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Metrik MAB 901
Metrik MAB 901
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Old 13th June 2019, 07:53 PM   #11
barber02 is offline barber02
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I’m getting +51.6 and -51.7 on the using the primary ground.
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Old 13th June 2019, 08:00 PM   #12
Perry Babin is offline Perry Babin  United States
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OK. I was concerned that you may have had an intermittent primary to secondary transformer short. You may, but it could be intermittent. 50/62 is a huge difference and hard to have due to a mistake if you were measuring on the main rails.
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Old 13th June 2019, 08:09 PM   #13
barber02 is offline barber02
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The voltages I stated earlier were taken from the center pins of the output mosfets grounded to the primary of the transformer.

Last edited by barber02; 13th June 2019 at 08:20 PM.
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Old 13th June 2019, 08:19 PM   #14
barber02 is offline barber02
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When I measure the center pin of the output mosfets grounded to the secondary side of the transformer the voltages are almost equal at about 56 vdc + and -
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Old 14th June 2019, 09:21 PM   #15
barber02 is offline barber02
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Ok. So I pulled the rectifiers and the amp still comes on briefly and the stops oscillation and and never trips the protection LED. Then I decided to bring it up on low voltage and the power supply comes up happy and stays in oscillation. I started at 10 volts and slowly increased the volt and when the supply voltage hits about 12.6 volts the power supply stops oscillating. What gives?

David
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Old 14th June 2019, 09:25 PM   #16
Perry Babin is offline Perry Babin  United States
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It's hard to say without a diagram. You need to start at the control IC. See which pin changes in voltage as it shuts down and follow the circuit back to see what's causing it.
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Old 15th June 2019, 01:42 AM   #17
barber02 is offline barber02
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Bummer. This amp is eating my lunch. But, on the bright side, I’m learning.

David
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Old 15th June 2019, 02:38 AM   #18
barber02 is offline barber02
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Ok. This is the drive wave coming off of pin 9 and 10 of the TL494 with 12.3 volts of input voltage. If I go higher than 12.5 volts then the chip shuts down. This drive wave doesn’t look healthy. It’s not turning on and off fast enough in my opinion. Pin 3 goes high when I raise the input voltage and shuts the chip down.

With the chip running at 12.3 volts pin 1 is sitting at 1.48 volts and pin 2 is at 3.43 volts. Pin three sitting at .077 volts.

When I raise the voltage above 12.5 volts then pin three goes high at 4.7 volts and pin 1 is at 1.77 volts and pin 2 is at 3.44 volts.
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Last edited by barber02; 15th June 2019 at 02:48 AM.
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Old 15th June 2019, 02:42 AM   #19
barber02 is offline barber02
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This is the area around the TL494 chip.
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Old 15th June 2019, 02:46 AM   #20
Perry Babin is offline Perry Babin  United States
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Switch to DC coupling. AC coupling should only be used under the rarest tests.

Are you using your probe set to 1x or to 10x?
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