HH Electronic MX1200 Power Amplifier Fuse shorted

[9w2tzw]

Hi,

Currently i got one unit of HH Electronic MX1200 power amplifier.it can be turned on without any indicator of protect LED being in ON state.But the problem is, it can't detect any input signal.So, when i open the cover, i noticed that the 1A fuse of both channel keep blown even i had replaced it.Original owner said it the power amp has gone down since he "misshorted" the + and - terminal of the speaker.Any idea? by the way i had attached the schematic for reference.
It uses 10 pair of BUZ901 and BUZ906 Mosfet transistor.total 20 for both channel.

[Th3_uN1Qu3]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

The 1A fuse is for the 70v rail as per the schematic. Measure between either end of the fuse holder and ground. You'll find one of the ends is shorted. Then it's a matter of tracing thru the circuit and see which part has caused the short.

Also, have you checked the output transistors already? If they are blown, it's gonna be an expensive repair.

A word of warning: This power amplifier uses high voltage rails and has large capacitors. Make sure the main capacitors are discharged prior to attempting any work on this unit, otherwise serious damage to you, your tools, or the amplifier itself may occur.

If the caps still show over 30 volts after several minutes after unplugging the unit, use a regular mains voltage lightbulb to discharge them.

[9w2tzw]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

The 1A fuse is for the 70v rail as per the schematic. Measure between either end of the fuse holder and ground. You'll find one of the ends is shorted. Then it's a matter of tracing thru the circuit and see which part has caused the short.

Also, have you checked the output transistors already? If they are blown, it's gonna be an expensive repair.

A word of warning: This power amplifier uses high voltage rails and has large capacitors. Make sure the main capacitors are discharged prior to attempting any work on this unit, otherwise serious damage to you, your tools, or the amplifier itself may occur.

If the caps still show over 30 volts after several minutes after unplugging the unit, use a regular mains voltage lightbulb to discharge them.

i had 2 times replacing the fuse.and they both got blown after i powered on the unit.

thanks for reminder, can i use 82 ohm 5 watt resistor to discharge the capacitor?for smaller capacitor, i use this method to discharge them.

i still dont know the exact ways to test the mosfet transistor.any guide?

[budm]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

Did you check the 4 1n4007 D40~D43 to see if they are shorted out?
If the MOSFETs shorted out the fuses FS1~FS4 will blow also.

[budm]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

Did you check the 4 1n4007 D40~D43 to see if they are shorted out?
If the MOSFETs shorted out the fuses FS1~FS4 will blow also.

[9w2tzw]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

Did you check the 4 1n4007 D40~D43 to see if they are shorted out?
If the MOSFETs shorted out the fuses FS1~FS4 will blow also.

D40-D43 i had checked and they just doing fine.

How to tests out the MOSFETs shorted or not? Thanks for reply

[rievax_60]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

D40-D43 i had checked and they just doing fine.

How to tests out the MOSFETs shorted or not? Thanks for reply

There is no reason to suspect the MOSFETs at this stage. Are there shorts to 0v on the VS2 rails?

[budm]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

Then check the resistance reading on the output of the D40~D43 (full bridge setup) output to see if they are feeding shorted loads. You have shorted circuits that are causing the fuses to blow.
"D40-D43 i had checked and they just doing fine" What are the readings?
You are using Time Delayed fuses, right?

[9w2tzw]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

Then check the resistance reading on the output of the D40~D43 (full bridge setup) output to see if they are feeding shorted loads. You have shorted circuits that are causing the fuses to blow.
"D40-D43 i had checked and they just doing fine" What are the readings?
You are using Time Delayed fuses, right?

I cannot managed to get reading at ON State since i am not using time delayed fuses.I just use normal 1A fuses since at my area are hardly enough to get this type of fuses.During OFF state, i managed to get 0.45 /0.47 V at all diodes , D40-D43.

[9w2tzw]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

any helps?

[ben7]

Re: HH Electronic MX1200 Power Amplifier Fuse shorted

any helps?

Check transistors T3, T4, T5, T8, T9, and T10 for shorts (desolder them from the board if you aren't sure if they are shorted or not, then measure them)
I think it's highly likely that at least one of them will be shorted out.