Trying to repair a Crown Grounded Bridge 460CSL. This is a cut down/ cheaper variant of the Micro-Tech and Macro-tech. The Dim bulb is full brightness. Traced to one channel on high side.
Removed drivers and output devices on high side, switch on and short clears. All devices measure fine/no shorts. Installed with known good devices, Crown graded outputs and Sanken drivers from my spares, switch on and dim bulb full brightness. Removed drivers and dim bulb is dim!
Removed ribbon cable to high side and short clears!
Tried with a known good main module and the exact symptoms appear.
Removed op-amp from board and no short!
I'm at a total lost to why this happens.
Schematic is the Geodyne version (similar)
Removed drivers and output devices on high side, switch on and short clears. All devices measure fine/no shorts. Installed with known good devices, Crown graded outputs and Sanken drivers from my spares, switch on and dim bulb full brightness. Removed drivers and dim bulb is dim!
Removed ribbon cable to high side and short clears!
Tried with a known good main module and the exact symptoms appear.
Removed op-amp from board and no short!
I'm at a total lost to why this happens.
Schematic is the Geodyne version (similar)
Attachments
I’m still trying to get familiar with this amp’s circuitry, but have you tried replacing the opamp? What are the output voltages of the four opamp sections?
I think it might be insulation break down between the hot/live heatsink and chassis.
Circuit is quite cleaver. Actually very cleaver. The ground is floating and swinging in proportion to the sinewave output. For an example when the sinewave goes positive, at the same time the ground swings low.
This means it can get around the limitations of output transistors soa. Running then at lower voltage . Kudos to Gerald Stanley of Crown who invented and patent it back in the 70s.
I'm sure someone can explain it better than me though.
The voltage translator stage is quite interesting too.
Circuit is quite cleaver. Actually very cleaver. The ground is floating and swinging in proportion to the sinewave output. For an example when the sinewave goes positive, at the same time the ground swings low.
This means it can get around the limitations of output transistors soa. Running then at lower voltage . Kudos to Gerald Stanley of Crown who invented and patent it back in the 70s.
I'm sure someone can explain it better than me though.
The voltage translator stage is quite interesting too.