P
Phil Allison
- Jan 1, 1970
- 0
Hi to my pals here,
In October 2005 I bought myself a DSE G7659 STB.
It worked like a charm for 17 months or so. Then, it began to misbehave just
as the Commonwealth Games was being broadcast from Melbourne - first just
a few pixellations, cracking noises and the odd audio muting. This soon
became much worse and affected all digital channels.
It *had* to be the STB and it was exhibiting the same symptoms reported by
others on usenet.
Once on the bench and open, I probed the various rails coming from the
MPS - a separate module on its own PCB.
The 5 volt rail showed a bit more HF noise than I expected but all voltages
were OK. I left it powered off overnight ( no AC supply) and the next day
the symptoms were drastic, ie no pic at all !
This time the 5 volt rail measured only 3.4 volts with even more HF noise
than before - I reckoned that would stop the processor in its tracks all
right.
With the aid of my trusty Bob Parker ESR meter, it was soon clear that both
the 1000uF, 10 volt electros ( Asiacon brand) on the 5 volt rail had gone
high ESR - to about 1.5 ohms each !
New ones tested only 12 milliohms and were soon installed and that fixed the
5 volt rail very nicely and returned the unit to full operation.
The PROBLEM with the G7659 SMPS is that all the electros are tucked under
an L shaped heatsink that runs hot - circa 75 C even with the box in free
air.
The easiest, permanent fix is to install a 40 mm, 12 volt, 0.6 watt fan
blowing onto the heatsink. The wiring loom from the SMPS to the main PCB can
be easily broken into to access the +12 volt rail and 0 volts.
The full 12 volts not necessary fro the fan and as little as 8.5 volts does
the trick as far as cooling the heatsink is concerned. This involves fitting
a series resistor of about 100 ohms and an electro across the fan of
220uF - without the electro the fan may not start on power up.
........ Phil
In October 2005 I bought myself a DSE G7659 STB.
It worked like a charm for 17 months or so. Then, it began to misbehave just
as the Commonwealth Games was being broadcast from Melbourne - first just
a few pixellations, cracking noises and the odd audio muting. This soon
became much worse and affected all digital channels.
It *had* to be the STB and it was exhibiting the same symptoms reported by
others on usenet.
Once on the bench and open, I probed the various rails coming from the
MPS - a separate module on its own PCB.
The 5 volt rail showed a bit more HF noise than I expected but all voltages
were OK. I left it powered off overnight ( no AC supply) and the next day
the symptoms were drastic, ie no pic at all !
This time the 5 volt rail measured only 3.4 volts with even more HF noise
than before - I reckoned that would stop the processor in its tracks all
right.
With the aid of my trusty Bob Parker ESR meter, it was soon clear that both
the 1000uF, 10 volt electros ( Asiacon brand) on the 5 volt rail had gone
high ESR - to about 1.5 ohms each !
New ones tested only 12 milliohms and were soon installed and that fixed the
5 volt rail very nicely and returned the unit to full operation.
The PROBLEM with the G7659 SMPS is that all the electros are tucked under
an L shaped heatsink that runs hot - circa 75 C even with the box in free
air.
The easiest, permanent fix is to install a 40 mm, 12 volt, 0.6 watt fan
blowing onto the heatsink. The wiring loom from the SMPS to the main PCB can
be easily broken into to access the +12 volt rail and 0 volts.
The full 12 volts not necessary fro the fan and as little as 8.5 volts does
the trick as far as cooling the heatsink is concerned. This involves fitting
a series resistor of about 100 ohms and an electro across the fan of
220uF - without the electro the fan may not start on power up.
........ Phil
