Ampeg BA115

[guitar54]

Hi - New here...looks like a great resource!   I have more than novice experience with amp repair, but this one is challenging.  BA115.  Replaced the 2 mosfets - since this is the most common issue with the amp - I've fixed another and this was it - based on what the BA115 history, but the one I'm working on....flip on the power, the LED lights for a second, then nothing.  I'm thinking a power supply issue. 

Anyone have any other thoughts?  Thanks!

[Enzo]

Amps are amps, and circuits are circuits.  Start with power supply.  If the LED goes dark, I'd wager we lost the +16v supply.

But start at the start, is the fuse holder going open?  Is the power switch going open.  Does 120vAC make it to J7 and J17?  Is there AC on the secondary wires?  Are +40 and -40 volt supplies present?  Those 40v supplies drop through 270 ohm 5 watt resistors to 16v zeners.  Are either of the resistors open?  Or more likely is the solder to either of them cracked?

[DrGonz78]

Do all as Enzo said...

Also if you still have those mosfets you removed test them with a meter to make sure they were faulty, then at least it confirms that part. When changing out the output transistors due to output transistors failure it is a good idea to replace the driver transistors for the outputs. First time powering up an amp, with such a repair, it is good practice to use a light bulb limiter or current monitoring variac to make sure we don't fry the outputs or something else.

[guitar54]

Thanks for the tips - I'll check them out with the amp and reply back....appreciate your suggestions!