Jock Strap
jacksonsinliss
I have an Onkyo M-504 amp that blows fuse F803 on the left channel when switched on. I found the main power transistors were bad so I replaced those but I could not find any other components bad, which does not avoid the fact that something else is wrong in there to cause them to blow. Any tips on what it might be would be helpful. The small transistors all checked out OK, as did the diodes, the big caps and the small caps. I am about to tear it down again to check out the other components.
The failure is probably my mistake?:
a) I replaced the meter lamps with LED, which work perfectly and are powered from the right channel, anyhow.
b) I replaced one set of speaker binding posts with 4mm banana sockets: I disturbed some mainboard components (C453 & C454, Q427-430) removing the speaker binding assembly so this was the most likely part where I introduced a problem but I checked it out and all looks good.
c) I cleaned up a previous repair to the mainboard where the big caps are mounted. Looks like it had a big problem in the past, see pics. The damage appears to have been caused by a screw shorting, there is a piece missing from the screw! The white wires were the original repair and I replaced them with blue wires after cleaning the area. I had to remove the copper plate connectors to test the big caps and one thing led to another.
I am using a Variac and 60W lamp to start up to avoid further damage: the right channel works fine, with F803 removed, and the new LED meter lamps are excellent. When I replace F803 then the meter lamps are not lit and the lamp glows... I quickly switch off the mains and nothing is damaged. I have tested all caps with my Mastech ms6013 and transistors using diode setting on my Mastech ms8200g.
Any ideas are welcome,
regards,
Roger
The failure is probably my mistake?:
a) I replaced the meter lamps with LED, which work perfectly and are powered from the right channel, anyhow.
b) I replaced one set of speaker binding posts with 4mm banana sockets: I disturbed some mainboard components (C453 & C454, Q427-430) removing the speaker binding assembly so this was the most likely part where I introduced a problem but I checked it out and all looks good.
c) I cleaned up a previous repair to the mainboard where the big caps are mounted. Looks like it had a big problem in the past, see pics. The damage appears to have been caused by a screw shorting, there is a piece missing from the screw! The white wires were the original repair and I replaced them with blue wires after cleaning the area. I had to remove the copper plate connectors to test the big caps and one thing led to another.
I am using a Variac and 60W lamp to start up to avoid further damage: the right channel works fine, with F803 removed, and the new LED meter lamps are excellent. When I replace F803 then the meter lamps are not lit and the lamp glows... I quickly switch off the mains and nothing is damaged. I have tested all caps with my Mastech ms6013 and transistors using diode setting on my Mastech ms8200g.
Any ideas are welcome,
regards,
Roger