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Old 8th May 2012, 02:52 AM   #1
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Default Original Meridian 508 skipping and disc reading problem

Hey there guys. I just got an original Meridian 508 (18 bit) and I have a few concerns and questions. First of all, it sounds absolutely stunning. It is as close to the "liquid" sound of vinyl I have ever heard out of digital source, BUT it has a lot of difficulty reading CDs. It will only play a pristine CD and sometimes not even that. It will begin on the first track and after about 3-5 seconds, begins skipping through the tracks playing a few seconds of each.

Second, I listen to a lot of independent music that I download. I have always burned Audio CDs through iTunes and never had an issue playing them. Unfortunately the Meridian doesn't read them either and seems to treat them as I mentioned above. Do these players simply not read burned CDs?

I had some hope after reading some of the threads mentioning grease hardens on the mechanism and can cause skipping so I opened it up tonight and gave it a good alcohol swabbing. Unfortunately, this didn't have an effect and now I'm wondering if I need a new a new CDM 12.4. What do you think? If so, do you all know of a reliable source (meaning they aren't Chinese fakes)?
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Old 8th May 2012, 06:39 PM   #2
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I wrote this for a Micromega so just pick the bits relevant to the CDM12.4 itself,

This procedure applies to any player with the CDM12.4 or 12.1 pickup. Also make sure the lens is clean and if possible confirm the output with a scope.


"To repair properly (assuming this is the issue... it almost certainly is) involves unplugging the complete loader assembly and mech and laser and removing from the player. This allows you to work on it easily.

First eject the drawer normally, then pull the mains plug out. The drawer is fully removed by bending a plastic end stop out of the way and just pushing the drawer fully out... obvious when you look down at it. When you refit the drawer just push it back firmly. There are no timing problems etc or anything to align. When moving the drawer manually, always move it slowly because the loading motor acts as a generator when turned...

There is a clip on a plastic cover over a couple of gears at the front of the mach and a loading belt. These gears, or the spindles rather, is what cause the noisy drawer. Just remove the gears, clean them and the shafts and lubricate with the grease listed. Don't lubricate the teeth. The belt can be replaced too, round or square cross section it doesn't matter although square is best. These can be ordered in one offs from CPC etc, just measure the size.

The whole loader is secured by three screws under the player.
Also look where the flexi print runs from the laser to main board... make sure you see how it fits over the mouldings of the chassis.
The flexi print is released by pushing the "locking bar" on the socket forward. Thats two clips at each end... it doen't come off just moves forward a millimeter or so. That releases the foil. There is no high static risk with this pickup as it contains circuitry on board the laser.

The pickup... first draw where the six wires go (just in case) with their polarity (colours), two lots of two to the spindle motor and tiny sled motor and two to a micro switch. Carefully and quickly unsolder all. It can be better to snip them rather than linger with heat.

Now remove the pickup assembly. There are four neoprene supports. These are best removed from the pickup by using a small screwdriver to just push them to the outside of the pickup. There is a barb on the mech but it won't damage the support... just push them out.

You should have the laser mech on its own now. Be careful not to get grease etc on the lens, easy to do while handling.

The worm gear can be turned manually to move the pickup. You need to remove blue nylon gear and fully clean it in iso etc. Its held by clips so be carefull. Use card to clean all the teeth fully and the centre hole. Worth mentioning at this point that these can suffer with burrs... if so you have a problem, hopefully they are OK. Now clean the worm gear using card etc to get all the old grease out. The loading motor pops out, its held with a metal spring clip. Also clean the spindle shaft for the gear. Also try and clean the grease from the "toothed rack" on the laser itself. With the gear out the pickup is "free" to move. Clean the one rail and look at all the friction points as the pickup move.

Now reassemble using the grease shown. Lubricate the spindle of the nylon gear and the worm gear... just a smear on all the teeth.
Add some grease to all the friction points that the pickup moves on, the rail and plastic runners etc.

That should be it, reassemble the mech and resolder all the wires. Refit the flexiprint... hopefully all should be well. The front of the drawer, the metal trim, is held by sticky tape... unbelievable... and most are misaligned or creep. You can remove it, clean it and super glue it on the drawer. Make sure to get the three screws holding the loader correct as there is a bit of room for physical alignment. Then get the front plate correct.

The grease I use is this and its always performed faultlessly. The viscosity of the grease is important, too thick and it causes problems as a CD is read. The Stage players are unusual in that they read and store all track locations when a disc is inserted giving super rapid track access."


http://cpc.farnell.com/electrolube/s...l/dp/SASPG35SL
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Old 8th May 2012, 09:39 PM   #3
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Thanks Mooly. Great instructions but I did it already Cleaning the mechanism is time consuming, but easy enough to do so I might try again...I have a scope someone gave me but haven't gotten so deep into DIY as to learn how to use it. I've read up on the basics, but how would I use it to check output of the mechanism?
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Old 8th May 2012, 10:27 PM   #4
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Another thing:

I'm playing an old Stones CD now that actually has a few scratches on it. It's tracking without a hitch! I tried some that are pristine and it tracks all over the place. What's up with that??? I'm thinking this may not be the laser mech since there is no consistent pattern here. Could this be something else entirely?
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Old 9th May 2012, 07:16 AM   #5
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You would need to identify the "RF" test point to check with a scope. This will be one of the leads on the ribbon cable that goes to the pickup although it's easier to find a convenient point on the main PCB.

The RF signal should be around 1.2 to 1.5 volts pk/pk with a clear outline and no jitter. It's important to use the correct grounds for the scope to get a clean signal.

It should look at least as good as this and is the same for any disc,
NDP 4 Quality Assurance

If the disc runs true (no wobble at edge) then it is possible the pickup or spindle motor is faulty. A scope check is needed though to get an idea of what is happening.
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Old 9th May 2012, 12:45 PM   #6
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Mooly,

I think I have some time this evening so may open it up and try to figure it out (and clean it again). I know the ribbon cable you are talking about (it's orange). You will have to forgive my ignorance, but I don't see how I could play a disc with my scope in there testing that point. Do you have any idea where a good test point might be on the main PCB? Would I simply follow the trace to a point on the PCB?

FM
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Old 9th May 2012, 01:57 PM   #7
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I think it's pin 4 on the flexiprint for the CDM12.4

If you can identify the chipset used then you can find the RF signal that way. If it's hard to get at then solder a small loop of wire onto the PCB (pin 4 of socket) to connect the scope too.

This was for the SAA7345 signal processor. The line marked in red goes to pin 4 of the CDM12.4 socket as best as I can make out.
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Old 11th May 2012, 02:54 AM   #8
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Mooly,

I put a scope on the Meridiant today and cleaned the transport again. The second cleaning uncovered a speck of hardened grease in the worm gear I had missed. This seemed to help it read discs that it wouldn't even begin to play, but still no recorded discs. It recognized how many tracks are on the disk, but skips through them all until it puts on the brakes and stops.

I really don't know a lot about what I'm doing with the scope, but voltage seemed to be around 1.3 which is within target. The wave did not look "clean" though. It looked a lot like a roller coaster with bumps. Jitter? The chip was actually SAA7310GP. I couldn't find a test point leading into it, but measured at the leg of the chip. I'm not sure if this affected results.

Thoughts?

FM
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Old 11th May 2012, 07:08 AM   #9
Mooly is offline Mooly  United Kingdom
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Grease is the big problem but if you have stripped and cleaned the gears and are sure all is well then the pickup has to be suspect.

When using the scope it is important to use the correct ground for these high frequency signals and also to use a proper probe, preferably a "divide by 10" as that raises the loading and reduces the capacitive load of the probe.

These are the pins for the SAA7310. It might be worth reading to the "left" on the 2.2nf cap. Use the same ground as the 1uf cap goes to. Note the absolute value of these parts may differ in your player but they will be present. The alternative pin numbers depend on the type of package, SMD or DIL
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Old 15th May 2012, 10:33 AM   #10
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Quote:
Originally Posted by fmjunkie View Post
Mooly,

I put a scope on the Meridiant today and cleaned the transport again. The second cleaning uncovered a speck of hardened grease in the worm gear I had missed. This seemed to help it read discs that it wouldn't even begin to play, but still no recorded discs. It recognized how many tracks are on the disk, but skips through them all until it puts on the brakes and stops.

I really don't know a lot about what I'm doing with the scope, but voltage seemed to be around 1.3 which is within target. The wave did not look "clean" though. It looked a lot like a roller coaster with bumps. Jitter? The chip was actually SAA7310GP. I couldn't find a test point leading into it, but measured at the leg of the chip. I'm not sure if this affected results.

Thoughts?
FM
The actually question is, whether you have a genuine Sharp hologram laser diode inside or a bad clone from an unknown china manufacturer. In first case you will not observe any issues by replay of burned compact disc (only CDR, not CD-RW !!!).
check out this threads:
Stripdown/Clean of CDM12.4
new Brand of Hologram Laser (LDGU) LT0H30PA inside by Philips CDM12 and VAM12 mech

Try to find a CDM12.4 laserhead from NOS or a completly mechanism with genuine Philips sticker - this is the only possibility I know.
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