Good afternoon
I followed your recommendations by sitting an IRFB4227 on the HO. So getting all new and replaced component in place.
In parallel, I was thinking that it could be good to reduce the input voltage of the amp, I have a VARIAC (0Vac to 300Vac) and moved from 235Vdc to 190Vdc main input so, I have +/- 56 VDC like the original schematic, and other low voltages are pretty closed to what is expected.
You know what ? it works !
I have 9,31 stable dc voltage on pin 2 CSD and 2Vdc on Pin3 with 400Khz PWM !
![ThumbsUp :-+](https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif)
with a load of 8R connected to the output and no input signal.
I plugged into a CAB ang got a nice sound, for the moment I didn't go forward, because I don't know if it is because of the low input voltage that finally adjust rails on +/- 56Vdc or I did something else.
I'm just afraid that if I move from 190Vac to 235Vac so getting +/- 75Vdc on rails that could destroy again the power amp part.
If that is the case we need to investigate on the SMPS power supply. That in my case was also burnt at the beginning, and I replaced some components there.
From the power amp part the only thing I changed :
- IRF20957s x1
- IRFB2742 x2
- C61 with another 10uF capacitor
If only an Ampeg tech could confirm that rails voltage on this release should be
+/- 55Vdc or
+/- 75Vdc with
REV H that could help to investigate on the SMPS.
Julien