Ok I am stumped with this amp from the start. First off the green power light is on, as well as a solid blue "Protect/ESP" light. The manual is confusing, saying that "POWER LED: This lights up green when the amplifier is turned on. This represents normal operation if the Protection/ESP Status LED is on solid, and the Thermal LED is off"
So according to that it seems having the protect light on is normal. But the very next line says "Protection/ESP indicator LED: This LED lights up blue if the amplifier goes into protection"
So I am confused right from the get go.
Measurments
- Amplifier relay clicks on once amp powers up
- Power supply is producing ~47V+ and ~47V- rail voltage
- Output transistors have clean square wave to gates
- +rail voltage is present on half of the outputs drain legs and -rail voltage present on the other 1/2's source legs.
Symptoms
- Amp produces clean audio at low volume, becomes more distorted as volume increases until it cuts out completely, when volume is decreased audio returns slowly.
- Gain control on front panel has no affect on amplitude what so ever. "Master, Gain, Copy" switch also has no change.
The amp is only drawing around 2.8-3A no matter what the volume of the input signal. Audio increases on speakers, but as stated above quickly becomes distorted and dies off.
So according to that it seems having the protect light on is normal. But the very next line says "Protection/ESP indicator LED: This LED lights up blue if the amplifier goes into protection"
So I am confused right from the get go.
Measurments
- Amplifier relay clicks on once amp powers up
- Power supply is producing ~47V+ and ~47V- rail voltage
- Output transistors have clean square wave to gates
- +rail voltage is present on half of the outputs drain legs and -rail voltage present on the other 1/2's source legs.
Symptoms
- Amp produces clean audio at low volume, becomes more distorted as volume increases until it cuts out completely, when volume is decreased audio returns slowly.
- Gain control on front panel has no affect on amplitude what so ever. "Master, Gain, Copy" switch also has no change.
The amp is only drawing around 2.8-3A no matter what the volume of the input signal. Audio increases on speakers, but as stated above quickly becomes distorted and dies off.
If the amp has 10 ohm resistors on the output of all of the heatsink mounted regulators, confirm that the resistors are within tolerance.
Perry, you never cease to amaze me. Yes one of the 10-ohm resistors was out of spec. It also seems to have gotten hot enough that one side has come desoldered and loose from the board. It is for IC772 which is an LM337.
Anything I should check before just replacing this resistor? I assume there would bea cause for this to fail.
Anything I should check before just replacing this resistor? I assume there would bea cause for this to fail.
I've been replacing all of the 10 ohm 0805 resistors on the regulators with 1206 resistors and haven't had any come back. I've been told by a reliable source that there is also a problem with electrically leaky capacitors that can cause these to fail. I assumed it was from inrush current since I never found any of these with excessive voltage across them (exceeding their power rating) but since the leaky cap info came from a reliable source so I always check.
They were already 1206. But I replaced that one resistor and the amp seems to be working fine now. Gain control is functioning as well.
Thanks again Perry
Thanks again Perry
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