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-----Original Message-----
From: Electronics_101@...
[mailto:Electronics_101@...] On Behalf Of Randy
Sent: quinta-feira, 27 de Janeiro de 2011 6:42
To: Electronics_101@...
Subject: [Electronics_101] Sony replacement parts

I have a Sony 400 disc DVD changer model DVP-CX995V. My
repair man says it needs the laser assembly and it has now
been at his shop for over eight months. He is not a ripoff
guy, he used to live in my apartment building and was friends
with everyone and his shop is in good standing with the
Better Business Bureau. His parts supplier did verify
receiving his parts request, so, I am wondering if anyone can
shed some light as to why it is taking so long to get the
Sony part that he needs.

Thanks.
Randy

I'm trying to determine the best way to hook up to the connector shown in the Photos section under Miscellaneous/unknown.connector.jpg.

It is a stepper motor driver board. I have searched the internet by the board's id and found nothing. I can not find any product ids on the connector itself.

Any suggestions?

Thanks

Bill

I wonder why TV manufacturers never thought of adding a fan.

Because they want it to break sometime after the warranty is over so
they can sell you a new one.

Ben

I wonder why TV manufacturers never thought of adding a fan.

Because they want it to break sometime after the warranty is over so they can sell you a new one.

Ben

The layer of oxide is not static, it is in a dynamic equilibrium. That is one of the reasons why there will always be a small leakage current. As parts of the oxide lose oxygen atoms and become conductive, a little bit of current forces the aluminum atom to oxidize again.

That is why antique electronics should never be just plugged in and turned on when they've been off for a long time. If you do, then a high leakage current may flow, causing a lot of heat and the caps will fail. Sometimes catastrophically, sometimes the fuse just blows.

We call it "reforming the electrolytes", and we don't mean that we send them to a bootcamp for teenage delinquents. You connect it to a variac (variable power transformer) and start with it at a low voltage and bring it up slowly over a period of days or weeks while monitoring the current draw and temperature of the electrolytic capacitors.

In normal operation, this oxide layer is constantly losing oxygen and then being "reformed" (reoxidized) by the leakage current.

Running an aluminum electrolytic capacitor at well under its rated voltage will cause the oxide layer to not reform correctly and the leakage current may rise. Then the heat can cause pressure that causes leaks around the seals, drying out the electrolyte.

You do need to make sure that the voltage rating is high enough for the peak voltage that the cap will see.

I don't have a link to give you, I learned this long ago. Since most engineers get it drummed into them to save costs and so parts get derated as little as possible, this is more of something that techs learn through experience.

Steve Greenfield AE7HD

That's just not plausible. The dielectric layer will always be sufficient
for the applied voltage, it is a self regulating process. It might not be
sufficient for the rated voltage if operated for very extended periods very
much below it, same as if it was stored without any voltage, but even that
condition can be rectified by reforming. There is just no mechanism that
causes a capacitor to fail sooner if operated at lower voltage. Just the
opposite, if you use a 400V capacitor in place of say a 25V one it will last
much much longer simply because the can is physically much larger which
always leads to a higher lifetime. I regularly replace capacitors in old
test gear with the largest can size that can be accommodated, which means a
higher voltage rating at the same capacity.

There might be things tech learn through experience, but there might
actually be things the capacitor manufacturers know for sure and techs may
just have misinterpreted.

Anyway this whole reforming issue isn't of all that much importance unless
you are dealing with decades old equipment. Even then it is usually not
needed. Only very old gear (with linear supplies) may be powered up with a
variac, and even there are dangers such as overloading components with the
low input voltage, regulator valves for example.
The jury is divided over the idea, and the only undisputed way to reform
capacitors in such situations is by feeding the internal supply rails with
external current limited supplies. Not worth worrying about in all but the
most exceptional circumstances.

ST

On Wed, Jan 26, 2011 at 11:08 PM, AlienRelics <alienrelics@... <mailto:alienrelics%40yahoo.com>> wrote:

Running an aluminum electrolytic capacitor at well under its rated

voltage

will cause the oxide layer to not reform correctly and the leakage

current

may rise. Then the heat can cause pressure that causes leaks around the
seals, drying out the electrolyte.

Running an aluminum electrolytic capacitor at well under its rated voltage
will cause the oxide layer to not reform correctly and the leakage current
may rise. Then the heat can cause pressure that causes leaks around the
seals, drying out the electrolyte.

Steve,

Do you have a reference for that? I have never heard that before and
would like to understand the science behind it.

Thanks,

Ross

On 26/01/2011 12:53 PM, AlienRelics wrote:

Do NOT give in to the temptation to get caps with much higher voltages. Electrolytics must run at something not to far under their rated voltage.

I'm not sure what the voltage derating is supposed to be, but I usually try not to use caps at less than 70% of their rated voltages.

Steve Greenfield AE7HD