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It seems that I inadvertantly deleted the pic that I posted of the DT-40 pot assignments in this thread: http://www.photonlexicon.com/forums/...ght=dt-40+pots
Does anyone have a copy or can tell me what the pot assignments were? I was working on a show and my X scanner went nuts. Now that I have that problem resolved it needs some serious tuning.
Thanks
Yaddatrance does a great write up here:
http://www.photonlexicon.com/forums/...ead.php?t=2266
there is a PDF attached to the post about 3/4 the way down. There are some great tips there and things you can do to bypass some of the nonsense that was incorporated into the DT-40s because 'the other guys were doing it'
Thanks mliptack, that thread is regarding the DT-40pro's. I'm looking for the pot assignments for the original DT-40's. Unfortunatly, quite a big difference between the amps.
Oh shoot.... sorry, I just glanced over the post. My mistake.
Well with my stupidity aside... sorry I can't help you out then :o
No problem, thanks for trying though!Quote:
Well with my stupidity aside... sorry I can't help you out then :o
Ok, so I thought I had the issue fixed, now it looks like I don't. Check out this video. Whatcha think? I've isolated the problem to the X amp, not the galvo. Visual inspection yields no clues. I pulled out the O'scope and check around a bit. What I've found, is that when it occurs, the signal from the amp to the galvos become cliped on both the positive and negative rails. Just still haven't figure out why.
Video is 17meg, not sure how to cut it down.
https://home.comcast.net/~djzurcher/dt40.MPG
Have you tried heating and cooling sections of the board to narrow it down to one area? Perhaps its a feedback problem?Quote:
Originally Posted by DZ
I haven't tried that yet. It could indeed be a heat problem, makes me wonder if the LM3886 IC is bonded well enough to the heat sink (Frame). The problem only seems to start with that particular abstract, which is rather complex. It seems to do rather well with everything else and its never had a problem with that abstract before.Quote:
Have you tried heating and cooling sections of the board to narrow it down to one area? Perhaps its a feedback problem?
I still could use the pot assignments if anyone has them.
Thanks
Hmm,
If its a problem with a abstract, perhaps it has something to do with the power limiter?
I'm not sure, the Y axis is completely unaffected. I've displayed that abstract for a few minutes and the Y never collapsed. Oh well, I'll have to play around with it more tomorrow. I'm starting to think that it is heat related. Perhaps, if there is any thermal compound between the audio amp IC and the heat sink, maybe it has broken down and is now acting more like an insulator. If thats the case, eventually it will happen on the Y axis. Anyone else experience strange issues like this with the original DT-40's? Aside from this small problem, they've been flawless for me. Must have something to do with that damn smiley in my avatar, how did that get there I wonder? :pQuote:
If its a problem with a abstract, perhaps it has something to do with the power limiter?
I've had the X galvo collapse when displaying a complex abstract at too high a scan rate with my original DT-40's. In fact, there was an image in the original version of my "Pop Music" show that would kill my X galvo each and every time I played the show, so long as the speed was at 30Kpps and the scan size was set to anything above 20%. I finally deleted the image from the show to prevent it from happening.
The only way to get the X galvo to come back was to kill power to the scanner amp and then power it back on. When I did that, it would come back on just fine and continue to perform just fine. But it only took about 5 seconds of displaying that one file to cause the amp to drop out again.
I haven't tried that pattern with the DT-40 PRO's yet, so I don't know if it will kill them or not. (my guess is, not.) I believe that the cause of the problem is some sort of built-in over-current protection on the amp that cuts it off. That, or else it's a safety circuit that kills the amp if the galvo lags behind the points long enough and with a large enough error... I dunno for sure, but I know that I can reproduce the problem at will.
EDIT: Ok - I just watched your video, and yep; that's the same behavior I experienced. Except that once my X axis collapses, I have to cycle the power to the amp to get it back. (A quick down and up is all that is required - less than a second total.)
Adam
Ok, problem resolved. Took a bit of digging and going down alot of wrong roads. It ended up being a fuse, well, I suspect its a fuse anyway. On the board the component is labeled FU, and I suspect the SE was just dropped. I have not been able to find any details about it online, here is a photo of it. Maybe someone out there has some more info about it. Its a dead short, however when the problem occurs it seems to develope a high resistance yet doesn't completely open. With the component removed and a bare wire in its place, its worked fine with that abstract for 10 minutes straight.
Adam, are you still using the original DT-40's? Might want to try shorting this component and see if it solves the problem you were having. I'm going to leave it in place on the Y amp and see if it will eventually fail.
That would be a polyswitch. Its much like a self resetting fuse.. Goes open when too much current is drawn, but then self resets..
Sounds like the abstract is a bit too taxing for this particular scanner...
Thanks Dave! Would you happen to know what the specs are for this component? I'd like to test it and see if its out of tolerance. If it is, then problem solved. If not, then maybe I have more issues to deal with. With it out, the head runs fine, ilda test pattern at 30K is as good as it gets.Quote:
That would be a polyswitch. Its much like a self resetting fuse.. Goes open when too much current is drawn, but then self resets..
Sounds like the abstract is a bit too taxing for this particular scanner...
I had a feeling it was some sort of overload protection. Would be interesting to see if it really is out of spec, or if the pattern is just too much for the scanners. (Would hate to short it out and then blow the galvos!)
Adam
Quote:
Originally Posted by DZ
You could always swap the polyswitches between scanamps and see if the problem moves or stays with the same amp.. I guess that would quickly tell you if the polyswitch is the issue..
Thats not a bad idea! I may give that a try. I also found the specs for that polyswitch: http://www.littelfuse.com/data/en/Da...elfuse_30R.pdf So now I know what it should be capable of. I'm still betting its out of tolerance, since when the abstract is being displayed, its taxing the Y amp just as much as the X amp. Unless of course the Y amp polyswitch is over-tolerance!