• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

MCD7008 Horrible Distortion/Static

smartin53

smartin53

Well-Known Member
OK so I am attempting to bring an MCD7008 back to life. At first the loading mechanism wasn't behaving but I fixed that by cleaning the belts (I'm sure it just needs new ones ultimately).

Now, its alive and loads up a CD, reads it and gets the track numbers, but then it stops. Sometimes I can get a track to play here and there, and when they do the audio is terribly distorted and staticy on all outputs.

Any thoughts? Bad laser mech maybe? Motor not spinning fast enough? FUBAR circuit board?
 
Register to hide this ad
MCD7008 Horrible distortion

Hello smartin53

1) without the unit in front of me it is difficult to understand what distortion you have at the output :no:
2) reading the track and output distorded are two different things with different cause :thumbsdn:
3) output distorded is possible when muting transistors at the output are defect and this is caused by user playing with cables (in and out) :nono: when unit is on ! I have refixed some MCD7008 with this problem :scratch2:
the ref of these transistors is Q801L and Q801R on the PCB (see my picture)
4) do you have this problem on the both channels ?
5) do you have the service manual ?
6) do have check all the voltages ?
Come back to us with report
 
Last edited:
Simple first thing to try is to clean the optics, a Q tip, some alcohol and a gentile swab to the lens that is on the top of the optics, all it takes is a spec of dust in the right place to mess things up.
 
Clean lens, lube rails and cogs (be frugal, clean old grease first), check if belts need replacement, inspect visually all caps and solder joints, test transformer, change main caps by default, change opamps, change powercable. Bad motors also can distort audio signal badly.

Nothing else you can do about it... its an old Philips CDP with a Mac badge...
 
MCD7008 is Nacamichi based, uses Sony optics that sell for as low as $12, KSS part number is on the back side of the optics.
 
Thanks for the feedback I'll take a look at some of these. Already tried the lens cleaning as this was my first thought. I'd have been surprised if it was that though considering the level of distortion. Of course there is a good chance there are multiple problems too. I miss the simplicity of the older vintage mac stuff which I find much easier to diagnose.
 
OK I've done a visual inspection and don't see any obvious issues and swapped out the laser module since it was a cheap and easy option ($10) but no go so far. To maybe help troubleshoot, linked is a recording of the audio output. This distortion is on both channels. Also, even with the new laser, its still has trouble reading tracks at the beginning an end of the CD. Maybe a motor issue? BTW you may want to turn down your speakers initially and then bring them up. Its really bad sounding.

http://www.reimuchan.com/ohdeargod.wav
 
MCD7008 Horrible distortion

Hello Smartin53
Good idea for the audio file ! :thmbsp:
It is perfect because the sound that we can hear is quantification noise above normal sound (all together mixed ) :yes:
This is a precious indication and your problem is probably coming from the DAC section not from the optical pick up .
If you want to be sure of that , just use your CD player with external DAC through the coaxial digital output .If the sound is clear and perfect , your DAC section (inside the MCD7008 ) is bad ! (RAM or other IC) :scratch2:
Let us know if you have tried that !:thmbsp:
 
Well I tried the digital coax out and the same distortion occurs which tells me that the problem is farther back in the line somewhere. Also, I can tell there is some noise that syncs up with the motor speed. Its less audible in the audiofile since that's from track 6, but when I can get track 1 to play, it is much worse.

I'm wondering if it is the filter cap(s) for the power supply, but no matter how much I pour into the service manual I can't determine which ones are the correct caps to test. I'm really rusty at reading the diagrams which is one of the reasons I am doing this. Trying to gain some lost skills back.
 
Oh yea, one other thing worth noting. I do not think the unit is getting a proper ground. I'm sure most of you know that feeling you get on metal surfaces when the ground is bad...a kind of tingly/fuzzy feeling as you move your hand along the metal. I know that on my laptop when this was happening, I was getting all sorts of noise on the audio digital or otherwise from all the components...HD spin, CD player spin, wifi, etc. When I fixed it, the noise cleared up. I wonder if something similar could be happening here which would indicate the PSU is possibly at fault.
 
Had distortion from one channel on my '7008 and it turned out to be a bad muting transistor. At the back, right, near the outputs.

Probably not the same issue you're having but perhaps something to check out.

Murray
 
Well I solved that grounding issue. Someone had just flipped the connectors on the power plug itself so the polarity was off. When I switched them back the ground was good again. Didn't solve my distortion issue though.

I was reading a thread that described a similar issue and it was the dram that was bad in that person's case. I'll just keep plugging away. I'm gonna swap the motor when I get that to see if it fixes my read issues. Then I'll go from there.
 
You might need to consider it a Nak and use their service manual to get scope traces to confirm your problems. I was able via the Phillips community to find solutions to "laser" problems that were really bad cap issues and have had great success applying this to early MCDs.
 
Well I was able to at least rule out most of the op amps at least. I decided to troubleshoot em since I have extras on hand and also converted them to sockets for an idea I have assuming I get this thing going later. Just have to test 2 more tomorrow. I know these were less likely components to have failed, but it was fun. I also replaced the filter caps (I think) but no impact there.

I've actually been going off the Nak MB-3 and CD Player 3 service manuals since they are similar (there are diffs though in some layout and components on the mainboard).

Now I need to determine exactly what each chip is and source replacements. Fingers crossed I also get the new motor tomorrow to try.
 
Well I've swapped out most of the ICs that are in the digital path at this point with no luck so far. I'm starting to wonder if the RF board could need adjustment. Its hard to get at though so I haven't messed with it yet.

The player still has read issues, and of course the sound hasn't changed from what I posted earlier. Still trying to figure out what could cause both an audio distortion, and also CD read issues at the same time (assuming they are related). I do notice that when the CD player tries to read a CD, the lapts dim a few times initially. Its not significant but its there.
 
When I decided to dive into the MCD7000 I had closeted for 8 years I first researched all the international posts of repair efforts by Phillips techs. Gave me great insight into resoratation approaches to the Phillips based Mac units.

Have you sorted through all the Nak repair threads for this Nak based unit?

It sounds like a laser focus issue.
 
Yea I've been hunting down all the nak info I can find. I've tried adjusting the focus a few times but no go so far. Also been working the spindle in case it was a bit off with no luck. Thqts why i'm wondering if I need to adjust the rf board at this point.
 
Got it finally. Good chance it was the issue from the start but I didn't think about it until now. I kept going back at the laser focus since I could not imagine it being anything else...well for some reason I never thought to adjust the pot on the laser board itself. On the original one it was glued into place. I didn't catch that the new one was not. I've almost completely eliminated the distortion and read issues at this point. Its a very very fine adjustment though so it may take a but...but I think I finally have it solved :)
 
MCD7008 Horrible distortion

Hello Smartin53

Do you adjust the small pot on the pickup PCB ? Did you make it without laser beam meter ?
Do you know the leader LPM8000 ? IF you can find one I give you the value you should get when you adjust this pot (see my picture ) :thmbsp:
Do you have an oscilloscope to make the EFM adjustment ? :thmbsp:
 
Last edited:
Yea i was adjusting the pickup pot. In my case though it was a very scientific method of tweak it and play it. I don't have any fancy equipment so it's just a matter of guesstimating till i get it right.

Odd thing though. I can get it running 100%...but only if I loosen one of the one of the pickup guide bar hold downs and leave the cover of the unit. Tighten the bar and I get noise, put on the cover and it has trouble reading CD tracks if I try to go directly to them.
 
You must log in or register to reply here.
Back
Top Bottom