I realize this thread goes back quite a few years so I hope that adding to it doesn't cause any problems. I picked up a mint CT-F9191 about 11 or 12 years ago at a yard sale for $3 - yes, three dollars! I tried it out at the time and it ran perfectly and sounded beautiful. I didn't actually need it so it's being sitting all this time doing nothing. After noticing the prices these units are currently fetching (one just sold on eBay for $1,100), I decided to see if I can put it up for sale.
It still plays tapes perfectly, FF works really well but RW doesn't do so well on certain C-90 cassettes and I'm wondering if the cassette design is a factor to be considered. For example, if I rewind a standard TDK D-90 cassette and set the counter to 000, it will run to about 528 (72.5%) when it will struggle then stop, compared to 728 for a full tape run on FF. However, when using a Reader's Digest commercial recording which also runs to 728 on FF, it will rewind the full tape without any problem, although it does slow down graduallly as it gets closer to the end. So, without testing a load of different tapes, it would appear that different cassette manufacturers perhaps use different methods and materials to reduce drag. One thing I should state is that the TDK tape had only been used to record one side and was not used again whereas the commercial one had been played a number of times. I don't know if this would have any bearing on the rewind results.
After cleaning and lubricating the transport mechanism and counter, I decided to do some voltage checks as suggested by Mark back in September, 2012 but first I removed the secondary counter belt. That didn't seem to help with the rewind of the TDK tape, unfortunately. I manually operated the middle microswitch to simulate a cassette being inserted and measured the voltage. So with no counter hooked up and no tape causing drag, measuring directly across the Red and Blue wires of the motor gave 11.30V (FF) and 11.44V (RW). Actually, I found it easier to measure between chassis ground and the motor terminals as I could jam one of my probes into one of the many holes in the chassis, so all the following readings are referenced to chassis ground.. The FF voltage at the blue wire was 12.35V and the RW (red wire) voltage was 12.44V. One thing to note is that when running RW with no tape, you only get about 2 seconds to take a reading before Stop is engaged. This is because the right hand shaft, which drives the speed sensor, is not being turned as it normally would when a cassette is in place. No such problem in FF as the sensor is constantly being driven. After hooking up the third belt again and still with no tape, the voltages were 12.41 (FF) and 12.49 (RW).
What I also noted was that when running the TDK tape, the voltages in both FF and RW dropped as the tape progressed, presumably due to increasing load on the motor. For example, FF of the TDK tape started at 12.41V and gradually dropped to 12.33V when the tape ended. On RW, the start voltage was 12.45V but dropped to 12.35V when the tape stopped at 528 (from 000). The weird thing is that when running the commercial tape in FF, the FF voltage increased from 12.26V (start) to 12.29V (end) but RW showed 12.39V (start) to 12.29V (end). Not only were the voltages inconsistent between the two brands but the typical trend seemed to vary on FF. The only consistent thing I noticed was that the RW voltage was always higher than FF but I have no idea why.
All belts and rubber surfaces seem to be in good condition and I'm assuming the clutches are working as they should as the FF and RW are okay on the commercial C-90 cassette. I have Deoxit D5 and L5 on order and will try to spray all electrical contacts. Any further advice would be very welcome.
Regards,
Al
