Channel Pulsating

[zman]

Hey guys, been a very rough year on the personal and home front, and I am just now really getting down to business on the display. I know I have some bad triacs on a few LE's so tonight I sat down grabbed one LE, and in fact there are 2 bad triacs.

However a new problem is on this controller. Did a forum search and no hits.

One channel is pulsating. About every 5 seconds it pulsates power to about 5-10% and goes off. 5-6 seconds later same thing. it is not like an instant on, rather a ramp on/off. It keeps doing this until unplugged.

If it makes any difference the bad triacs are 8 & 12, and the pulsing channel is 9.

Is this related to the triac or something else. Thanks

[rm357]

That is really odd.

Things I would try:
- reflow all of the solder joints on that channel. Cold solder joints do weird things.
- put the pic in another Le and see if it does the same thing. If it does, reflash the pic and try again
- swap the opto with another channel that works (the 6 pin chips between the pic and heat sink - each channel has its own)
- if all the above fails, replace the triac.

[rrowan]

Try replacing the input RS-485 chip (the one next to the DMX Input)

Rick R.

[zman]

Thanks guys, I will try Rick's input first. (Least effort)

[zman]

Hmmm different behavior tonight, even before I did anything.

The pulse was only after plugging in the string. But if I un-plugged and plugged it was consistent. Lat night it was doing it while plugged in.

Swap 485 chip, same behavior

Swap Opto, same behavior

Reviewed all solder joints OK

Swap PIC - Viola, no pulse, BUT, there is a small pinpoint of light on the LEDS, so that tells me that the triac is going??

Next question, I know we try to get units these more economical with the coops. Are there a bit more dependable triacs? Understanding that they may be more cost too. Any vendor/partnumbers?

[rm357]

I'm not sure what the deal is with the triacs.
Most people have no issues at all while some seem to have them failing left and right.

Very curious...

Obviously we only hear from the folks having issues... If it ain't broke, there's nothing to fix.

[tbone321]

The triacs are isolated from the LED's by the opto's so they have nothing to do with the pinpoint of light from the LED's.  If it is happening on all of the LED's then I have no idea what is causing that.  If it is happening on just the LED of the channel that was flashing, then I would look at your solder joints for possible intermittent shorts and make sure that the board os clean.  I would also look at the socket that the pocessor is in and the socket for the opto for possible shorts.

[zman]

Doh, I guess I was clear in my mind, but not in my typing.

When I say there was a pinpoint of light in the LEDs, they were the string of LEDs connected to the channel. They had about 5% power on them. Not the LED on the board for the channel.

[tbone321]

LOL, ok.  LED's use so little power, what you are seeing is the typical leakage of a triac and there is really nothing wrong with it.  What version of the Express is this.  If it is a Ver4 or older, this can be a typical issue.  The Ver 5 has bleed down resistors to help prevent this.  A common trick is to add a C9 or even a C7 bulb to the string and keep it out of site.  The added load from that bulb and the characteristics of the incandescent filament both keeps the LED's from lighting at the off position and also smooths out the dimming curve and makes them react much more like Icans,

[rm357]

Also, when using LED strings, you need to load one of the LED light curves. The effective dimming range for a LED string is only about half that of incandescent bulbs. They don't really start to turn on util about you hit something like the 30 to 40% mark (channel value something greater than 70) of the way up and reach 90% brightness before you hit the two thirds point.

The standard Incan curve is adjusted to make a standard mini light fade evenly from 0 to 100%.

[Jeffl]

I'm having a similar issue with a couple controllers.  One has one channel where it's just flaky.  Sometimes it works, sometimes it lightly pulsates. It's just one channel, all the rest are perfect.

The other controller has one channel that seams to slightly pulsate when it's all on.  Everything has been perfect until just the last couple nights when the temps have been below 0.  Right now it's about -3.  Last night was about -10.  I replaced the one and will have to test it when it gets warm.

I have spare parts and controllers so hopefully I can figure it out.