Need help! MCD7008 CD player won’t power up after rebuild.

saabracer23

AK Subscriber
Subscriber
I’m working on a MCD7008 that I picked up, it had distorted output. After doing some research it looked like it was most likely the muting transistors right before the analog outs, or the .47 uF caps on the laser board. After a bit of reading it seemed like the thought was while you had it open might as well recap the board, replace the lamps and belt.

Well I did the full recap, replaced all four muting transistors with proper replacements, and then thought I’d put it back together and power it up to make sure all was kosher before moving onto the lamps and belt. Well wouldn’t you know it isn’t powering up now. I’ve checked all connections multiple time and all is good. I’ve gone over all of my soldering work and it looks good (I solder often and I’ve been doing it quite awhile).

I figured the next step would be to measure voltages, especially on the ps/relay board as the relay wasn’t clicking.

Here are a couple of photos showing where I measured and the results.

07CD9915-0F2A-47D1-9604-C026E9F7E6A6.png
239F8C3D-8549-43C1-9BD9-DFB597A95E33.png

The markings on the schematic fall on the same place as the board layout.

On the anode side of D1 (red) I get 121vac
On the leg of R1 (green) I get .9Vac and 0Vdc. As the voltage passes through D1 isn’t it rectified to DC?
On the cathode and anode of D2 (blue) .5Vac 0Vdc
On SP6 and SP8 (light blue) which are pins that go to the input of the transformer I get .5Vac
The yellow marking are pins that go to the power switch board. I removed the cable and connected my meter to both sides of the cable going to the switch. I measured for continuity and had continuity regardless of how many times I pushed the power button, always had continuity.

I measure the resistance of both resistors on the board and using the diode reader on my meter measured both diodes in circuit and the measured okay. Should I remove them from the circuit and measure them with my Peak Atlas meter?

I’m stuck, I have a feeling that my issue is on the ps/relay board, but not sure where to go from here. I don’t fully understand the flow of the electricity on the boards to know where to measure next. Could it be the relay? Isnt the power switch responsible for tripping the relay? I have continuity in the switch though. I just find it odd that it powers up just fine prior to me capping it and now it won’t power up.

Thank you sooooo much in advance!

Dan
 
Distorted output on both channels is coming from muting transistors and have nothing regards power/on/off function

what do you mean by "proper replacements " ?

2SC2878 are original type in MCD7008 (Q801 and Q802 L & R )

Regarding your problem with the power on/off function , I don't understand what you have done
 
Distorted output on both channels is coming from muting transistors and have nothing regards power/on/off function

what do you mean by "proper replacements " ?

2SC2878 are original type in MCD7008 (Q801 and Q802 L & R )

Regarding your problem with the power on/off function , I don't understand what you have done

So I figured the distorted output was due to the muting transistors. By proper, I mean that I had another thread (I believe you commented in it) about finding a replacement as you can’t just throw any old transistor in. You need one with a high enough Vbeo (I believe that was it). So I replaced them with the 2sc3729. This would have absolutely nothing to do with the power issue, I get that. I was just explaining what I had done.

So basically in addition to replacing those 4 transistors I also did a full electrolytic recap as in past threads it was suggested since it’s getting older and worth the recap.

At the moment that is all that I have done, the recap and the transistors. All solder joints and traces look good.

With measuring voltage, I have 120v going into the relay board and nothing coming out. In the photos above you’ll see where I’ve take all of my measurements.

Dan
 
Back
Top Bottom