Help!

[Adrastos]

Hello folks!

So I got tired of waiting for Adafruit to stock the Fuzebox (still not in stock?!), so I decided to simply make my own. I connected everything up today and the chip responds just fine and I programmed it with the SokoWorld2.hex to test both video and sound. I plugged it into my tv and fired it up, but sadly - things weren't working very well.

The sound was more or less fine, though it had a squeal / hiss to it.

The video, however, was all off. It seems like it's a timing issue, but I really don't know what I'm doing here, so.. yea. Pix of the problem are below, and any help at all would be greatly appreciated!!!





Thanks!

[uze6666]

Could be a wrong fuse setting. Have you checked the wiki's troubleshooting section? There's help for that. A wrong crystal could also cause timing issues.

-Uze

[Adrastos]

I forgot to mention, the HSYNC is going at exactly 15.79 kHz, and I can't seem to get a lock on the 4FSC frequency. I'll try a bit more later.

What frequencies are they supposed to be clocking at?

And yes, both lfuse and hfuse are 0xD7, and everything is as per schematic E1 with the parts in the BOM.

[Adrastos]

Ok, I switched from the wall supply to a 9V battery, as I noticed there was *a lot* of 60 Hz noise floating about. Then I checked it on a scope, and the 4FSC frequency is about 14.2857 MHz (the period of the triangular pulses is 70 ns), however the pulses seem to be +- 5V instead of 0-5V.

I checked the HSYNC frequency on the scope, and I got a nice clean 0-5V 15.625 kHz signal (exactly).

I can't test to see if the 9V battery made a difference on the signal, as I'm at work. I'll try and let you know later tonight.

If the chip is outputting +-5V on PB3, does that mean that something is messed up? I feel like it is, but I don't know too well how the uzebox interacts with the ad725..

[uze6666]

Oh, you have a scope, that will help! All signals out of the 644 should be 0-5V. Perhaps you have a floating ground problem. How does the composite video out look like? Should be 0-1V with very minimal overshoot/undershoot. Insure the AD725 decoupling caps are correctly connected. If you have doubt about the signal at a specific point, let me know and I'll try to post a snapshot from my scope. If you can post a snapshot of the composite out zoomed and synced for a scanline that has active video content, that could help too.

Edit:

(the period of the triangular pulses is 70 ns)

??? Where do you see a triangular signal?

-Uze

[Adrastos]

I have a scope at work, but no tv. I have a tv at home, but no scope

If memory serves, the composite video is 0-1V. Could it simply be that my crystal is a bit slow? Or am I just getting too much noise? I think my board looks a little cleaner than some boards I've seen posted that work fine, but I don't know..

I tried creating a simply avr program that turns PB3 into an output and toggles it high and low - the result is 0-5V. But when I have an Uzebox ROM on it, it goes -5-5V (or 0-10V, not really sure, the scope at work is waaaayyy too overcomplicated!). I'll try to capture some pictures tomorrow.

[Adrastos]

Is it possible to drive the AD725's 4FSC signal from an oscillator separate from the Uzebox? I can't figure out exactly what that input is for..

[uze6666]

You sure can drive the 4FSC pin of the AD725 with an dependent oscillator, but this will result in regularly periodic "tearing" in the image. The 4FSC input on the ad725 is mainly used to generate the NTSC color information. The "4" part is related to being 4 times the NTSC color carrier (~3.58MHz).

-Uze

[Adrastos]

Ok, I tested the oscillator frequency (setting CKOUT fuse bit), and the oscillator is running at 28.57 MHz. I feel like this is my timing problem, but there's likely other problems as well. I've attached pictures of the oscilliscope readings at various locations in the circuit:

CKOUT signal:


HSYNC signal:


4FSC signal:


NTSC signal:

[uze6666]

Holy crap, you have a hell of undershoot in that last picture, no wonder you have sync issues. Between hsync pulses, the signal should never get below .3v or the TV will get confused. All these spikes would suggest the decoupling/filter caps on the AD725 or the PSU are wired incorrectly or insufficient. This reminds me of the Fuzebox AD725 "capacitor" issue which I help troubleshoot. This was the signal before (noticed the undershoot):



and after the capacitor was applied:

Ok, I tested the oscillator frequency (setting CKOUT fuse bit), and the oscillator is running at 28.57 MHz.

Hmmm, that's a tad to far from 28.63636MHZ. This will cause some sync issue, but color will be the mostly affected. And that CKOUT should definitively be square, well unless you scope has a 40MHz bandwidth or something (which I doubt for a digital one).

-Uze