Working on this Class-D 4250D. Had a shorted mosfet output, FET101 is the ID number. Replaced mosfet to see the speaker output pinned to one of the rails.
Q117 has a fairchild logo, marked D124 A42, no idea what type of transistor this is, but it is shorted. all resistors are in tact, no burns, no opens, checked them all out. everything A-OK here.
any ideas what the actual part number for Q117 would be? its an SOT-223 style SMD transistor by the way...
Q117 has a fairchild logo, marked D124 A42, no idea what type of transistor this is, but it is shorted. all resistors are in tact, no burns, no opens, checked them all out. everything A-OK here.
any ideas what the actual part number for Q117 would be? its an SOT-223 style SMD transistor by the way...
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yea i figured it out. i replaced it too and it was still pegging the rail around 50v. then out of nowhere, it quit pegging the rail, but i still had rails.
Then the output mosfets exploaded again. lol. **** it. these are the worse amps made in history. i had another one before this with similar issues.
Then the output mosfets exploaded again. lol. **** it. these are the worse amps made in history. i had another one before this with similar issues.
These aren't bad amps but you can't expect to repair one by replacing only a single part.
When you have a failed output, you should replace all of the ones working together (in this amp, all of them). In class AB amps, a leaking transistor (one that's defective but not shorted) will cause excessive current draw but you can generally shut the amp down before any damage is done. In class D amps, a leaking output can cause instantaneous failure of other outputs and driver components. That's why you need to replace them all.
I don't have anything on this amp but in similar amps, the following components fail:
* gate resistors (confirm that all are within tolerance)
* driver transistors (generally the smaller ones but sometimes the PZTA drivers)
* VAS transistor (Q115 and Q116?)
* High side supply transistor (Q114?)
* Low side supply transistor (Q110)
* Various other resistors (virtually always obvious when you look at them through a lighted magnifying glass).
When you have a failed output, you should replace all of the ones working together (in this amp, all of them). In class AB amps, a leaking transistor (one that's defective but not shorted) will cause excessive current draw but you can generally shut the amp down before any damage is done. In class D amps, a leaking output can cause instantaneous failure of other outputs and driver components. That's why you need to replace them all.
I don't have anything on this amp but in similar amps, the following components fail:
* gate resistors (confirm that all are within tolerance)
* driver transistors (generally the smaller ones but sometimes the PZTA drivers)
* VAS transistor (Q115 and Q116?)
* High side supply transistor (Q114?)
* Low side supply transistor (Q110)
* Various other resistors (virtually always obvious when you look at them through a lighted magnifying glass).
No the caps are not vented. the inductor is epoxied, and has heat pads that make contact between it and outer casing.
Ok, which components and thier respective ID numbers should i check/replace? I have to place an order with digikey for new FETs and thier respective source resistors, so i might as well get others out of the way also... both gate resistors are fine. although its odd, one fet has a 220ohm gate resistor, and the other fet has a 330ohm gate resistor. Why? they appear to never been replaced, and i havent replaced them as they were within tolerance before, and still are.
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