Yamaha CDX-700. Skipping. Read FAQs for this but no joy.

Since you didn't post any basic cd player troubleshooting information, there is little anyone can do to help other than suggest you do standard cd player troubleshooting.

RF output on the laser? Focus and tracking waveforms? Laser current draw? etc

Get out the service manual, o'scope, and do some troubleshooting.

There's a good reason I didn't post such things, and they also explain why I posted here in the first place: if I had a service manual, I probably wouldn't need to post for help. I cannot find a service manual. The troubleshooting info you want is not available if I do not know where to check for these things.

There are two connectors going to the laser assembly. Which one of the total of 14 conductors has the RF output? Which the focus? Which the tracking? What should they look like if all is well? Which conductor should I interrupt to measure current? How can I state that a waveform shows signs of trouble if I have no reference?

Can't get the service manual. Had the oscilloscope on all 14 outputs. Nothing resembling the "eye pattern" as shown in the troubleshooting guide on any conductor. If I touch the scope to any of a certain four conductors, the audio output ceases and it also makes it skip terribly. All other troubleshooting has been mechanism-based and shows no problems.

I had simply hoped someone might know the usual causes of such a clear problem and offer guidance on what to check and possibly advice on how and where and what to expect to see if all is well in that department. Perhaps I should have made it clear I had no service manual.

What you are describing is not such a clear problem. There are many causes for that type of problem.

Is there anything marked on any circuit boards as that is usually where the test points are located? (especially on the older cd players)

The 14 conductors going to the laser are not likely going to contain any of the test points. Depending on how old the cd player is, some of the 14 conductors will be: 2-focus coil, 2-main laser power, 4-tracking coils, 2- laser power feedback, optical assembly output, several ground lines.

The test points will be near the connector on the main board in the middle of the circuitry somewhere. Depending on how service friendly Yamaha was, the points may or may not be marked.

Yamaha was not a widespread brand when it came to service.

A google search finds that anatechlabs.com has the service manual for sale.

Thanks for the info. There are three blocks of pins which are not for connectors, maybe these are test points? If so, then something has to be made of the letters printed adjacent to each pin: THRD, TDI, Q, TE, TER. EFMI, FDT, E, FO. R, Q.

I found the service manual for sale at the same place when I Googled, but due to the way the trade is now, there's little chance I could include the cost in the repair and have it accepted...

Take a look at those with the o'scope and see what is there.

Typically things that start with F are related to the focus servo, T

-tracking servo, Q might be ground as there are two of them.

The one you need to find is the rf output that has the eye pattern. If the rf level is less than 1.2V, then the laser is probably simply worn out and working in it marginal zone.

If you can find any Yamaha CD player service manual from that era, the test points probably are all the same and you can figure it out from there.

In other brands, F0=focus offset, TE=tracking error, E=ground.

If the laser were to be worn out, would it not be provable by increasing the laser voltage via the pot on the assembly, i.e. increasing it should improve the performance?

Increasing the current to the laser diode, you mean?

Diodes are current dependent devices, the voltage drop across them is a function of the diode itself.

Laser diodes have an automatic light output circuit which automatically increases the current as the diode ages. The adjustment is for the initial setup. Increasing it now can cause immediate and permanent damage to the laser diode rendering it completely useless.

You need only look at the rf waveform when you find it and measure the peak to peak voltage to determine if the laser is bad.

Don't increase the laser diode current. Common service items, include cleaning the lens, replacing the loading and sled belts, lubricating the spindle motor, lubricating the clamper bearing, if any (it's under the white nylon piece at the top of the clamper), cleaning / lubricating any sliding surfaces, including the rail, and any slider surface on the other side of the pickup.

Fixes a majority of problems like these.

Also, make sure the disc is not scraping on anything as it plays.

Mark Z.

Ocassionally I had CD players with similar problems. An alternative low-tech diagnostic technique to try: The motor that spins the CD has an IC contoller that tightly controls it's speed. I found more than once that the IC did not provide enough current to keep the CD up to speed under all reasonable conditions. Motor drivers usually fail in an obvious abupt way, but apparently this is not the case with CD motor IC's.

No test equipment required, just your finger. Under proper conditions, the motor IC will provide more current if something, like my finger, tries to slow down the CD. So the technique is to see how much your finger can drag the CD before you hear the audio fail.

I can't say in numbers exactly how much reverse torque your finger needs to produce before a properly working CD system will fail. But a bad system may fail with the slightest touch.

Replacing the motor driver IC fixed the problem. All this may be academic considering how cheap CD players are these days. But it's still interesting though. Of course this may or may not apply to the OP's problem.

Dennis H.