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Video output issues with my Colecovision.


Evilmaxwar

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Hello there,

This month i bought a Colecovision at the flea market. Got the thing for a good price with a couple games.

Only it never worked right.

I will try to explain all the symptoms it had and also describe all i have tried so far.

 

 

First thing I did is give a good clean to the power switch with lubricated contact cleaner as the thing was stuck in goop.

I also likewise cleaned the channel selector switch.

I tested the power switch with a multimeter and all seemed good.

 

After the switches were working smoothly I could get to play some games with it but at first i got the following symptoms

 

-Analog type Parasites/distortion and blurry image.

I tried fiddling with the channel switch, changed nothing.

 

After playing around and wiggling the RF cable, sometimes the image would come sharp . I tested my RF cable with a NES and i found the cable itself was all right.

 

Then it started doing another thing. The Image sometimes had no color, all black and white.

When this happened i could not restore color by playing with the cable, only reseting the console could change it.

 

At this point when i booted the Coleco it would either be a sharp colorless image or a distorted color image. ( Please note that at this point im powering the console with no cart to rule out that factor )

Whenever i got the color image I could try to make it sharp by wiggling the cable

When that worked i noticed some kind of rainbow effect on the white characters. ( Do no know it that is normal as i never had a colecovision before )

Once the color image was made sharp it would stay that way until I reset the console.

 

Eventually it started doing more and more the Black and white screen and less often the distorted color one.

 

I started to think the RF module was failing and that maybe i could "bypass" the problem by doing a composite mod.

So i made the BenHeck AV mod: http://benheck.com/G...o/Video_Mod.htm

 

Mod did not fix the problem. I always had a black and white image out of the composite. I also had to put the pot all the way up and the image was still not perfect.

Now If i connected the console with RF out and restarted it until i got a color image, the colors would disappear as soon as i Connected the composite out, and not come back it i disconnected it.

 

I began suspecting the Power supply, I tested all voltages with a multimeter and they seemed spot on.

I tested under load at the plug and it was ok.

Still to rule out a possibility, i made a custom wire job to try with an ATX power supply and the Coleco had the same symptoms with the ATX.

 

Only lately it suddenly got Much worse.

Now all i see on the screen is snow but i can still make out the coleco boot screen hidden behind all the noise, sometimes its color, sometimes its not. Fiddling with the RF cable cannot bring a clear image back.

I removed the MOD, which did not help. I inspected the board visually for cold solder joints but cannot see anything. The RF connector looks all good.

 

Next im probably going to try to reflow everything around the RF adapter section. I was even wondering If i should remove the RF metal casing in case i see something in that PCB sandwich. That thing looks like a big hassle to unsolder though...

 

Im kinda working blindly as i have no prior experience in Colecovision Fixing. Fixed all sorts of issues successfully on many other consoles, Im pretty good with a soldering Iron but im not an electronic expert.

Searching about fixing these issues on google only turned out the same few things, "Clean the power switch, check the channel selector switch, check the power supply

 

I was hoping that some of you guys maybe could help me, spot something i missed and point to some more tests or give me a good idea about what might be going on with this console.

In any case all help would bee appreciated and i will keep this updated.

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Hi Evilmaxwar :)

 

Now that you have soldered components, be also aware of the short circuits, because Tin tends to flow out and you may have to scrape.

 

On the PAL version (CBS), is there adjustment for picture and sound separately on HF (RF) module, perhaps also on your NTSC version.

 

Maybe this link can help you, there is some schematics.

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Thanks for all the suggestions.

My Colecovision is still having the issue but at least i made some progress.

 

Apparently ive been fooled over by several problems happening at once.

I did the whole toothbrush+alcohol PCB cleanup followed by a complete reflow of the PCB in the RF adapter.

It did not change anything, I was still having a snow saturated image...

 

Then i realized a few very basic things.

1. Nintendo RF adapter cable apparently does not work with the colecovision, this is why i had the terrible noise issue.

In the begining i was using a simple 75 ohm coaxial cable which worked well. At some point I had only a blank screen and switched to the nes cable when trying to troubleshoot, I knew the nes cable to be perfectly good and when I switched i did not make a big case of it as I believed one RF cable or the other would be the same but no, NES RF CABLE DOES NOT WORKS ON COLECOVISION! You learn new things everyday, I do not know why they are different but apparently they are.

 

When i switched back to a regular coaxial cable I got the sharp image back. Either in color or in black and white. Only this time its always sharp, no more distortion. No longer having to wiggle the cable. Maybe its the reflow, or possibly the RCA-Coaxial adapter im using was not tightened enough in the beginning. I cannot say but at least this seems to be settled.

 

2. The Ac adapter connector was making poor contact, this is what gave me the blank screen issue i occasionally experienced. Not only was it dirty, but the crimped wires made poor contacts. I realized about cleaning the pins thanks to Akito on the other Colecovision issue thread. After a good contact cleaner job it worked better but it still was glitching when i played with it. With the PCB powered, if i played around with the four wires connecting the plug, the coleco would glitch and distort like crazy and usually hang. Apparently the contacts in the four crimped connectors were quite poor. I cut all four wires flush to the connectors, removed 1 inch off each wires and soldered them directly on the connector after cleaning them with sand paper. Now the connection is rock solid, i can play around with the plug or the wires and the connection stays perfect, no more glitches on screen.

 

However when i was making glitches on the Coleco by playing around with the four Power adapter wires, i noticed sometimes it would fix the no color issue, this may prove useful for further troubleshooting.

 

Now I always get a nice sharp video everytime I turn on the console but I still get either a black and white or color screen. Interesting point is that Reset has no influence on this. If its in color, i can press reset over and over and it stays with color, same thing if its black and white. If it boots in color, I can use the machine and it will not lose the colors, i just played Slither for 20 min and it was all good.

 

So what is making this machine sometimes boot with colors and sometimes in Black and white???

I wondered is the issue could be caused by non simultaneous contacts? At some point i though It seemed that activating the powerswitch quickly worked better but after repeating many times it seemed to have no influence.

 

I think both the power connector and the Power switch are working good at this point I can wiggle and tap and manhandle both of em when the machine is on and it does not glitch anything, the contacts are just good.

I made a test to try to rule this out. Connected the Coleco on a power bar, always left the coleco power switch to on and would only power it on or off with the powerbar switch. It still behaved the same.

 

Now i suspect two things. The power supply or the TMS9928 chip.

 

I tested the voltage again under load and all is fine, even in B&W mode.

I tested 12v on the RF pcb under load, its fine, do not know where to test other voltages.

 

Possibly a dodgy TMS9928 chip? I guess id have to solder in a replacement to verify, and i dont have one...

I know a dude who used to repair alot of old consoles, i bought him a bunch of NES consoles 2 years ago and he still had huge piles of stuff, ill try to contact him, maybe he has parts.

 

Will keep this updated.

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Desoldering the 9928 from the CV motherboard takes some doing without damaging the chip or the board's pads/traces. If you do remove the 9928, I highly recommend you install a socket instead of soldering a replacement VDP back down to the board. Also, the 9928 should have a heat sink on it. If it does not, it will definitely over heat.

 

A 9928 is not terribly hard to get, but an alternative for you might be to replace the 9928 with an F18A (a little self promotion here). The F18A would take care of any 9928, DRAM, or output section failures since it bypasses those sections.

 

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  • 4 weeks later...

OMG I solved the problem... I can't believe how misled I was...

It was actually my TV set!!

 

I was cued when i connected my Sega genesis on my TV and the blasted thing was having the same black and white problem!

I had not used the genesis in over a year and in the meantime i had gotten a new CRT Tv set, a 32" Sony WEGA Trinitron. ( KV32XBR250 )

I made some research on Genesis black and white issues and found a thread with some dude having the same problem with a genesis he had just bought.

 

Guess what his TV set was? A Sony Wega Trinitron. The thread was also solved as it turns out this is a common problem with Sony Wega trinitron sets and old console users.

Sure enough I had only tried my Colecovision on this Trinitron set so i immediately tried it on another TV and the problem disappeared. Say i was about to try to order a replacement 9928 chip and all the crap that comes with swapping it and all...

 

The Trinitron Is an AWESOME TV, but its also a bit picky it appears when it comes to input signal specs. I do not have enough knowledge about this to comment on the technicalities of the problem but here is the thread i got the info from.

http://shmups.system11.org/viewtopic.php?f=6&t=41711

 

There is also a "cheap" fix to get to color back on a trinitron that's being picky on your console. Switch the input selector to another Channel with a working color input and back to your troublesome consoles. Seems to return the color most of the times. Its annoying as hell but at least there is a way to deal with it...

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I'm glad you solved it.

 

Actually I've a LG LCD TV that does something curious, if you leave it in channel 3 for a while it will lose synchro and will not show anything when you turn on the Colecovision, the only way for it to work is to change channel and get back to channel 3.

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