I pulled this amp off the back burner to work on it again. I've read back through this post to refresh my memory of the problems and steps that were taken with this amp. I think it's best to start new as I've since discovered some new issues with it.
When I applied power to the amp it would power up but blow the resistor circled in the attached photo. I found the MSPU57 transistor also circled in the attached photo was shorted and causing that resistor to burn out. After replacing the MSPU57and resistor, the amp would no longer power up and the PS FET's on that same side of the board as that MSPU57 (just using that as reference to which side of the board I'm referring to) were rapidly heating up. I have replaced a large majority of the components on the power section of this amp. So I checked the DC rail voltage and it was at -12v and -4v. I pulled the rectifier that had -4 volts (should be + voltage on that one) and it checked good. As the amp was powering up prior to my having replaced the faulty MSPU57 I decided to pull it along with the MSPU07 in line with it (not the one next to it but in line). The amp powered up and rail voltage when up to -41v and +12 volts. I pulled all of the MSPU57's and MSPU07's and checked them, all tested good. Given the voltage rose as it did when I pulled those transistors it appears that the problem is in the audio section any thoughts on what else I should check?
When I applied power to the amp it would power up but blow the resistor circled in the attached photo. I found the MSPU57 transistor also circled in the attached photo was shorted and causing that resistor to burn out. After replacing the MSPU57and resistor, the amp would no longer power up and the PS FET's on that same side of the board as that MSPU57 (just using that as reference to which side of the board I'm referring to) were rapidly heating up. I have replaced a large majority of the components on the power section of this amp. So I checked the DC rail voltage and it was at -12v and -4v. I pulled the rectifier that had -4 volts (should be + voltage on that one) and it checked good. As the amp was powering up prior to my having replaced the faulty MSPU57 I decided to pull it along with the MSPU07 in line with it (not the one next to it but in line). The amp powered up and rail voltage when up to -41v and +12 volts. I pulled all of the MSPU57's and MSPU07's and checked them, all tested good. Given the voltage rose as it did when I pulled those transistors it appears that the problem is in the audio section any thoughts on what else I should check?
Attachments
Are you using parts sourced only from reputable distributors (not ebay)?
Were there any leaky caps in this amp?
You may have to remove parts from both channels and compare the voltage on the corresponding points in the circuit to see if there is a difference. This may not be a check that can be done then moved on to the next point. You may have to connect the meter and heat, cool, flex the board to see if there is any difference. This may need to be done on the same point over a few days to see if there is any change.
Were there any leaky caps in this amp?
You may have to remove parts from both channels and compare the voltage on the corresponding points in the circuit to see if there is a difference. This may not be a check that can be done then moved on to the next point. You may have to connect the meter and heat, cool, flex the board to see if there is any difference. This may need to be done on the same point over a few days to see if there is any change.
If you remember, you asked me about the parts before. I only buy parts from, Mouser, Digikey, Arrow, etc..
When I removed the caps I didn't notice where any had leaked. I also cleaned the board well before installing the new caps. Although I'm with you on that line of thinking, as this seems very reminiscent of the HCCA 225 in which electrolyte had soaked into the board and had us chasing our tail all over the place.
When I removed the caps I didn't notice where any had leaked. I also cleaned the board well before installing the new caps. Although I'm with you on that line of thinking, as this seems very reminiscent of the HCCA 225 in which electrolyte had soaked into the board and had us chasing our tail all over the place.
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