Film-Tech Forum ARCHIVE: dts processor sound failure

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Posted by Bajsic Bojan (Member # 4928) on 07-12-2011, 11:54 AM:

hello, looking for input:

DTS XD 10P sound processor,

we get signal to the processor, input LEDs light up well,
output LEDs light up well, no failure LED lights up.

on the output we get nothing but an occasional pop (when i run a loop through the projector, at the splice). So basically, really really low noise and loud "pop". No audio.

Tried with different audio output cables, made new ones, tried with different input cables from projector, no change.

Sometimes the unit works well for only 5 minutes or 2 hours, then the sound becomes hissy and distorted and then goes out. Sometimes it runs for 10 days. It is not running hot now but did once overheat probably (when we first noticed this problem).

Any ideas what i can try?

Posted by Bajsic Bojan (Member # 4928) on 07-13-2011, 01:06 PM:

just an update, hopefully someone can chime in:

- same problem present on all inputs (even nonsync)
- same problem if i change to projector2 input
- when connected through the pc programme, pink noise sent from the processor is not heard
- re-seated all three boards, no change
- when re-seating only the fader board and reseting the processor, i get sound for 2-5 seconds, then it quickly distorts, starts hissing and poping and goes completely dead in about 1 minute

was told by passing technician its probably a fader board failure and i should try replacing that (since i own the only dts processor in the country, that just might be a challenge)

Posted by Marin Zorica (Member # 1716) on 07-13-2011, 05:28 PM:

Also it can be problem in analog power supply lines, so symetrical +/-15V and capacitors near IC's which are on that rail of supply. Don't know how much are you experiance in electronic, but try to look on those.

Posted by Bajsic Bojan (Member # 4928) on 07-13-2011, 05:47 PM:

will check out with local electronic tech, but from looking at it all capacitors are ok, the boards look good, no dust, no junk or anything, they are 2 years old

Posted by Harold Hallikainen (Member # 5405) on 07-13-2011, 10:54 PM:

Some have mentioned power supplies. All the digital circuitry is run off the 5V supply, and much of the analog is run off the +12V and -12V supplies. There are front panel LEDs to tell you if the supplies are working.

In your original post, you indicate that the input and output LEDs light, indicating signal presence. I assume you see flickering LEDs on the output board (the middle one) with audio and the LEDs go out when there's no audio. The left channel audio output LED is driven by U25B, which is driven by U4D, which drives the negative side of the balanced audio output. The only thing between this chip and the output connector on the rear panel is the solid state mute switch (U5A and U5B for the left output). So, I'm wondering if there's something wrong with U5 or the signal that drives it. When not muted, U5-16 should be +5V. If it is not, the system "thinks" it is muted. Does the control processor seem to otherwise be working (buttons and LEDs work, fader changes display, etc.)? If so, you may have a bad UCN5832 on the control card (far right). This chip drives the parallel automation outputs AND the mute switches. The chip is in a socket. It should do no harm to pull it out of the socket. Parallel automation outputs won't work anymore, and mute won't work anymore. But, that may bring back your audio.

Good luck!

Harold

Posted by Bajsic Bojan (Member # 4928) on 07-14-2011, 08:32 AM:

great reply, thanks for the input. i will try it today to see if it this chip on the control board. loosing the automation is not an issue as we don't use any, i think i can survive without the mute button too.

Just as a side note :

quote: Harold Hallikainen
In your original post, you indicate that the input and output LEDs light, indicating signal presence. I assume you see flickering LEDs on the output board (the middle one) with audio and the LEDs go out when there's no audio.

not true. the LEDs light and flicker on both input and output boards, even when there is no audio in the speakers. LEDs dont go out.

Posted by Marin Zorica (Member # 1716) on 07-14-2011, 05:28 PM:

I supposed that led's are flickering without audio, that's why I did suspect on power supply. I do service many of DSP processors and they first start to act crazy because of power supply, even I know on some DSP processor you have +5V, but on scope you can see some AC ripple coused by bad cap's and that can start problems, also to just look cap's on them is not enought. I had problem with one Sony output cards, there were almost no sound on one of channels, even system test was OK. Problem was in bad capacitor which was connected to D/A converter reference voltage, even cap did look just like new, it was bad.....

Posted by Harold Hallikainen (Member # 5405) on 07-14-2011, 09:18 PM:

OK, sorry I misread the original post. The output LEDs do watch the audio just prior to the mute switch. Of course, there should be nothing there with no audio in. So, it may be something else, including bypass capacitors as mentioned by others. On working on these, it's nice to do board swaps to get an idea as to which board has the problem. I recognize that's difficult for you to do without an additional unit.

Good luck!

Harold