The power supply fets were all shot so I've replaced them. I've checked for shorts on the output and all seems to be OK. I've powered up the amp and the power LED pulses and the current draw reflects this and will draw to up 4 amps but doesn't settle down. I've also noticed that R85 & R86 get very hot very quickly. Sometimes the pulsing stops and the relay clicks but R85 & 86 still get hot. I've now pulled both these resistor and powered up the amp again. Now it starts up clean and I've got a clean 55 volts on the supply rails.
I'm not sure what to check next and that's why I asked for a diagram.
I'm not sure what to check next and that's why I asked for a diagram.
The heating is likely normal.
Were you powering the amp up through a current limiter or did you have it connected directly to a power supply easily capable of supplying more than 10 amps?
When the amp powers up and the relays engage, do you have any significant DC voltage across the speaker terminals?
Were you powering the amp up through a current limiter or did you have it connected directly to a power supply easily capable of supplying more than 10 amps?
When the amp powers up and the relays engage, do you have any significant DC voltage across the speaker terminals?
The resistors get too hot to touch in a matter of seconds and they look to be only 2watt.
The amp is connected to a 20A normal 24A peak PSU without a current limiter but with a 10A fuse.
There's very little across the speaker terminals. With the resistors R85/86 in 8mV and with them out nothing at all.
The amp is connected to a 20A normal 24A peak PSU without a current limiter but with a 10A fuse.
There's very little across the speaker terminals. With the resistors R85/86 in 8mV and with them out nothing at all.
On both occasions the relay did engage.
I did measure the resistance of both resistors or R85/86 and they look to be about 10% out of tolerance. I think they should be 220 ohm as I can't really make out the colour code but I'm reading 200 ohms. I think they are both being used as shunt resistors in a regulator cct but I don't know how much of a difference this out of tolerance is going to make and if this is causing the initial surge of current. Will try and find some replacements to try.
I did measure the resistance of both resistors or R85/86 and they look to be about 10% out of tolerance. I think they should be 220 ohm as I can't really make out the colour code but I'm reading 200 ohms. I think they are both being used as shunt resistors in a regulator cct but I don't know how much of a difference this out of tolerance is going to make and if this is causing the initial surge of current. Will try and find some replacements to try.
You have to remember that electronic components can operate at much higher temperatures than are comfortable to touch. As long as the resistors are not so hot that they're desoldering themselves, it's probably not an issue.
You can measure the voltage across them and calculate the power dissipation. If it's below 2w, you can ignore the heating for now.
It appears that the resistors are used to drop voltage or limit the current into the regulator transistors but that's a guess since I only have photos.
When they're in the circuit, did the regulators produce ±15v?
You can measure the voltage across them and calculate the power dissipation. If it's below 2w, you can ignore the heating for now.
It appears that the resistors are used to drop voltage or limit the current into the regulator transistors but that's a guess since I only have photos.
When they're in the circuit, did the regulators produce ±15v?
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