ekimezeerf
New Member
Hey everyone, long time lurker, first time posting.
A friend brought me a dead CA-800, would not power on and many signs of heat stress on main amp and power boards. Our thought was the PO has dumped a bottle of cologne on it due to it's aroma and the goop present everywhere inside.
I've worked on the main cap board, power supply, main amp boards, and mode switch - deep cleaned, changed all electrolytic capacitors, signal + power transistors, fuse resistors, micro switches, trim pots, diodes...
I've cleaned every switch, every pot, pre out- main switch, checked all grounds, re-soldered cracked joints on rear panel, re-worked all wires with signs of fatigue, checked all resistors I thought relevant...
I've read almost every post on AK that even mentions a CA-800 or CA-1000 and learned so much more than I ever wanted to know about this amp. But, it came alive! So thank you to everyone who ever took the time to leave their experience and knowledge here. I'm definitely standing on your shoulders.
Now, here's where I'm completely stuck. It's sounds terrible at any volume past ~ 10-15%. Distortion in the bass is most obvious at higher volumes but the treble is no better. When attempting to adjust the main amp boards (specifically the Class A/B Bias) in class B mode the lowest I can set the bias is 0.085V on both boards (but as high as 0.120V)
In Class A mode, the highest I can set the bias is 0.130V (and as low as 0.080V)
Differential voltage is right at 15V and the Mid-Point Potential is right at 0.0V. The +/- 50V supply is there and in Class B Mode I have +/- 45v and in Class A Mode i have +/- 20v (which is too high right?)
The Bias problem is the same on both boards which made me think there was a problem with the power supply or maybe the mode switch. I've exhausted myself going over both, even took the mode switch completely apart and cleaned the rails and contacts inside.
I have many more details and voltages to report if someone is interested in giving my a hand up. I'll include a few photos here of the before/after type. Maybe I've made a simple mistake, overlooked something, or maybe its a dying transformer...any help would be great!View media item 15301View media item 15302View media item 15303View media item 15305View media item 15304
A friend brought me a dead CA-800, would not power on and many signs of heat stress on main amp and power boards. Our thought was the PO has dumped a bottle of cologne on it due to it's aroma and the goop present everywhere inside.
I've worked on the main cap board, power supply, main amp boards, and mode switch - deep cleaned, changed all electrolytic capacitors, signal + power transistors, fuse resistors, micro switches, trim pots, diodes...
I've cleaned every switch, every pot, pre out- main switch, checked all grounds, re-soldered cracked joints on rear panel, re-worked all wires with signs of fatigue, checked all resistors I thought relevant...
I've read almost every post on AK that even mentions a CA-800 or CA-1000 and learned so much more than I ever wanted to know about this amp. But, it came alive! So thank you to everyone who ever took the time to leave their experience and knowledge here. I'm definitely standing on your shoulders.
Now, here's where I'm completely stuck. It's sounds terrible at any volume past ~ 10-15%. Distortion in the bass is most obvious at higher volumes but the treble is no better. When attempting to adjust the main amp boards (specifically the Class A/B Bias) in class B mode the lowest I can set the bias is 0.085V on both boards (but as high as 0.120V)
In Class A mode, the highest I can set the bias is 0.130V (and as low as 0.080V)
Differential voltage is right at 15V and the Mid-Point Potential is right at 0.0V. The +/- 50V supply is there and in Class B Mode I have +/- 45v and in Class A Mode i have +/- 20v (which is too high right?)
The Bias problem is the same on both boards which made me think there was a problem with the power supply or maybe the mode switch. I've exhausted myself going over both, even took the mode switch completely apart and cleaned the rails and contacts inside.
I have many more details and voltages to report if someone is interested in giving my a hand up. I'll include a few photos here of the before/after type. Maybe I've made a simple mistake, overlooked something, or maybe its a dying transformer...any help would be great!View media item 15301View media item 15302View media item 15303View media item 15305View media item 15304