Originally Posted by
meBob
Hello All,
Recently I bought a 405-2 from a private AOS seller and the amp was as described by the seller, that is to say recently serviced by Quad, fully working and sounding good. I am happy with the amp and decided to do a few mods, such as lower the sensitivity to 1.5v and add higher capacity psu caps, there were also a few other Bernd Ludwig mods I was concidering.
I took the top cover off and had a look around, the boards are a 12565 ver 6 and everything was pretty much standard except for the new Kemet 10000uf psu caps, having never been inside one of these before I had gentle root around, but perhaps not gentle enough.
With in minutes of switching back on the right channel started to fail, becoming blared and then suddenly dead (very dead!), initially I thought it was the speaker and after testing it found it wasn't. Upon opening up the amp again, I quickly discovered the problem, one of the LED wires had come away from its solder pad, where it had only been just slightly embeded into the solder, all it took was the slightest of nudges to free this wire from the solder.
After testing the good and bad board side by side and comparing values with a multimeter, TR9/TR10, TR8, D13, D5, D10, N1/N2 are all dead, I feel lucky the short only damaged the right hand side. I actually stopped testing and decided to replace all the transistors and Zeners/Diodes, I also don't want to have different TR9/TR10, TR7/TR8 transistors on each board and so both boards will get the same new ones.
I'm really pissed off with the workmanship, I was careful with the wires and it took no pressure at all to dislodge the LED wire.
I am now where I am and it's in for a penny in for a pound, It's become a full project I'll be chucking money and time at it.
N1/N2 are not replaceable and so they'll have to go from both board along with R35/R36 and C18/C19.
I'd like to also replace C15/C16 and C11 but I'm not sure what types they are?
My mindset is to replace anything (or future proof) now while the boards are out. If there's any anything else that might need
attention I'd be grateful for opinions.
Cheers.