EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: acemc on April 21, 2024, 04:29:13 pm
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Hi everyone. I hope someone can offer some assistance here.
I am repairing a RamAudio V12044, High Power, 4 channel PA Amplifier.
This amp has some serious power, putting out 4x 2950W into 4 ohms. It is basically 2x class-H amps inside a single enclosure.
This applies to the power as well, 2x independant switch mode power supplies with pfc.
One channel blew & subsequently took out that side's power supply with it.
This is a rather straight forward repair except that the IGBT's used in the psu are now obsolete.
I've tried looking over various IGBT datasheets trying to match the majority of the specs,
but to be totally honest I simply don't know what's important & what isn't too critical to match.
The original part doing the switching is 4x IRG4PC50U: https://docs.rs-online.com/5211/0900766b8140cd8a.pdf (https://docs.rs-online.com/5211/0900766b8140cd8a.pdf)
The original part for power factor correction is 2x STGW40NC60W: https://www.st.com/resource/en/datasheet/stgw40nc60kd.pdf (https://www.st.com/resource/en/datasheet/stgw40nc60kd.pdf)
Now to me, these 2 parts both seem like they would do the same thing (apart from different current ratings).
However they were chosen by the engineer for their specific task and obviously one must be better suited than the other for that specific part of the circuit.
Please can someone offer some advice on rock-solid replacements for both - preferably that are fairly common or easy to find/get.
And if you have the time & patience to try explain to me what I should be looking for when doing a substitution like this,
that would be absolutely incredible & extremely appreciated.
Thanks in advance.
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if this is really a class H system, then you need to forget about exact replacements for the power transistors, and spend your time to get it working first using cheaper parts you don't care about, because you may blow them up a few times. you have likely blown up all the gate drivers as well, which may be very complex.
https://en.wikipedia.org/wiki/Power_amplifier_classes
H is basically a 3 level inverter designed to reduce power losses. you mention 4 IGBTs... you should have at least 16 total in that system.
as for the igbt replacements, find one of similar gate charge, amp ratings, turn on and turn off losses. the mosfet does not appear particularly special, is it a 2 channel interleaved CCM? is the control chip blown up?
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Thanks for your input Johansen.
So this is definitely a Class-H amp, The amplifier section has already been repaired.
The PSU has 4 rails of ±35/±70/±105/±140 which all come from different taps of the transformer.
The commutation of the rails actually happens on the amplifier board.
I "think" it is a 2-CH CCM as it controls 2x Hi & Lo sides. The control board was damaged. I have already repaired it though.
I have replaced all damaged components including the IR2110s Drivers & related circuitry.
I have repaired many of these amps before, so Im quite familiar with the repair process.
This is actually the last step of the repair. The last time I did this, I recall taking the last stock RS had.
Now wherever Im looking, Mouser, Digikey & RS, they are obsolete.
I need to find suitable replacements, but I simply don't have the knowledge required to make the correct choice myself.
Well, not confidently anyway. Hence I'm asking for assistance here.
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If I replace the IGBT's with alternative's that have an internal diode, would I then need to remove the diodes D19-D22 on the pcb?
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If I replace the IGBT's with alternative's that have an internal diode, would I then need to remove the diodes D19-D22 on the pcb?
No, you can leave the existing parallel diodes in place. The IRG4PC50U datasheet shows that they have internal diodes anyway.
However they were chosen by the engineer for their specific task and obviously one must be better suited than the other for that specific part of the circuit.
The lower current parts have less capacitance and so better switching efficiency, and they should cost less.
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If I replace the IGBT's with alternative's that have an internal diode, would I then need to remove the diodes D19-D22 on the pcb?
How fast are the body diodes of the igbts compared to mur460's?
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If I replace the IGBT's with alternative's that have an internal diode, would I then need to remove the diodes D19-D22 on the pcb?
How fast are the body diodes of the igbts compared to mur460's?
They are about the same in this case, 50 to 75 nanoseconds.
The external diode will share some of the current, reducing heating from recovery losses of the IGBT's diode. I wonder if they were having failures and added the external diodes.
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"The IRG4PC50U datasheet shows that they have internal diodes anyway."
100% - Sorry, I must've been looking at the other datasheet & got mixed up.
Can you please give me your opinion of this one as a substitute: https://mantech.co.za/datasheets/products/FGH60N60SFD-FC-5T.pdf
That would be to replace the IRG4PC50U.
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"The lower current parts have less capacitance and so better switching efficiency, and they should cost less."
That makes sense, there are so many different specs on them that I wasn't sure if one was too slow to work in that part of the circuit.
I wasn't even considering efficiency. Thanks for your input.
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"The IRG4PC50U datasheet shows that they have internal diodes anyway."
100% - Sorry, I must've been looking at the other datasheet & got mixed up.
Can you please give me your opinion of this one as a substitute: https://mantech.co.za/datasheets/products/FGH60N60SFD-FC-5T.pdf
That would be to replace the IRG4PC50U.
I do not see any reason that the FGH60N60SFD would not work. It is larger with a little more capacitance but should work.
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Thanks you so much David. I'll put them in & let you know the outcome.