DT-40 Pro + FB3 Kit having grounding issue

[clandestiny]

i guess i missed it somewhere, but from the beginning- what was the modification bill performed to the amps? I didn't know he was implementing
fixes in the chinese units-
please explain-

[VaThInK]

I'm actually waiting for Bill to give me permission on whether or not I could post the PDF file that he emailed to me in this forum. I'll post it here as soon as he gives me the green light. Basically, he said that the modification would allow the scanners to perform better and also easier to tune.

i guess i missed it somewhere, but from the beginning- what was the modification bill performed to the amps? I didn't know he was implementing
fixes in the chinese units-
please explain-

[The_Doctor]

The multi meters that I have are all digital and they don't have bar graph feature unfortunately.

Get a cheap analog sometime, always useful when you want to see something fluid and moderately fast happening.

With or without the fix, all the scanned images are in proper orientation but at 100% size they don't look nice and square so that's the reason I did geometric correction.

No problem, was just making sure you were looking at a modulation noise that was inverted on one channel, which in this case, you are if you haven't flipped either axis at ANY point, digitally or otherwise between design and scanners. It makes a difference in figuring out where it originates and how to fix it.

I think those clips show the speed in real time. The variation in oscillation speed depends on the size of the projected image and the complexity of the image. The oscillation speed will be slower if the image is bigger and more complex.

VERY interesting. I didn't think you were seeing an AC line voltage leak, because those are at 50 or 60 Hz. You'd not be seeing wobbling ILDA patterns, a pattern that complex and demanding would fight such strong and swift noise modulations, you'd be seeing utter scrambled craziness, at those amplitudes the pattern would be unrecognisable. No AC line voltage bleed will change frequency according to the complexity or size of your image either.

Can you tell us how it looked to you? (Cameras don't relay things well, they have their own frame rates to interfere with what they show). Did it look like a complete, maybe slightly distorted pattern leaping up and down a diagonal line, and could you distinctly see by eye that diagonal motion? If so, that weird signal is a lot slower than line frequency, and originates elsewhere.

[Pangolin]

Hi Vathink,

The two solutions that I described are close to one another in terms of the effect. You could do either. The choice depends on ease of implementation and exactly where you can get a reliable ground connection.

With Dan's system which we modified after yours, we saw the problem you are having. We didn't see it on your system because we used a different (better) power supply.

With Dan's system, we tied FG to the ground pin of the AC outlet, and then tied the "ground" of the power output to FG. That will work as long as you have a RELIABLE ground pin on your AC plug. If not, then it is best to run a "third wire" from the ground of your PC to the "ground" of the power supply.

In fact, I just thought of a better idea, which is similar to the second solution, but probably easier. You could run a wire from pin 25 on the DB25 ILDA connector to the "ground" on the power supply. Note that whenever I say "ground on the power supply" I am not talking about the FG, but the power supply "common" between the +24 and -24 volts. I forget what it's called on that power supply.

I have read other solutions being batted around here, and, unfortunately I really don't have the time, fortitude, patience, etc. to debate this and explain why people should do what I say. You can either follow what I said and have your problem completely solved, or not. It's really a matter of choice... Other solutions will either create their own problems (as you may have discovered) or, well, I guess that's it -- create their own problems.

As I said, there are very good reasons why we do what we do and why we recommend what we recommend, even these things aren't well-understood. In fact, sometimes I like it when we say and do aren't well understood. It keeps competitors from doing the same and getting the same great performance...

Bill

[VaThInK]

Problem is solved then. Thanks Bill .

Now, I have a couple of related questions to all of you.

1. Would switching between single ended and differential signals affect the scanners optical angle? At the moment I can only manage to get 34° peak to peak with my current setup. Is this normal for DT-40 Pro?

2. If you have seen my ILDA test pattern, you'll notice that the circle is actually outside the square. What does it actually tells me? Is it a bad thing? I find it a little bit annoying since when Bill tuned them the circle was inside just touching the sides of the square.

Thanks.

[Pangolin]

Hi Vathink,

Changing from single ended to differential will, in many cases, affect the scan angle. It depends on some factors such as how the amp is wired internally...

The circle outside of the squre means that the scanners are tuned faster than they are being displayed. In a private email, I already told you that I tuned your scanners to 36K to give you a little better performance. Gosh, that'l teach me...

And lasty, the far-right pot on the scanner amp controls the "gain" of these amps. You can increase the gain and get wider scanning, but for a hobbyist I wouldn't recommend it. Yes, the scanner can conceivably scan wider, but one thing we saw is that there is an artifact of the DT-40 scanners. Jian doesn't use the right kind of LED in the position sensor and there are other problems, so wider scanning will lead to image distortions. Also, wider scanning will generate to more "heat". Basically, I start to wonder if a hobbyist really needs these potential problems as much as they need a wider scan angle... so I purposely reduced the gain on your scanner amps when we shipped. I can say the same thing about the system we recently shipped to Dan.

Anyway, you can increase it if you want but... be careful. And ask yourself if you really need the wider scan angle.

Bill

[VaThInK]

Thanks Bill. Great explanation. Just the kind of answers I'm looking for. Definitely clear things up . Yeah, I know you've told me via email that my scanners are tuned at 36K but I had no idea what it actually means at that time. Now I understand what you were trying to say . Thanks for the warning. I won't touch any of the pots on those amps. In fact, I sealed them since the day I received the package from you to prevent any accidental adjustments .

I'm sorry though for asking too many newbie questions. It's just that I don't know much about these two products that I just bought and what to expect from them. Hence, the stupid questions . I'll refrain myself and do more reading next time . My bad.

PS: Could anyone recommend me a good link to learn more about scanners?

Thanks heaps to everyone else who helped me. You all have been very helpful .

Cheers.