Class D car audio amplifier repair - Page 1
Forum section: electronics / repair

author: justin66
author_rank: Regular Contributor
timestamp: September 09, 2017, 12:46:54 pm
content: Hello guys im pretty stuck with this repair. I desolidered all output mosfets as well as power supply mosfets. I also took out the driver board and changed the oscilator tl494 and the allarm( protection) is still triggered with all the components out. No comonents seem to be broken or burnedThe amplifier is excurion hxa 2k 1200w rmsPlease help any ideas?

author: justin66
author_rank: Regular Contributor
timestamp: September 09, 2017, 05:41:56 pm
content: I found an smd micro chip but i cant find any info about it i suspect it may be brokenFirst row says :393Second row : st semiconductor logo YR0903Can anybody help me find some info about it?

author: drussell
author_rank: Super Contributor
timestamp: September 09, 2017, 06:16:05 pm
content: If it is an 8-pin chip, it is probably a 393 dual comparator. Google LM393 or even just "393 datasheet."

author: justin66
author_rank: Regular Contributor
timestamp: September 09, 2017, 06:49:00 pm
content: Thanks i found info, but desolidered part didnt help. I know it must be something wrong with the power supply part. I discovered that when the amplifier is fed 6v it doesnt protect. But when its anything abovr 7v it goes to protect.

author: Armadillo
author_rank: Super Contributor
timestamp: September 09, 2017, 07:03:52 pm
content: Quote from: justin66 on September 09, 2017, 06:49:00 pmThe Protect alarm could be for other events aside from overload, and reverse polarity is amongst one of them. Measure the DC current when you power it up to actually tell if there is in fact a short or overload event. With the voltage, you can tell what power is being drawn by the board vacant of those mosfets.Current = X amps, Voltage = Y Volts, Power = X X Y  [At alarm condition];If high current, then diode check all the diodes or remove them to try measure the current again.If still high current, while powering up, use your fingers to feel each component to identify which one is hot. The small smd grey color capacitors should be also be suspected.Hope it helps.

author: justin66
author_rank: Regular Contributor
timestamp: September 09, 2017, 07:42:36 pm
content: Thanks for the tips. I tired keeping it at 12v current is almost non existant. At 6v when protect led slowly goes off as the voltge goes to 6v mark the current is super small too it seems like only the led using it.I have tried this with 1 mosfets in each side and no rectifier diodes inNo components feels hot, nothing seems to be shorted out even the small smd transistors

author: Armadillo
author_rank: Super Contributor
timestamp: September 09, 2017, 07:59:46 pm
content: Quote from: justin66 on September 09, 2017, 07:42:36 pmThat's what I am saying, the alarm could simply means the boost is not working because you have taken all the mosfets out!. I don't think that's the way to troubleshoot the amplifier. Maybe you should describe what was/were the problems before you decided to take all the mosfets out, so that people here could help you.

author: justin66
author_rank: Regular Contributor
timestamp: September 10, 2017, 11:45:18 am
content: Ok thanks for the tip, i managed to get it running with components back in circuit. I powered the amp with the power supply that has an over current protection. It was running in protection constantly. So silly me i tried charging up a big capacitor. And it fried the pwm controller tl494 along with two mosfets( it had one per side )getting stuck in closed state permanently. The tl494 was new and good. Should i replace it again and hope for the best or what should i do? Next thing i will try is replace both tl494 and 393 opamp chip. But i think some of the smd transistors may be fried at this point. I bought an esd meter hope it will help me when i get it.

author: Armadillo
author_rank: Super Contributor
timestamp: September 10, 2017, 08:53:44 pm
content: Hi Justin;I think you should break down the amplifier into sections and test each section by section to avoid turning a small headache into a major brain surgery, won't you agree.There are various Mosfets in the 2 rows and between them there are the Rectifiers in between that separate the Mosfets.You take out the Rectifiers out of the board from the 2 rows to separate the switching power supply from the amplifiers.Then please draw a location Map to tabulate the Mosfets part numbers and the Rectifiers part numbers here so that we are on the same page and understanding of the Parts and Pins and location, using the Power supply input facing your stomach. See attached.After you dismantled the Rectifiers, Put the meter into diode mode and check all the Mosfets for short circuits between D-S, G-S etc... Please documents here in the table which ones are defective. [write it besides].You also check the Rectifiers for anomaly.Do you have;1. Oscilloscope2. Component Tester3. 9V 3A switch mode power supply4. Audio Signal Gen5. 4ohm Test Loads 1000 watts? [optional if we ever reach here].It's OK to update your country and location?Cheers!