I have an Elf E1500D on the bench. It goes straight into protection and stays there. I removed the board and found that one solder joint on the output inductor was missing all of it's solder. I fixed the joint, installed the board back into the heatsink and powered it up. It still stayed in protection. I removed the inductor and tried again. No change.
I have checked for blown outputs. None found. Checked pre drivers(mpsa 42, 56 & 92's), found none were shorted or open. I'm running out knowledge on this one. Anyone have an idea?
I have checked for blown outputs. None found. Checked pre drivers(mpsa 42, 56 & 92's), found none were shorted or open. I'm running out knowledge on this one. Anyone have an idea?
Sorry for taking so long to reply. The voltages on the SG3525 are all about what I've seen on other amps. The LM393 is where I see the difference. Pin 1 never goes above 2v and pin 7 starts to increase but around 2.6v, the amp tries to come out of protection for an instant and the voltage on pin 1 and 7 drop to nothing. The only other thing I found is, the first opto-coupler from the left in the photo, across its top 2 pins, I have 56v. I'm scratching my head...
I have 2 of them, with the same symptoms. The one I'm taking measurements from is complete and in the heatsink. The one in the photo I'm using to remove and test components and trace circuits. U6, pins 1 and 7 are where the voltage is low. U7-2 is where I measured 56 volts, across the pins adjacent to R89-R90. Q40-41 and Q48-49 are the output drivers. I am reading about 40 volts on there collector and emitter, while the protection LED is lit. That doesn't seem right to me.
I'm trying to figure out how to do that, this morning. I went back and checked the 3525, but with a graphing multimeter. It turns out that pin 8 is being shut down. It is happening so fast that my Fluke didn't catch it.
Further testing shows that the U6 LM393 pin 5 is very low. Around 3.5 volts. The other 393, U16 is connected to the OC resistor at pin 8. Pins 5,6,7&8 all have 40 volts. Pins 1,2&3 have 26 volts.
I haven't found how either 393 is controlling the 3525 pin 8.
Further testing shows that the U6 LM393 pin 5 is very low. Around 3.5 volts. The other 393, U16 is connected to the OC resistor at pin 8. Pins 5,6,7&8 all have 40 volts. Pins 1,2&3 have 26 volts.
I haven't found how either 393 is controlling the 3525 pin 8.
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