Help!!! SNES Component mod.. My first mod EVER!!

Let me preface this with saying that I have never modded a console before, have only soldered 3-5 times, and just learned to read schematics 2 days ago. Anyway, on to the show. I have a 2 chip SNES with a non S-ENC BA6592f.

This is the circuit I built.





Its based off of this.



I tapped pin 7 on the multi av for lumi, and built the amp shown here (with the SN3904) for B-Y and R-Y. I don't have the diodes it calls for between the video chip and the transistor so I used 100k resisters. I have red, blue, and lumi but no green. This is what I'm getting.. No green...




I checked continuity from the encoder to the circuit and that is good. Checked from the caps all the way to the component jacks and that is good. Ground is good. Both transistors are getting 4.97v. Resistors are showing correct ohm rating also.. Here are some more pictures.. If there is anything specific you guys need let me know.. As I said, this is my first ever mod and the first circuit I've ever built so everything about this is new to me.

 

Tip: don't blindly follow circuits you find on the internet. (This one is garbage--there's zero engineering discipline.) That said, it looks like your problem is with the Pr connection.

 

im not sure about component but shouldnt there also be a 220uf cap on green(and maybe res)?

 

While I do not disagree in principle, can you point at what is so wrong with this circuit? And/or provide a better alternative circuit?
The circuit is very simple. It mostly does two things that I see.
1. Adjust the signal levels (either by amping or by resisting )
2. Acts as a buffer between the chip and the cruel world outside.

This being said I just took a SNES console with the same encoder as OP and just connected a 220 uf cap to each Pr and Pb and got a pretty decent picture already. Then I added a pot to Y because It was a bit too strong compared to the colors. I will work from there tommorrow to calibrate the colors with amps.

@Synrgy87 The Y is tapped right at the output port so should be no need to add any cap there, there is likely one already in the SNES.

 

As I said.. I learned to read schematics 2 days ago and have never modified a console.. I have no other choice than to follow circuits blindly at this point. I did a little more testing though, and it seems that when I have either Pr or Pb on the circuit green comes back and it amps the one color fine.. I tried with Pr and Pb.. Both amps work on both lines.. The way I have it wired is that both amps share the same 5v source and ground. I tried to add separate grounds but that didn't work.. Still no green.. The only other thing that the two amps share is 5v. Could that be the problem?

 

XD that's like saying the entirety of electronics is very simple since it's only about manipulating signal levels.

It's doing things you presumably aren't seeing due to unfamiliarity with video signal levels, video source and endpoint termination, the common collector/emitter follower transistor amplifier topology, stage coupling, transmission lines. The issues stem from those subjects.

I already have critiqued it (or its predecessor, I forget) in this thread: http://forums.nesdev.com/viewtopic.php?f=12&t=8979

Or you could choose not to mod things with circuits you aren't confident about yet. In my experience internet circuits are so glaringly bad I'd go so far to say don't trust anything not from a journal, datasheet or application note. And I say this as a pretty poor electrical engineer myself. Most people putting circuits "out there" absolutely have no business doing so. They may believe they're sharing "knowledge", but truthfully it's just more noise one has to navigate through to learn anything.

This is quite confusing. Again the circuit is terrible, but if you're following the diagram there is precisely one amplifier for Pr (the transistor). I'm also at a loss what you're talking about with 5V. The only 5V point is the collector of the transistor.

 

Calpis, what is you user name on NesDev? I could not find your critique.

That is because he put an amplifier on both Pr and Pb

 

kyuusaku. Pretty sure I'm the only person critiquing. I just responded to NightWolve's rant.

 

Hello again Calpis. I read a good lot of that thread and some of the links you provided and tried to make sense of some infos you provided.

I appreciate your concern for the importance of doing electronic stuff the "correct" way. I myself try to better myself and my knowledge of this stuff, but sometimes in ways that you probably would not approve of. We cannot all be trained electrical engineers and many(most) modders see this as a hobby, Including myself, you cannot change this fact.

I read datasheets and check how things are done in service manuals and read theory but I also do a lot of experimenting and I consider it one of the most efficient way to learn, just do stuff and see what happens. And yes I did some experimenting on precious retro consoles... In 3 years I did not fry any though, and repaired a lot, so I guess I have points?

Anyway, I am intrigued by the concept of Impedance matching in analog video.
The way I understand it, the effective impedance of both input and output should not be something easily measured as you would have to take into consideration the effective impedance of all the parts for the given signal frequency that will go through the circuit. ( Advanced application of Thévenin theorem? )

However, If I measure the resistance of my Component inputs on the back of my TV with a multimeter, I get a solid 75 Ohm. Same thing If I measure the outputs of my DVD player. Is it possible that the manufacturers are taking " shortcuts" to make sure that both sides match? Like putting some pull down resistor to make sure the effective impedance under AC signal will always be roughly the same?

For example, by opposition, the composite input of my TV is 75 omh, but the composite output of my SNES isnt. I actually cannot measure it with my multimeter, because it goes through a capacitor. And it is hard for me to assess the effective impedance of capacitor on an analog AC signal. I lack the knowledge of how to calculate this.

However I still cannot see what is so fundamentally wrong with using a Transistor to amp signal in the case of this mod ( something you seem to be strongly opposed to ).
As long as the color signal amplitude is correct, that DC offset is removed and output impedance matches 75 ohm, should it not be fine??
I mean, even if it is not 100 perfect, but pretty close, and safe for the hardware, and use off the shelve parts instead of having to order specialized video op-amps, should not this an acceptable trade-off?

 

I don't expect people to be anything they're not. I do however think it's unreasonable for circuit benders to sell and sometimes even spread their "work", and especially engage in confidence tricks with the public over said work. Honesty is key so if someone has no idea what they're doing they should be careful not to create the illusion that they do. I realize it's human nature to be unaware of one's own ignorance, and prideful, and greedy, but that doesn't excuse the behavior.

Do stuff like what? I'd understand if you mean adjusting LED current through a R between a range of safe values, but brute forcing an amplifier is counter productive because not everything can be "tuned into submission". With amplifiers you often have to design specific bias networks that satisfy voltage, current and impedance requirements and there's no way around the obnoxious algebra (or calc for hardcore analysis).

This is true if you have reactive parts in the signal path, but in general people design output stages using just transistors and resistors since resistors will have a given impedance over a huge bandwidth. Generally people only use L and Cs to augment the behavior of R (compensating like a scope probe).

Anyways the impedance is not really all that hard if you use integrated video amps--they do all the heavy lifting and provide a very low output impedance so that all you need is a single 75 ohm series (or sometimes parallel) output R. On the other hand a good amplifier made from discrete parts takes a lot of skill and consideration because amplifiers made from 1-3 transistors are far from ideal, and they won't behave linearly = significant distortion.

That's not a shortcut, a resistor (or multiple) is the only reliable way to terminate the input for a constant impedance since resistors are ideally constant over infinite bandwidth.

You can't always get the full picture with a multimeter. Most of the time you actually can't--it has to be calculated. A low impedance amplifier output stage acts like an ideal voltage source, so those as well as V+ have a more or less constant impedance which is seen as ground to AC. The output impedance is the equivalent resistance to the Thevenin resistance on the amplifier output in parallel with the pull-up network to V+ and pull-down network to GND (as well as networks to any other DC source).

It's hard for anyone and even for impedance instrumentation to figure it out as a black box.

.
I have no issues with a single transistor amp if:

-It has approximately 75 ohms output impedance
-It delivers approximately the correct amplitude into the 75 ohm TV load
-It operates fairly linearly

Some extra nice to haves: designs are efficient in terms of parts to performance as well as power to performance.

You actually don't even need to remove the DC offset. Doing so serves to save power at the expense of video quality and also offer short protection (instead of designing current-limiting into the transistor output stage).

But yes, it'd be absolutely fine! The problem is the crap circuits meet *NONE* of the criteria.

I believe so absolutely, when possible. Unfortunately it's rarely easy to make good or even reasonably performing circuits from discrete components. Integrated circuits due to their physics will ALWAYS have an edge on discrete components when it comes to accuracy and speed, that's something a designer/app engineer just has to accept (though most today accept it only too well).



I hope this is the end of the discussion for me, I've spent a lot more time on it than planned and the explanations are feeling a little too generous since it's been a long struggle to get a hold of this stuff myself (school glossed over, de-emphasized or completely ignored these practical topics).

 

I totally agree, honesty is the key. When someone is not completely sure of what he's doing, it should be stated. Still, this is often not a black and white thing. One can have a fairly good general idea of what he's doing yet still be in the fog for the fine details. And btw, the people trying to pull off a component mod over the other thread are not what I would call circuit benders. I mean, they do not deserve being compared to fools like this : o_o

Basically the idea is that what you learn while doing practical work usually stays with you forever compared to pure abstract theory from a text book. At least it works that way for me.
I could give you several exemples, like how I ve recently fried an IC gate chip by connecting its output to a transistor switching a relay which led me to investigate the cause of failure and then found that my transistor shorted and then someone explained me about the voltage spike induction produced by relays when they are switched off and the need to protect the circuit with a diode. Not likely to forget this one, and it all started with me bursting a chip aflame while experimenting.

Ok I get what you say minus the comparison with scope probe but its ok, ill ponder that.

Being a perfectionist myself ( sort of ) I like the idea of integrated video amps. But to be honest, I just remade that component mod with transistor amps on both color channels ( basically what OP of this thread tried to make ) and the result is very good for me ( unlike for poor op trying his first mod .. ) The picture is MUCH sharper compared to S-video out of the SNES. Colors are also very good after the amps. So despite your claim of it being far from ideal and of significant distortion, its seems to me that two transistors, two caps and a couple resistances just significantly upgraded my SNES video output. It may not be perfect but its still a great improvement. Could a dedicated Video amp IC do better? Probably, but how much better seriously?

Ok , I get that, but it seems that it is not that simple all the time, Judging by the Composite output schematic of the SNES Im looking at right now both resistors and capacitors are prevalent. http://console5.com/wiki/File:SNES-Schematic-RGB-Processor.png

I know enough to know my multimeter cannot tell me everything I am not alien to calculations, and I understand the need for them, despite being a mere biology bachelor
As for the analogy between low impedance amplifier output and ideal voltage source, I will ponder that some more. Thanks for the food for thought.

Imagine for a heathen like me!!

All nice but considering that even commercial products often fail in such regards, satisfying those criterias in an amateur mod design is certainly worthy of at least a nice smile and acknowledgment

Hmmm, Ill have to take your word on that. I was led to believe that DC offset, as a general practice was undesirable in video outputs. But really I do not know. It seems that TV inputs can deal with it as Ive experimented.

Correct me if im wrong but I figured the simple transistor amp circuit above was actually pretty good in that regard.
1."It has approximately 75 ohms output impedance.''
- I was assuming the transistor ''emitter'' output impedance was rather very high, which leaves only the 80 ohm pull down resistor and the effective impedance of the 220uf cap as sole component of the total output impedance. Which puts the whole thing quite close to 75 ohm.
2.''It delivers approximately the correct amplitude into the 75 ohm TV load''
-To be fair I do not know what is the Ideal Vpp of a color Pb Pr signal, but I figured that by using a reference display and adjusting signal strength with variable resistor prior to the transistor I could get the color signal amplitude close to perfect while keeping the +/- 75 ohm output impedance as per described above.
3.-''It operates fairly linearly''
- Back when I first messed with this mod last year I had made a screen to screen comparison of colors using simple transistor amps compared to reference S-video or Composite. And honestly, to the naked eye, after simple adjustments I could get colors and brightness levels to be pretty much identical to my S-video or Composite reference display. Not saying it was perfect but by all empirical evidences so far, it seems to me this Single-Transistor-Scheme has the potential to be fairly linear. But to be fair, I like to do proper objective comparison of things using precise methodology so I will acknowledge that my own personal subjective first impression should not be considered a reliable measurement.

+1 to this, today's engineers are just spoiled

Fair enough mate
I do not require any further discussion from you. You already helped me by challenging me to go read stuff and try to make sense of stuff by myself. And by taking the time to answer a lot of it back you already have my appreciation.
But I hope you realize that you brought that upon yourself.
Whether you are right or not to begin with does not matter. When you challenge others and/or make a critique of their work, they will expect you to come up with something that makes sense to them otherwise they will just challenge you back or disregard you. As you observed with nightwolve. I thought he made a pretty good case against you tbh. Despite being a bit emotional about it, he raised good questions.

 

It seems the OP has lost the will to live... So have I , reading this. Wouldn't it be great that when people asked for help they could just get help rather than endless ego fuelled political debating. At the end of the day we're talking about toys in this forum. Toys are supposed to be fun.

 

Well said and I was thinking the same thing.

To the OP sorry but I don't have solution to your problem but I'll share what I've learned getting back into older consoles in the USA with NTSC televisions. I discovered RGB that outputs to a SCART plug and is not the same as component that we are used to. Also of the older consoles output it natively like the snes, sega genesis, and sega Saturn for example and that is best picture you can get out of them. The n64 and snes mini have it as well but they didn't connect to the output plug so you have to wire it up and/or amplify it. So I modded my n64 to output RGB and I've got my first snes just recently but its a mini so I'm planning on modding it so the RGB makes it way to the output plug on the back. But I've never seen a TV with a scart plug and I don't want to spend the $$$$ on a frameister so I picked up an older plasma tv that is 8-9 years old that supports low resolution outputs that the older consoles put out. Then I picked up a scart to yuv (component) converter off ebay and so far that works well with my setup. I drilled a hole and soldered a 3.5mm audio jack wired up the scart input so audio also comes out.

If your snes is not a mini/slim then you can just get a snes scart cable then use scart to yuv/component converter if your tv doesn't have scart input.

http://www.ebay.com/itm/SEGA-SCART-...=US_Audio_Cables_Adapters&hash=item564f2d3151

but a year ago I found one for $30 shipped though

 

Perhaps but it's not far removed since instead of jumping points A and B often it's inappropriately copying circuit A into circuit B. IMO electronics are 80% science, 20% art, and most of the art is just coincidental. People who treat it primarily as an art just haven't learned enough.

I agree that "labs" are important to get a feel for things, but just like in school it should supplement theory.

This one is in every textbook

Eyes are non-linear, and not very sensitive to chominance. It'd be very hard to tell the difference without a side-by-side comparison with an ideal amplifier.

Perhaps the SNES doesn't have the best modulator, or your TV doesn't have the best chroma demodulator. Chroma bandwidth doesn't contribute much to sharpness sharpness, but the low bandwidth + delay = color bleeding.

It doesn't have TOO significant distortion (that's the point of this topology), but it is non-linear with a passive current sink (80 R).

The capacitors here make low pass filters and AC couple the signal, the impedance is dominated by the resistors and the transistor.

All TVs need to deal with AC coupled signals so they have DC restoration (clamp) circuits on inputs making the output capacitors redundant, plus they cause a first order low pass filter with the termination resistor which attenuates low frequency components (sync, in-game flashing video effects).

The opposite, it's very low. The minimize voltage loss in amplifier stages you want a very low output and very high input.

It makes the transmission line back-terminated close to 75 ohms which dampens reflections, the actual output impedance is far lower. The transistor is connected as a current amplifier, it simply mirrors the input to the output. Because there is no voltage gain there cannot be any output impedance because it will attenuate the signal at the TV end. I don't think this stuff was considered in the design, just coincidental through trial and error.

It depends on your accuracy requirements. In general yes, a common collector with passive current sink (resistor) can be tolerable for video games where 10, 20, 50% distortion may go unnoticed, but as a stripped down textbook example it's nothing to write home about.

NightWolve appears to have felt I was nitpicking a more or less "working" circuit. I feel the circuit is a farce because it doesn't appear to have a single educated design choice. That's about all there is to it.

 

That method of criticism is itself a farce. Criticizing our circuits without providing your own as reference, so we could see if its actual usage on a TV screen performs significantly better.

 

So it's a farce to point out problems, suggest improvements and push people into learning a thing or two? And why is it my burden to provide modders with a better circuit? Did you not notice my corrections and signing off on the op amp circuits?

If I put out a functionally perfect discrete circuit (not that I have one) I don't see what I have to gain. I shouldn't have to spell it people's work for them; if you comb through both threads you'll find improvements from me you can make immediately and at no cost...

 

Well I got it working.. I made a total newb mistake. Insted of the 100 ohm resisters (cant find 80 around here) off of the positive leg of the cap I put on a 100k ohm. I was continually misreading the schematics as 100k ohm. Got that sorted and it looks awesome now. I built another amp with the diodes too.. I'm starting to feel pretty comfortable soldering this stuff. As far as the elitism/snobbery stuff goes, I just ignore that. If the design does what it claims to do, looks decent, and doesn't damage anything then I'm happy.. If something better pops up later then I will try that. This is my first time modding a console or building a circuit so I'm happy that I was able to accomplish this.

 

The greater good is who will gain. Once a circuit is out there, everyone interested has their work spelled out for them.

Myself what I'd do in your position is gather up my research in one place. Then work on forming it into a guide of some form.

 

I don't mind the way Calpis makes you work a bit to work out the feedback he gives - while I haven't built my switchbox yet, he pointed me in the right direction so I could learn about switching relays for video signals which I absolutely appreciated.

 

In my experience, I dont just rely on a guide I do research on multiple sources take the best suggestions from all angles combine them then formulate my own guides, cause like has been stated in this threat many many guides on the web are bad guides with reversed caps, diodes, and many other things in them, It really does take some knowledge to get a perfect result with almost all guides online, in my experience Sony CXA s-video guides are extremely notorious for being just awful generally...like people suggesting trying to pull 5v from a ground pin on a voltage regulator (there is vcc from 2 pins on the model 1 board) (ughhh)....your picture looks kind of over saturated with red to me but it may just be my eyes or the pictures but a pretty good job with your little amount of experience