"Arfa Daily" wrote in message
...
"b" wrote in message
...
On 23 ene, 04:51, "G B" wrote:
Hi,

I have a Sony SLVN750. It failed such that it had no time display and
would no longer power up when pressing the power switch. I tore it
apart
and "shot-gun" replaced the nine capacitors in the general area of the
power
supply with capacitors of the same value. It now will power up and
even
play a tape BUT when it is powered down (in standby) the display
blinks on
and off. It seems the power supply is cycling on and off. Any idea
what
would cause this? Any help is appreciated...


"G B" wrote in message
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The display isn't flashing per say...

The display goes blank after the supply apepars to shut itself down. It
returns after say 500 msecs.. then stays on for about a second.. then
goes blank and starts again. Also every time the display blinks, the
carriage motor appears to go through its position check...
I did replace the all the "big" electrolytic caps.. the largest were a
couple of 1000uF... I suspect that section of the circuit is working
properly.. I think there must be a standby power section of the circuit
which is toast... any ideas?


Have you replaced any electros in the front end or were they all secondary
side ? This sort of odd behaviour in switchers can be symptomatic of small
caps - often only from 1 to 47uF in value - situated around the oscillator
/ control IC having gone high ESR. You will often find them located close
to some other component or heatsink, which runs hot. Do you have an ESR
meter ? Just as an aside, it makes a thread and the replies much easier to
follow if you bottom-post rather than top. :-)

Arfa



I replaced 9 caps all in the area of the switcher, or at least where I think
the switcher is. I replaced the large regulation cap (82uF @ 200V) and I
replaced a small (4.7uF@50V) on what I would consider the primary side.
(prior to the large transformer). I replaced all the electorlytics: 10uF,
100uF, 330uF, 470uF, and 1000uF values on what I think is the secondary. Do
you know if the switcher provides the boot-strap voltage in standby mode?
Or do they have another regulator somewhere off the line regulation
circuitr? I have also what appears to be a hot-spot on the circuit board
around QIP107, RIP110, QIP108, ZDIP05, and DIP109. It doesn't feel warm to
the touch after it has been running for a while.. so the hot-spot is a bit
of a mystery. I don't have an ESR meter here. I guess I could probe the
removed components at work... of course I don't know what the ESR of the
original caps. I thought I could use a DMM to get an indication, but it
must be marginal enough I can't tell which one is the bad actor.

As for the posting at the top vs bottom... thank Outlook for always starting
at the top rather than the bottom of the post