On 2/03/2008 23:00 Art wrote:
Good Information Gents,
Thanks for the post, and a specially G'day to you, Bob Parker!!
From frozen Michigan, US. {art}

"Arfa Daily" wrote in message
...

"Bob Parker" wrote in message
...
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


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


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