Re: PRF Members Tech Journal
Posted: Mon Sep 16, 2024 2:52 pm
Aguilar AG500SC:
One of the earlier ones that still used the Tripath modules. New Korg-made ones use an ICEPower brick or something, I assume.
Sold as borked. Went straight into protection mode on startup. Found the two output MOSFETs were shorted and the +/-90 V output rail fuses were blown. 12V gate-drive regulator was also fried. Removed the RA2500 driver daughter board and found this:
Found a used Tripath TA0105A module on ebay that didn't appear to be counterfeit. It's the previous gen board, but still functions nearly the same in this application. Slight differences in the protection circuitry. Dropped it in, replaced the discontinued STW34NB20 MOSFETs with some more modern types (IRFB4227), and replaced the fuses and blown regulator. Decreased the MOSFET gate resistance from 5.6 ohms to 3.3 ohms and added a reverse-biased Schottky diode to the gate to help with MOSFET turn-off times.
Fired it up, and it immediately blew the fuses again and made a sound that was most likely arcing. I found a melted spot in the case of the output load relay, so I pulled that off and found some carbonization on the PCB that had presumably been there before and started arcing again. Also had to replace the MOSFETs a second time, as they were now shorted again. Methodically checked everything in stages, then fired it up again and it's working fine now.
One of the earlier ones that still used the Tripath modules. New Korg-made ones use an ICEPower brick or something, I assume.
Sold as borked. Went straight into protection mode on startup. Found the two output MOSFETs were shorted and the +/-90 V output rail fuses were blown. 12V gate-drive regulator was also fried. Removed the RA2500 driver daughter board and found this:
Found a used Tripath TA0105A module on ebay that didn't appear to be counterfeit. It's the previous gen board, but still functions nearly the same in this application. Slight differences in the protection circuitry. Dropped it in, replaced the discontinued STW34NB20 MOSFETs with some more modern types (IRFB4227), and replaced the fuses and blown regulator. Decreased the MOSFET gate resistance from 5.6 ohms to 3.3 ohms and added a reverse-biased Schottky diode to the gate to help with MOSFET turn-off times.
Fired it up, and it immediately blew the fuses again and made a sound that was most likely arcing. I found a melted spot in the case of the output load relay, so I pulled that off and found some carbonization on the PCB that had presumably been there before and started arcing again. Also had to replace the MOSFETs a second time, as they were now shorted again. Methodically checked everything in stages, then fired it up again and it's working fine now.