Scanner Problems

[norty303]

Do you really need to be scanning beam shows at 30k?
Taking 5 to 10k off the scan speed should stop the problem I'd have thought with no easily discernable difference to the show.

[buffo]

The problem is almost certainly caused by pushing your scanners too hard. It's common among the DT-40's, and while the behavior might be annoying, it beats the alternative: (other scanners just keep building up heat until they fail catastrophically). Buying a larger power supply to power the amps and/or shorting out the polyswitch won't solve the problem, but it is likely to result in early scanner death.

As Norty suggested, try reducing your scan speeds a little. That will allow you to scan wider before running up against the limits of the scanners, and for beam shows you'll never notice the speed difference. But if you expect to be able to scan graphics at 30K speeds with 75% of full angle deflection, you are living in a pipe dream. Even the most expensive scanners on the market today (Cambridge 6215 HC's) can't do that.

To figure out how wide is too wide for graphics, start with the maximum scan angle that you can reliably run the ILDA test pattern. (The 12/24K pattern that is - not the one with the much larger square surrounding the pattern, but the original one that has just the pattern itself.) Go ahead and run a couple of tests; you want to stop increasing the size as soon as the center circle STOPS getting bigger (even if the rest of the pattern still increases in size) an/or starts to pull apart at the top. (It might also start to skew to one side in an oval shape.) A good rule of thumb is to never scan graphics shows at more than double the width of your max angle for the test pattern. Write down the size settings that you come up with, and post them on an index card so you (or your employees) won't forget.

Some simple graphics shows might let you push this to 3X the angle, but other shows will overheat your scanners very quickly once you go past the 2X size. In particular, shows that are very complex and/or shows that have lots of abstract elements are going to give you real problems when you exceed the 2X angle. Bottom line: if the graphics start to look funny, back off on the angle.

Finally, I should point out that it is possible that once scan amp has a bad polyswitch that might be triggering prematurely. In that case, however, you will notice that your scan angle is very shallow (close to the maximum angle that you can scan the ILDA test pattern at, but nowhere near 2X or 3X that size). From the description and pictures you provided, it does not appear that this is what is happening with your gear, but for anyone else reading this, it is worth mentioning that polyswitches can go bad...

Adam

[KGB]

Do you really need to be scanning beam shows at 30k?
Taking 5 to 10k off the scan speed should stop the problem I'd have thought with no easily discernable difference to the show.

Good point....But these are 40K... QS will only run them at 30k and i normally turn them down to 25k..I shouldn't need to turn them down that much.


After talking with Rob, I think im going to go with a pair of traco tmp 30124 http://www.tracopower.com/fileadmin/...sheets/tmp.pdf

Ill report back if this fixes the problem


-Brooks

[KGB]

The problem is almost certainly caused by pushing your scanners too hard...............

Thanks Adam. That's allot of great info and I'm definitely going to try those things you mentioned next time I have everything setup.... Ill also be running my next show at 15K to see if I can completely keep the problem from happening. I rarely ever do graphics so I can live with 15k if it works..... I just thought it was weird that one laser is always fine and the other always acts up... Do you think it would even be worth it to try and replace the scanner PS on the one that's acting up?



Thanks,
-Brooks

[DZ]

With the power off, carefully grab the edges of the mirror on either scanner and slowly turn it one way, then the other. If it feels gummed up or "crunchy" then it's a failure of the scanner and the polyswitch is just doing it's job. I've seen this a lot with the early DT-40's, but not so much with the DT-40Pros. Unfortunately, it seems to be a rather common failure mode for Chinese scanners, though I have felt crunchy bearings on a set of 6800's before. If it is a failing scanner you should be able to pick up a replacement for relatively cheap, drop it in and retune.

[dnar]

Talking of DT PSU's...

In my RGB projector, I run the Stanwax ILDA board from the scanner supply.

If I run really ludicrous abstracts wide wide scan angles then the PSU "blips", my interlock also trips (resets) and I can see that on my safety switch LED.

It kind of worked out well this way, it doesn't happen often but when it does I know I'm pushing things. Plus rather than have the scanners hammer on with the PSU cycling, the interlock kills the drive and I correct my driving habits.

[buffo]

I'll also be running my next show at 15K to see if I can completely keep the problem from happening. I rarely ever do graphics so I can live
with 15k if it works.

Hey Brooks;

I find that 15K usually looks just fine for beam shows. In fact, when I'm performing live, I have a slider on my Novation remote zero set to adjust the scan speed. I can adjust it from 30K all the way down to 8k, which makes for a cool "staccato" effect. (Great for bass drops, etc.) When I have a smooth section of music with less percussion, I run the scan speed up to 30K and select slow moving waves and fans, but when the bassline comes back on, I drop the scan speed, and the smooth fan becomes a stabbing, strobe-like pattern instantly. It's almost like having twice the number of cues available.

I just thought it was weird that one laser is always fine and the other always acts up...

It could be that one scan set is worn more than the other. Or, as DZ said, you could be developing a bearing problem in that one set. (Early DT-40's used to overheat, at which point the glue that was used on the rotor would melt and flow into the bearings. When it cooled, it created hard spots that felt "crunchy" when you moved the shaft.) Unfortunately, there's no fix for that apart from buying a new set of scanners.

I would check your scan angle first. Figure out how wide you can display the ILDA test pattern, and then see how much wider you are scanning when you have the size set to 75%. If it's more than 3X, then you are definitely over-driving your scanners. On the other hand, if at 75% size, you are only 2X of the limit for the ILDA test pattern, then you've either got a bad poly-switch or bad bearings.

Do you think it would even be worth it to try and replace the scanner PS on the one that's acting up?

I don't think it will help, no. As a quick and dirty test, you could swap the PSU with the other scanner in the second projector just to satisfy your curiosity though.

Adam

[norty303]

I scan all my beams at 18-20k, and use a scan speed fader like buffo does to 'bring the strobe'
18k is fast enough to give smooth flat beams and liquid skies.

[Phredy1]

I have had this happen with my DT40 too. What triggered mine to do this was moving the animation speed up too high. Turn off the projector for a few seconds and slow the animation down and everything was fine again.

[KGB]

I have had this happen with my DT40 too. What triggered mine to do this was moving the animation speed up too high. Turn off the projector for a few seconds and slow the animation down and everything was fine again.

that's exactly how I first noticed this problem...... How wide can you set your scanners in the projector settings menu of QS?