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American Bass VFL 110.1 protection after relay
American Bass VFL 110.1 protection after relay
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Old 10th September 2019, 08:41 PM   #1
barber02 is offline barber02  United States
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Default American Bass VFL 110.1 protection after relay

Iím working on an American Bass VFL 110.1 (very similar to AudioQ amps) that had a damaged output section. Many of the output mosfets were shorted. I replaced all of them, high side and low side drive.

This amp has the 11 pin driver card for the output section. I also replaced the TL072s on the driver board. The amp boots up and pulls normal amps (about 2 amps or less) after the initial spike when it first boots up. The relay clicks in and the amp immediately protects and turns the relay back off.

I do see a DC voltage across the speaker terminals it climbs quickly to about 10 volts before the amp protects.

I am wondering what could be causing this behavior as all of the output mosfets are new.

David
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Old 10th September 2019, 08:56 PM   #2
Perry Babin is offline Perry Babin  United States
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Did you replace the two 1D transistors that commonly fail?
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Old 10th September 2019, 10:21 PM   #3
barber02 is offline barber02  United States
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I got pushed out of my lab by a thunderstorm so I shut down and unplugged everything quickly and went to the house.

In my rush to finish my post I forgot to mention that I did replace all the 1D and 2D transistors on the driver board.

David
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Old 11th September 2019, 12:03 AM   #4
Perry Babin is offline Perry Babin  United States
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Is it driving DC to the output filter inductors?

If you disable the control for the driver board, does it go into protect?
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Old 12th September 2019, 02:02 AM   #5
barber02 is offline barber02  United States
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I didn’t get much time to work on this amp today.

Yes, the amp is driving DC to the output inductor and if I turn the voltage down from 14 volts to 12 volts I can watch the DC voltage on the inductor and speaker terminals slowly creep up to just over 3 volts DC before the protection circuit disengages the relay and the power supply shuts down.

That’s about as far as I got with it.

David
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Old 12th September 2019, 03:23 PM   #6
barber02 is offline barber02  United States
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This the drive signal on the high side and low side drive. Itís hard to tell from pictures but the drive signal isnít stable. It fluctuates between 190 and 230 kHz at 0.5 volts on the high side and low side FETs.

I am using a battery powered Oscope because I canít get the drive signal to show up clearly on my mains powered scope. Iím not sure why. But I digress.

High side rail voltage is approx 59 volts and low side rail voltage is approx 62 volts.

Photo one is high side drive and photo two is low side drive.

David
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Old 12th September 2019, 03:32 PM   #7
barber02 is offline barber02  United States
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I get even rail voltage at D21 and D23 of 62vdc and -62vdc.
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Old 12th September 2019, 03:48 PM   #8
barber02 is offline barber02  United States
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On the 7812 voltage regulator I read 51vdc and on the 7815 voltage regulator I read 62vdc.
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Old 12th September 2019, 03:58 PM   #9
Perry Babin is offline Perry Babin  United States
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Are you using the secondary ground when measuring the rail voltage?

What sort of problem are you having with getting a waveform on your scope?

Have you tried using it in differential mode?
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Old 12th September 2019, 04:01 PM   #10
barber02 is offline barber02  United States
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Ok. Either D23 is bad or C51 is bad because the 7812 is only getting approx 41vdc fed to it after D23.

David
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