Colecovision corrupt graphics after 5V vram mod

[zCRP]

Hi, I just modded my colecovision by replacing the vram chips and making the 5v only modification. This CV is also AV modded.

 

When I turn it on everything works perfectly, but after a few seconds the whole screen becomes garbled. See video below.

 

https://youtu.be/9oTzC-_4fhA

 

I assume that the vram chips are fine, and the kind of corruption does not look like what is usually experienced with failing ram (I refer to the screenshots in the technical manual).

 

I have cleaned the power switch repeatedly, so for now I would exclude that as well.

I have also tried to use a second power supply, and I get the exact same symptoms.

 

Thus my focus is now on the VDP failing. Given what you see in the video, would you replace it? I have two spare VDP chips, just wanted to hear second opinions before starting (another) surgical intervention.

 

Thanks

Chris

Edited August 9, 2017 by zCRP

[Keatah]

If you let it run for like 10 minutes, turn it off, then back on, does it work? Or does it get corrupt right away.

 

I'm thinking something is overheating or temp sensitive. Might be a good place to start noninvasively.

[zCRP]

I have just had the CV off for approx.45 minutes. Then I turned it on with Q*Bert inserted, but have not touched the controller. The blue screen with invitation to press 1-6 shows up correctly. I have waited a minute or so and nothing seems wrong. The I press 1 to start the game, and after 4-5 seconds the screen starts scrambling. Now if I turn off the console and turn it back on after 2-3 seconds the screen becomes garbled right away (i.e. the blue screen is already wrong). If I wait a minute or so before turning back on, I get the same behaviour as at the beginning: the blue screen "works", as soon as I start a game graphics corrupt after a few seconds.

In all this, audio and input continue to work correctly, so this is a video only issue.

Is the VDP overheating? If yes, why? This whole mess has started only after I replaced the VRAM.

[+5-11under]

You could look for a bad solder connection, but otherwise I'd guess VDP.

[zCRP]

I took an infrared snap of the CV (see attachment). As can be seen, the places getting hot are as expected (CPU, vram etc.), the only unexpected place getting hot is where the RF chip is, more or less at the center of the board. not sure if that is the capacitor on the left getting hot or the chip itself. Incidentally, this is close to the region where I removed the coils in order to change voltage for the ram chips.

 

The CPU tops at around 50°C, the ram chips around 40-42, the place I mentioned above reaches about 45. Those temperatures seem all pretty "safe" to me, given that chip specs usually mention 0-70°C operating ranges.

 

I will now try re-checking all solder spots for the vram chips I replaced. Any idea on why a bad solder spot could cause a delayed corruption such as I am experiencing?

 

Next on would be replacement of VDP. How do I get the heatsink off, and what do I need to do to attach it to the replacement chip?

 

Thanks

[Tursi]

Strange.... but I wonder about the heatsink on the VDP. Since you were in there, perhaps you damaged the thermal connection between the VDP and the heatsink. If the VDP was overheating and the heatsink was not making good contact, you wouldn't see that from the top (maybe from the side?)

[zCRP]

I do not see any sign of the VDP heating abnormally.

 

I just resolder all vram chips, but that did not make a difference. I also checked all contacts between the vram and the VDP and they appear fine.

 

While poking around with the multimeter I noticed that my power brick supplies +5 and +12V as expected, but the negative voltage is -2 instead of -5. Could this be the issue?

[zCRP]

Never mind my last post, I read in other posts that -5v is not relevant here.

 

So I went ahead and desoldered the VDP. I carefully removed the old chip, installed a socket, then tried the old chip and two spare chips. Unfortunately, the situation only got worse, in that previously the console would work for a few seconds, while now I get the gibberish right away.

Underneath I can hear music and reaction to joypad inputs, so I would say that CPU, ram, audio and inputs work correctly, only the video portion is not working.

 

I have no spare vram chips to test, but I will look for some online. What else can I try at this point? The console has socketed vram and vdp. I doubled check all pins for continuity and found no lifted traces. Please help!

[Osgeld]

Not totally helpful but artic silver makes two wonderful heat sink 2 part epoxies

 

Since it was asked and they perform great and are fairly cheap

Edited August 10, 2017 by Osgeld

[Keatah]

If I'm reading that IR image right, it looks like the areas immediately to the right of the ram is getting warm. Warmer than the chips themselves. Just questioning the uneven heat distribution. Are the bypass caps for the chips fighting noisy power? Just a thought..

[Osgeld]

If I'm reading that IR image right

 

A flir image without a scale on the side is almost pointless, it could be a 100c difference or a 3c difference tween orange and yellow depending on the min,max, &average as the color patterns are non linear

 

(ie dark blue to light blue could be 20c delta, but from orange to yellow could be whatever, I can take a very similar image showing a product where the dark area's are ambient and the glow area's are 145c giving a 120ish delta, or I can produce the exact same image pointing the stupid thing at my leg)

 

FLIR actually has a nice post processing tool that takes the image metadata and make it into data one can process for free on their website

Edited August 11, 2017 by Osgeld

[zCRP]

I have noticed that the flir App has misaligned the infrared image with the optical one, in fact the "hot spots" correspond to the chips, not to the caps on their right. Regarding the temperature range, the dark areas are in the 29-30°C range, while the brighter ones are in the 40s with some getting as high as 45. The RF out chip (which should not be used since the console is AV modded is one of the hottest getting to 45.

 

But sadly, as I mentioned above, after tampering with the VDP I get the garbled screen right away when I turn on the console, even after it was off for a long time, so not sure it is an overheating issue.

 

I guess while desoldering I fried some other component or broke some trace, but I could find no evidence of either. Does anyone have other suggestions for further diagnose?

 

Thanks

[alortegac]

I have had issues with 5V Ram mod. consoles a couple of occasions. Only after the mod, I have noticed the console creates a voltage drop in the circuit and to the power supply output. The power supply is +5V or over like 5.2 V in OFF. When I turn the console ON, drops below 4.8V creating artifacts (like bad memory)..

I have tested with different games, and some games withstand the voltage drop and the console works just fine.... For example, DK vs. Cosmic Avenger....DK does not work at all below 4.8 V.

I have replaced the power switch, checked all sorts of capacitors, inductors, ground, etc. Try to follow the V drop going from the power supply, through the switch, inductors, capacitors.....but there is a loss of about .5v... I have never found the issue. Any ideas or suggestions? The power supply otherwise works fine with other non mod. consoles....so it has to do with the 5V RAM. The drop is only in the 5V not in the 12V supply. Memory chips are all fine, I have correctly installed them, socketed, check continuity, etc. Again, this has happened to me in more than 1 console.

 

Any ideas, will be Greatly appreciated.

 

Thanks!

Edited May 9, 2018 by alortegac

[Ruggers Customs]

I have had issues with 5V Ram mod. consoles a couple of occasions. Only after the mod, I have noticed the console creates a voltage drop in the circuit and to the power supply output. The power supply is +5V or over like 5.2 V in OFF. When I turn the console ON, drops below 4.8V creating artifacts (like bad memory)..

I have tested with different games, and some games withstand the voltage drop and the console works just fine.... For example, DK vs. Cosmic Avenger....DK does not work at all below 4.8 V.

I have replaced the power switch, checked all sorts of capacitors, inductors, ground, etc. Try to follow the V drop going from the power supply, through the switch, inductors, capacitors.....but there is a loss of about .5v... I have never found the issue. Any ideas or suggestions? The power supply otherwise works fine with other non mod. consoles....so it has to do with the 5V RAM. The drop is only in the 5V not in the 12V supply. Memory chips are all fine, I have correctly installed them, socketed, check continuity, etc. Again, this has happened to me in more than 1 console.

 

Any ideas, will be Greatly appreciated.

 

Thanks!

 

 

 

Hey there! Just out of curiosity, where did you purchase your ram chips?

[alortegac]

Console5. And all their products are great. Were do you buy yours? You do Nice work on the Colecovisions too. I have never tried the pause function. Thanks for your response! Al

Edited May 17, 2018 by alortegac

[Ruggers Customs]

Hey thanks Al, I appreciate the compliment! I purchase most of my stuff from Luke at Console5 as well. If he doesn't have it, I get it from DigiKey. I've done countless 5v ram upgrades so I'm trying to narrow down what could possibly be the issue with your colecos. With the ram chips removed from the sockets, what voltage readings are you getting from pin 8 and 9 on each socket?

[alortegac]

Hi,

Sorry for the delay, I never saw your message until today. 

I have a console that has the problem, voltage on an otherwise good power supply drops from 5.16v to ~4.76V causing random artifacts sometimes, not all the time, and not as severe. This console has the new 5V RAM and a new power switch installed very nicely.  I have check VRAM test with the atarimax, funny sometimes it passed and sometimes it fails, randomly.

I have also checked the RAM IC's with logic probe, one by one. All are working as they should, perfect readings.

Finally, I checked continuity between RAM and VDP, all pins are good.  I followed C5 troubleshooting guide to the dot and VDP test guide I found here in a different post.

I will now check PIn 8 and 9 without IC's as you suggested. With IC's in,  all are in high in the probe, reading ~4.76V with multi meter.