Archive for October, 2007

Hammond B250 repair and cap replacement

Sunday, October 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 ;-) .