Weird video problem with TurboGrafx CD Interface Unit

[Ace]

I managed to pick up a TurboGrafx CD(after 3 years of searching), and sure enough, it didn't work.  While that notorious gear was still intact(but discolored to hell), I found out it was jammed(laser wasn't moving, no click, no nothing), so I had to loosen it a little bit and lubricated that gear, the neighboring gears and the sled for the laser with some silicone grease(will lubricant make the gear last longer?).  However, I noticed a very weird video problem that I just can't seem to figure out: when I plug in the Composite cables to the back of the Interface Unit, parts of the video output get wavy and it looks like the video's going to go out of sync.  Here's the very weird part: when I plug in an RF cable in the TurboGrafx's RF box, the waves go away.   I've never heard of such problems with the TurboGrafx CD Interface Unit.  I've already ruled out that the RCA connector on the TurboGrafx CD is not the source of the problem.  Is it a problem within the TurboGrafx, the Interface Unit, or something else?

[esteban]

Is it a problem within the TurboGrafx, the Interface Unit, or something else?

Solar eclipse.

[BlackandBlue]

Sounds like a ground loop.  Not sure why you are getting it, or which unit is to blame.  You dont have any of the cables in a loop do you?  There is interference being introduced somewhere.  Or maybe it is that damn solar eclipse.

[Ace]

Solar eclipse?  I highly doubt it'd have something to do with the interference.

I have the RCA cables hooked up like this: TurboGrafx CD to Pelican switchbox to TV's Composite input.  Even with a direct connection to the TV, the interference doesn't go away.  And now, I think the problem might not come from the TurboGrafx because I remembered when I region-modded it that I never resoldered the top RF shield, so there was a loud humming noise in the sound output.  Resoldering the RF shield got rid of the humming, but did nothing to fix the video problem.

As a word of note: I didn't get the official NEC power supply for the TurboGrafx CD.  Instead, I took a 12V power supply I found(DC12V, 3.33A) and hacked it up, as the polarity wasn't right for the TurboGrafx CD(power supply was center positive while the TurboGrafx CD requires center negative).  This power supply actually has a grounding pin, so I'm wondering if that grounding pin is what's causing all the problems.  If that's the case, I have another power supply made by Yamaha rated DC12V, 1A which I think should do the trick, but I think the tip won't fit.

[Ace]

Well, wouldn't you know it, it WAS my power supply.  I pulled out that Yamaha power supply and reversed its polarity(plug was the perfect shape, but polarity was backwards), and all the video problems are gone.  Now, I'm really starting to think the grounding pin on the other power supply was at fault, causing the ground loop.

[BlackandBlue]

Well, wouldn't you know it, it WAS my power supply.  I pulled out that Yamaha power supply and reversed its polarity(plug was the perfect shape, but polarity was backwards), and all the video problems are gone.  Now, I'm really starting to think the grounding pin on the other power supply was at fault, causing the ground loop.

Good to hear you figured it out.  Now you said the polarity was incorrect.  You didn't plug it into the system like that did you?  You had to switch the wires around before you plugged it into the console right?

[Ace]

Of course I reversed the polarity beforehand, duh!  However, I did put in a power supply with reversed polarity by accident into my PC Engine SuperGrafx.  Strangely, after having reversed the polarity, it still worked no problem.  What I find even weirder is that nothing blew inside the console.  Shouldn't something blow the minute you insert a power supply with the wrong polarity?

[esteban]

Shouldn't something blow the minute you insert a power supply with the wrong polarity?

Usually it causes a solar eclipse.

[Ace]

You sure are obsessed about solar eclipses, huh?  But, seriously, wouldn't something blow inside a console the minute you plug in a power supply with reversed polarity?  And I even flipped the power switch on my SuperGrafx several times while the power supply was in.  Can't believe the thing still works.

[Necromancer]

Just count your lucky stars that you didn't kill something; fortune smiled upon you that day.

Usually it causes a solar lunar eclipse.

Fixed that for you.

[Ace]

Not just for that, but also for my ColecoVision.  I know this is off topic, but a failed attempt to get it working off a standard 12V power supply resulted in something blowing up inside.  When I got the original power supply for it, it actually was still functional!  And it works perfectly to this day.  Let's just say fortune smiles upon me when I have a power problem with a console.

[Charlie]

The TG16 has circuitry in it to protect from reverse polarity application.  Perhaps the TG CD does also.

Charlie

[BlackandBlue]

The TG16 has circuitry in it to protect from reverse polarity application.  Perhaps the TG CD does also.

Charlie

Really?  That's pretty interesting.  You would think that more electronics would have this property.  Have any idea how it works?  I mean, It sounds like it still runs under positive ground, just with side effects.  This is similar to what happened when I put a couple transistors in reverse in a video circuit I made.

Ace, good thing you didn't touch any metal on the console, probably would have gotten shocked.  Not sure how much amperage it would have been, but you probably would have felt it.

[Charlie]

For the TG16, it's very complex! .  There is a protection diode in series with the input.  No way it should run under reversed polarity.  But it could attempt to function if the power supply happened to be an AC supply rather than a DC supply.

As for the other stuff like the CD???...

As for things like the Coleco, here's a guess. There is a second type of protection circuit that uses a diode in parallel with the input.  When a reverse polarity is applied, the diode causes a short and thus it's expected that the fuse on the power supply will blow.  If the power supply doesn't have one, it's very possible the diode will blow.  That will not prevent the Coleco from operating if the second attempt uses a power supply of proper polarity.  Of course, if the third attempt again has the wrong polarity?!?!?...


Charlie

[BlackandBlue]

See, he said the tg worked with the polarity reversed, which is why I thought it was some crazy circuit. With just a diode, there would be a missing polarity, thus it shouldn't have turned on.