U8 and MPSA56 was installed when I took the amp apart. Someone had previously de-soldered it though so it's wrong.
TL431 / LM431 is a new part for me. I dont have any. Are these common to any other amp?? I have parts amps for testing but I dont think that part is on any of them. Can I make equivalent say out of zener diodes for testing prior to placing an order?
TL431 / LM431 is a new part for me. I dont have any. Are these common to any other amp?? I have parts amps for testing but I dont think that part is on any of them. Can I make equivalent say out of zener diodes for testing prior to placing an order?
The 431 was used in the 'type 2' amps. They are near the large 6.8k resistors near the 3525 driver IC.
Ah shoot I was looking at the MPSA56 in Q25 in the last few posts.
U8 is an LM431. Referencing non-bridging terminals fully powered on
1: -68
2: -69.5
3: -26.4
U8 is an LM431. Referencing non-bridging terminals fully powered on
1: -68
2: -69.5
3: -26.4
R66 is a 200K resistor measuring fine out of circuit. Looks like this resistor has been replaced previously. I see in the service manual its supposed to only be 20k. Could be the issue?
OK. 20K resistor and I could not get the rail voltage past +-36vDC. I put a 30K resistor in R66 and I can adjust to +-48vDC. The amp seems to stay powered on and keeps regulated voltage. Passes audio. I'm going to re-install all the prot resistors and get this to a testable state.
Thank you
Thank you
Oh..... Theres a power-save button next to the speaker terminals. This button cycles the amp between +-50vDC and +-36vDC. R66 with a 20k resistor actually does dial-in perfect.
That's right. It's just a voltage sensing circuit that triggers the power supply driver to go to a higher voltage so that it can produce higher power. This is to allow the amp to run cooler and more efficiently than it would if the amp had a constant ±50v.