elsewhere in this blog.
I found a blown 2 amp inline fuse in the power supply, which can be disassembled (with the help of a drill). I am sure quite a few of these units have found their way to a trash can, with their only issue being this blown fuse. 2 amp fastblow and slow blow Pico fuses are available all over the internet.
I checked the voltage rails first, and noticed the 9 volt rail was substantially low. Through a process of elimination, and disconnecting one rail at a time, I came to find out that the 5 volt regulator had actually failed, and was sending excess voltage into the 5 volt rail, and consequently dragging down the other rails. It wasn't an extremely high voltage, at about 6 volts, and but it was enough to drag down the other rails.
This posed a substantial problem as this particular Korg uses a tiny surface mount switching regulator, and a tiny surface mount FET in conjunction with it. I found these parts in China, on ebay.
Once installed, the new regulator, fet, and a few caps (for good measure I replaced the filter capacitors around the regulator), the power rail came up and the unit turned on and worked. I also added a small 5.6 volt zener diode, which would short the rail to ground in case the voltage ever exceeds the specs again, in the hopes of protecting the chips.But this was too late...
Apparently, one of the PCM roms was damaged... probably by the previous over voltage, when the regulator first failed. There are four of these PCM roms on the Triton LE, and they provide the basis for all of the preset sounds and programs.
On this particular unit, after its resurrection, some of the sounds, predominantly the organs and some brass sounds, sounded great. But others were distorted... primarily all of the piano patches and string patches. These must be looking for those damaged PCM samples.
Sadly, Korg no longer supplies these PCM roms, and so we had to settle for a partial repair, until such a time as I can scavenge these chips.
On the bright side, the sampling feature was restored, and many of the cool organ patches.. and probably about 50% of all the other patches sound perfect. But there was nowhere I could obtain those PCM roms.
However, if someone reading this has an old triton LE mainboard for sale, from which we could scavenge these chips, please let me know!
Sunday, April 6, 2014
Saturday, April 5, 2014
I am always skeptical when I receive these Cx3 organs for repair because of the known issues with the Seimens chips.. at the organ's heart are a couple of divide down oscillator chips that create the oscillations and gate them for each note. Their failure is a serious issue, because they are very hard to find and replace, and can only be replaced with other used chips that are probably very close to failure themselves. It seems someone was offering replacements, but apparently the supply dried up and I suppose they found it was no longer worth it to sell them.
But here was an instrument that didn't have that particular problem, rather it suffered from intermittent failures due to these badly leaking electrolytic capacitors seen below. The acid from inside of them ate through several traces on the boards, which had to be repaired.
The good news is that replacing them brought the keyboard back to life... the bad news is that there are about a thousand 10uF capacitors of this type sprinkled all throughout this keyboard. In this instance, due to financial and time constraints of the customer, we did replace only those that were seriously leaking... and left until later a full recapping, which is certainly necessary.
Currently the organ is working again, and sounding great, but most likely it will need some more caps replaced... unless the chips fail first!.
The failing capacitors were all 10 uF 16 volt capacitors. I doubt that it is coincidence... but it seems to me that the most frequent capacitors, in all gear, that I have to replace, are those rated 16 volts and less. I am not sure what is different between the processes used to make 16 volt caps and 35 and 50 volt capacitors, but I seem to rarely find failed 50 volt capacitors, unless they are too close to a heat source.
For this reason, I always use 50 volt capacitors, where possible, to replace them.