About a year or so ago I have purchased two Luxman L-85V amplifiers. Both not working. One was an easy fix as it only needed fuse. About $1.10 later, I had a nice working amplifier. The other amp had bigger problem. The amplifier boards had missing and mismatched transistors, burned out resistors and overall, they looked terrible. Swapping the boards from working amplifier brought the other amp to life so even with my limited electronics knowledge, I have decided to rebuild them. $55 later I had all the parts needed to do a complete rebuild. Honestly, the whole project took me about a year since I got distracted by family, other projects and bunch of other things. Just recently, I remembered that I have the boards in the closet. They were about 95% done. About an hour later all components were soldered in and the boards were ready for a test phase.
As always, I use DBT (dim bulb tester) to connect every project I am working on. In this case the DBT proved itself very useful. The moment I switched the power on, I got a bright light from the DBT. Back to the test bench checking every component. I have started with the obvious: transistors. I was almost sure that I got something wrong here. Well, I was right. I had two transistors incorrectly positioned on the board. After correcting the problem, I gave it another try. DBT still brightly lit. Since there was no smoke I have decided to check if I get any output. After connecting my iPod and cheap set of headphones, I got sound. Next I have tried to adjust BIAS and DC offset. That dimmed the light a bit but I was unable to get the BIAS down to 50mA as indicated in the service manual. The lowest setting on the trim pot got me down to about 190mA. That made the heatsinks very hot.
So again, I took the boards out and started checking the resistors values. To my surprise, I have put two resistors on the board according to the service manual and not the actual value of the resistor that was replaced. I am glad that I took a detailed picture of the boards before the disassembling them. I was able to read the resistor color codes of the old resistor. So I have replaced the parts with correct values and now I was able to adjust the BIAS down to 50mA. DBT was finally off.
Another test thru the headphones revealed what a great amplifier the Luxman is. It clearly tops all of my other gear that I own. On one hand there is no surprise as I own some low powered Marantz and Sansui models. But on the other hand this is a first amplifier that I can enjoy listening with all the tone controls disabled. The Luxman L-85V is very musical. Still a week after the rebuild was finished, I am listening to the Luxman amp with only loudness button on. All the other tone controls are defeated.
So now, few pictures from my rebuild. Here is a picture of the amplifier boards before rebuild. You can see mismatched transistors, burned out resistors and crappy service work that was performed in the past.
Here are the same boards with some new components (NOTE: this picture was taken before the transistors and resistors were fixed).
Here is the amplifier in my stereo rack next to the matching Luxman T-88V tuner.
I already bought capacitors to do a recap of the power board so that’s going to be my next project. I also need to clean the switches and Deoxit all the pots. I did not want to bother with that before I was sure that I had a working amplifier.
Thanks for reading.