Primare laser change - diyAudio
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Old 12th December 2012, 10:18 AM   #1
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Default Primare laser change

I have replaced the dead laser (there were no movements and motor didn't spin the CD) with CDM12.4/05 as should be and my Primare is alive

Everything is fine expect that 10% of CDs are skipping on one or two tracks, mostly in the first seconds. Some of them are quite scratchy and I could understand the issue, though others have little and barely noticeable marks, so that makes me feel puzzled.

The whole mechanism has been replaced very carefully and pot on the laser's head has been adjusted in similar position to the previous one. Is there something wrong with the laser itself or some other adjustments could be made?
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Old 12th December 2012, 11:51 AM   #2
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Altering the pot "to match the other" is (could be ) a fatal mistake. The pot is calibrated such that the laser power is correct for that pickup.

All is not lost however, unless turned up significantly too high the laser won't self destruct. You need to play a known good red book standard disc (any commercial CD in other words but NOT a CDR or RW) and adjust the pot to give around 1.5 volts pk to pk RF measured on the outout of the RF amplifier. That point will be available on the main PCB, you don't have to try and measure on the pickup itself.

From a realistic and practical point of view, the quality of a lot of the so called new CDM12.4's on the market is terrible. They are not original Philips parts and can be anything from poor copies to reclaimed parts. It may just be a duff laser assembly.
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Old 12th December 2012, 01:35 PM   #3
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Quote:
Originally Posted by Mooly View Post
Altering the pot "to match the other" is (could be ) a fatal mistake. The pot is calibrated such that the laser power is correct for that pickup.
thanks mate!

I'm pretty sure that the adjustments I made didn't make the things worse as it skipped same tracks before the adjustment.

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Originally Posted by Mooly View Post
adjust the pot to give around 1.5 volts pk to pk RF measured on the outout of the RF amplifier. That point will be available on the main PCB
that could be a bit difficult for me. How can I trace that rf amp?
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Old 12th December 2012, 01:44 PM   #4
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The RF amp is on the CDM12.4 but you get to the RF on the other end of the ribbon cable.

Its pin 9 or 10 on the TDA1302 IC on the pickup. You would have to see where that goes on the main PCB.

The RF is usually dead easy to pick up when you start measuring. Often there is a test point or some such. Obviously without the knowing the player I can't say exactly but you'll find it for sure following the output pins on the TDA1302.

Skipping on the CDM12 is often mechanical such as dried grease etc. That was the big problem with the original Philips stock 20 years ago.
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Old 12th December 2012, 01:56 PM   #5
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many thanks for clarification
will check that today/ tomorrow and post here my findings.
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Old 12th December 2012, 02:02 PM   #6
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OK and good luck.
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Old 13th December 2012, 07:40 AM   #7
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according to TDA1302 pinout, RF amplifier is 10th pin, however it's almost impossible to get to the ribbon cable and take the measurements. What I did is turned on the player without a CD and measured the pot (there are even soldered marks for that, so I supposed this is how it should be adjusted). I set the voltage to 0.92 vdc as on my other working VAM1205 laser on T+A

To be honest it skips almost the same tracks as previously when it was accidentally set by me in 1.05 position. However few tracks now are readable. That is a good point! I have also tried other adjustment positions in the range of 15-85% of the pot scale. The lowest voltage is about 0.55 and highest is 1.07 where laser is unable to read the CD.

So I guess it's the problem of the laser, probably it's not that good as original Philips lasers.
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Old 13th December 2012, 08:12 AM   #8
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The measurement of approximately 1.5 volts pk to pk is as viewed on a scope. There's no other way to do it. If its difficult to access then you can solder a wire tag to connect the probe to.

It does sound like a suspect pickup. Even 6 years or so back I returned two CDM12.4's back to the supplier (I won't name them but they are one of the biggest suppliers to the repair trade). I was sent a boxed "Japanese" made CDM12.4 mech that was absolutely unbelievable in quality. The RF was amongst the cleanest I have seen. The other pickups looked and even smelled used and dirty.

No easy answer I'm afraid.
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Old 13th December 2012, 09:13 AM   #9
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thanks Mooly,

will connect the scope then, looks interesting for me just to confirm, the ground should be connected to 15th pin, right?
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Old 13th December 2012, 10:48 AM   #10
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Yes, pin 15 but connect to the ground on the main PCB. There will be different "grounds" such as digital or signal. All are essentially the same but if you connect the scope to the wrong one the RF will look a bit noisier than it really is. To initially find the RF though you can just use the chassis ground for convenience.

It should look like this,
NDP 4 Quality Assurance

Thats a typical good quality signal. I would assume the scope is on 0.05V/Div and using a divide by 10 probe. So around 1.5 volts pk/pk.
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