RT-909 Capstan Speed Drops
Hello everybody, I have been a happy owner to a nice looking exaple of the well known RT 909 for the last 13 years. It has performed flawlessly over all those years (after replacing the belt, pinch rollers and the infamous Q214 and its sidekick). Even though control board B showed the signs of extensive work, it gave me no trouble... until last month. Capstan motor started to slow down every now and then... until one fine day it slowed down to zero and wouldn't come back up. I went into it and found a toasted R29 on the capstan motor board. Replaced it. Worked for a couple hours. At thah moment I figured R29 was only a victim, and after some research, I replaced Q214 and its partner. it started running, but only on reverse mode. Found a video on youtube which pointed to Q210>Q213 which I suppose do the switching. Replaced all 4. Worked, but a little unstable in fwd mode. I ckecked voltage output on posts 24 and 25 on both modes. in fwd mode, I get 24v from 25 and 10v or so on 24. In rev mode, output voltage readings get inverted. I noted that when in fwd mode, voltage in 24 fluctuated around 12- 15% up and down, randomly. Replaced Q205 and 208. got a little improvement. After working for several minutes, it was running perfectly... Checked voltages...24v on post 25 and 10v on p24... let it run for 30 min and checked...24v on p25 and 6v on p24. one hour later speed dropped. I got 24v on p25 and 2v on p24 and this inverts perfectly when i put rev mode. No toast resistors or zener diodes. Only 3 or 4 caps that looked suspicious were replaced. All 4 drivers get hot after a while of being in usebut no heatsink so I'm not sure how hot they're supposed to get. Any help would be greatly appreciated.