Digicrystal SDT-9077P STB remote control problems

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    I've been investigating intermittent temperature-related strange
remote control operation in a brand new SDT-9077P. When some buttons are
pushed and held down e.g. 'Menu', it behaves as though the button's
being pushed twice or more, very quickly.
    Turned out that the 47uF electrolytic cap in parallel with the
battery had an ESR of 16 ohms and might as well not have been there.
Replacing it with a decent quality 220uF completely fixed the problem.
    There are lots of complaints about this issue with the SDT-9077P on
various forums. Looks like a batch of defective electrolytics have found
their way into these remotes.
    To open the case, push your thumbnail into the gap between the top
and bottom case mouldings at the end furthest from the IR LED, then
carefully pop the clips apart on each side until you get to the LED end.


Bob





Re: Digicrystal SDT-9077P STB remote control problems

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Hi Bob. A bad electrolytic across the battery used to be a problem for all
sorts of remote controls a few years back. Seems that they drive the IR
LED(s) at a very high pulse current to get a long range, and the internal
resistance of the batteries is too high to allow them to supply it, so a low
ESR cap supplements them during the pulse peaks. Interesting the sort of
symptoms that you got from this one. Typical symptom from the ones that I
mention, was poor range. Maybe in the case of the Digicrystal, the battery
voltage was dropping low enough on the peaks, to upset the IR code generator
IC in there ?

Arfa
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Re: Digicrystal SDT-9077P STB remote control problems
Good Information Gents,
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From frozen Michigan, US.

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Re: Digicrystal SDT-9077P STB remote control problems
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Hi there Art in Michigan & Art in England,

    If it's any consolation, we've just ended the coolest summer since
about 1956. :-(

    This remote control uses a SC6622 chip which has a minimum operating
voltage of 2.2V.

    It was difficult to connect an oscilloscope across the battery
voltage to see exactly what was happening, but I suspect that after
sending out the first code burst, the battery voltage momentarily dipped
low enough to reset the chip, causing it to send the 'leader' bits out
again as though the button had been released then pushed again.

    Yes, they pulse the IR LED to relatively high current levels. As far
as I could tell by looking at the PCB tracks, there's only a 2.2 ohm
resistor in series with the LED.


Bob

























Re: Digicrystal SDT-9077P STB remote control problems
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That sounds a very reasonable assumption. I guess that the only way that you
would see it for sure, would be with a storage 'scope, but as you say, it's
difficult to work on these things with the batteries connected, and the case
open ...

Arfa




Re: Digicrystal SDT-9077P STB remote control problems
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   At least you didn't have to put battery blankets on the kangaroos.
;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
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Re: Digicrystal SDT-9077P STB remote control problems
On Sun, 02 Mar 2008 23:28:28 +1100, Bob Parker

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I'm betting that fresh alkaline batteries wouldn't exhibit this
problem. Did you measure the ESR of the batteries?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Digicrystal SDT-9077P STB remote control problems
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    I didn't measure the ESR of the batteries but I agree. The unit and
remote were only one week old. It took that long for the impedance of
the cheap horrible Chinese carbon-zinc AAA cells supplied with the
remote to increase enough to make it start playing up.

Bob


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