CD optical block shorting links

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?

Reply to
N_Cook
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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.

(etc...)

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Jeff Liebermann     jeffl@cruzio.com
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Reply to
Jeff Liebermann

So you need to leave the anti-static shorting links on when its operating then?

I thought they were just for transit and handling!

Reply to
Ian Field

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.

Reply to
N_Cook

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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    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ 
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Reply to
Samuel M. Goldwasser

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.

Reply to
Mark Zacharias

but

to

static

including

is

in the

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?

Reply to
N_Cook

So what likely went wrong with the laser? Old and new both measure about

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.
Reply to
N_Cook

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.....

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Reply to
Samuel M. Goldwasser

4.6V

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.

Reply to
josephkk

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

Reply to
Arfa Daily

And some models like the KSS-240 have the power limiting circuit built in; no shorting required.

Mark Z.

Reply to
Mark Zacharias

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

Reply to
Arfa Daily

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.

Reply to
Mark Zacharias

are

This generic Sanyo one , oriental script only, had the pot "set" at zero ohms as well as zero ohms across the laser

Reply to
N_Cook

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

Reply to
Arfa Daily

that

being

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.

Reply to
N_Cook

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

Reply to
Arfa Daily

from

experienced

back.

know,

hickup.

as

dividers

washers

one

numbers

also

you

are

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.

Reply to
N_Cook

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

Reply to
Arfa Daily

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