Leaky Electolytics in Philips 'scope

[Arfa Daily]

Whilst it was out of the scope I did test it and it was dead; no chopping
and no supply volts even to the PWM chip. HOWEVER, ISTR from somewhere
that these things shut down if they don't see a load, so I'll leave my
"outthinking" behind for a mo (you're not the first to say that) and
reconnect everything back in circuit and re-try.
I'll report back in due course.

Be very very - and I mean VERY - careful what you are measuring, and how.
For a start, you should never work on a switcher without having it on an
isolation transformer. Secondly, it's not easy to safely measure voltages on
the primary side of the PSU without knowing what you are going to use as a
ground reference for your meter or scope. Usually, it's the -ve side of the
bridge reccy, but always check the schematic to be sure. In the case of the
Philips, that does appear to be the right place. Bear in mind we are talking
peak rectified mains here, limited in current capacity only by the value of
any primary side fuse. Skull and crossbones stuff ... If you are not
confident measuring with two hands in this sort of environment, solder a
wire to the -ve reference point and clip your meter -ve probe to it. Then
put the hand that you would have been holding that probe with firmly in your
pocket, and don't bring it back out again until you've finished measuring
and moved away, or turned it back off. Even with it operating on an
isolation transformer, you aren't safe against hanging yourself *across*
either the mains input or the output side of the bridge. I'm sure that you
probably know all this, but better safe than sorry, and worth mentioning for
any other readers who might not be aware of the potential dangers of working
'live' on switchers ...

Supply volts for the PWM chip are on pin 1, and are supplied initially from
the rectified mains via the circuitry around V1803 and 1804. Once the supply
gets going, it is self-supplied via the diodes at V1816, 17. I don't
immediately see any active feedback from the secondary side, so I would be
surprised if it didn't at least try to start without secondary side loads,
but switchers always have the capacity to do things that you don't expect !
There is some DC feedback from the primary side via V1818 and 19, but I
would still expect it to start whilst monitoring for a control voltage
coming back from there. It looks as though it uses the level of voltage from
there to control the PWM output to set the base level of output volts and
keep them stable against secondary side load.

I have a copy of the datasheet for the chip if you would like me to send it.
It details the operation of the chip pretty well, and shows some sample
implementations of it which are pretty close to how it's being used in the
Philips, if you can get your mind to re-arrange the way they have been drawn
....

Arfa

 

[Arfa Daily]

I managed to get a DS for the chip pretty quickly, it was the scope
schematics that were the big problem. I'll have to check out that site
you mentioned in your email and see what's there. I've got another 2 or 3
Philips scopes to sort out when this one's done so I'm sure it would pay
off.

If you use Google to search for service info, elektrotanya.com and
eserviceinfo.com are often right at the top. I usually use the search string

manufacturer - model - free schematic download. You can of course use + and
" " operators (and others) in the string to make it more specific

elektrotanya tends to yield better results in that eserviceinfo will often
find anything in its database which matches any of your search criteria,
whereas any elektrotanya 'hit' usually takes you straight to the manual.
It's not immediately obvious how to get the manual, though. Ignore all the
big "Download" buttons that you see dotted around. These are all for
'helper' software or PDF readers. Look in the text block under the preview
pane, and you will see the word "processing" in a different colour. Small
and hard to spot. After a while - and I have known it to be several
minutes - the word will change to "get manual". If you then click on it, the
download process will start normally, and depending on your computer OS and
what antivirus blockers you have, you will probably get the "do you want to
open / save "etc dialogue box

Arfa

 

[Cursitor Doom]

On Sun, 29 Mar 2015 02:47:52 +0100, Arfa Daily wrote:

If you use Google to search for service info, elektrotanya.com and
eserviceinfo.com are often right at the top.
[...]

Cheers, Arfa. You're a diamond.

 

[Ian Field]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:hRIRw.491026$7E1.151824@fx31.am4...

I managed to get a DS for the chip pretty quickly, it was the scope
schematics that were the big problem. I'll have to check out that site
you mentioned in your email and see what's there. I've got another 2 or 3
Philips scopes to sort out when this one's done so I'm sure it would pay
off.

If you use Google to search for service info, elektrotanya.com and
eserviceinfo.com are often right at the top. I usually use the search
string

manufacturer - model - free schematic download. You can of course use +
and " " operators (and others) in the string to make it more specific

elektrotanya tends to yield better results in that eserviceinfo will often
find anything in its database which matches any of your search criteria,
whereas any elektrotanya 'hit' usually takes you straight to the manual.
It's not immediately obvious how to get the manual, though. Ignore all the
big "Download" buttons that you see dotted around. These are all for
'helper' software or PDF readers. Look in the text block under the preview
pane, and you will see the word "processing" in a different colour. Small
and hard to spot. After a while - and I have known it to be several
minutes - the word will change to "get manual". If you then click on it,
the download process will start normally, and depending on your computer
OS and what antivirus blockers you have, you will probably get the "do you
want to open / save "etc dialogue box

Have you got a link for that?

The one I found isn't in English, so I don't know whether I'm seeing the bit
you describe.

But then I've recently stripped and re-installed my browser to sort some
problems - I had a translate button then, now I don't.

 

[Arfa Daily]

"Ian Field" <gangprobing.alien@ntlworld.com> wrote in message
news:GuXRw.192255$ID3.162851@fx01.am4...

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:hRIRw.491026$7E1.151824@fx31.am4...




I managed to get a DS for the chip pretty quickly, it was the scope
schematics that were the big problem. I'll have to check out that site
you mentioned in your email and see what's there. I've got another 2 or
3
Philips scopes to sort out when this one's done so I'm sure it would pay
off.

If you use Google to search for service info, elektrotanya.com and
eserviceinfo.com are often right at the top. I usually use the search
string

manufacturer - model - free schematic download. You can of course use +
and " " operators (and others) in the string to make it more specific

elektrotanya tends to yield better results in that eserviceinfo will
often find anything in its database which matches any of your search
criteria, whereas any elektrotanya 'hit' usually takes you straight to
the manual. It's not immediately obvious how to get the manual, though.
Ignore all the big "Download" buttons that you see dotted around. These
are all for 'helper' software or PDF readers. Look in the text block
under the preview pane, and you will see the word "processing" in a
different colour. Small and hard to spot. After a while - and I have
known it to be several minutes - the word will change to "get manual". If
you then click on it, the download process will start normally, and
depending on your computer OS and what antivirus blockers you have, you
will probably get the "do you want to open / save "etc dialogue box

Have you got a link for that?

The one I found isn't in English, so I don't know whether I'm seeing the
bit you describe.

But then I've recently stripped and re-installed my browser to sort some
problems - I had a translate button then, now I don't.

Ok. Let's go for an example on both sites. Get the Google search box up, and
type in :

Sony DAV-S300 free schematic download

and click search. A link to elektrotanya should be right there at the top.
Click that, and it should take you to the download page for that manual. The
page is in English, and there is a preview image for the manual in the main
pane. Immediately below that pane, is some text and on the third line it
says "This manual is downloadable free of charge ... processing"

Keep watching that word "processing", and it will eventually change to "Get
Manual", underlined. If you now mouse over that, you will get the clickable
hand. Go ahead and click it, and the manual should start to download,
subject to any restraints imposed by your OS / antivirus software. The site
has always been totally trustworthy for me - otherwise I wouldn't recommend
it - and is a very useful resource.

A bit further down the Google results list, you will see a link to the same
manual at eserviceinfo.com. If you click on that one, it will take you to a
copy on their site. Note how the page presents. It is only when the page
looks like this, that you are actually on the manual. If the page looks more
like a list made out of boxes and there seems to be a lot of writing and
model numbers, then the chances are that the manual you are looking for is
not actually there, and it is just eserviceinfo having its 'best go' at
finding you something.

Going back to our example of the Sony manual, you will see half way down
that it says "Multipart" and to the right of that "0 1 2 3 4" with the "4"
highlighted in orange. This means that the file has been saved on the site
as a rar archive of five files, and all five need to be downloaded and saved
to your machine to get the complete manual. Click on the "0" which will then
turn orange. Scroll down the page until you see :

Download >> To download the file, please, click here ! << Download

Click on the middle bit and the first part will download. Scroll back up,
and highlight "1", then back down to

Download >> To download the file, please, click here ! << Download

again and so on until all five parts have downloaded to whatever directory
you've put them in. Now just click on the first one and your Winzip or
whatever software should open to extract and recombine them into the
original pdf.

eserviceinfo also has binaries for reprogramming a lot of TV eeproms. Again
a useful resource, and one that has never caused me any problems.

Arfa

 

[Ian Field]

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:ZN0Sw.1720468$i22.279643@fx07.am4...

"Ian Field" <gangprobing.alien@ntlworld.com> wrote in message
news:GuXRw.192255$ID3.162851@fx01.am4...

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:hRIRw.491026$7E1.151824@fx31.am4...




I managed to get a DS for the chip pretty quickly, it was the scope
schematics that were the big problem. I'll have to check out that site
you mentioned in your email and see what's there. I've got another 2 or
3
Philips scopes to sort out when this one's done so I'm sure it would
pay
off.

If you use Google to search for service info, elektrotanya.com and
eserviceinfo.com are often right at the top. I usually use the search
string

manufacturer - model - free schematic download. You can of course use +
and " " operators (and others) in the string to make it more specific

elektrotanya tends to yield better results in that eserviceinfo will
often find anything in its database which matches any of your search
criteria, whereas any elektrotanya 'hit' usually takes you straight to
the manual. It's not immediately obvious how to get the manual, though.
Ignore all the big "Download" buttons that you see dotted around. These
are all for 'helper' software or PDF readers. Look in the text block
under the preview pane, and you will see the word "processing" in a
different colour. Small and hard to spot. After a while - and I have
known it to be several minutes - the word will change to "get manual".
If you then click on it, the download process will start normally, and
depending on your computer OS and what antivirus blockers you have, you
will probably get the "do you want to open / save "etc dialogue box

Have you got a link for that?

The one I found isn't in English, so I don't know whether I'm seeing the
bit you describe.

But then I've recently stripped and re-installed my browser to sort some
problems - I had a translate button then, now I don't.


Ok. Let's go for an example on both sites. Get the Google search box up,
and type in :

Sony DAV-S300 free schematic download

and click search. A link to elektrotanya should be right there at the top.
Click that, and it should take you to the download page for that manual.
The page is in English, and there is a preview image for the manual in the
main pane. Immediately below that pane, is some text and on the third line
it says "This manual is downloadable free of charge ... processing"

Keep watching that word "processing", and it will eventually change to
"Get Manual", underlined. If you now mouse over that, you will get the
clickable hand. Go ahead and click it, and the manual should start to
download, subject to any restraints imposed by your OS / antivirus
software. The site has always been totally trustworthy for me - otherwise
I wouldn't recommend it - and is a very useful resource.

Thanks - got it.