absinthe77
New Member
There are some similar issues on the forum but not the same, at least not that have been solved. This thread is the closest I have found, but remains unresolved. I have two RT-909 units on the bench and both are doing the same thing!
The issue: Transport controls operate normally with a tape mounted, both directions of play, FF/REW, pause and stop all do as expected. The issue only occurs when auto-stop is engaged, in other words, when you let the tape run out and the tension arm switches close. If the tension arm switches close and trigger auto-stop the brake solenoids stay activated, preventing braking, and in addition the transport logic gets confused and locks all controls (no stop, pause, play, etc). This condition remains until the power is cut, at which time the solenoid current is discharged and the brakes engage once again. This also resets the logic and transport controls work normally on the next power up.
Tension arms: I have ruled out the tension arm switches as I replaced them on one of the units with no change, and bypassing them completely has no effect either. This is kind of obvious since the capstan motor behaves as expected when the switches are opened or closed. Please don't post about the tension arm switches, I am well aware of them. It is not the tension adjustments themselves either as the tension is well within spec during normal operation. The issue is triggered by the change in voltage from the auto-stop circuitry, there are absolutely no symptoms until auto-stop engages.
According to the service manual, the brake solenoids are activated by transistor Q226, which is fed by IC 508. I tested Q226 and it has no issues and sufficient gain. It's also hard to jump to the conclusion that IC 508 is bad because it works fine when the Stop button is pressed, the issue solely exists when auto-stop occurs as I said above. The "Control Section" diagram on page 10 shows the tension arm switches in series with the counter circuit as well as the "running detector" however this phrase is never used again at all in the manual. I have inferred them to be referring to step number 7 on page 20 under the "electronic counter 6.7" section. According to this, IC 100 feeds transistor Q204 which is used as the magnetic brake / frequency detector when FF/REW is switched to Stop or Play. Once again, I can't find a fault in either component, Q204 tests excellent and IC 100 is working fine for the counter circuit as well as manual pressing of play, stop, FF/REW, etc. I cannot find anything pointing to a unique condition that can only be triggered by the tension arm auto-stop, and yet that's exactly what I have here with two different units.
Any insight is much appreciated and I will update this thread with my own progress.
The issue: Transport controls operate normally with a tape mounted, both directions of play, FF/REW, pause and stop all do as expected. The issue only occurs when auto-stop is engaged, in other words, when you let the tape run out and the tension arm switches close. If the tension arm switches close and trigger auto-stop the brake solenoids stay activated, preventing braking, and in addition the transport logic gets confused and locks all controls (no stop, pause, play, etc). This condition remains until the power is cut, at which time the solenoid current is discharged and the brakes engage once again. This also resets the logic and transport controls work normally on the next power up.
Tension arms: I have ruled out the tension arm switches as I replaced them on one of the units with no change, and bypassing them completely has no effect either. This is kind of obvious since the capstan motor behaves as expected when the switches are opened or closed. Please don't post about the tension arm switches, I am well aware of them. It is not the tension adjustments themselves either as the tension is well within spec during normal operation. The issue is triggered by the change in voltage from the auto-stop circuitry, there are absolutely no symptoms until auto-stop engages.
According to the service manual, the brake solenoids are activated by transistor Q226, which is fed by IC 508. I tested Q226 and it has no issues and sufficient gain. It's also hard to jump to the conclusion that IC 508 is bad because it works fine when the Stop button is pressed, the issue solely exists when auto-stop occurs as I said above. The "Control Section" diagram on page 10 shows the tension arm switches in series with the counter circuit as well as the "running detector" however this phrase is never used again at all in the manual. I have inferred them to be referring to step number 7 on page 20 under the "electronic counter 6.7" section. According to this, IC 100 feeds transistor Q204 which is used as the magnetic brake / frequency detector when FF/REW is switched to Stop or Play. Once again, I can't find a fault in either component, Q204 tests excellent and IC 100 is working fine for the counter circuit as well as manual pressing of play, stop, FF/REW, etc. I cannot find anything pointing to a unique condition that can only be triggered by the tension arm auto-stop, and yet that's exactly what I have here with two different units.
Any insight is much appreciated and I will update this thread with my own progress.