Ma audio hk-802sx

mike49504 · 21st June 2010, 02:53 AM

I recieved this amp in for repair. I pulled the first 2 legs of the power supply fets off the board. Leg 3 is still solderd to the board. I also pulled the rectifiers and power supply drivers in this amp.

I still read a short directly across power and ground terminals of the amp.

Wondering what could cause this?? Transformer maybe??

Perry Babin · 21st June 2010, 04:06 AM

D1-d3?

mike49504 · 21st June 2010, 04:09 AM

I lifted 1 side of D1,D2,D3 out of the board And i still read a short between positive and negative terminals

Perry Babin · 21st June 2010, 04:20 AM

If there are no other large diodes and the FETS are out of the circuit, I'd suspect a solder bridge.

mike49504 · 21st June 2010, 05:40 AM

I looked over the entire amp i dont see any solder bridges and no other diodes.

The amp worked for a few secs when it came in but then started drawing high current and reading shorted

Perry Babin · 21st June 2010, 01:33 PM

Does it read shorted with your meter as well as drawing high current when connected to 12v?

mike49504 · 21st June 2010, 03:25 PM

It reads shorted with my meter. And draws high current with just power and ground hooked up to the amp.

Perry Babin · 21st June 2010, 03:31 PM

It's possible that a primary filter capacitor has failed but that's unlikely. Have you cleaned all of the flux off of the board around the power supply FETs and examined the area with a magnifying glass? Sometimes a tiny thread of solder can be hidden in the flux and cause this problem.

mike49504 · 21st June 2010, 03:33 PM

I will clean it right now and let you know in 5 mins

mike49504 · 21st June 2010, 03:46 PM

Perry,

I cleaned the board . Guess i overlooked the first time i found a solder bridge between legs 1 and 2 for one of the power supply fets.

Next question is The guy had this amp hooked up in his car. He ran 4 guage wire to it. And he added a 2.5 farad cap.

When he had it up and running he said the amp was not as loud as it should be . He said it was only putting out 1/4 of its power and his 600 watt amp was louder.

I told him that his ground and power wire was way to tin for the amp and that his ground wire was also to long (3 ft).

He then told me that the cap he has in the car went from 13.90 volts down to 8 volts with the amp playing and now the cap wont turn on at all and the amp has very low output.

Anything i should check for when putting it back together?

21st June 2010, 02:53 AM	#1
mike49504 diyAudio Member Join Date: Sep 2006	Ma audio hk-802sx I recieved this amp in for repair. I pulled the first 2 legs of the power supply fets off the board. Leg 3 is still solderd to the board. I also pulled the rectifiers and power supply drivers in this amp. I still read a short directly across power and ground terminals of the amp. Wondering what could cause this?? Transformer maybe??

21st June 2010, 04:06 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	D1-d3? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

21st June 2010, 04:20 AM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	If there are no other large diodes and the FETS are out of the circuit, I'd suspect a solder bridge. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

21st June 2010, 01:33 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Does it read shorted with your meter as well as drawing high current when connected to 12v? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

21st June 2010, 03:31 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	It's possible that a primary filter capacitor has failed but that's unlikely. Have you cleaned all of the flux off of the board around the power supply FETs and examined the area with a magnifying glass? Sometimes a tiny thread of solder can be hidden in the flux and cause this problem. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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21st June 2010, 04:09 AM	#3
mike49504 diyAudio Member Join Date: Sep 2006	I lifted 1 side of D1,D2,D3 out of the board And i still read a short between positive and negative terminals

21st June 2010, 05:40 AM	#5
mike49504 diyAudio Member Join Date: Sep 2006	I looked over the entire amp i dont see any solder bridges and no other diodes. The amp worked for a few secs when it came in but then started drawing high current and reading shorted

21st June 2010, 03:25 PM	#7
mike49504 diyAudio Member Join Date: Sep 2006	It reads shorted with my meter. And draws high current with just power and ground hooked up to the amp.

21st June 2010, 03:33 PM	#9
mike49504 diyAudio Member Join Date: Sep 2006	I will clean it right now and let you know in 5 mins

21st June 2010, 03:46 PM	#10
mike49504 diyAudio Member Join Date: Sep 2006	Perry, I cleaned the board . Guess i overlooked the first time i found a solder bridge between legs 1 and 2 for one of the power supply fets. Next question is The guy had this amp hooked up in his car. He ran 4 guage wire to it. And he added a 2.5 farad cap. When he had it up and running he said the amp was not as loud as it should be . He said it was only putting out 1/4 of its power and his 600 watt amp was louder. I told him that his ground and power wire was way to tin for the amp and that his ground wire was also to long (3 ft). He then told me that the cap he has in the car went from 13.90 volts down to 8 volts with the amp playing and now the cap wont turn on at all and the amp has very low output. Anything i should check for when putting it back together?

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