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CDX woes

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sonavor
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sonavor posted on Tue, Aug 19 2014 11:38 PM

Back in 2012 on the old workbench forum, I (kind of) got my first CDX working. The unit required the door hinge fix on the eject switch side and I was able to get the CD player working for a short while. Then it started acting up (working intermittently). Resolving that it was an alignment problem with the hinge switches, I put the CDX up and worked on other projects.

Later, I received a second CDX that had good hinges.

I spent the last week trying to get one good functioning CDX out of the two. I actually had the unit playing CDs for one night. The next morning, it wasn't working again.

So far, I have resoldered the griplets on the two main boards of the first CDX.  The second CDX looks to be a later version and has nicer looking griplets. For now I haven't touched those.

The problem I am having right now is the CD motor spins all of the time. When the lid is open, I checked all of the switches and they measure as expected. Yet the motor spins. Two days ago the CDX unit started functioning correctly.  I could turn power on, open the lid, observe the motor wasn't spinning, insert a CD, hit play and the unit would start right up. It sounded really good when it works. The next morning I turned the unit on, inserted another CD and was surprised the the motor was already spinning the platter. So it broke overnight. 

So at various times I have seen both of my CDX main chassis operate correctly while, right now, they both behave the same and will not stop turning.

That makes me suspect the problem is common to both so it would have to be in the common pieces of my latest tests...which are the lid components: eject assembly, lid door motor assembly and control panel assembly. The only thing is - I have seen it work with those same components. Maybe a loose wire somewhere?

As I said earlier, the two switches on the door open motor assembly and the one switch on the door eject assembly appear to be operating correctly. I can measure continuity and open on the switches as the door hinges go through their travel.

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sonavor
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Okay Jacques and Martin....Apparently, the griplet re-soldering fixed the CDX. I did just the servo board first, it didn't fix the problem.  Next I did the Decoder board. When I reconnected everything, there it was - the motor powers on stopped. The stopped voltage was less that a volt.  I put the cover back on and tried a CD. The CD played.

This is a goofy piece of audio equipment for sure. I wish I had just soldered one griplet then tested before I moved to the next one. It would have been nice to know which part of the circuit was actually causing the problem.

Another strange thing was that I have two CDX units that fail in the same way (motor wouldn't stop spinning), yet the problem must be two separate issues with the main assembly. I thought that was not a likely scenario and the problem must be something common to both. That theory started falling apart when the problem remained regardless of what lid I used.

So I still have the second (CDX 001 in my earlier references) unit that I will put away for now until I get a door motor gear for it. On that unit I had already reworked the griplets but I guess I will have to retry that again. Of course there could be an actual failed component on the unit...but it had worked as recently as last week.

I will see if this working unit (CDX 002) continues to work tomorrow.

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sonavor
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This afternoon I decided to run a couple more tests.
Using the CDX main chassis I have been focused on (the one I had working yesterday), I verified it still doesn't work correctly with the lid and all connections in place.

Next, I disconnected and remove the lid completely (again) and verified the platter motor turns when power comes on.

Adding something different to the test, I connected up the other CDX lid (and control/display board). That means a different set of switches (lid, laser, load).  Another thing about this set of lid components - the door motor assembly is disassembled because I pulled the bad gear.  I went ahead and wired everything up to the CDX main chassis, then turned it on. The same problem is there. With this new set of switches, I can manipulate them manually very easy as they are exposed. I was unable to find a combination of the switches that would affect the platter motor. It just keeps turning.
I also noted that when I turned on power, the laser head would try to focus.

With that test over, my next step was to switch out the CDX main chassis with the other one (my first one and the one where I re-soldered the griplets).
I first noted the same behavior where the motor comes up turning immediately when power is applied and nothing connected to the chassis (no lid components). It behaves the same as the other one.

Now I connected up the lid components. I got the same result of the motor always spinning but I notice on this combination of components that the laser does not try to focus at start up, with the lid open like the other chassis did. 

Here is a picture of this crude test set up. In both set of tests, the CD interior light functions in response to the door lid switches opening and closing.


sonavor
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I decided to dig in and measure what the CDX turntable motor control voltage is.

In observing the turntable motor as I powered the CDX on and off (with no lid components attached), I can see that sometimes the motor turns clockwise, sometimes it turns counter clockwise and sometimes it starts out stopped for a second or two...then turns clockwise.
So checking the voltage at the motor control at the Pre Amp + Laser PCB, I measure +5.053 VDC when the turntable goes clockwise (looking from the bottom of the CDX) and -5.841 VDC when it goes counter clockwise. For the brief, occasional times the motor doesn't turn, I measure 0.285 VDC.

Here is a picture of the typical mode it starts up in.


sonavor
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From the Pre Amp + Laser PCB I traced back to the Servo board circuit that drives it. I am not sure why the CDX motor starts up in different states other than it could be due to none of the lid components being attached.  I would think that the logic would be to not allow the motor to operate if the lid components were not connected. I will re-measure these nodes tomorrow with the lid in place. However, in my earlier trouble-shooting, I observe the motor turning all the time when the lid is attached...so it will be interesting to see.

Here is the schematic showing the servo circuit that controls the turntable motor. I have put in red, the voltages I measure at those places when power is on the CDX and no lid components are connected.


sonavor
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I re-measured the CDX turntable motor control circuit with both lids and both main chassis assemblies today. Here is a new picture of the schematic with the voltages from the other CDX assembly.  There are differences in the voltages but the result in both cases is the same - the turntable motor is always in turn mode.  I am thinking that both CDX units have their own problem that affects the motor drive.  During these tests, I can see that the CDX logic it responding to the door hinge switches and I have tested two sets of door hinges. So I think the problem is somewhere in the main chassis assembly.  On the schematic, it shows some expected values.  The values that are circled are for the Stop condition.  The values in a rectangle are for Play.  My CDX units are supposed to be in the Stop mode, but stopped as in stopped with the lid open.  The schematic may be describing Stop for a CD inserted with the door closed.  The Stop I am looking for should produce a voltage at 23-5 between about +-1.2 VDC.  That what I observed when the motor came up stopped a couple of times. I wasn't able to reproduce that condition today though. However, I can see that the motor will start turning as soon as it gets +5 or -5 across 23-5 and 23-6. 

I guess the next step is to start looking at the signals that feed pins 5 and 6 of the MC1458 OpAmp.

 


sonavor
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After looking at those last measurements something didn't look right to me so I re-measured them. The update shows the CDX 002 (as I have named it) with voltages that are in line with the schematic listed values.  Those are the Stop mode voltages but are the same on this unit regardless of the position of the door switches. 


sonavor
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The control voltages on the Servo board for the turntable motor look pretty much like they should except for the final output at 23-5 (+5.071 VDC). That should be down under 1 volt I believe. So if the controls for those signals leading up to the 6209 OpAmp are in the correct states, then the motor control problem must be elsewhere.  I decided to look at the Motor Stop signals on the Servo board to and from the Motor Stop board.  I had originally looked at the Motor Stop board first because it made sense that it would control the stopping of the motor. On my first look I couldn't see how that worked. So I measured the voltages on the CDX involved in the turntable motor and the Motor Stop board.

Here are the signals on the Servo board. I get the same voltage values with the lid open or closed.


sonavor
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Here is the Motor Stop board with the measurements there.


sonavor
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With the measurements I have made, it doesn't make sense to me why the CDX is putting the turntable motor in that turning state.  The are other lines
      ___                                                                                                                                                                                                                           ___
like DO that go from Motor Stop 64-1 and Servo 29-1 to Servo 29-3 and on to Decoding 33-3.  The CDX Circuit Description Manual does say that DO is used to determine if the motor is actually stopped or not.  My measurement shows that it is high, so it is in Play mode.

At this point I concluded that the problem is in the logic of the boards somewhere difficult to find. My decision now is to go ahead and re-solder the griplets of this CDX (CDX 002) unit. I had done that on the first unit and not had any success. But I decided it was the easiest thing to try at this point before going any deeper into the board. The boards on the CDX are a strange mixture of old, full-sized components soldered to the boards and tiny surface mount components. That makes trouble-shooting the components a little trickier. So, time to re-solder the griplets.

sonavor
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Okay Jacques and Martin....Apparently, the griplet re-soldering fixed the CDX. I did just the servo board first, it didn't fix the problem.  Next I did the Decoder board. When I reconnected everything, there it was - the motor powers on stopped. The stopped voltage was less that a volt.  I put the cover back on and tried a CD. The CD played.

This is a goofy piece of audio equipment for sure. I wish I had just soldered one griplet then tested before I moved to the next one. It would have been nice to know which part of the circuit was actually causing the problem.

Another strange thing was that I have two CDX units that fail in the same way (motor wouldn't stop spinning), yet the problem must be two separate issues with the main assembly. I thought that was not a likely scenario and the problem must be something common to both. That theory started falling apart when the problem remained regardless of what lid I used.

So I still have the second (CDX 001 in my earlier references) unit that I will put away for now until I get a door motor gear for it. On that unit I had already reworked the griplets but I guess I will have to retry that again. Of course there could be an actual failed component on the unit...but it had worked as recently as last week.

I will see if this working unit (CDX 002) continues to work tomorrow.

sonavor
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FYI, here is what I measure on the Motor Stop board when the circuitry is working (CDX is on and the motor is not running).


chartz
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chartz replied on Fri, Aug 22 2014 7:11 AM

Well done John. I admire your perseverance!

The vias or griplets I always do by inserting a piece of wire through the hole and solder on both sides. Just to be sure.

Philips CD104 machines (upon which CDX is based) suffer the same problem.

Jacques

sonavor
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sonavor replied on Sat, Aug 23 2014 12:24 AM

Thanks Jacques.

I am happy to report the CDX is still working great today.

Today I went back an ran a circuit simulation of that motor control. I see now how that DO signal from the Decoding board controls the motor drive on the Servo board. So it makes sense why the griplet re-soldering didn't work until I did that (Decoder) board. Now I know if the turntable motor won't stop turning, the first thing I need to do is check the control signal (DO) from the Decoding board. That other CDX appears to have the same problem but I had already re-soldered those griplets with new wire through to connect the layers. That unit could still have a bad connection or some component actually failed. I'll take another look at the second CDX this weekend.

For now though, I am enjoying the working CDX and I think is was well worth the effort to get the problem solved.

-sonavor

sonavor
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I dug back in to the other CDX unit (the one I refer to as CDX 001 because it was the first one I worked on).

This CDX 001 unit is the one I had already repaired the griplets on but behaves the same as my (repaired) CDX 002 unit. So the griplets should be fine. To double-check them I tested continuity between all of the griplets to each other and the ground plane as well as the trace side where the griplets connect to. No problems were found.

The next step was to power up the CDX and check the DO signal. Sure enough, it was high (+6.2 VDC). It should be low. I also checked right at the signal source (Comparator LM339N device), IC 6508 - pin 13. Checking the other 6508 pins I noticed that pin 5 was +7.5 VDC. It is supposed to be fixed at +2.5 VDC.

I decided to pull the 6508 chip and tie the pin 13 DO signal to the pin 12 (ground). That will make sure the DO signal is low and prevent the motor from turning. I observed it did nothing. The DO signal was still high.

I took the unit apart again and checked the 6508 pin 12 ground pin to the board ground. It should measure continuity with the griplets and ground plane. It didn't. Tracing the IC grounds around the trace side, I found that the IC grounds were connected between 6508 (pin 12) and 6501 (pin 14).  6501 pin 14 is supposed to connect to the griplet that is nearby it.  When I checked for continuity between those two pins, I got nothing. I could see the board trace (less than 10mm) connects them but they aren't connecting.  So I created my own jumper between the griplet pin and the 6501 pin 14 lead.

The CDX 001 unit now powers on with the motor off as expected.  The Decoder board 6508 comparator chip has a low on pin 13 (output for DO) and the 6508 pin 5 signal is now back to +2.5 VDC as expected.

Jacques is gracious enough to send me a spare CDX door motor drive gear to replace the broken one on this unit. Once it arrives I will reassembly this CDX 001 unit completely and expect it to work.

Here is a picture of the schematic showing the CDX DO signal to the Motor Stop.  The red circled area is where the missing ground caused problems for the DO signal.

 


sonavor
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Here is the CDX Decoder board repair I had to make to reconnect IC 6501, pin 14 (ground) with the griplet pin. The jumper is soldered to the IC pin.  A better fix might be to install a 14-pin socket for IC 6501 and solder the jumper to the socket pin 14 (instead of the actual IC). But for now I will leave it like this and put this unit up until the new door motor gear arrives.


chartz
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chartz replied on Mon, Aug 25 2014 9:58 AM

What I like and look up to John is that you actually do your repairs in a very insightful way, while we amateurs "just do the griplets" and pray. Most of the time, it works, but not always!

Thanks for your time and the invaluable illustrations and thorough explanations.

Yes - thumbs up

Jacques

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