Hi again!
I'm having some trouble with a Technics RS-B505. The belts are new and everything moves freely but it just wont stay in any mode (play/ff/rew). it picks up for a few seconds and there is sound but then it stops. The digital counter doesn't move so I focused on what they call the rotary detection. There is a little device that emits and receives light and sends it to a circuit as pulses (the back of the reel has black and reflective alternating surfaces) to detect the tape is spinning and to indicate the speed to he microprocessor that controls the counter. At first there were no pulses at all so I replaced the part (rvsgp2s24bc) and now the pulses are present and strong. The problem is that before R913 the voltage is moving from 1 to 4.8V and after 913 it's only varying between 0.737 and 0.640v which clearly is still to much to turn of Q905 which in turn doesn't send the pulses through to Q911 and in turn IC801. I checked both transistors out of circuit and they are fine, also if I ground the base of Q905 the voltage at the collector does go to 3.2V as indicated on the schematic and Q911 reacts as should as well. I checked every component around there (R913,914,915,926,927 and D925) and they are all measuring ok. There is a little error in the schematic as the collector of Q911 should also be tied to line 19.
Any help would be very welcome at this point.
I'm having some trouble with a Technics RS-B505. The belts are new and everything moves freely but it just wont stay in any mode (play/ff/rew). it picks up for a few seconds and there is sound but then it stops. The digital counter doesn't move so I focused on what they call the rotary detection. There is a little device that emits and receives light and sends it to a circuit as pulses (the back of the reel has black and reflective alternating surfaces) to detect the tape is spinning and to indicate the speed to he microprocessor that controls the counter. At first there were no pulses at all so I replaced the part (rvsgp2s24bc) and now the pulses are present and strong. The problem is that before R913 the voltage is moving from 1 to 4.8V and after 913 it's only varying between 0.737 and 0.640v which clearly is still to much to turn of Q905 which in turn doesn't send the pulses through to Q911 and in turn IC801. I checked both transistors out of circuit and they are fine, also if I ground the base of Q905 the voltage at the collector does go to 3.2V as indicated on the schematic and Q911 reacts as should as well. I checked every component around there (R913,914,915,926,927 and D925) and they are all measuring ok. There is a little error in the schematic as the collector of Q911 should also be tied to line 19.
Any help would be very welcome at this point.
I guess R914 was just to high a value to be able to pull the base of Q905 low enough. I tried different values and settled for 1.2K (I know, that's very far away from 47K) and the pulse is now stable, counter works and tape stays in play mode (ff and rew also work). I don't know the reason this this suddenly stopped working as it should because again, other than changing the value of this resistor all the other components are fine.