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Old 23rd November 2020, 10:40 AM   #11
Threedengineering is offline Threedengineering
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I'm going to replace the tc4427 with the ucc drivers and see if that solves the issue
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Old 24th November 2020, 01:35 PM   #12
barber02 is offline barber02  United States
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Your undervolt circuit it located in the circled area.

I have previously post good voltages for that circuit.

You can bypass the protection for undervolt at the PIC16 IC. I have posted about about how to do that as well.

I havenít seen one of these amps build full rail and then shut down. But when that happens, does the rail voltage coming out of the power supply sag significantly or is there a spike in the current draw from your power supply just before the shutdown. This could indicate something is shorted or damaged in the output section of the amp.

If you donít spot any anomalies then the problem is most likely the undervolt circuit. I would bypass the protection first to see if the amp will boot up and stay operational. Then youíll know if the problem is in the undervolt circuit without a doubt.
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Old 24th November 2020, 02:58 PM   #13
Threedengineering is offline Threedengineering
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I have removed R127 and bridged pin 8 and 14 on the pic, still getting the undervoltage fault
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Old 24th November 2020, 03:48 PM   #14
Perry Babin is offline Perry Babin  United States
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I think that's going the wrong way. When there is sufficient voltage, The 7.5v Zener conducts, pulling the base of Q23 up which drives its collector to ground.

I'm using your R127 and pin 8 as a key but the diagram I have is for a different model.
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Old 24th November 2020, 06:47 PM   #15
Threedengineering is offline Threedengineering
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Does the pic handle just the power supply and protection circuits or does it do both ps and output?
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Old 24th November 2020, 08:20 PM   #16
Perry Babin is offline Perry Babin  United States
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I was wrong about pin 8/14. I'm used to seeing pin 14 as the +supply on logic ICs. You had it right.

I'm not sure that the PIC is the same in my notes as you have. What's the PIC number in your amp?
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Old 24th November 2020, 09:29 PM   #17
barber02 is offline barber02  United States
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The PIC is the heart of the amplifier. It does the power up self check, it sends out the pulses to the power supply driver ICs it handles all fault codes.

Grounding pin 8 should have eliminated that fault code. The amp will do one of two things. It will boot up and run or it will give you a different fault code which will most likely be the underlying fault. Iíve had to do this a few times to discover what the real fault was.

Double check your work to make sure that pin 8 is grounded. If no mistake was found then you can be fairly certain that your problem is not an undervolt at this point, but rather something in the output section could be triggering the fault.

Have you checked the rail voltages to see if they sag quickly? Amp draw spike?
Can you get a glimpse of the drive signal in the output section? Is the drive going all the way back to ground? Do you have equal voltage on you speaker terminals as referenced to ground? Each one should have half the rail voltage on them and should be even within a volt or two.

In these Amps like this that Iíve dealt with that give a false undervolt is a sometimes a leaky transistor, mosfet, or the current sensing ICs located close the output mosfets. They look like tiny 5 legged ICs but only 2 sometimes 3 of the legs are utilized. Since yours is faulting after rail voltage has built I would look at the output transistors and the current sensing ICs closely. Make sure that the insulators are in good shape. Pull the board from the heat sink and make sure that you donít have some foreign conductive object floating around. Sometimes just a little piece of speaker wire in the wrong place can do this. You may have to pull the output transistors from the board and test them individually.
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Old 25th November 2020, 01:45 PM   #18
Threedengineering is offline Threedengineering
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Ok so amp is now stripped out and in the process of being stripped to test individual components. will post up results soon
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