I recently did a very successful White Oak upgrade on a nice PL400 Series II, no problems. That is a very awesome amp now. This left me with a good condition PL-36 board. So, I used this board to fix up a different PL400 Series II that was in pretty sorry shape.
I replaced all caps on the good PL-36 board and put it into the sorry PL400II. I also put new main caps in this amp, 10,000uF 100V. Also on the back panel, 4 2n4004 diodes that looked toasty In addition, I put in a speaker protection board that I built, detailed here:
http://audiokarma.org/forums/index....protection-board-for-phase-linear-400.835770/
For the purpose of bring-up, I jumpered across the relays in the speaker protection board, and applied 8-ohm loads on each channel. I fed in a 1kHz Sine wave, starting at 100mV and increasing. The amp did not clip as expected, it behaved very strangely and glitchy as seen in this video, and drew more input current compared to my other PL400II:
https://youtu.be/cYIUkyhmPms
Outputs are 10V/div, input is 200mV/div.
In hindsight, I wouldn't have changed so many things at once, but that is where I am at unfortunately. Has anyone seen this kind of behavior? The PL-36 was known good before I recapped it. This amp had 1 channel much quieter than the other and popped very loudly when shut off. One of the Zobel networks was 500 ohms (!), the other was 11 ohms. I tested all of the output transistors with a diode tester and they all tested with almost identical voltages, none open or shorted. All 16 of the transistors are MJ15024's, so quasi-complementary. When putting the transistors back in, I used mica pads and thermal paste. Based on the transistors looking good, I figured most of the problems were in the PL-36 board. I have not adjusted the bias pots on this board, I just left them where they were at, about in the center position.
I replaced all caps on the good PL-36 board and put it into the sorry PL400II. I also put new main caps in this amp, 10,000uF 100V. Also on the back panel, 4 2n4004 diodes that looked toasty In addition, I put in a speaker protection board that I built, detailed here:
http://audiokarma.org/forums/index....protection-board-for-phase-linear-400.835770/
For the purpose of bring-up, I jumpered across the relays in the speaker protection board, and applied 8-ohm loads on each channel. I fed in a 1kHz Sine wave, starting at 100mV and increasing. The amp did not clip as expected, it behaved very strangely and glitchy as seen in this video, and drew more input current compared to my other PL400II:
https://youtu.be/cYIUkyhmPms
Outputs are 10V/div, input is 200mV/div.
In hindsight, I wouldn't have changed so many things at once, but that is where I am at unfortunately. Has anyone seen this kind of behavior? The PL-36 was known good before I recapped it. This amp had 1 channel much quieter than the other and popped very loudly when shut off. One of the Zobel networks was 500 ohms (!), the other was 11 ohms. I tested all of the output transistors with a diode tester and they all tested with almost identical voltages, none open or shorted. All 16 of the transistors are MJ15024's, so quasi-complementary. When putting the transistors back in, I used mica pads and thermal paste. Based on the transistors looking good, I figured most of the problems were in the PL-36 board. I have not adjusted the bias pots on this board, I just left them where they were at, about in the center position.
