T
tuinkabouter
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On 7/8/2013 4:36 PM, Arfa Daily wrote:
But then they sell less. Remember the TV sets working for 20 years or more.
Now they cripple the equipment. Most flat screen TV sets do 5 to 8 year.
Probably it is intentionally."Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b3uqfmFc5lbU1@mid.individual.net...
"Arfa Daily"
"Phil Allison"
** Would you be thinking of low value electros ( like 1 or 2.2 uF at
400V ) that are used to " kick start" SMPS ?
I was thinking more the typical 47uF 35v ones that hang across the
supply pin to the controller IC,
** Like the UC3842N ?
Yes, that series of IC. There are quite a few UC38xx chips about
see so many caps in that position that are high ESR and stop the
supply from starting, that I order them fifty at a time.
** So you are doing warranty work on home studio powered speakers that
run 24/7 ?
I do work for several hifi shops, and see quite a few powered subs, some
of which have switchers in them, and suffer from caps, but I also do a
fair bit of work on other items that are powered 24/7 like DVD players /
home cinema systems and set top boxes.
And one particular supply that I repair lots of for a company, has
the Yellow Glue syndrome as well, and where is it ? Yep, all around
the base of that same 47uF cap ...
** The PSU board in the " Alesis M1 Active" - right ?
The actual one that I was thinking of is from a commercial hot drinks
machine. The company that sends me them, has them rented out into
workplaces and takeaways and educational establishments all over the
country, so there's never any shortage of them for repair. It has a
small vertical sub-pcb that has the switch mode controller and driver on
it. The 47uF is laid over on its side, and then fixed to the board with
the dreaded yellow glue. The actual mix of faults is about 50 / 50. If
the glue has started to go brown, chances are that's the primary
problem, and the cap is actually ok, reading normally on the ESR meter.
If the glue hasn't gone yellow, then most times, the cap reads bad. But
to be honest, whether it's actually cap or glue, I always just go ahead
and remove the cap, clean up the board, and then fit a new cap. They are
so cheap, it's not worth doing anything else and risking it bouncing a
couple of months later.
Where the problem is not due to bad electros at all.
But a 2W resistor that almost touches the cap and heats it to a high
temp for 8,760 hours per year.
Yes, I've never understood this. It seems to be almost a 'design rule'
that any electrolytic should be mounted as close to a heat source on the
PCB as possible ... Anyone in the repair business knows that this is
going to lead to problems after not too long a life. If I suspect a cap
problem on any piece of circuitry, the first ones that I check are those
near to big resistors and heatsinks. How come this has never managed to
get back to the designers, and the supervisors who approve the designs ?
First manufacturers learned how to make almost perfect stuff.Seems to be common across all manufacturers.
But then they sell less. Remember the TV sets working for 20 years or more.
Now they cripple the equipment. Most flat screen TV sets do 5 to 8 year.