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Quantum Audio QB2000D component id
Quantum Audio QB2000D component id
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Old 25th June 2019, 06:18 PM   #11
cajones65 is offline cajones65  United States
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I am not getting voltage across the emitter resistors. I have my ps set for 3amps and voltage drops to 7.3vdc.

Think it may be a good idea to pull the outputs and check the resistors that away?
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Scope: Kenwood CS-1065, Meter: Fluke 87v, Hakko FX-8888D soldering station, 858D rework station. PS: 30v/10a variable
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Old 25th June 2019, 06:22 PM   #12
Perry Babin is offline Perry Babin  United States
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The voltage would be in the mv range. If the output stage is the problem, the current almost certainly has to be flowing through the output transistors.

If it's not clamped down, check the heating of the outputs to see if they're heating up.

A current limiting resistor typically works better than the limiter in a power supply.
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Old 25th June 2019, 06:30 PM   #13
cajones65 is offline cajones65  United States
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Problem must be in power supply, outputs are not heating up at all. I am getting 4.8 to 5 mv across the emitter resistors.

Some of the fets in the ps are heating up. I have been shutting off the power supply when the amps rise. Not giving it time to heat anything up.
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Scope: Kenwood CS-1065, Meter: Fluke 87v, Hakko FX-8888D soldering station, 858D rework station. PS: 30v/10a variable
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Old 25th June 2019, 06:33 PM   #14
Perry Babin is offline Perry Babin  United States
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What work have you done to the power supply?

Sometimes letting it draw current for a few seconds lets components in the problem area heat up and can help with troubleshooting.

Have you clamped it to the heatsink and powered it up with no limiting to see if the current draw was simply inrush?
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Old 25th June 2019, 06:40 PM   #15
cajones65 is offline cajones65  United States
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I have not done any work in the power supply section. The only thing I have done is replaced a blown diode in the output section. I believe this to be the over current circuit.

I have not clamped it back in the heatsink. I will try that before I go any further.
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Scope: Kenwood CS-1065, Meter: Fluke 87v, Hakko FX-8888D soldering station, 858D rework station. PS: 30v/10a variable
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Old 25th June 2019, 06:41 PM   #16
Perry Babin is offline Perry Babin  United States
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Also check the operating frequency.
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Old 25th June 2019, 06:58 PM   #17
cajones65 is offline cajones65  United States
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It is not an in rush issue. All transistors are clamped down. Amps go up and voltage drops. Have a power light and not a protection light. Fixing to pull her back out of the heatsink.
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Scope: Kenwood CS-1065, Meter: Fluke 87v, Hakko FX-8888D soldering station, 858D rework station. PS: 30v/10a variable
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Old 25th June 2019, 07:00 PM   #18
Perry Babin is offline Perry Babin  United States
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Are you still limiting the current?
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Old 25th June 2019, 07:05 PM   #19
cajones65 is offline cajones65  United States
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No sir, well actually I have a 10 amp power supply and had the current wide open. Plus it is paralleled with another 12 amp power supply
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