ColecoVision blackscreen

So if I got a 5 volt from anywhere (even another 5 volt power I push against the contact) it should work to see if there is a short? Also it should be DC right?
I dont have one of those fancy variable voltage regulators, so the 5 volt from a USB device work? (I have those slaughtered all around)

 

USB only provides 500ma, I am not sure what a colecovision draws on the 5v line.

But I was suggesting testing the PSU, rather than use another PSU on the console.

 

ahh, how would I go on to do that? All the ways I found using google suggest that the PSU is ok. With 5,-5 and 12V intact but the moment I turn the system on the 5 volts dip to 1.3...

 

basically try to power something from the 5v rail, then while powered measure the voltage again. If its still 5v, then your PSU is OK. If not, replace PSU.

 

I've tried it with that USB device (a old tiny mouse) which got the full 5V (but the light flashed did flash dim to good, which it doesn't do in the PC)

So it's likely a short?

 

try something that takes a little more power than a mouse.

Also, you could try measuring resistance between 5v rail on the console and ground.

 

I could power a gameboy without game (and of course batteries) with it and it still ready 5V

And I get a resistance of 325 ohm.

So am I right here to suspect a short?

 

Probably.

Check for obvious shorts, also recap (there are like less than 10 caps if memory serves, all same value I think). Dried out caps could cause a short and an easy first line of repair.

 

I think I've found the short, one of the caps have an equal resistance as the ground and +5V line and is directly connected to both!

So time to recap it and see if it fixes it. Also for the record 7 1uf caps, 2 4.7uf caps and a crapton of ceramic caps.

 

Leave the ceramics alone, it's unlikely to be those

 

I wasnt planning on touching those, those seem like happy campers.

 

recapping it didn't fix it... I did stop getting a resistance at ground to 5 volt though (but if I measure backwards I get -1035 ohm).
And I now get, what looks like a really scrambled and scrolling picture but it all looks the same, if I enter a cart or not so I'm not sure how much of a picture it is. And i now consistantly get a quite hum, but that cant be said for the picture, so atleast some progress.

And it still gived 1.38 volt when turned on...

edit: I've made pictures of the chip and solder side as I couldn't find suspicious areas (except for the wires, they are used to repair connections, but they check out fine with 1600 ohm resistance like most other RAM chip traces).

http://i60.tinypic.com/23lid74.jpg
http://i61.tinypic.com/2wpp9hs.jpg

 

OK, this is weird as all hell I think. I just checked the RF boards 5 volt line, as revision D or Pal system have them separate, and that DOES get 5(.8) volt even though it gets voltage from the motherboard. Yet the output still says ~1.4V. I would have expected that also being ~1.4V

edit: apaerently there was a resistor on the RF board making 12V to 5V...

 

I've tried to check if there were rust traces under the IC's (there werent) with a piece of paper but I found an iremovable piece of gunk under the graphics chip, is that suppose to be there?

edit: detached the RF board, no change. So nota problem on the RF board

edit2: tried a snes to power using the AC adapter, did get a bit a voltage trough but not enough to power. But it still gave 5 volt.

 

I've found what MIGHT be the problem, I've removed the RAM chips and now it does get 5V and a quick tone+scrambled colored screen. I can add up to 2 IC's, at any spot, after which (more than 2) that voltage drops again also they become incredibly hot...

 

sounds like 5v mod is wrong?

Picture of your board and work you have done.

 

The black spots are marks for me where to find the 5V line and al those wires are to reconnect lost connections (probably wired one wrong). And I installed the IC's (CD4516BE) with the notch to the closest side of the board.
edit:what I've noticed is that when the bridge is broken on L3 the voltage stays longer close to 5V (but likely also wouldn't make the chips function well).

Edit: if I read this right: http://console5.com/wiki/4516 and http://www.datasheetarchive.com/dlmain/Datasheets-12/DSA-228419.pdf it seems I've placed the IC's backwards. Now I do get 5V but it also seems that they are incompatible for the most part, could anyone confirm it? At any rate still no picture, if they are compatible I might have broken them by putting them wrong way around. Also may I not that now the actual Videochip get warm instead of the RAM.

 

well i do see some of the ram sockets in backwards, dont know how that happened. what ic's are you talking about?

as long as you followed pin alignment, pin 1 should be the same direction on on every ic other than u18 and u20 (if i remember correctly). with the board facing you as installed in the console, pin 1 is facing the right.

 

Some sockets are backward because I didn't know why those notches were there (but it's drawn on the board and functionally they are still the same so no big problem).
Yea, I found that out too. (and found out I used the wrong IC's so I've ordered some NOS)

 

quick question, what is the wiring on the underside of the board? also, for the 5v ram mod did you remove the -5 and +12 coils (l2 & l3) and connect +5 to l3 via?

yeah the ram sockets dont really matter unless your picky, but functionally they will work just fine. which ic's did you reorder / replace?