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Dreamcast VGA cable.

Started by TJ_Kat, February 02, 2005, 02:30:07 pm

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TJ_Kat

I think to myself, "DC outputs VGA directly, my TV accepts VGA. I should get a VGA cable!"

So, my eternally bargain hunting self goes and finds himself a DC VGA cable nice and cheap. But when everything is all hooked up, the picture is tinted yellow - like and extra big dose of yellow was infused into EVERYTHING.

To rule out my TV being the problem, I hook it up to a PC monitor. Same deal.

To rule out my DC as the problem, I connect the composit video, colors are fine.

Must be the cable.

So I open up the cable, get this page and this page tabbed up for reference, and start tracing circuits.

First odd thing I notice is that there are 12 wires connecting to the circuit board from the DC. 3 of them trace to the audio plug, 8 connect the circuit board to the vga conector, and i'm not sure what the other one is. To make things more difficult, there is no apparent relation to a wire and it's function. To make things worse, colors coming from the DC that I KNOW are for audio find themselves heading off to the VGA connection.

Next oddity. The circuit diagram shows that a 220 uf capacitor is required for each of the red, green, and blue signals. My circuit board has 4 100 uf capacitors.

Oddity #3. The circuit diagram shows 2 74HCT244 chips. My board has a single 74HC32D chip. I'm not too concerned about the number of chips - it looks like the second one is only really for switching from VGA to non-VGA mode - but is the chip on my board equivalent to the chip in the diagram?

In summary, my questions are:
1: Does anyone know offhand why everything is tinted yellow?

2: How many wires should be coming out of the DC to produce stereo audio and VGA video (I only counted 9 or 10)?
2b: There are 12 wires inputting to my circuit board, and only 11 outputting. Where might a wire have gotten lost?

3: 220 uf vs. 100 uf capacitors. Could the use of different capacitors be the problem?
3b: Why do I have 4 capacitors?

4: 2x 74HCT244 vs 1x 74HC32D. Could the use of a different chip be the problem? Could the use of less chips be the problem?

5: Is there a way that I can test which color wire goes to which pinout on the DC and VGA connectors?


If anyone is interested in helping me in depth, I've also taken pictures.

NFG

Tinted yellow generally indicates there's no blue, so all you're getting is red and green.  Remember that red and green combined make yellow, but if you add blue you get white (and various other shades, of course).

Check to see that the blue pin is connected properly.  You may get results by wiggling the cables around.

Aidan

4) The 74HCT244 is a octal line buffer that supports tri-state.
The 74HC32D is a quad 2-input OR gate.

The circuit diagram you linked to has two HCT244s in it. The second HCT244 is not connected to any signal as far as I can see. Seems to be a waste of a HCT244. The HCT244 is being used as a signal buffer and output enable for the two sync lines. As such, the HCT244 is actually wasted, as it's capable of handling eight lines, not just two.

If the adapter you are building is solely for VGA, and is not designed to support TV modes, then the 74HC32D is fine part to use. It's actually overspeced by a couple of gates, but it's hard getting anything smaller.

In any case, the logic present is just to buffer the sync signals - you'd soon know if they weren't working properly!


5) Yes, use a multimeter to trace the signal from a connector to the board. Then you can trace the signals on the board.  
[ Not an authoritive source of information. ]

TJ_Kat

Well, on my pc monitor, I removed all the red, and there is blue present. So I don't know about that. Removing the red makes it better, but still not good.

And I have no clue which wire connects to which pin on the connectors. So, it would appear I'm going to be getting a multimeter (I'd hoped to avoid that).

However, on closer inspection of the wires, A LOT of them have cuts in them and exposed wires, and are generally in really poor shape.

Ah well, if nothing else, i now have a nice little circuit board to build my own with.

p.s. This is probably a really dumb question, but what are the cylinders towards the ends of the cables?

NFG

Those cylinders are probably capacitors.  They'll have two ratings on them: uf (microfarads) and V (volts!).  The side with a stripe is the negative leg.

dum dum

i think he means those thick things you get on your monitor cables and some joypads (doesnt the xbox have them?). as far as i can figure, they are ferrite toriod cores and probably used to surpress rf energy/magnetic fields?

so, "anti-interference dongle" might be a good description

NFG

Hey, yup, those are the other cylinders.  =D

atom

TJ, why dont you buy a decent cable? Lik-Sang sells this stuff, and its not going to cost you much. Sounds like your cable was made by slave children whipped by korean pirates in some country without electricity.

http://www.lik-sang.com/info.php?category=...products_id=82&

And hey, dont those cylinders sometimes even just have some of those other cylinders in them?
forgive my broked english, for I am an AMERICAN

dj898

QuoteSounds like your cable was made by slave children whipped by korean pirates in some country without electricity.

Huh? o_O
since when Korea has pirates?
I've heard of 'em in Southern part of Asia but not in Korea nor Japan?
if you are referring to those from N.Korea, they are not pirates but actually N.Korean armies doing some private business... ;p

atom

February 05, 2005, 12:28:16 am #9 Last Edit: February 05, 2005, 12:30:46 am by Atom
Its not big like China but when my brother served over there for a few years he said there were piracy stores. Highly illegal (as was porn) but they were there.

Edit: (I removed the words "Um nope..." in the front of my post for fear of my coming off arrogant and someone getting extremely pissed at me again. Thank you have a nice day.)
forgive my broked english, for I am an AMERICAN

Endymion

Why go to lik-sang (and deal with import duty and international shipping) for a ten dollar Dreamcast VGA? I don't know why a "cable" is suddenly popular either, isn't a VGA box more versatile? They're only ten bucks and all over ebay.

Unregistered

To be honest, I believe there is only 1 chip in the DC VGA circuit diagram that was referred to above, even though its drawn using 2 diagrams. Just trace the pin configs and you will see why.

TJ_Kat

Actually, I've just been informed that this VGA cable DID come from Lik-Sang (this one actually). So, scratch that plan.

Endymion

February 06, 2005, 04:25:19 am #13 Last Edit: February 06, 2005, 04:26:02 am by Endymion
The ebay plan is looking pretty good, the same cable is there and several VGA boxes a pittance each.

TJ_Kat

After you add shipping, and duty, and taxes, I fail to see how buying a second crappy cable (for about the same as I paid for the first one) will improve the situation with my first crappy cable.

I will probably be better off turing the first crappy cable into a half decent and functional cable... Besides, this option will be more fun ;-)

My only setbacks right now, are:
-I don't know which wire is which (but I have a friend with a multimeter, so this will be solved soon)
-I don't really understand how the chip on the board works (or why it's necessary for that matter.)

Once those two things are dealt with, I shouldn't have any problems *knocks wood*.

atom

Quote-I don't really understand how the chip on the board works (or why it's necessary for that matter.)

I don't see why either. I see how it works, but I dont at all understand why you would actually NEED IT. Waste of money for a part. I havent actually built the box so maybe someone who knows what the heck their talking about can clarify.
forgive my broked english, for I am an AMERICAN

Endymion

QuoteAfter you add shipping, and duty, and taxes, I fail to see how buying a second crappy cable (for about the same as I paid for the first one) will improve the situation with my first crappy cable.

a. You can't polish a turd, and that cable looks extremely crappy. Woe betide you if the fault turns out to be an inside fray or such.
b. A VGA box is a lot nicer to have with its multiple outputs, and easier to fix when you have problems.
c. Atom? Doesn't make sense to you? Did it make sense to you when you suggested he buy another cable?
d. I still don't get the obsession with a VGA cable, what's wrong with the VGA boxen?

TJ_Kat

Ah, but that's assuming I don't have a nice collection of "useless" junk (incl. PC VGA cables) that I can hack up sitting in my closet. Therefore, cost on that = 0 (in the event there is a problem with that).

The obsession with the cable is that I already have it. Buying a VGA box will double my cost, or worse.

Once I get my hands on a multimeter, I will be able to finish my circuit diagram, and happieness will ensue  :P  I've already isolated the audio, video, and synch lines (of course, I still don't know which is which in each category). 3 of the other 4 wires, I'm guessing are all grounds (since they're all connected to eachother anyway).

Now, since Atom indicated he knew how the chip works - but failed to elaborate - could someone enlighten me? I went to the manufacturer's site, and I can't mentally transpose the diagram onto the actual chip. I'm still missing some key piece of information.

Aidan

It's just a buffer. (Although it might well also be a level translator, as I don't know if the sync pins on the DC are 3.3V or 5V logic)
[ Not an authoritive source of information. ]

Guest

The chip is fairly useless and I believe all it is there for is to block sub 31khz horizontal scans from passing through to your monitor,to protect the monitor's circuitry.However I have yet to see a monitor that is hurt by it,even old ones from the 1980's.Your colour issues could be because of the lack of resistors on the sync lines or possiboly they are there but with incorrect values.They should be 150 ohm or thereabouts,I used 135 ohm for my own cable as I had plently of 75 ohm resistors on hand and just ran 2 of them in serial on each line.That is another option btw,hack up the cable you have their and rebuild it yourself...you can add support for 15khz rgb and composite while your at it too :)  

TJ_Kat

Yeah, it's been a while since grade 11 chemistry, and I don't remember how to read (or identify) a resistor properly... =(

The ones on the sync lines (I'm almost positive they're sync) are black and have 331 printed on them. The ones for the audio are black and have 102 on them and there are two more black ones with 472 on them. There is also a green one with 5R1 printed on it, and an orange/yellow one with no printing on it. To be honest, I'm not even sure these are all resistors at the moment. That, and the fact that I still have 4 mystery wires coming in from the DC, and 3 mystery wires going out to the monitor (I checked the pinout, and was reminded that the DC doesn't have specific R ground, G ground, and B ground wires).

Actually, never mind all that babble, here's my circuit diagram (yes, I know it doesn't use proper symbols for anything, I just found it easier to draw the EXACT layout of the chip this way.):

Key:
A = 47 uf capacitor
B = 100 uf capacitor
1 = resistor. black w/ 331 written on it
2 = resistor. black w/ 102 written on it
3 = resistor. green w/ 5R1 written on it
4 = resistor. black w/ 472 written on it
5 = resistor. orange/yellow

The blue squares are the audio jack, the colored rectangles are the wires, and the pink/purple spider is the 74HC32D chip.

On the right side, coming from the DC:
black = ground
brown, red = audio
orange, yellow, green = video
dark blue = +5v (I think ???)
purple, grey = sync
white, pink, light blue = ???

I don't understand the lower left hand side at all... everything is interconnected with everything else.

Questions? Comments? Explanations of what resistors are actually there (or if they're actually resistors at all?)?

Darklegion

That is actually the same layout as the vga cable I hacked up I believe.Does it have a purple/blue label with a yellow "-DC- VGA CABLE" written on it? These use crappy connectors and you tend to not fit in the port correctly.Since the rgb pins are at the end of the connector (blue being the last) it could be that the blue pin is slipping out.

NFG

those resistors with 3 digits can be decoded thusly:

First two digits are the numbers, followed by the number of zeros the third number indicates.  For example:
331 = 330 Ohms
472 = 4,700 (4.7k) Ohms
750 = 75 Ohms  <-these might sometimes read just '75'

TJ_Kat

February 14, 2005, 04:48:31 am #23 Last Edit: February 14, 2005, 07:45:31 am by TJ_Kat
Thank you Lawrence.

Any idea what the green and orange/yellow ones might be?

Darklegion: Isn't the red video the last pin on the connector?


So no one thinks the problems has to do with using much too strong of resistors for sync, and wimpy little capacitors for the video?



UPDATE: Got myself a multimeter, and I think I have found the problem. At some point, the blue video line is coming into direct contact with both syncs and the ground. This could cause me to have very little blue?

Darklegion

Yes you are right TJ,the red is the last pin.In my case the cable was kinked just before the ferrite bead and so flattening it out helped things(the connector is still dodgy though)As for your blue issue,clean up the circuit board with desolder braid and a pin,there may be some hairline shorts that you cannot see with the eye (or just haven't noticed)

NFG

Green ones are usually coils, and the yellow ones are typically capacitors.  

TJ_Kat

I don't think the problem is on the circuit board. The blue video circuit doesn't go anywhere near any of the other circuits it's connected to.

The problem must be inside the cables... or at the connectors at the end. *grumble grumble*

Is there an easy way to remove vga and dc connectors without breaking them?

PS. Forgive my ignorance, but what's desolder braid?

kendrick

For lack of a better term, desolder braids are like wiry 'sponges' that soak up solder, moving it away from the circuit board or join or whatever place it's sitting. Other options include the use of a desoldering bulb, which actively suctions solder up and away from the join. Some people use a combination of gravity and a plain old stranded copper wire, which has the advantage of being cheap and disposable.

-KKC, feeling manly after changing the oil in his old Toyota.