Hi, hopefully somebody can help with this... I'm troubleshooting a CR-620 that won't come out of protection and I started to suspect low voltage from the transformer. Does anybody know the transformer specs such as number of turns or output voltages? Across the two OR terminals, with F801/F802 removed, I only get 34V. The schematic shows the output voltage from the regulator circuit (collector of TR802) should be 46.2v. Seems difficult to make 46v from a 34v source. Any help would be much appreciated!
Yamaha CR-620 Transformer Voltage
- Thread starter rredfern
- Start date
When I refereed to the regulated output, I meant to say that the schematic says I should have 46.2 at the collector of TR802, but I only have ~30. The regulated output of TR802 is correct at ~30V but that low voltage made me wonder if something is wrong with the transformer since the BE drop seems to feed other transistors in the protection circuit.
There doesn't seem to be any DC on the amp output lines and I even pulled R811/R812 to make sure there is nothing entering the protection circuit. If I manually bypass TR809, the relay clicks so it's not the relay. Tks again!
There doesn't seem to be any DC on the amp output lines and I even pulled R811/R812 to make sure there is nothing entering the protection circuit. If I manually bypass TR809, the relay clicks so it's not the relay. Tks again!
Oldsansui441
Super Member
Good call avionic, l just replaced one in the protection circuit of an M-70 for intermitant protection on start up. I believe they are a low esr cap.
Ok, so after a bit of a hiatus, I'm back at this one. I recapped the protection board as suggested by Avionic and also did the power amp electrolytics while I was right there. Sure enough, came right out of protection. Set the bias, stable at 8.5mV, and proceeded to listen for while. After about 15 minutes, R751 (the 4.7 ohm emitter resistor of TR721) went up in smoke and it went back into protection. I shut it down and checked TR721 and it was shorted so I replaced transistors 719/720 & 721/722 with KSA1220/KSC2690. I also checked and replaced all of the 4.7 ohm resistors. I started it back up and readjusted the bias but again R751 is getting very very hot. So I guess something is biasing TR721 on and sinking current through R751.
Anyways, just an update for anyone who may be following.
Anyways, just an update for anyone who may be following.
