rschweitzer
Audio Fuse
I have a Yamaha CA-1010 amp that was operational when I got it, powered up, produced audio although very distorted and scratchy sounding. Initially found some bad caps on the power supply. Replaced all the electrolytic’s on that board and checked all voltages and they were stable.
The amp distortion issues appeared to be out of tolerance fuse resistors. I replaced those and the few electrolytics on those boards. I cleaned the output transistors, replaced the MICAs and added fresh heat sink compound. And this is where I made a huge mistake that I hate to admit. I inadvertently installed the outputs transistors backwards. PNP where and NPN should have been and I did this to both amps. Naturally the main B+ and B- fuses blew. Once I saw that , I retraced my steps and proceeded to check every component on the amps starting with the outputs TR318/320 and TR 319/321. Then I went backwards to TR316/306 and TR 317/308. I removed these components, then removed the pre-drivers, checked the diodes, zener, etc. Everything checked out. No opens, no shorts. Fuse resistors had already been replaced with metal films and those where checked again and are good.
Upon power up with one amp installed, no protection relay click. Voltage checks are not good. At TP 1, I have 23 V with the output transistors installed. Removing those, I am back to 0v and the protection relay will click on. But that is expected since there is no output signal. B+ is 64 volts. It starts at 51v and climbs to 64v and this is still without the output transistors installed. B- sits at 51v.
Without any amp connected, B+ and B- are fine at +-/55V.
Further back, the collector of TR306 should be 2.4 V and is 55V.
This is quite puzzling especially with components that all appear good. Problems like this are normally right up my alley. I could use a fresh set of “eyes” on this one.
Thanks,
Rick
The amp distortion issues appeared to be out of tolerance fuse resistors. I replaced those and the few electrolytics on those boards. I cleaned the output transistors, replaced the MICAs and added fresh heat sink compound. And this is where I made a huge mistake that I hate to admit. I inadvertently installed the outputs transistors backwards. PNP where and NPN should have been and I did this to both amps. Naturally the main B+ and B- fuses blew. Once I saw that , I retraced my steps and proceeded to check every component on the amps starting with the outputs TR318/320 and TR 319/321. Then I went backwards to TR316/306 and TR 317/308. I removed these components, then removed the pre-drivers, checked the diodes, zener, etc. Everything checked out. No opens, no shorts. Fuse resistors had already been replaced with metal films and those where checked again and are good.
Upon power up with one amp installed, no protection relay click. Voltage checks are not good. At TP 1, I have 23 V with the output transistors installed. Removing those, I am back to 0v and the protection relay will click on. But that is expected since there is no output signal. B+ is 64 volts. It starts at 51v and climbs to 64v and this is still without the output transistors installed. B- sits at 51v.
Without any amp connected, B+ and B- are fine at +-/55V.
Further back, the collector of TR306 should be 2.4 V and is 55V.
This is quite puzzling especially with components that all appear good. Problems like this are normally right up my alley. I could use a fresh set of “eyes” on this one.
Thanks,
Rick