EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: darkflow on July 10, 2023, 10:59:16 pm
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I'm hoping for some advice with strategy for replacing an open circuit diode in the gate drive circuit for a Yamaha subwoofer class D amplifier.
The failed diode is D118 (indicated by a red arrow, on the right) in the attached schematic. Being open, there is no turn off path for Q110, various protection mechanisms cut in, and the thing can't run.
The MA2J111 is a fast recovery, low capacitance diode: 80V, 100 mA / 225 mA, 3ns, 0.6 pF. It's obsolete, and I'm struggling to find an equivalent.
What I'm thinking of doing is relocating D139 (indicated by red arrow, on the left) to replace D118 and just using a 1N4148: 100V, 200 mA, 4ns, 4 pF to replace D139.
The rationale is to keep the output stage symmetrical and hope that a slightly slower / higher capacitance diode in the D139 position will be OK, as it's in a digital signal path.
I'd really appreciate any advice, thanks.
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BAS516, BAS16L, or BAS316 would probably work as equivalents.
But I like your idea of stealing the diode from another area of the circuit, I'm sure that would get it up and running faster. They clearly just used MA2J111's in multiple places where they needed a generic diode.
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Many thanks for the diode recommendations.
I went ahead and did as I planned, and it seems to have worked out OK - powers up, no protection cut out, DC offset voltage at the speaker terminals within spec.
The only problem now is that my previous quick continuity check on the 4 ohm voice coil missed the fact that it is actually way less than 4 ohms, and a different protection mechanism now cuts in if the speaker is connected. This thing has been through some adventures before coming into my hands and there is evidence of past repairs on the amplifier PCB, so I assume the voice coil is fried.
Ah well - time to replace the expensive driver with an affordable one, or to learn how to re-voice coil a speaker ...