ColecoVision blackscreen

I've just bought an CBS ColecoVision with some game and ran into the issue of actually using it. I can only seem to get a black screen, I've checked the PSU and got some nice 12, 5 and -5 volt lines and the powerswitch also gives 5 (right) and 12(Left) volt on the 3 prong on the sides. What else could give the blackscreen issue?
The seller told it froze during gameplay and has been in this state since.

Edit/summary:
I've got one of those nice "blackscreens of can be anything" on my recently acquired colecovision... But I can't seem to fix it. It is a revision D PAL system. I suspect it having a short somewhere on the 5V line. Powered off it gives 5V but turned on ~1.38V. And my guess is low voltage to chips = black screen.

-Cleaned it at least twice with alcohol.
-Jumped the powerswitch, but that was a no go.
-I've checked the PSU (its one of those plastic bricks unable to work on if I wanted) but that seems to be fine, as I could power a gameboy over the 5V line of the PSU.
-I've replaced the RAM chips with CD4516BE using the 5V mod, thinking one of those chips might have caused the short.
-Recapped it but with similar result. (there was some lower resistance between ground and 5V line, but that was gone after but apart from that nothing changed)
-Checked if it could be on the RF board, but that seems to get it's 5V from the 12V line.
-detached the RF board, no change. So nota problem on the RF board

So what else might cause this problem, and if its a short how can I find it?

 

Could be some deads capacitors, rusty traces or dry-up welding . Is there any sign of leaks capacitors?

 

bad ram possibly. the ram should constantly get -5v. heres a link to the colecovision service manual.

http://www.colecovisionzone.com/page/coleco%20industries/tech.html

 

All caps seem fine, nothing looks like it's damaged.

All ram chips get -5volts

Something to add, the seller told it froze during gameplay and has been in this state since.

Edit: I'm trying to follow the chart.
Are these values normal ont these pins on chip U9?
pin 35 and pin 36, 3,75V
pin 38 0.98V

 

Colecovision blows up very easily. I bet at one time someone tried to hot plug controller, that usually causes the chip to blow. The easy parts you can try:
check and clean power switch. If it's dirty it may cause issue that prevents CV from working at all.
check and clean cart connector and cart board too. Don't stop until you can see your own reflection maybe not that much but it needs to be clean to work right.

If all else fails, use fire. Oops, wrong game, you should try replacing the RAM chips. They are the obsolete version but there are guide on the internet that uses different RAM chips that doesn't need weird -5v and +12v to run. http://console5.com/wiki/Colecovision_5V_RAM_Modification The replacement chips and sockets can be bought for under $10 if you have the soldering skill and experience to perform it.

 

The service manual didn't help...

I probably need to do that mod and hope it works but I doubt it a bit as all RAM IC's seem to function properly (at least in voltages), or find something else that might work. But even if I turn it on without game it should show the colecovision logo thingy.

 

Bad power switch, bad power supply, bad RAM, bad caps; the Colecovision has a lot of random issues. Mine didn't display graphics reliably until I discovered the power supply had a bad power wire coming out of it. Switched to a secondary supply and bam, graphics.

Course it was the -5v rail.

 

Id change the ram for 5v chips. Doing away with the -5v and 12v issues for the most part.

http://console5.com/wiki/Colecovision_5V_RAM_Modification

 

you check the rf circuitry? all it does is black screen upon power up? no garbled video, no audio (even garbled)?

 

Going to buy the components as we speak.

Yes, I occasionally get a tone (my TV filters a lot of things) and when touching most pins with the multimeter prong I get a garbled/snowy side on 1 side of the TV.

 

I just removed all 8 RAM chips, but most holes still have solder in it. I've tried a solder sucker and wick but no luck, is there a trick to it?

 

Desolder gun like the Hakko 808 or desoldering Station.
But solder wick is ok but you have to take your time.

 

Wick works fine, you must not be doing it right. Add more solder to the home that's giving trouble and try again.

 

I've successfully changed the ram and triple checked every connection (used a toothpick in the liquid solder to get the holes) but still a black screen... What I now notice is that it displays on multiple frequencies (might have done that before but I didn't notice), which is weird I think.

edit: I think I might have found something, the new chips dont get 5 volt. I've used the mod for revision D by omf at Atariage.

Edit 2: I found out why, when turned on it only gives 1.3V instead of 5 maybe I forgot to check with power on...

Edit3: Tried to open the AC adapter, it's one of those lovely once filled with plastic, it's like a pure plastic brick I don't even know how that would work, so that is a no go... I think I need to build my own but I dont know how (as finding one would likely mean pay a damn load or buy a new console with it here in europe)...

Edit4: Putting some resistors between 12V and 5V wouldn't work/is safe would it?

 

placing those resistors wont work. which 5 volt mod guide did you use?

check your voltages from the back of the outlet inside the console while off, then on.

 

At the outlet it 1.3 volt.

Like I said, I used the in by omf at atariage for a revision d board

 

You could install something like this though - http://www.ebay.co.uk/itm/LM2596-Vo...mponents_Supplies_ET&var=&hash=item2c6d713559

But, its possible there is a short or something on the 5v line. Have you tried getting the value from the PSU when its not connected to the console at all first of all?

 

I do get 5 volt when its not connected. I actually haven't thought of there being a short

 

if you get the proper voltages out from the power adapter but when you plug it into the system, turn the system on and check the voltages from the back of the outlet, more than likely you have a bad power adapter.

 

Or a short on the 5v line (bad cap, other stuff).

You should put load on the 5v source that's known OK and then measure it. Measuring it in a system you don't know if there a short or not is pointless, as you won't be pin pointing where the fault is.