BX-12 Digital Bass Processor Blows Fuse...

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Hi All!

Im my car audio system i have installed many components.

I have a HU Sony-BX-12 bass driver-MPQ-5XO Equalizer-2 amps and etc...

Yesterday i was trying to hear the radio in the HU and it was not working, i cant hear anything. Well, long short history, the BX-12 had his 2 amp Agu fuse blown and it was not turning on, so no audio. I had an spare fuse laying around with the same rating and blown again instantly. Well, i have been reading enough in BCAE page about fuses, so i stopped there.

Took the Bass Driver to my test bench, used a 1 amp fuse with my psu and blows again instantly. Needless to say this unit is connected the same like and amp (Power, Remote and Ground) If you connect -B and Remote nothings happens obviously. If you try to connect only -B and +B fuse blows.

Opened the case and inspected visually both sides of the board, and no components looked burned or damaged, no smell, no burned traces, nothing. Im not very familiar with this but i think i can give a shoot. Where i can start? can i start to looke the same like a burned amp ?

I have been searching in the net and in the forum about similar issues but i have not found anything.

Here are some pics of the board. I hope somebody can bring some light to this. Thanks in advance...


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Has this been installed and working perfectly or did you just recently install it to find that it was not working?

If it's been working, has the car been jump-started or has a battery charger been used on it recently?

It's possible that the reverse-protection diode is shorted (D1, possibly) or the power supply IC (LT1072) has failed.

It appears that there is a brown substance on the board. If that's a fixative/adhesive, it may have become conductive. If it has, it needs to be removed.
Hi Again Mr. Babin, good to hear from you!

This Unit has been working perfectly with the current installation from at least one year, even 5 days ago i was using this (the bass restoration effect) with no problems at all.

But yes, you are right! my truck battery got drained and was jump started.And from there i have not used the radio because i though the system drained the charge.

Everything in the system works normal (at least the HU and the amps, i have not tested the EQ)

Ok, i tested D1 with the DMM and reads 770 ohms, it wont let pass reverse current with the the probes inverted.

At other hand, ZD1 which is at the side of D1, reads near zero ohms at both sides.

Going to find the datasheet of LT1072 to find if there is a way to check it. And going to remove the brown sustance of the board. Ill keep you posted. Thank you again!
I´m back.

Well, like you said Mr. Babin, i started to check the diodes D1 & ZD1. Like i said before, D1 reads 770 ohms (i have researched and its a 1N44001 diode) and the ZD1 reads 1 ohms at both ends (which it seems to be a BZX85C15)

I Lifted a leg of the D1 and applied power, so no luck, but no blown fuses, just nothing happened applying power to +B and Remote. I redonde the solder and next, i lifted a leg of ZD1, at the same circunstances. The Unit powers up like normal (i dont know if it works, didn´t connect to an audio source...) and nothing seems abnormal, smeelly, hot , but i didn´t want to break another component so i removed quickly from the power, stayed there like 3 seconds or less.

Sooo, it will be safe to only change ZD1? i will be glad to hear any suggestions.

Here are some pics, maybe they will help somebody later...

Thank you very much!

EDIT: And yes, right now im cleaning the board .....


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If the 1N4001 reads 770 ohms, its defective. I don't think you read 770 ohms. It appears that you have your meter set to diode check. If so, the meter would indicate that the forward voltage drop of the diode is 0.770 volts. If the reading remains the same as when the probes are open when you reverse them on the 4001, it's likely OK but 0.770 is a bit higher than I'd expect from that diode. It could be your meter. Read page 37 of the car audio site for more information on the way multimeters work.

The Zener is definitely defective.

Never power up a circuit when the Zener diode is out of the circuit. It's probably not a serious problem here but in some circuits, it can cause extensive damage.
Thanks for your valuable help Mr. Babin.

Yes, you were right about the DMM reading.I was too tired to find out, but im reading right now your page about it.

Well, i´m heading to the electronic parts store, but i think these would not carry the exact replacements. Here what i found:

Closest match for 1N4001 (50V 1A) = Diodo rectificador de propósito general de 50 Volts a 3 Amperes.........can i use this part? it has a higher amperage rating, that would be safe right?

Closest match for BZX85C15 (15V 1Watt %5 Tolerance) = Diodo Zener de 15 Volts a 1/2 Watt, con tolerancia del 5%..........i couldn´t find in my town the proper replacement, and i think the half watt replacement would not disipate enough heat and blown quickly, but can i use this part temporary?

I´m glad that im learning every day with this. Thanks in advance.

Hi All!

I Want to say thank you Mr. Babin, i did what you instructed me to do, and worked perfectly. I put the 2 zener in parallel and all works well by now. I tested the unit for five minutes and everything worked very well.

Yes, i have pics, here are they.

Thread solved! Thanks you! Greetings from Mexico!


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