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Old 19th December 2012, 01:48 AM   #1
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Question Help Fixing BXI2607D

Hey guys,

Long time reader new poster... I've never fixed an amp before but I am an embedded engineer and do a lot of work with hardware. I recently acquired a free and blown BXI2607 amp. The amp goes red then green then red as soon as it is powered up from my bench supply. I have 30 amps available to be and the amp isn't drawing anything excessive. From the outside the amp has had it's speaker terminals melted and joined together.. :S really ugly site. I thought I would open it up and find a mess inside!

So here is where I'm at so far.

I opened up the amp and took a look at the inside first .. Just a visual inspection. I didn't see any burn marks any cut wires and broken legs or any blown up caps.

I then went further and pulled the amp apart. I got rid of the Tabs using the allen key tek which I read about on this forum. It works like a dream! Just put in the L side and pop em out.. Took all of 2 seconds for each. I feel like I may have gotten a little lucky here with those. I know some people struggle.

So I got the amp apart and inspected the solder area under the speaker terminals... The solder seems to have melted at this location and some of it has splashed around onto surrounding areas. The splashes are just removed tho with my finger and I don't see any other issues except for some charring around this area. I tried powering up the amp again and it did the exact same thing.. so my problem was deeper.

I didn't want to check the input or output fets on the actual amp so I removed every FET on the board except I left the FMU32 Diode doublers in place .

I tested every single fet starting with the P/S fets. (Big ones) I get the following on all fets.

G to S 7.5MO
G to D 7.5MO
D to S 3.4MO

I then tested all the 640's I got

G to S 7.5MO
G to D 7.5MO
D to S 3.4MO

I then tested all the 9640's I got

G to S 7.5MO
G to D 7.5MO
D to S 7.5MO

To me these fets all seem to be okay. I suppose as long as the gates aren't busted on every single one of them the same way. I didn't bother testing the fets further.

I then decided to try to power up the amp again. This time as the last time.. nothing changed. RED GREEN RED...

I pulled out the old scope and looked at the gate of the P/S to see if I am seeing anything there. I didn't I tried powering on and off the amp while triggering on the Gate and still didn't see any square wave forms.

I probed all the legs of the KA7500 on the PWM board and got some DC voltage on almost all the legs but I got a funny looking seesaw waveform from pin 5-6 Sorry I'm not exactly sure which one it was but it's nothing square thats for sure....

I then went ahead and removed the PWM board for closer inspection. I didn't see anything that caught my eye.. But I did try the amp out again and this time I got no LED's .. This was to be expected as I know the PROT circuit in this amp uses a signal from the PWM board to display it's faults.


Now a few questions for you fellas.. First off anything stand out?

Secondly .. Even if the amp goes into Prot.. If the PWM card is working I should see a square wave form at the gate no?

Is there any way to bench test the PWM card out of the amp?

Any idea why the fool running this amp managed to get the speaker terminal to melt?

I did remove the Speaker terminal header as well and cleaned up the area where there was soot. No damaged traces.. But there are several diodes and such in that area.. But I had assumed those weren't essential for the functionality of the amp.

I hope Ive given you guys enough information to go on. Any help would be great!

Mo
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Old 19th December 2012, 02:01 AM   #2
DUG is offline DUG  Canada
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I guess your friend was not able to get the schematics from the other forums he was on.

Did you manage to get any schematics?

It would really help.

Not knowing the amp but just a wild shot in the dark: Might be a current sense resistor that went open or high R.

This would signal over current with out much effort.

Just a guess.
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Old 19th December 2012, 02:06 AM   #3
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Double Post.. My bad..

Last edited by mystamo; 19th December 2012 at 02:27 AM.
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Old 19th December 2012, 02:14 AM   #4
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Mississauga? No way I'm from Mississauga too.
Crazy!

I'm not exactly sure what your reference is to my friend and another forum.. I don;t think this amp was tampered with before it came into my hands.

I doubt I need a schematic to make this amp work tho it's essentially comprised of 4 parts. PS Fets, PS drive, Out Fets, Out Drive.. And gack in the middle ..

I will probe around a little more tho see what I find.

Mo
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Old 19th December 2012, 01:30 PM   #5
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Hey Guys,

So after looking at the Datasheet for the KA7500 I think the pins I was seeing the Seesaw waveform on was the CT RT pins which are the chips Osc pins.

I'm just wondering if maybe I have a bad KA7500 chip. Most likely blown Transistors as well on this board. I think I should be getting PWM to the gates of the amp when powered up if the board is actually not fried. Can I sub this chip for the TL494?

Mo
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Old 20th December 2012, 02:32 AM   #6
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Ah crap... So I touched somthing to somthing not exactly sure what happened but I heard a spark and now I don't even get a Power or Protect LED.. Every second that goes by I don't get expert help..a hemmm perry? I mess this amp up a little more..

Mo
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Old 20th December 2012, 06:14 PM   #7
Mooly is offline Mooly  United Kingdom
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Moved to car audio
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Old 20th December 2012, 06:53 PM   #8
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The KIA7500 and TL494C are the same IC you can sub the TL494C in its place. Did you check the p/s drivers Q7, Q7A, Q8, Q8A?

Do you have relay engagement or is the protect keeping the relay from engaging?

Test or replace the p/s drivers listed above to make sure they are OK. If they need replaced use BD139 and BD140 transistors.

Getting the square wave from the drive circuit is your first priority. You might want to leave the outputs out of the amp until you get the supply up and running.

What scope settings are you using to view the gate signal?

If the speaker terminal were melted, make sure there is no contact between terminals underneath the melted plastic. The terminals should be soldered and held by screws to the board. Worst case you could remove them to get the melted plastic off.
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Old 20th December 2012, 07:34 PM   #9
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Post the DC voltage on pins 10, 11 and 12 of the 7500.
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Old 20th December 2012, 10:19 PM   #10
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Hey guys,

Perry - The voltage on 10 11 and 12 are the following

10 = 0V
11 = .75V
12 = .75V

These measurements are at the 7500 pins and amp main GND

Before I managed to get this amp into a further state of distress (When I had protect and power LED's) I was getting all kinds of voltages on pins on the 7500 now it seems as tho the 12v from the supply is no longer feeding the board.. I measured the pins entering the P/S board and found 12v on a few of those pins.. But it's not even making it to the 7500 V+ pin .. Before I was also seeing all kinds of voltages on the P/S connection pins now also only 12v on a few of the pins.

I wonder what I blew there that would cause that to happen. I was messing around with my probes near D31 and I managed to short the Gate pin next to it and the D31 pin got a small spark and the protect light went out.

One thing to note here tho is that after this happened the relay would engage when I would plug my supply in. It would take about 3 seconds then click.. would engage.

I pulled the gate drivers 7, 8 7a, 8a

I swapped them with 139 140's No voltage on gate before and after gate resistors.

Problem seems to lie from main P/S board pin inputs to actual IC's on the board.

Anything for me fellas?
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