Odd VGA output on known circuit

johnfl68

I have a build of boards, know working circuit and program (standard Prop VGA output using 8 resistors).

VGA output lines are progressively smearing horizontally upon start. First time I have seen this, in about 50 boards.

I thought it might be a bad crystal, so I changed the crystal, and get the same result.

Anyone have any thoughts??? Bad Propeller perhaps???

Thanks for any input!

John

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Whistler: I want peace on earth and goodwill toward men.
Bernard Abbott: We are the United States Government! We don't do that sort of thing.
Sneakers (1992)

Phil Pilgrim (PhiPi)

Something similar happened to me with a new monitor. 'Turned out to be the width of vertical sync pulse. You can read about it here: http://forums.parallax.com/showthread.php?p=817803.

-Phil

johnfl68

Okay - just to be clear - same monitors - same board circuit design, etc. I have tested several of these - all the same way. I test on several monitors, they all behave the same (but others I have built before, and in this current batch work fine).

The pixels in the image that come up on this one board, the smear from left to right. The longer the propeller runs, the more the pixels smear (a clock issue of some sorts?). This is using the VGA Tile drivers. If if it were resistors to VGA connector, colors would be off, caps are on the power side, eprom works fine, I changed crystal (2 bad in a row??), that leaves the propeller.

I don't know, I'll move on to the next board for now.

John

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Whistler: I want peace on earth and goodwill toward men.
Bernard Abbott: We are the United States Government! We don't do that sort of thing.
Sneakers (1992)

Phil Pilgrim (PhiPi)

Could it be the cable you're using? Have you tried different ones? In my own case, it's still a mystery to me why the vertical sync width would have anything to do with the colors gradually brightening, but it did. And I was testing with the standard VGA object, which I had to modify. I guess it's like "referred pain": the source of the problem may seem completely unrelated to the symptoms.

-Phil

johnfl68

Here is a video of what it is doing - what should be displayed are solid color blocks:

www.jrbtechnical.com/media/DSCN2033.wmv

John

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Whistler: I want peace on earth and goodwill toward men.
Bernard Abbott: We are the United States Government! We don't do that sort of thing.
Sneakers (1992)

Phil Pilgrim (PhiPi)

Oh, that's timing jitter, judging from the patterns. (Your use of the term "smearing" is what threw me.)

Can you post a picture of your board layout and schematic, please? This may be a matter of the PLL going flaky due to power distribution/bypassing issues.

-Phil

johnfl68

Board schematic is almost the same as the Propeller Demo Board, but only has the VGA output, eeprom, crystal, and switch to 1 input, layout is very similar. All unused pins are tied to ground via 10K resistors. Power is 9 volt battery, through 5V reg and 3.3V reg.

This has to be a component issue, as there are many of these units that have been working for almost 9 months. Circuit hasn't changed, program hasn't changed.

You think PLL going flaky - then I guess I should probably chalk it up to a bad prop chip.

John

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Whistler: I want peace on earth and goodwill toward men.
Bernard Abbott: We are the United States Government! We don't do that sort of thing.
Sneakers (1992)

Phil Pilgrim (PhiPi)

johnfl68 said...
You think PLL going flaky - then I guess I should probably chalk it up to a bad prop chip.

I'm guess I'm confused about the problem's prevalence. Is it one board in 50, or all 50 of them?

-Phil

johnfl68

Just one board out of 50 - so I am trying to figure out what the failure is.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Whistler: I want peace on earth and goodwill toward men.
Bernard Abbott: We are the United States Government! We don't do that sort of thing.
Sneakers (1992)

Phil Pilgrim (PhiPi)

In that case, I'd be looking for a bad solder joiint in the horizontal sync part of the circuit: Prop pin -> resistor -> connector.

-Phil