Music & Gear

Korg 01/W „no sound“ repair

Sonntag, August 3rd, 2008

A few weeks ago my 01/W started sounding „hissy“ and distorted and the output level dropped audibly. After a short power off it recovered without further action. But then, on the next day, all analog outputs were dead.

When I opened the housing I found two leaked electrolytic capacitors on the mainboard’s sub-PSU for the DAC and analog stages. This ±5 volts sub-PSU with two 100 mA voltage regulators is disposed behind the ±12 volts stabilisation circuitry of the main PSU and supplies stable and noise-free local voltages.

The caps C95 and C96 had ruptured and the sub-PSU and even more distant parts were spattered with electrolyt. And the really bad thing about leaked electrolyt on a printed circuit board is that it causes corrosion and damage of metallic parts and circuit traces. See the „overgrown“ capacitor C100 or the diode D3 on the photos for an impression of how this affects and proceeds.

To clean this type of mess I prefer cotton swabs heavily soaked with isopropanol (isopropyl alcohol). There’s no need to spare with the isopropanol, it does not do any harm to electronic components and evaporates without residue. And the cleaning should be repeated a few times with fresh swabs.

What has been left over from the „acid attack“ on my 01/W did not look dramatic at first. I replaced the two evil caps, connected the mainboard and powered up the 01/W, but there was no sound. While measuring I found that the negative leg around the IC52 (79L05) was operational but IC53 (78L05) floated around at 0 volts on it’s output and input. Then I noticed that one of the C100 capacitor’s leads had been „eaten“ by the acid and — more important — the +12 volt trace below the lead had also been etched away.

So I replaced C100 and patched the broken trace by scraping off a bit of solder resist and bridging it with solder. As you can see on the photos I also replaced IC53, which stabilised at 4.5 volts and not 5.0 volts. Of course, it is not state of the art to replace an SOT89 SMD component with a TO92 through-hole component, but firstly it would have taken some amount of effort to get the SOT89 variant and secondly it is yet a robust and well-functioning replacement in this case (fitting pinout and leads, no thermal or mechanical aspects to be considered).

The other capacitors on my 01/W were apparently in a good condition, so I would not estimate this to be a general case of „bad-caps-alert“ for all the other 01/Ws around. However, in the recent past I read about 01/W owners on the net who have asked for advice on their whatever natured „no sound“ problem, and so this article may give you a hint towards the possible cause.


Update (October 07, 2008):

J-man sent me photos of his „no sound“ repair on a 01R/W, the rackmount variant of the 01/W. He writes: „I’m sending you the pictures of my fixed 01R/W, before and after the repair. […] I’m sorry about the quality of the pictures before the fixing: they are quite blurred, expecially one of them.“


Battery replacement on Korg M1R

Sonntag, Juni 15th, 2008

My M1R came up with a „battery low“ warning just a few months after I did the replacement on the TX802. Possibly these oldies start a conversation on their sicknesses each night after the boss has gone to sleep. The CR2032 button cell is sitting in a socket, so there is not much to tell about the exercise itself, but it was still an opportunity to take photos of the innards.


Battery replacement on Yamaha TX802

Sonntag, Juni 8th, 2008

My TX802 started behaving like it was broken: strange characters on the display and strange sounds. Not even a factory reset and a following sysex dump helped to remedy this situation. Although there was no „battery low“ warning, I first replaced the 20 years old battery before going on with error search. It turned out, that this was a good decision; everything is fine now and the box is back fully operational. As you can see on the photos, it is fairly straightforward to open the housing and reach both sides of the mainboard. The new battery holder did not fit exactly into the soldering holes, but I found a decent workaround by twisting the pins a bit and underlaying the holder with hot glue.


Hammond B250 repair and cap replacement

Sonntag, Oktober 14th, 2007

Recently, after having visited the Tasten-Festival at Herdecke, I felt inspired to sit down on my Hammond B250 and move my fingers. This sadly happens seldom enough, and so the organ hadn’t then been powered on for months. And although the B250 is a quite reliable oldie in my experience (just one repair within the past 10 years, a voltage regulator on the PSU had to be replaced), it now came up with a dead „G“ pedal tone.

So I first checked the pedal unit and then opened up the B250 and found a broken connector on the bass tone generator board. The pin just broke in pieces after being unclipped and pulled out of the housing (see red circles on image). With an appropriate replacement part this was quickly fixed. But there was another thing that soon concerned me much more: Electrolytic capacitors with green corroded pins.

Approximately 80 percent of all caps on the B250’s PCBs showed more or less visible signs of aging and deterioration. I started to replace a few caps on the bass tone generator board, measured their ESR and capacity values and – to my surprise – couldn’t detect any problems. »Dude«, you may say now, »it is too obvious that these caps have to be replaced«. You are right, but the organ still plays and a complete swap would mean a total of 98 caps. »Replace them immediately. They will soon lose capacity and the leaking acid will irreparably damage the PCBs «, an expert told me after I sent him a photo. Ok, I’m persuaded, this is a case of „bad caps alert“.

While removing and „recaping“ the panel PBCs I took the opportunity to refurbish the drawbars. Although my B250 lives in a smoke-free environment and a deep cleaning was not necessary, it was still a good idea to remove the dry old grease and lubricate it with fresh „white“ lithium based grease. See this excellent Hammond Service page for instructions and tips.

All in all it took two workdays to complete this operation. Below is a photo of my B250 after wakening up, and I think the organ looks happy now. The overall sound is a bit more bright and substantial, due to the all new coupling capacitors. It also smells like a new one ;-) .


JX-8P reloaded (2)

Samstag, April 15th, 2006

Before going into work with JX I cleaned the keyboard in the last few days. The keys were sticky and smeary from nicotine and dirt, so I put them all into denture cleaner over night and on the next day brushed them with dish liquid.

A small plastic strip on the bottom side of the keyboard must be removed to get the keys out. It puzzles me that Roland glued the strip instead of choosing a solution that would be faster to recover at service. One also has to manually (un-)clip 61 springs with a pliers, one for each key. Compared to the Yamaha keyboard on the Korg 01/W this is cumbersome.

Having the best opportunity, I checked the aftertouch sensor for proper operation. As you may read on analog.no or synthzone.com, early JXs may suffer from oxidation on the metal films of the sensor. With not having the sound engine operational yet, I measured the resistance changing on pressure and, to my feeling, didn’t find any anormalities (equally somewhere below 20kΩ along the sensor).