CD optical block shorting links
N_Cook
had forgotten about those antistatic shorting links, wasting time trying to
find the short. Nothing on the box about the shorting link, only graphic
showing use antistatic wrist strap for assembly
Do they all have these solder-across semicircle land pairs?
This one Sanyo SF-P101 has them , so do KSS213 and K SM213, all ?
Is there something in the laser assembly that is especially prone to static
damage?
Jeff Liebermann
wrote:
>Is there something in the laser assembly that is especially prone to static
>damage?
Directly adjacent to the laser is a spinning piece of plastic
sometimes referred to as a CD or DVD. Like all good plastic parts,
it's quite capable of turning into a Van de Graaff generator. The
rubber pad on the center spindle is slightly conductive and bleeds
away some of the static charge, but some charge may accumulate.
There is also a substantial chance of discharging static electricity
from your body in the process of inserting or removing the CD. Since
the optics are exposed during the insertion, they must be protected
against being the first point of contact.
Some applicable patents.
<http://www.google.com/patents/about?id=XjoWAAAAEBAJ&dq=5684775>
<http://www.google.com/patents/about?id=5PcmAAAAEBAJ&dq=5684775>
(etc...)
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Ian Field
"Jeff Liebermann" <je...@cruzio.com> wrote in message
news:bvb4h61ha2gophksc...@4ax.com...
> On Wed, 22 Dec 2010 08:55:50 -0000, "N_Cook" <div...@tcp.co.uk>
> wrote:
>
>>Is there something in the laser assembly that is especially prone to
>>static
>>damage?
>
> Directly adjacent to the laser is a spinning piece of plastic
> sometimes referred to as a CD or DVD. Like all good plastic parts,
> it's quite capable of turning into a Van de Graaff generator.
So you need to leave the anti-static shorting links on when its operating
then?
I thought they were just for transit and handling!
N_Cook
news:kDqQo.48843$jO1....@newsfe07.ams2...
And for confusing absent minded electronic engineers.
The whole unit was in an antistatic bag for transit purposes, inside the
box, so whatever these links are for is for just the mechanical fixing and
connecting in cables, with m/c off -line off course.
I'd never considered any problems associated with mini Wilmshurst
generators.
Samuel M. Goldwasser
Yes, the laser diode. There's generally very little circuitry between the
cable and laser diode and it can be damaged by any number of things including
ESD.
--
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Mark Zacharias
It is just for transit and handling. Ideally, one removes the short AFTER
the pickup is connected to an approriate circuit. Sometimes this is
impossible, and a anti-static grounding strap is needed while installing.
Mark Z.
N_Cook
news:uei994...@repairfaq.org...
But is a CD laser diode any more susceptible to ESD damage than a bulk
standard red LED or a 1N4148 say, in otherwise the same poor handling
circumstances?
N_Cook
0.65V DVM diode test but powered in circuit the old one was dropping 4.6V
over the diode and the replacement, working one, about 1.8V across the
laser.
Samuel M. Goldwasser
> Samuel M. Goldwasser <s...@repairfaq.org> wrote in message
> news:uei994...@repairfaq.org...
> > "N_Cook" <div...@tcp.co.uk> writes:
> >
> > > First time for years (no salvaged one on hand) I replaced old with new
> but
> > > had forgotten about those antistatic shorting links, wasting time trying
> to
> > > find the short. Nothing on the box about the shorting link, only graphic
> > > showing use antistatic wrist strap for assembly
> > > Do they all have these solder-across semicircle land pairs?
> > > This one Sanyo SF-P101 has them , so do KSS213 and K SM213, all ?
> > > Is there something in the laser assembly that is especially prone to
> static
> > > damage?
> >
> > Yes, the laser diode. There's generally very little circuitry between the
> > cable and laser diode and it can be damaged by any number of things
> including
> > ESD.
> >
> > --
> > sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
>
> But is a CD laser diode any more susceptible to ESD damage than a bulk
> standard red LED or a 1N4148 say, in otherwise the same poor handling
> circumstances?
YES! A 1 ns current spike with a peak just above the laser diode's maximum
rating can destroy it. Accidentally connecting a charged 0.01 uF 5 V cap
across a laser diode will destroy it. Etc., etc. Look at it the wrong
way.....
josephkk
The old laser has ceased to lase, though damaged ones may still emit light
(IR). You old one apparently does not even emit light, thus the high
terminal voltage from the (IR) output regulation circuitry.
Arfa Daily
"Samuel M. Goldwasser" <s...@repairfaq.org> wrote in message
news:uzkrw6...@repairfaq.org...
All absolutely agreed. However, to answer one of Mr Cook's earlier
questions, given that they do have this extreme static sensitivity,
curiously, the answer is no - not all replacement optical blocks *do* have
the laser diode shorted for transit. As well as shorting blobs on the pcb,
other methods of shorting that may be found are a thin metal plate in the
ZIF connector that some have, and a tiny switch that I have seen fitted to
some DVD optical blocks. And of course the solder blobs on the flexiprint
tail rather than on the board, and the 'snip-off' piece of flexiprint (two
varieties) to be found on some Panasonic lasers.
Arfa
Mark Zacharias
news:5IiUo.37568$E44....@newsfe30.ams2...
And some models like the KSS-240 have the power limiting circuit built in;
no shorting required.
Mark Z.
Arfa Daily
"Mark Zacharias" <mark_za...@sbcglobal.net> wrote in message
news:4d21c7a5$0$13466$c3e8da3$3863...@news.astraweb.com...
Yes indeed. And talking of 240's, have you had problems with some players
which use one - particularly Sonys themselves - just not liking the generic
replacements, and suffering all sorts of playability problems after
replacement ? Whenever I had a Sony in that needed a 240, I always used to
quote for a genuine original part ordered from Sony, but it seems that they
are now no longer available from them. I have just picked one up for repair
from one of my feeder shops, and he has asked me to try a stock 240 in it,
but based on experience, I'm pretty sure that it's not going to provide
acceptable performance. I wonder why this should be, given that there
doesn't seem to be a problem with generic replacements in any other Sony
models, or problems using a generic 240 in any non-Sony players ?
Arfa
Mark Zacharias
Hey, Geoff.
Actually there's been so few replaced by me in recent years, I don't think
I've used a generic 240 yet. I've gotten "original Sony" pickups from a
reliable supplier, but none lately, so those "NOS" pickups may be gone.
I do believe that a lot of the "flaky KSS240" problems we experienced over
the years were actually bad flat wires. Had one a couple months back.
Of course I can see where a generic might be shipped unadjusted and that
could be disastrous. The are three adjustments on the 240 as you know, not
just the laser power adjustment. Kind of hard to adjust them while they are
playing!
Mark Z.
N_Cook
This generic Sanyo one , oriental script only, had the pot "set" at zero
ohms as well as zero ohms across the laser
Arfa Daily
"N_Cook" <div...@tcp.co.uk> wrote in message
news:ifv58m$ke5$1...@news.eternal-september.org...
That seems very odd. I don't think I've ever seen that. So, when you'd
removed the solder blob short, did it still not work ? Or was the pot being
"set at zero ohms" equivalent to it running flat out ? Again, and odd
situation ... Did you reset it to some other value ? How ? Laser power
meter ?
Arfa
N_Cook
Pedants and purist look away now
I set the pot to the value of the original one and worked without hickup.
Then used the following , adjusting pot, which turned out to be centred as
far as I could tell by this method, to optimal as first set.
For checking error correction /immunity to errors.
An out of favour audio CD but otherwise in perfect playable condition.
With an assortment of potentiometer back nuts and washers ,small motor
pulleys find a combination that will "fill up" the hole in the centre of the
CD leaving
just a small hole at the very centre> With a set of "geometry" dividers
put one point
in this hole and lightly scratch a gouge about halfway along a radius of the
CD and about 1/4 of the circumference at that radius. Remove the washers
etc and play on a known good player.
Repeat the groove cutting deeper/wider/number of nearby grooves until one
track
or part of that track fails to play.
Make a note of the track number and start seconds and finish seconds
into the track/sections of track/s that are absent.
For your own machine every now and then (months) play and note the numbers
to note
long term drift. More absences/ longer absences over time indicates
deterioration in optics /correction . Use the same CD for checking in CD
repair of other machines and crude adjusting of optical power etc.
Arfa Daily
"N_Cook" <div...@tcp.co.uk> wrote in message
news:ifvha0$rgu$1...@news.eternal-september.org...
That's quite novel. I actually have a test CD from Panasonic, that has
similar linear defects literally 'burnt' into the play layer. There is also
another one I have, which has a piece of PCB masking tape (the old black
lines used when making your own pcbs) right across a radius. This allows you
to look at the recovery times of the servos at various rotational speeds.
I'm still a bit puzzled though as to why this 'new out of the box' laser,
came from the manufacturer in an apparently unadjusted condition. I don't
think that I have ever seen this. Most are factory set and sealed. There are
a few notable exceptions, such as some Pioneer lasers where setting the
output level is an integral part of the service and set-up procedure, but
even then, they are set 'ball park' and seldom require much adjustment to
achieve the 'standard' 1v p-p eye pattern
Arfa
N_Cook
On most occassions I've had a salvaged one , so I automatically change the
pot to whatever the setting was for the current repair as an initial set. So
naturally noticed this new one was at the end of track, 0 ohm. Plugged in
forgetting about the shorting links as I'm not accustomed to seeing them. No
magic smoke, just absolutely no dull red glow in a dark room.
Arfa Daily
"N_Cook" <div...@tcp.co.uk> wrote in message
news:ig1ai6$p96$1...@news.eternal-september.org...
Hmmmm. If you've got away with that to date, I feel that you have been
lucky. Normally, the optical block is factory adjusted to give the correct
output power for the laser diode fitted. I understand that the output power
of laser diodes for a given bias, is quite variable, hence the need for the
adjustment. These diodes are also very sensitive to over-drive, and the
smallest amount can damage them in short order, which is why just turning up
a worn one is seldom successful for more than a few weeks, before total
failure. If swapping optical blocks from scrappers to repairs - which is not
in my opinion a very worthwhile practice, given the low price of most
replacement lasers anyway - I would feel inclined to leave the pot set where
the factory put it to suit the particular diode fitted to that particular
block.
Arfa
Cydrome Leader
a plain audio CD with black electrical tape "spokes" across the disc was
how we tested CD players for being faulty. I don't recall how wide the
strips were, but probably 1/8"th inch or so. It was obviously homemade
like a VHS cassette shell with the windows popped out for testing takeup
reel torque.