc. Even if it wasn’t the case, we need to keep in mind this is an open forum, people are free to come here and post whenever they want. In fact we should welcome back those that have been away for a while, we are a small group, so the more the merrier.

Finally, I fail to see how this thread can be “ridiculous”. It is a fellow CV enthusiast asking for help to fix his CV. And we always have the option to ignore people we don't think deserve help.

 

Eduardo

 

I am looking for info on the same problem as CVGus so I saw this post and clicked in and I was also shocked at the rudeness of certin members,glad I didnt ask for info!

Im a long time member too but I guess Im lucky that my Atari's and other retro consoles are up to par,would hate to be belittled for asking a simple question!

Will search elsewhere :0(

[Kiwi]

I haven't post here for awhile too. I think that kind of rudeness isn't necessary. People do look up to you for your advice as I do too. I love these forums and this hobby. I really LOVE the Colecovision. I want to share that sometime my personal life and my ability to focus prevent my from proceeding with this hobby. My mood and my mind goes into cycles. I'm about to focus on Colecovision stuff a bit more now. I sorry I don't post often, and I'm having a hard time knowing that I may not be accepted here. I usually try my best to be polite as possible even though I'm sometime bit hyper.

 

Topic on hand:

 

I'm pretty positive that the BIOS ROM may have worn out like some atari games due to age. Some Masked ROM don't retain there data as long as it should. I have a dead DKjr cart, some posted posted on the atari 2600 about their dead Atari 2600 cartridges. I believe that the component processor chip, z80 chip, would be the least likely to fail. The 1K of RAM maybe be higher quality than the 8 2K video RAM. The Video processor unit would have shown signs of failure before going completely.

 

I think it is best to replace the BIOS ROM chip with a new one would be the first thing to replace, before troubleshooting further. Most of the stuff like processor and RAM are always changes while the BIOS ROM is suppose to be static. I know the previous statement may not make sense.

 

This is just my analytic what may be wrong with your unit. I wish you luck with your system.

[flemishdog]

Ok, this is crazy because this has happened to my autralian colecovision when I decided to play it. I have the exact same problem. I am not tech savvy in the slightest, so if anyone could offer to help fix it that would be great. I love my colecovision too much to just let it be a glorified (and gigantic) atari 2600!

[pseudo_intellectual]

I thought I'd document some of my troubleshooting experiences for the same issue.

 

I have a ColecoVision which is doing approximately the same thing as the OP. The screen is black and I hear no audio. Trying to "fly blind" with the controller in attempt to start a game without video yields nothing.

 

After poking around I believe I have bad SRAM. I will find out in a few days if this is true once I get replacements. Here's how I am making that conclusion:

 

Using a logic probe, I can see that there is bus activity. Various chip selects are being pulsed. Most importantly, there is write access to the VDP consistently on startup. At this point I'm fairly confident that the CPU and at least some of the BIOS is functioning normally.

 

Could it be the VDP or its RAM? Well, I can see that the /RAS and /CAS signals are going to the VRAM. Based on the outputs on each of the RAM ICs, I can see that it is successfully clearing the video memory. I found the listing for the BIOS and I can see that this is one of the first things it does. There could be problems with the VDP (the /INT signal is always low; is that normal?). I happened to have a TMS9918 floating around which is pin-compatible except for the video output. I isolate these signals from the socket I installed and gave it a go. The bus activity is unchanged from the original VDP. This, I acknowledge, is probably not a good way to isolate the VDP, but it was all I have to work with at the moment.

 

Could it be that part of the BIOS is corrupted? I suddenly realize I have an eBay EPROM programmer and after wiring a socket adapter I dump its contents. Its checksum matches a version of the BIOS I downloaded. At this point I am convinced that the BIOS is good.

 

I look at the BIOS source code some more and I realize that the call to clear the VRAM pushes the stack. I wonder if the SRAM contents are corrupted (or the address lines are messed up somehow) and the CPU is returning to a bad location in the BIOS address space. Indeed I see that the CPU is perpetually accessing addresses in that area. At this point I am convinced that there is a problem here. I thought about doing a pattern test of the RAM on perfboard with a PIC or by wiring it to the EPROM programmer somehow, but I suspect by the time I get it going I will have received the replacement SRAM.

 

Soooo.... I will find out if my prognosis is correct. Perhaps there something others may want me to try?

[omf]

i have this issue on a french rgb scart board, i have replaced the dram though while it was bad so i can rule out that in my ocasion.

 

the bios chip is my next replace, unfortunately the bios chip is not going to be as easy to replace as i would like as the guides to replace the bios on a ntsc CV wont work because there are 24 holes and no spare holes to de solder, i am working on it however but it is slow progress.

 

i have attached a cheapo usb logic analyser to the Z80 and i am getting signals out of it of it so i don't think that this is the issue, although i could be wrong!

[pseudo_intellectual]

Update: I received replacement SRAM today and after installing it...

 

SUCCESS!

 

The COLECOVISION logo appears and I am now able to play games. With that in mind if anyone is having similar issues:

 

* The VDP and its RAM are not always to blame for no video. In my case the original 4116 VRAM was just fine, as well as the VDP.

* Pay attention to the outputs on U5 and U6 (74LS138). Observe chip select activity on the VDP. If there is activity here on each reset, the BIOS is probably working.

* If you see write access to the VDP RAM and the output (pin 14) goes low on all 8 of the RAM ICs, the BIOS successfully executed its VRAM clear routine. That is assuming you also see activity on the VDP RAM refresh and address signals.

* If everything else appears to be working, the SRAM may very well be the culprit.

 

I'm using MBM2148 SRAM, which at 55ns is quite overkill. However, I happened to find a pretty good deal for a pack of 10 on eBay, so I went with that. NTE sells a direct replacement for the 2114 SRAM, but you do not want it: I've seen it priced between $10-$12 APIECE (because you'll be needing 2).

 

So now all I need to do is get the composite mod done and I can sew this bad boy up.

[chart45]

go for f18a since you got the skill