Class D amp, blown MOSFETS. Help on troubleshooting further. - Page 1
Forum section: electronics / repair

author: Yamin
author_rank: Frequent Contributor
timestamp: June 13, 2021, 07:48:00 pm
content: Hi guys, I've got two faulty amplifier boards of powered speakers. I was informed that there was a mains overvoltage (measured 300V between L and N yikes!) situation that the speakers were exposed to. The speakers weren't being used at the time but was on at the time.The power supply FETS were blown along with the gate diodes and the resistors. Luckily had spares for those.Before powering up, I had a look for other faulty components and found that two MOSFETS for the amplifier were also shorted out on one channel that is. I am not super familiar with working on Class D amps and was hoping to get more ideas on what to looks for before just changing the FETS. I probed around components near the fets and didn't find anything which were faulty. The control IC is IRS2092. I have included a photo of the good side for reference. How could I check the IC whether the IC is faulty or not. I haven't got access to an oscilloscope at the momentLastly I understand that its not a good idea to power up Class D amps without a load attached which may cause ringing otherwise. Was wondering whether it would be okay to power up the amp to check whether it powers up and not apply any input signal.Thanks in advance

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: June 13, 2021, 10:18:13 pm
content: First I would make sure that the various power rails are good before wacking in some new fets, especially since there were PSU problems. It looks like the IC drives the FETs directly, so as long as the IC is not dead you could probably just change the fets without issue.That's just my first thoughts anyways...

author: Yamin
author_rank: Frequent Contributor
timestamp: June 14, 2021, 07:06:16 pm
content: I spoke too early, the power supply is also not fixed. Replaced the power supply fets diodes and the resistors. I figured the control IC IR2153 would be ok as I checked with the FETs removed and it I didn't measure the gate signal to be latched which I have seen before on faulty ICs. I powered on with the FETs and nothing. Removed the IC and put in to a test circuit and turns out the IC was faulty.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: June 14, 2021, 08:16:38 pm
content: Usually, if one or more output MOSFETs are toast, the controller IC is dead as well.If in doubt, replace them.Also, make sure your measuring equipment is properly isolated. F*ing around with those circuits and tools on GND level will result in catastrophic failure.Also, if you do not have schematics for the specific amp, you might want to take a look at the IRS2092 application notes.https://www.infineon.com/dgdl/iraudamp7s.pdf?fileId=5546d462533600a40153569addc92bfb

author: Yamin
author_rank: Frequent Contributor
timestamp: June 15, 2021, 07:23:36 pm
content: Quote from: frozenfrogz on June 14, 2021, 08:16:38 pmThis is what I'm afraid of. Very hard to source this IRS2092 IC locally. Would have to order them in which takes months now.Any suggestions on good resources on class D amplifier design and troubleshooting. I've been going through youtube videos and some forum posts.Thanks for the help

author: perieanuo
author_rank: Frequent Contributor
timestamp: June 17, 2021, 02:45:00 pm
content: off topic, after repair, voltage monitoring relay+contactor like 180V lower voltage, 250-255 higher voltage, better on the safe sidelower one's are most tricky for our smps