Fosi Audio BT20A Pro blown capacitor help

[geauxwandering]

I’m new to anything audio. Seeking some guidance as to what is the role of this capacitor in the amp? Also, curious what was the likely cause. I was running the amp pretty hard at 48v when this occurred. I replaced the blown capacitor with an equivalent Nichicon cap. I am still not getting any output to the speakers. Any input on what else to check would be greatly appreciated.

 

[Penelinfi]

48V?
Is this not a 12-24V input ?

 

[geauxwandering]

48V?
Is this not a 12-24V input ?

Rated for 24v-48v input. You can buy it from Fosi with a 48v power supply.

Specifications	Details
Model	BT20A PRO
Output Power	300Wx2 @4Ω
Terminating Impedance	2-8Ω
Input Mode	Bluetooth + RCA
Output Mode	Passive Speakers + Pre-out
Frequency Range	20Hz-20kHz(±1.2dB)
THD	≤0.005%
SNR	≥108dB
Chip Set	TPA3255
Bluetooth Transmission Distance	Up to 50Ft
Bluetooth Transmission Format	SBC/AAC
Device Dimension	5x5x1 inches
DC Input Range	24-48V

 

[DVDdoug]

I wonder if a rectifier in your power supply shorted and you were/are getting AC. AC can blow an electrolytic capacitor and other things could be damaged too.

Or maybe the capacitor just shorted for some unknown reason, pulling excess current and causing something else to be fried at the same time.


"Running an amplifier hard" shouldn't cause that. Pushing an amplifier hard can heat-up transistors/MOSFETs but a blown MOSFET should hurt any capacitors.

 

[IAtaman]

Do you think it is the power supply? Looked more like the input stage / tone controls section to me with NE5532s and inductors around. The cap really exploded with its gut everywhere. It might have taken the opamp with it maybe.

 

[geauxwandering]

Do you think it is the power supply? Looked more like the input stage / tone controls section to me with NE5532s and inductors around. The cap really exploded with its gut everywhere. It might have taken the opamp with it maybe.

This is in a mobile set up. It’s running from a 48v battery pack. Pack was showing 46.9v when it failed. Are there any simple checks with a multimeter or oscilloscope I can do on the op amp?

 

[AdamG]

First thing I see is all that hair/debris/lint whatever it is you might want to vacuum that out and clean up with a q-tip or gently with a toothbrush. Whatever that fuzz is get rid of it. Make sure you disconnect the power and let it sit for a while before doing anything.

 

[Doodski]

Check D5 on the multimeter diode test function and look for shorts. While you are at that check those leads coming from U3 for shorts. Make sure L4 is not open and it reads some kind of resistance across the two leads. We won't know the resistance value but it might be anywhere from several ohms to even tens of Ohms or more. Clean that capacitor stuff out and use isopropyl alcohol to clean and rinse it with the tooth brush or a long paintbrush and massage it around till all that stuff is out. We don't want you touching the stuff because some of that stuff is bad for you.

 

[Doodski]

and... check the 48 V DC power input on the diode test function. Look for a short. If you provide more images of the PCB front and rear I can point out better the stuff you can check.

 

[IAtaman]

This is in a mobile set up. It’s running from a 48v battery pack. Pack was showing 46.9v when it failed. Are there any simple checks with a multimeter or oscilloscope I can do on the op amp?

I think probably best to start with the cleaning and measuring the passive components as Doodski suggested. In circuit measurement of components might be tricky, especially with SMDs. If all seems to be fine, download the datasheet of the chips (crisps if you are from the UK) and see if they are getting the correct rail voltages. If all is fine maybe you can connect an input signal, hook up the outputs to a scope and see how far the signal goes.

 

[geauxwandering]

Thanks all! I did clean it up with a toothbrush, swab & alcohol. I’ll check your suggested measurements and get pics of both sides of the board when I get back.

 

[Doodski]

Thanks all! I did clean it up with a toothbrush, swab & alcohol. I’ll check your suggested measurements and get pics of both sides of the board when I get back.

Thank you.