Original Meridian 508 skipping and disc reading problem

[fmjunkie]

Originally Posted by tiefbassuebertr

Which devices are on the foil PCB of your new optical pickup?

In those days there was only three kinds of foil PCBs:
1) with TDA1302T (i. e. integrated RF amp section and APC) mostly CDM12.4 - and VAM1205/VAM1252 with brushless disc motor (spindle motor)
2) discrete solution (discrete APC and without RF amp section)
3) with TZA1022TS (successor of TDA1302T, CDRW compatible - mostly used in VAM1250, not compatible to CDM12.4 head - check out picture number 7 by post #10 about
Stripdown/Clean of CDM12.4

For your Meridian I think, the best solution is to order the VAM1252 head (professional version of CDM12.4) from the Marantz CD Player model CD7. Unfortunately the cost therefore is at least ten times higher, but you will get perfect NOS quality standart.

check out also this threads:
VAM1204 VAM1205 VAM1206 VAM1250 VAM1252 VAM1254 CDM12pro VAU1254=CDM12.4 compatib
Meridien 560 mod mech from 1205 to CDM12.4
Vam 1205 /vam1250 / Cdm12.5
Vam 1205 CDM 12.5 Naim CD5

P. S. A cost effectice burner/player, where the CDM12.4 is in use, is the model CDR765 from philips. For checking the RF signal and other measurement places is the service manual from this model helpful (check "hifi engine" or "hifi manuals").

On the pickup, both used the TDA1302T, but a different spindle motor and worm gear motor. They also had ribbon cables that were different (though same size, shape, etc.) The pickup I received in the mail was used and had some dried grease in the gears, so I simply switched out the laser assembly.

I got a little frustrated with the thing and started some speaker projects that I should finish this week. (I'm restoring some Snell J IIIs and Klipsch Heresys.) As soon as I get my workspace clean again, I'll take some photos of what I got and will probably ask you all for some more help scoping it...I'm close to taking it to my tech who will charge an arm and a leg, but will give it one last go for the sake of knowledge if nothing else.

[Mooly]

The original CDM12.4 pickup and mech with the "soft flexible" blue nylon gear doesn't seem to work when used with the harder white nylon type gear. The backlash is different and the pickup has trouble reading the TOC's constantly scanning the disc for many seconds. Sometimes it will then play other times not. A strange issue but one I have encountered a couple of times.

[fmjunkie]

Originally Posted by Mooly

The original CDM12.4 pickup and mech with the "soft flexible" blue nylon gear doesn't seem to work when used with the harder white nylon type gear. The backlash is different and the pickup has trouble reading the TOC's constantly scanning the disc for many seconds. Sometimes it will then play other times not. A strange issue but one I have encountered a couple of times.

Mooly,

Good to know, but I actually kept the blue nylon gear. I haven't opened up the transport in a few days, but I'd like to check the alignment of its gears with the teeth of those on the "new" laser. That may be a problem too...The company may have also just sent me a faulty laser, but I'd like to assume the best and think it just has some compatibility issue.

[Mooly]

The gears have no special alignment, it's just a gear train driving the sled.
Another common issue are burrs in the soft nylon gear teeth on the inner part of the shaft. The pickup is never particularly smooth when you move it by hand (with the worm gear and motor popped out) but should run slowly from end to end with a 1.5 volt battery across the motor. Actually you need a low value resistor in series with the battery to get it as slow as possible and it should still make it end to end at whatever the slowest speed is you can get away with. An AVO 8 meter on low ohms range will just power the sled when placed across the motor.

[fmjunkie]

Originally Posted by Mooly

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

Finally finished those speakers and am back to the Meridian. The "new" laser didn't work and so I put the old one back in. Seems like the reading issue is worse. I didn't check the caps, but the values are no too common and didn't have any replacements on hand so I wanted to try to properly scope it to see if the laser is still at fault.

I'm attaching a photo of the chip and surroundings. Mooly, I followed your schematic a few weeks ago when we started this chat. I didn't get anything like the images you attached, but didn't feel like I could get a good ground and trace around that capacitor. After seeing the chip itself, do you have any recommendations?

[tiefbassuebertr]

at best you order the CDR765 mentioned about post #20.
You will find presently one device in used and working condition by ebay - go to
Philips CDR765 CD CD Recorder | eBay
Then you can replace crossover both the complete mechanism and the laser heads only and you will see, what happens (please note, the laser head you need is in use only in the replay-section and not in the recorder section).
This means, you have good conditions for your troubleshooting.

Without a second cd player unit for checking the optical pick up/mechanism stuff it is very difficult to obtain a clear statement concerning the right error-causing device.

[Mooly]

Try connecting the scope here

[fmjunkie]

Thanks, Mooly. Like I mentioned I don't know much about using the scope (and mine is very simple), but I did try the spots you mentioned and got a fairly good wave. Seemed when it skipped, the wave lost focus...I feel like I'm letting down the folks that contributed to this chat, but I'm going to have to take it to a pro. There is a tech near me who owned his own high end shop and repaired the gear he carried. He has done some nice work for me in the past and I hope he can get it going. I'll let you all know what he says. If he can't fix it, you all may hear from me again.

FM

[Mooly]

Hope you get it sorted

Another thought if you are interested in narrowing down the problem is to monitor the DC voltage across the sled motor as a disc is playing. The voltage is normally very low as the motor is "shuffled" along. If you watch the worm gear while playing a CD it almost trembles to and fro advancing a few degrees at a time. If the sled is sticking the voltage will suddenly start to rise until there is enough force to overcome the friction and the sled jolts forward and which you hear as it jumping.

[fmjunkie]

Mooly,

That's an interesting thought, but if that were the case I think the problem would be consistent across the board with every CD I played, not just a select few. It was this player's ability play some CDs well and others not at all that frustrated me...Oddly enough, it plays every Blue Note jazz CD I have. Do you think there is some kind of regional coding that prevents it from reading certain things--like a DVD player? I've never heard of such a thing, but who knows?