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XX-Goliath 5kW issues
XX-Goliath 5kW issues
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Old 3rd August 2019, 04:09 PM   #1
BumpinYota is offline BumpinYota  United States
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Location: Venice, FL
Default XX-Goliath 5kW issues

This korean half bridge has me stumped a bit.

Previous owner states he purchased the amp, it was playing perfectly, and then suddenly shut down. Upon initial inspection the amp had been previously repaired and im guessing the repair tech incorrectly placed all the mosfet clamps between the fets and the sink!

Consequently ALL of the output fets are smoked and all have been removed. No solder bridges present after removal. Power supply fires up beautifully on 10v. Then the muting relays click off and the amp immediately shuts down (rail voltage is usually around 110v when this occurs).

I then inspected the 12v voltage regulation circuit which employs a pair of TA78t12. One was destroyed showing continuity across all pins. I removed both and measured voltage at the veirs. To my horror, full negative rail voltage was present on the input of the regs at powerup!

I do recall something about some amps using the negative rail voltage as a virtual ground so the 12v supplied to other components is stable. Is that the case here? Or should I not have negative rail voltage to the input of the 12v regs?

Thanks in advance.

Ps Im also having a difficult time finding a replacement for said voltage regulators. Origionals were a 3amp capacity in a to-220 case.

Last edited by BumpinYota; 3rd August 2019 at 04:19 PM.
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Old 3rd August 2019, 05:45 PM   #2
Perry Babin is offline Perry Babin  United States
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Virtual ground isn't a term commonly used.

The driver ICs and the regulators are referenced to the negative rail. When measuring any voltages for these components, you need to place your black meter probe on the negative rail.

Do NOT connect any mains-powered scope ground (or any mains powered equipment ground) to the negative rail.
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Old 3rd August 2019, 07:35 PM   #3
BumpinYota is offline BumpinYota  United States
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Thank you and roger that. I don't want the oscilliscope to explode in my face......LOL!!

Any ideas on where i should start looking to ascertain why the amp keeps shutting down when it tries to power up the output section?

As I understand it, this type of amp should power up without the output fets in place and the low side should oscillate?

I was thinking that i should remove the driver board and see if the problem remains at power up in an attempt to isolate the problem?

Last edited by BumpinYota; 3rd August 2019 at 07:51 PM.
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Old 3rd August 2019, 11:16 PM   #4
Perry Babin is offline Perry Babin  United States
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Post a photo of the audio driver board in YOUR amp.
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Old 5th August 2019, 01:00 AM   #5
BumpinYota is offline BumpinYota  United States
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The whole output driver board:
Click the image to open in full size.

Left and right respectively:

Click the image to open in full size.

Click the image to open in full size.

Last edited by BumpinYota; 5th August 2019 at 01:04 AM.
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Old 5th August 2019, 06:11 AM   #6
Perry Babin is offline Perry Babin  United States
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Do you have any DC on the output filter inductors before the relays engage?
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Old 6th August 2019, 04:17 AM   #7
BumpinYota is offline BumpinYota  United States
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Yes, I have full negative rail voltage on all sides of all filter inductors. (Ground probe is on negative power terminal.)

When the relays do engage for a moment I'm also seeing a LARGE dc offset on the channels.
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Old 6th August 2019, 04:23 AM   #8
Perry Babin is offline Perry Babin  United States
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The relays engaging is driving the DC to the protection circuit which is shutting the amp down, most likely.

Do you have a 120v incandescent lamp that you could touch to the rail voltage on the inductors to see how much current the source can supply?

The short could be direct, or just through a resistor. The lamp would help determine what the problem is likely to be.
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Old 6th August 2019, 04:54 AM   #9
BumpinYota is offline BumpinYota  United States
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Join Date: Jul 2019
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Quote:
Originally Posted by Perry Babin View Post
The relays engaging is driving the DC to the protection circuit which is shutting the amp down, most likely.

Do you have a 120v incandescent lamp that you could touch to the rail voltage on the inductors to see how much current the source can supply?

The short could be direct, or just through a resistor. The lamp would help determine what the problem is likely to be.
Ok I just just tried that and the amp refused to power up at all.

Removed lamp, allowed to power up and touched lead to complete the circuit and something in the preamp section popped and let loose a whisp of smoke.

I cant see anything on visual inspection from were that whisp of smoke origionated from...
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Old 6th August 2019, 04:57 AM   #10
BumpinYota is offline BumpinYota  United States
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I did however connect the incandescent across the speaker terminals and powered it up. Light bulb lights up really really well until the relays open again. Ugh.

How often will these amps take out the enormous capacitors (1200microFarad, 200v)? Of the 20 caps of this size only 7 behave normally when tested for continuity accorss their terminals.

Last edited by BumpinYota; 6th August 2019 at 05:10 AM.
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