Help Diagnose Marantz / Philips CD60: Decipher Service Manual, Use O-Scope?

[Johnny_Law]

I am working my way through diagnosing a Marantz / Philips CD60 that will not read discs. The service manual is pretty good but I am having some trouble using my oscilloscope - which I've never used before. It's a Tektronix 2236 from an EE friend that he hadn't used since college. He says it works but I have no idea how to test it, so I'm just assuming it does work.

Before focusing on my specific issue, here's the background:

-Reported working before the previous owner attempted a re-cap.
-Now has all new electrolytics.
-Various solder pads were destroyed during the re-cap, I have fixed them all as far as I can tell.
-I also re-flowed various cold solder joints.

Current condition:

-Powers on.
-Tray ejects / retracts fine.
-When a CD is inserted, it will not read the CD.
-The CD spins briefly, and then stops.
-The display reads "00 00:00"

The service manual (available on HFE) requires the use of a multimeter, an oscilloscope, and various test CDs. I have a multimeter and know how to use it, I have an oscilloscope and have never used it before, and I don't have any official test CDs.

The service manual provides a troubleshooting fault finding tree, the first brand of which ("A"), I will copy below.



Following this tree ... I pass A-1 since my display works, I pass A-2 since there are no clicks or pops (as far as I can tell), I pass A-3 since I can load a disc in the tray, but I cannot pass A-4 since the TOC never displays.

So, I move to branch "B":



I engage B-1 service mode by powering it on with "STOP/CM" and "PLAY" both depressed. I can move through four settings (0, 1, 2, and 3). From here, the manual is light on details. It seems like I should then look at the "B-2 B0, B1, B2, B3 SIGNALS" section:



This chart makes little to no sense to me. The "low" and "high" are in a column with the oscilloscope icon, and "32", "33", "34", and "36" are in the column with the test point icon.

I found these test points in the schematic diagram, in the "SERVO" section between the 6530A/2 and the TDA8809 "RADIAL ERROR PROCESSOR".



Great. But .. uh.

What do I measure?
How do I measure it?
What settings on the oscilloscope do I use?
Where do I connect the oscilloscope leads?

Not knowing this, I took the clues from the "B" branch of the fault finding tree (boxed in red).



In settings "0" and "1", pushing Search >> or Search << results in the laser eye moving from side to side. I figure this is good, confirming that the "ARM FRICTION" and "FLEX FOIL" are OK. In setting "2", the "turntable" motor starts spinning very fast. In setting "3", I'm not sure what happens. In any case, no errors are thrown. I assume this is good?

Moving along. I do still have a working display, although it still displays "00 00:00". I move past B-1 and into B-3: CHECK OF THE PHOTODIODES.

According to B-3, I am supposed to hook the multimeter up to four test points which appear to correspond to the two LEDs and two sensors in the laser pickup assembly.



Drawing 38314A12 gives an idea, apparently, of what the oscilloscope is supposed to show after the unit is powered on.



Now, here's where I run into some practical questions. These test points ("4", "6", "7", and "8"), are present as pins on the ribbon connector socket for the CDM4 assembly. HOW AM I SUPPOSED TO HOOK MY MULTIMETER LEADS TO THEM?

Here's a picture of the underside of the harness connector, and my scope lead. There's obviously nothing to hook it to.



So, I tried to just CAREFULLY touch the exposed hook to each pin (pins 3,4, 5, 6 correspond to the test points), while holding the scope lead ground to a grounded pin (pin 7). When I did this, however, my scope did nothing. The line remained perfectly flat, at 0V.



Am I making this connection correctly? Am I missing some obvious place that I can hook my leads to?

Here is the scope display - and you can see all my settings as well. Please let me know if you spot anything wrong here.



If the settings ARE correct, and if my simple method of touching the leads to the test points is correct, I suppose this means my photodiodes are bad!

THANK YOU in advance for any help or advice or pointers here!

 

[petehall347]

the hook parts should pull off revealing a fine needle probe .. mine do .

 

[petehall347]

the black wire clips to chassis ground then you take 4 measurements ..
you you may need to set lower volts for div .

 

[Johnny_Law]

Thanks ... there was a fine needle under the hook. Nice!

For the ground. This player has a plastic chassis, so the ground is printed onto the PCB on the other side. I had to find a long enough grounded component lead to clip the ground to, but got it clipped.

Since I don't have a remote for this, I used my TV's remote to test it. I pointed the remote at the laser pickup. Then I hooked up the scope leads to the four test points one by one.

Back to the B-3 test points. On all four points, when remote's buttons were pushed, the scope would show a pulsing signal. I couldn't get the adjustments sorted out to make it stable on the display, but I could see the signal briefly. Instead of looking like a rounded-off sine wave, as pictured in the drawing above, it looked like a row of shark fins. In other words, there was only a positive voltage pulse, nothing negative.

I'm not sure how to interpret this. On the one hand, if anything appeared, I assume that means none of the diodes are open. On the other hand, if the only signal that appeared was shark-fin-shaped and positive-only, it doesn't match the picture in the manual.

Thoughts? If we think the photodiodes are OK, I can move to B-4 on the Fault Finding Tree.

 

[petehall347]

cant comment on cd players as never gone in with a scope . i have always replaced the laser unit or cleaned the lenses and mirrors to make them work again . i cant remember not getting one going unless it wasn't worth the price of new lasers .

 

[Johnny_Law]

I have even less experience with CD players. I've recapped a few and fixed various belts / trays but never fixed a player that couldn't read a disc. I'm wondering if this one is failing the photodiode test. If I had a known good CDM4 to swap in, I may give it a shot at this point, although the manual warns against doing that, as faulty laser power supply would just fry the next laser too.

Took a (horribly focused) cell phone pic of the scope during the B-3 Photodiode test. This is on pin 3, test point 7, but each of the other three look just like this. Needless to say, looks NOTHING like the manual's reference picture.



Since I don't have another CDM4 to try, and speaking of laser supply, I'm moving onto B-4 "Check of Laser Supply".

"LO" = "laser amplifier current output", this is pin 17 of the 6501 PHOTO DIODE SIGNAL PROCESSOR TDA8808, which is pin 9 of the ribbon cable connector.
"LM" = "laser monitor diode output", this is pin 18 of the same, which is pin 8 of the ribbon connector.

However, I have NO idea what "serv. pos. 2" means. The manual never defines any "serv. pos. 2".

The reference to "SK" refers to a replacement circuit ... is the manual saying I need to build a new circuit to use to test this? Oh wait, the manual is saying that I should build this to prevent frying the CDM4. That makes sense ...



... but, I can't do that right now, and if it's already dead, it's already dead. So I'll proceed just measuring these test points and see what they are.

Both test point measurements have the same reference values regardless of the position of SK. So I guess I'll just measure with the tray in, and see what I measure. Not sure what to make of step 3 though - how would power on differ from steps 1 or 2?

 

[Johnny_Law]

I measured the voltages once the CD player was on, and I had put it into B2 signal mode (that's the closest thing I could figure to "serv. pos. 2" ...)

Test point 9: 2.46V (a hair too high)
Test point 11: 8mV (way too low)

Hmm. Not sure where to go from here other than onwards through the steps...

 

[Johnny_Law]

For what it's worth, I tried following another CDM4 troubleshooting guide, no dice.

Apparently the CD40 manual describes the process of hitting "Play" at each mode of the 4-mode service positions, and then getting error readouts as a result. See the following:



However, this does NOT work with this player. At positions 0, 1, and 2, nothing happens when I hit Play. At position 3, it tries to start playing the CD, and fails back to "00 00:00" without displaying an error code.

 

[cpt_paranoia]

is the manual saying I need to build a new circuit to use to test this?

Yes. It is saying you should use the simple circuit to test the laser supply, removing the laser assembly. As it says, you can't test a feedback loop if you break the loop (remove the laser asst). That circuit takes the place of the laser asst, allowing you to test the laser PSU feedback loop.

 

[Johnny_Law]

I guess it won't be a big deal to build that circuit. I do have green LEDs on hand, just need the resistors.

Any of my conclusions or actions above seem suspect or incorrect to you?

 

[cpt_paranoia]

Needless to say, looks NOTHING like the manual's reference picture.

If you reduce the scope timebase (make the sweep slower), you might find that you do see ups and downs... The 'shark fins' you mention look like some ringing or noise pickup. You do have a rising edge and a falling edge. This suggests the photodiode is working.

I might also play wih the trigger settings. You say you've never used the scope before. Or any scope before...? There will be a calibration output on the front panel; this is usually something like a 1V, 1kHz square wave for adjusting probe compensation. You can use it to show the scope is basically working (sweep, trace, input amplifier, etc).

You need to connect that test circuit before you can start doing the LM and LO voltage measurements.

 

[cpt_paranoia]

BTW, have you checked these threads:

https://audiokarma.org/forums/index.php?threads/troubleshooting-cd-players.440522/

https://audiokarma.org/forums/index...-cd-players-and-why-they-stop-reading.617868/

 

[Johnny_Law]

Thank you! I had read the first one, but not the second.

From Laserology (http://lampizator.eu/LAMPIZATOR/TRANSPORT/laser/Laserology.html), it seems like my laser is OK (thank goodness): "6. If the 5 answer is - controlled speed and 2-3 seconds - the laser is alive and it can detect the beam reflection from silver surface."

Tips: if the laser is dead, the CD will not spin at all. The CD motor has a signal to start spinning only after the laser heads reports: "reflective surface detected on the height where CD is expected to be ". However, as someone rightly pointed out, some servo mechanisms will try spinning without checking if CD is in place or not. Apparently, they made assumption that a small motor spin in vain will not hurt.

That's a great tip. So I'll first need to see if the motor spins with no CD in place; if not, I'll figure out why the laser can't read the TOC.