Posted on Saturday, 7th January 2012 by Auw Jimmy
After the Part I has been done, now I continue to the Part II. On this 2nd part, I will see what’s wrong with the Marantz PM400AVK.
Simple testing method is to try it on other speaker. Initial diagnosis is the volume control problem, as I could hear some cracking and intermittent no sound on the speaker. But sometime the problem could be solved after turning the volume up and down. Definitely, initial problem is on the volume control. So let’s take a look inside.
The potentiometer on the volume control module seems has been swapped by unauthorized (or non-professional) repair person. As I can see on the volume control module, the original potentiometer should be ALPS or compatible with motor (so it can be controlled by a remote control). But as you can see below, somebody has changed it with a standard potentiometer.
A bonus: ‘very excellent soldering skill’ !!!
Remove the old potentiometer and clean the PCB. Another sad thing is, one solder pad is broken during the removal process. Well, old stuff + poor soldering skill = trouble! But off course this kind of small thing will not become a serious issue for a serious DIY, correct?
I use old potentiometer, should be from ALPS. This one actually got motor, but with different shape with the original one used on the volume control module. So, it’s not one-to-one exact replacement. Anyway, again, this such thing will not prevent me to use this potentiometer. Simply, I use extension cable to arrange the pin out from this potentiometer to match with the original pin out. But I don’t connect the motor as it doesn’t really needed at this stage.
The new potentiometer connected to the volume control module PCB via some cables. Not the best effort, but definitely it will work just fine.
I also take some time to clean up the PCB. Not they are as good as new PCB. The broken solder pad also has been solved by joining them with some tin. As simple as it can be…
The potentiometer plugged to the front chassis, then the volume control module PCB is lying around on the back. I put extra paper tape on the back PCB to prevent any shortcut possibility as the PCB is just lying around and not bolted into something.
I suppose this should solve all the problem? I do hope I make a right step, but within next few minutes, I just realize that I was wrong…
After around 30 minutes testing, the sound is quite enjoyable. No more cracking or intermittent no sound issue. But… now I can smell something hot. I think either my mom or my wife is cooking something on the first floor. Then, one channel suddenly produces no sound. After confirming the connection and everything are correct, then I start another detail examination. I find one of the IC underneath the main PCB is very hot. I think it should be either regulator or driver IC. Then after I remove the top PCB completely, I find two ‘pregnant capacitor’. Holy xxxx! I find some sign that this capacitors also not original one and have been replaced before. It could be this replacement is fake capacitor. I think 56V rating should be fine for most application and shall not produce any ‘pregnancy’. Arggggghhhhhh….
One of the IC underneath the PCB got very hot. Something could be wrong Jimmy… This can’t be true!
So, the challenge is not done yet. Tracing back the issue could be troublesome and takes some more time. I’m thinking to repair this, or to build another one. An Gainclone probably could be build with less time comparing to trace back this faulty unit? But will see which one could be the best option.