G B said:
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
Yeah, that's a problem with it. Nobody gets too upset on here, but on some
groups they get *really* arsey if you do it. Top posting can sometimes
confuse a thread, especially when specific questions are being answered, and
the majority are posting one way, and someone is posting the other ...
As to your question, I would expect that the standby supplies for the system
control micro are derived from the switcher, but I couldn't say for sure.
It's been a while since I did any work on any VCRs, Sony included. Knowing
what the ESRs of the original caps should be is not really an absolute. As I
have commented a number of times with regard to using ESR meters, a lot of
it is intuition, with the meter just acting as a backup. In general, the
smaller the value of the cap, the higher its ESR will read on a meter. The
small ones, such as your 4.7uF, should not read higher than a few ohms. 47uF
up to say 220uF should not be higher than a couple of ohms. Above this
capacitance value, ESRs will generally be in decimals of an ohm, and a
factor of 10 lower than that for the 'big' values of 2200uF and up. In
general, the higher the voltage working, the lower the range of ESR values
that would be 'normal' for any particular cap. Usually, if a cap has reached
a point where it is causing trouble in a switcher, its ESR value will have
gone off with the fairies, and be easily spotted as the bad one.
Interestingly, its capacitance value will often read near enough correct on
a C - meter.
What your remaining problem is, I really don't know without looking at a
schematic for the power supply, but one thing I would say is that it seems
odd that you have managed to cure the primary problem with replacing
whichever cap it was amongst the ones that you changed, and then been left
with this slightly 'odd' problem. A faulty cap is a good call for the
original problem, and was almost certainly the correct diagnosis, but it is
very rare, when this is the case, for there to be any other issues. If it
were me, I think that as a first move, I would go over all my work again
very carefully, making sure that I had got the right values in the right
places (for that you would need a schematic), and that I had not
accidentally put any in backwards (easily done :-\ ). Also, make sure that
the replacement types are 'suitable' i.e. the correct or very close value,
similar voltage working, low ESR type. They should also be 105 degree or
better types for future reliability. Also, I would not trust any caps that
you have had lying around in a drawer for years, or any radial leaded types
as being suitable.
Stating the obvious maybe, but also be sure that your soldering is all good.
If it's not something which you do all day, it is easy to get a poor joint
on a component, without realising it ...
Arfa
