Film-Tech Forum ARCHIVE: BACP DSTR 2000 led current adjustment

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Posted by Jeff Else (Member # 4063) on 10-13-2009, 07:41 PM:

is there any? or do i just need to replace the led's? i can't get dolby tone!

p.s. mine is the version for the FP-20

Posted by Jeremy Weigel (Member # 4208) on 10-13-2009, 08:14 PM:

Is this a new unit or has it been in service for a while?

First make sure the optics are clean as well as the LED it self.

If its a new unit and you're not able to get an initial Dolby level (assuming you're trained how to do an A-Chain) then there is a set of jumpers you can cut on the main circuit board on the reader to increase the voltage.

If this is a unit that has been in service for a while and was correctly set up by your service tech and he/she achieved Dolby tone without cutting those jumpers, then your LED is probably nearing the end of its life cycle.

I am also assuming that you're using the supplied non-variable power supply that shipped with the unit.

Posted by Michael Schaffer (Member # 1204) on 10-13-2009, 08:21 PM:

You should *always* be able to reach Dolby level *easily* with a new BACP reader. The jumpers are only meant to be cut after the LEDs have exceeded a certain lifespan.

On the FP20, it is quite possible that the LED holder is rotated and so the light from the LEDs does not hit the lens properly.

Posted by Jeremy Weigel (Member # 4208) on 10-13-2009, 08:39 PM:

quote: Michael Schaffer
The jumpers are only meant to be cut after the LEDs have exceeded a certain lifespan.

Do you reconnect them when you install new LED's?

Posted by Monte L Fullmer (Member # 2797) on 10-13-2009, 09:32 PM:

You could have oil in the lens itself. For I also have a "20" unit doing the same thing.

I swapped LED modules from one house to the other and I did get some of my Dolby Tone back up. Thus suspecting I've got a oil filled camera tube that is causing my levels not to be up where they should be.

..and my jumpers have already been cut.

All LED units do fade after awhile .. if your system is over 7 yrs old, I bet you could use a replacement LED, or to make it tons more easy but a bit more on the dollar.. some new modules.

I wouldn't worry on redoing the jumpers after LED replacement - just adjust your preamp accordingly since the PC board that the jumpers are on doesn't have the exact space to work in.

-Monte

Posted by Sam D. Chavez (Member # 1841) on 10-14-2009, 01:13 AM:

You all get an A from the teacher.

It is however and RSTR-2000 not a DTSR 2000. The card has a DC to DC convertor so the input voltage is not very critical. 9 to 12 Volts is fine.

The cutting of the links increases the audio gain of the circuit as well as the background noise by 6 dB. Dolby wanted the electronics to be as quiet as possible, so the gain links were a way to optimize this.

The FP20 LED assembly is unique as there was almost no room for the LED so it is held in place with thermal heat paste, and is not plug and play like most other models.

Posted by Demetris Thoupis (Member # 833) on 10-14-2009, 01:14 AM:

I agree with Michael,
Check whether the actual bracket which holds the LED assembly has rotated downwards for some reason (someone aplied pressure or it was not tight enough). The easies way to do it is have Dolby Tone loop running and rotate that bracket until you have the brightest signal level LEDs on the FP20 circuit board. These readers aling like a charm.
Demetris

Posted by Jeremy Weigel (Member # 4208) on 10-14-2009, 01:19 AM:

I haven't cut any of the jumpers on the 6 units I have. I just replace the LED when I'm not able to reach tone any longer. I would think that if you cut the jumpers just for a faded LED and then put in new ones later it would shorten the new LEDs life or am I thinking incorrectly that cutting those jumpers increases the voltage to the LED? or do they just boost the signal without increasing LED brightness?

Posted by Monte L Fullmer (Member # 2797) on 10-14-2009, 04:28 AM:

question:

quote: Jeremy Weigel
or do they just boost the signal without increasing LED brightness?

answer...:

quote: Sam D. Chavez
cutting of the links increases the audio gain of the circuit

LED voltage remains the same... hope this helps

If you got tired LED's it's best to replace the entire module. If you take a module out and look at it from the back side, it would be a pain to desolder and resolder the LED back on that ribbon strip.

So, basically what Sam is hinting at, is, (for us that have our jumpers snipped) - to make things quieter: redo the jumpers after replacing the module. - Monte

Posted by Sam D. Chavez (Member # 1841) on 10-14-2009, 09:57 AM:

There is a little flat screwdriver slot on the LED arm to ease in moving the LED arm. If you need to move the arm, loosen the Philips screws holding the arm very slightly while running Dolby tone and move the arm up and down watching the Dolby tone meter to make sure you are at maximum level

It's LED current, not voltage as an LED is a constant voltage drop across it while the current varies. Small but important detail.

Posted by Tony Bandiera Jr (Member # 2365) on 10-14-2009, 12:18 PM:

Just installed a pair of DTSR-20 on my Kinotons, pics to come soon. Minor threadjack if I may: Sam, I need to switch the LED's on those DTSR-20's..which is better: switch before the LED power board or after? (The processor will be on 24/7 and I don't want to run the LED's if I'm not running film.)

Back to our regular scheduled program:

I second the suggestion by Sam to use the screwdriver slot to gently raise and lower the LED to get Dolby tone. Especially if the loss of level came on suddenly, it means the arm was bumped out of position, a design flaw of the projector itself not the reader. I have had service calls on Kinotons where the solar cell was bumped out of line by ham-fisted operators.

If you have access to a RTA and some Dolby CAT 566 Illum. Uniformity film, run that too to make sure the full LED array is still working.

Try that before replacing the LED or cutting jumpers. And also re-solder the jumpers after an LED change, it isn't impossible if you're patient and have a fine-tip soldering iron.

Posted by Scott Norwood (Member # 30) on 10-14-2009, 12:27 PM:

How does the output on the RSTR compare with a solar cell? What about when the jumpers are cut?

I had to cut both in a setup with a Kelmar mono system to approximate the output of the old solar cell (after adjusting the LEDs to maximize output, as described above). This needed to be done for both projectors (changeover booth). Is something else wrong here, or is this normal?

I've not cut the jumpers in any setup with a Dolby processor, and can hit Dolby level with no problem, although the cat. 240A has a much wider gain adjustment range than the Kelmar.

I've installed a few of these and have not had to replace the LEDs, although all are in venues that run film only occasionally.

Posted by Monte L Fullmer (Member # 2797) on 10-14-2009, 12:43 PM:

quote: Sam D. Chavez
If you need to move the arm, loosen the Philips screws holding the arm very slightly while running Dolby tone and move the arm up and down watching the Dolby tone meter to make sure you are at maximum level

Thx for this tip since some of us didn't know this trick. Dang, where is that old 'filament image on the card' trick when you need it.

-Monte

Posted by Sam D. Chavez (Member # 1841) on 10-14-2009, 01:35 PM:

The screwdriver slot is only on the FP20 version

The LED should be interrupted after the board.

As to low output on the Kelmar; there is a solar cell loading resistor across the Kelmar as in most mono systems that is no longer required. Once you do this the output will come way up.

Posted by Michael Schaffer (Member # 1204) on 10-14-2009, 10:55 PM:

quote: Sam D. Chavez
As to low output on the Kelmar; there is a solar cell loading resistor across the Kelmar as in most mono systems that is no longer required.

One would hope that mono systems as such are no longer required!

Posted by Scott Norwood (Member # 30) on 10-15-2009, 08:03 AM:

Michael--agreed, but some (most?) theatre owners are super-cheap, and it's hard to justify the expense of a quality sound system for a venue that runs film only a few times per year. (Heck, things would be worse if I weren't doing minor improvements for cheap/free. If it were up to me, I'd have the owner of the place use a legitimate service company, but he won't.)

Sam--thanks for the tip; I will check this out when I am there next.

Posted by Louis Bornwasser (Member # 3063) on 10-15-2009, 10:42 AM:

Still plenty of MONO around. Thankfully, most are now recycled Kelmar units. Louis

Posted by Tim Reed (Member # 137) on 10-15-2009, 12:03 PM:

I have a lot of mono houses - in the NYC area at that. We have been replacing old Cinemeccanica C-55/PT's and Kelmars with Pyramid PA amps. At $160, they're cheap enough to buy several for emergency backups. They have a built-in preamp, XLR inputs, rack mounted, and either a 1 or 2 year factory warranty (don't remember which)... beats $1,000 for the Kelmar - and cheaper than repairing one. The only thing is you have to build a monitor for it.

Posted by Scott Norwood (Member # 30) on 10-15-2009, 01:16 PM:

Tim--do those have inputs for two projectors? If so, are you stuck with exciter-lamp (LED) changeovers, or is there an electronic changeover mechanism? What about non-sync switching?

I'm actually on good terms with the Kelmar units to the extent that they are reliable, fairly quiet, and sound quality is decent. I would prefer to have an electronic changeover circuit and a remote fader option, but those are pretty far down on my priority list.

But, still, this is 2009, and normal people can go in to Best Buy and walk out with pretty decent surround systems for their TV sets for relatively little money. Is it too much to ask that commercial theatres that don't exclusively show classic films at least upgrade to 1970s technology (Dolby Stereo)?

Posted by Mark Gulbrandsen (Member # 72) on 10-15-2009, 04:26 PM:

quote: Tim Reed
We have been replacing old Cinemeccanica C-55/PT's and Kelmars with Pyramid PA amps. At $160, they're cheap enough to buy several for emergency backups.

Oh pleeze Tim... What you're doing doesn't make any sense!! Is that the sort of crap Strong Technical puts in? I tested one of those amplifiers out a number of years back at Gords suggestion. It's absolute crap. For the price of several of those which is what you said you buy you could buy a nice QSC and never have to worry about replacing it in your lifetime, Use the second channel to monitor with. Ciontinue to use use the QSC some day when the theater has to go stereo. Even a rebuilt/recycled Kelmar makes more sense, is better built and more reliable!

Mark

Posted by Tim Reed (Member # 137) on 10-15-2009, 07:05 PM:

quote: Scott Norwood
Tim--do those have inputs for two projectors?

Yes. There are 4 inputs. It's decent for the money and reliable.

Mark: [fu]

Posted by Mark Gulbrandsen (Member # 72) on 10-16-2009, 11:27 AM:

Thats ok Tim,

You go right ahead and continue installing them [thumbsup]

! I've bench tested them and know how bad they actually are. You haven't had that luxury!

Mark

Posted by Jeff Else (Member # 4063) on 10-16-2009, 05:21 PM:

woops... rstr indeed... i wish they were dstr's! these were oreviously installed and running for about 5 years i think. i have tried adjusting the led position to no avail... looks like new led's will be needed.