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Digicrystal SDT-9077P STB remote control problems

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

Reply to
Bob Parker
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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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Reply to
Arfa Daily

Good Information Gents,

From frozen Michigan, US. {art}

Reply to
Art

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

Reply to
Bob Parker

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

Reply to
Arfa Daily

At least you didn't have to put battery blankets on the kangaroos. ;-)

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Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

On Sun, 02 Mar 2008 23:28:28 +1100, Bob Parker put finger to keyboard and composed:

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

- Franc Zabkar

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Reply to
Franc Zabkar

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

Reply to
Bob Parker

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