Colecovision No Audio or Video

[kf6rcp]

Hi! I was wondering if any one has ran on a problem similar to mine. I got this Colecovision from a thrift store complete with controls and alot of games and a roller control. Everything came with it and I hooked it up to my tv and it did not work. Before I turn the switch on there is static on the screen of the tv set to channel 3 and same with the rf modulator switch. When I turn it on the static stops and just goes to a blank screen. No video and audio. Same thing happens when I turn on the game console with out a cartidge. Can someone help me where I start troubleshooting. Will it be a bad rf modulator? I checked the reset switch and power switch and both checked out good.

[InsaneDavid]

Clean down in the cartridge slot and the connectors on each cartridge wit isopropyl rubbing alcohol if you haven't already.

[kf6rcp]

Hi thanks for the reply! So, I heard there should be like a welcome screen or something saying to put in a cartridge if not install? Will a dirty cartridge slot get this message? I will clean it anyway and see what happens. After cleaning it and it still does not work (hopefully it works) what is the next step?

[kf6rcp]

HI! I cleaned it and still no video or audio. What do I do next? Any suggestions!

[InsaneDavid]

Are you using an RF switch that has been confirmed as working, such as by using it with an Atari 2600, etc.?

[kf6rcp]

yes, I did try it with and with out an rf switch box. I also went straight in to the tv with an adapter I bought at radio shack. Both with and with out are the same. Still no video and audio.

[FABombjoy]

With the Coleco, you always want to verify:

1 - A fully functional power supply
2 - The power switch works correctly. Thrift store Colecos almost always need the switch cleaned.

[InsaneDavid]

2 - The power switch works correctly. Thrift store Colecos almost always need the switch cleaned.

That's where I was going to head next.

[kf6rcp]

Anymore suggestions on where to start? Please help me :-(!

[FABombjoy]

Did you actually test the power supply & clean the power switch? There's no magic fix here, if that's what you were hoping for.

[kf6rcp]

Yes, I did verify the power on each pin and also cleaned out the contacts for the cartridge. Do you know what I can replace? Will it be the IC's? Which one do I start replacing?

[FABombjoy]

Power switch. Clean the contact points on the power switch. Search the tech forum for tips on how to do it.

[kf6rcp]

HI! I did check the power switch and reset switch for continuity and both checked good. Anything else? I don;t know where to start

[Nitrosport]

Eh, nvm. I missed the part that you already checked the power supply. Other than what you have already done, sounds like a bad board.

[kf6rcp]

HI thanks! I cleaned the cartridge slot and the game. I also connected the rf cable diretly with an adapter to isolate an rf switch problem. Do you think the problem is in the rf modulator since there is no video or audio? Also, no screen saying that I need to install the cartridge when not installed.

[FABombjoy]

If the RF modulator was bad the screen wouldn't turn blank, it would just stay static. If voltage reads correct at the chips, then it's down to component level troubleshooting.

[kf6rcp]

Alright, so now do you know where I can get the volatage measurements or the scematic for the colecovision so I can troubleshoot it?

[omnedon]

We repair Coleco's professionally here. Usually a board like yours becomes a parts donor.

[FABombjoy]

I googled 'colecovision schematic' and it was on the first page ;)

I would verify +5, -5, and 12 on the 4116 RAMs since they're the only components that use all three. If those check out, then the next step is component level microprocessor board troubleshooting, which is really a pretty deep topic and probably outside the scope of this forum.

[kf6rcp]

That's what I need! I will bring out the multimeter. I will post what I find. Thanks!

Mike

[kf6rcp]

HI! I finally found out what was wrong with my system. I checked voltage with it powered up and found that the +5v was dropping to .228 volts when the switch was put to on. I unplugged the power supply from the board and i put a load on the +5 pin and ground with a bulb and it surely dropped so basically a defective power suppy. Made a temporary +5v and the system work perfect. Anyone knows where to get a schematic of the power supply? Thanks!

[FABombjoy]

It's probably a 7805 regulator or something of that sort. There shouldn't be too much to the inside of that supply, just crack it open and see what you see.

[kf6rcp]

yeah I got a 7805 but I am debating if I should jsut install it using the 12v as the inout voltage and jsut cut the 5v wire and connect it to the 7805. Have you cracked open a power supply? I was hoping there is a scew under the metal label but there was none. Let me know what your expirience is on this?
Mike

[FABombjoy]

I've never opened one, but in my experience most power supplies like that are glued around the edge. Sometimes you can hit them with a hammer & break the glue loose, sometimes you just gotta bust 'em. But hey, duct tape is available in black :D

[InsaneDavid]

I've never opened one, but in my experience most power supplies like that are glued around the edge. Sometimes you can hit them with a hammer & break the glue loose, sometimes you just gotta bust 'em. But hey, duct tape is available in black :D

LOL I go at it with a cutoff wheel on a dremel myself, after a couple slices the two halves seem to pop right apart with most power supplies.

[FABombjoy]

Well... I guess that could work too, but the hammer is such an underutilized diagnostic tool :D

[kf6rcp]

I opened up the power supply with the dremel and everything went good. Found a couple of regulators and power transistors that might be at fault. Regulator is a CA723CE and power transistor is TIP41A. Not really sure which is bad so I ordered both. I have a feeling its the voltage regulator. Any ideas?

[FABombjoy]

Sounds like there isn't much inside to troubleshoot, really. Maybe diode test the TIP41 first and see if it can be ruled out immediately. As long as you have the parts, might as well change all of them just for fun.

[kf6rcp]

Thanks! I did get the parts in and I first changed the CA723CE and still did not work. So, I changed the TIP41A. TIP41A did fix the the problem and now I'm playing with it. Thanks for all the input.