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No inputs to Capstan motor on Pioneer RT909 Tape deck

My tape deck developed intermittent speed control problems and ran significantly slower. The schematics I have from Pioneer on the deck have some errors in the capstan motor power supply areas.

It looks like the capstan motor runs from a pulse generated AC with a variable frequewncy for speed control. While checking this out I accidentally shorted the emitter of Q245 and lost all power to the capstan motor. Q245 pulse driver? shows zero vdc at base and emitter. The Darlington driver Q214 has 0 vdc as well since it's connected to Q245 base. I pulled both transistors. They seem to show normal junction behavior. The voltages at the open circuit points seem unaffected. My scope shows no input pulses going to Q245 of the capstan motor assembly board. I don't have exact matches for the transistors so would probably substitute others for them.

Meanwhile, I reinstalled the original transistors and got no change in results. All the electrolytic caps and current limiting resistors in that portion of the circuit seem OK (no shorts or opens).

Do you think the DC bias to Q245 base and emitter come from Q214 or somewhere else?

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  • 4 more comments 
  • Gocart1 Jan 25, 2008

    I replaced all of the drive transistors and speed control IC for the capstan motor. The motor won't turn under power. It has two windings, both of which continuity check ok. Is there a simple way to check out this pulse (?) motor. DC bias for the transistor circuits appear in normal range but the scope shows no pulse activity on them.

  • Gocart1 Jan 26, 2008

    If you don't have a schematic of the capstan motor control assy board, use the pin numbers from the main control B Assy RWG-105 to follow this msg. I'll show the connecting pin numbers for the capstan motor board in ( ). All measurements are VDC with the tape drive engaged in fwd mode.

    Pin 40 (8) Q245 E 23.8V




  • Gocart1 Jan 26, 2008

    Sorry my msg got cut off earlier today. Here is the rest of it.



    Pin 40 (8 on Capstan Motor Control Board) =Q245 E 23.8 VDC

    Q245 B 23.3 V

    Q245 C 22.9 V



    Across Capstan Motor winding 1,

    Pin 25 (2) 23.2 V

    Pin 24 (3) 22.9 V



    Pin 28 (1) Q22 C 22.4 V

    Pin 26 (9) Q22 E 0 V



    Pin 44 (4) lo side of Capstan FG winding 4.9 V

    no pin (TP.21) high side of Capstan FG winding 21.8 V



    Pin 28 Q213 C 22.2 V

    Q213 E 22.1 V

    Q213 B 21.2 V



    Pin 28 Q212 C 22.2 V

    Q212 E 22.6 V

    Q212 B 22.8 V



    Pin 25 Q210 C 23.2 V

    Q210 B 22.5 V

    Pin 31 Q210 E 23.0 V



    Pin 24 Q211 C 22.7 V

    Q211 B 23.0 V

    Pin 31 Q211 E 23.0 V



    Q214 C 33.7 V

    Q214 E 25.2 V

    Q214 B 24.1 V



    Q220 C 13.0 V

    Q220 B 13.6 V

    Q220 E 13.8 V



    Q245 C 25.2 V

    Q245 B 24.1 V

    Pin 40 Q245 E 24.1 V



    I installed new transistors for all the above. Most were OEM spec ID. The PNP power transistors were substitutes, all the same type for the flip flops Q210, Q211, Q212, and Q213.


  • Sam Palermo
    Sam Palermo Sep 06, 2012

    There is a 25 V zener diode that people not used to this deck neglect to check. The Q245 power supply regulator needs voltage at its base to give output and there should be some voltage at it collector.If there is still no voltage even at the collector then one of the safety switches might have opened up they are in series.

  • Sam Palermo
    Sam Palermo Sep 07, 2012

    I don't know where you are getting all the drive information but the Capstan motor is a simple DC governed motor with a FG coil that supplies feedback that gets converted from a frequency to a voltage and then compared in a comparator IC. The Q245 I don't see on the schematic due to good old Pdf files. I will have to check my paper schematics. Most Capstan motor problem stem from a lack of 24 volts going into that driver board. The lack of the 24 volts can cause a lot of problem as it supplies relay power for reel motors and other parts. The first thing is to make sure 24 Vdc is going into the card. We can discuss further if you want directly at skywavebe@sbcglobal.net.

  • Sam Palermo
    Sam Palermo Sep 07, 2012

    Now that I have found Q245 in the power supply section, this Q245 is not a pulse driver and if there are pulses at the transistor there are other things wrong. There shopuld be ONLY DC voltage there and if you are familiar with electronics, this transistor is there to provide current limiting based on the drop of the votage across R293. When voltage get to .7 on R293 the transistor shuts down the Q214 drive. The Q 214 transistor is where all decks that have had no movement when they came in to me have been. The Q210, 211, and213, 212 given the control from Q208 just switch the motor polarity around as this is a reversing deck. First get voltage on Emitter of Q214, then that will power the servo board on Pin 8, then deal with the tension arm switches- they routinely open up die to age. They should be replaced as the voltage for the motor goes through them and if they were resistive this was the problem all along. The voltage of E mitter Q214 should not have ripple or any noise it should be DC only.

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Could be a nasty fix this one. you will have 2 faults. Firstly the original fault, and secondly the man made one. I hate it when that happens. You dont mention what collector voltages you have. Check DC first is the oldest addage for electronics repairs. It is possible that you may have lost power supply to this stage when the short occurred by failure of a resistor somewhere in the supply line. It can be hard to check the junctions of a darlington transistor without replacing it. The transistor you mention is a series regulator that wont be providing pulses, but regulating to 24 volts. Check the Zener diode in the base of it(should have 25 volts here) and 37 volts on the collector. You wont have voltage at the motor but rather a AC drive generated and controlled by the the IC and FG coil and the 4 transistors q210-213 . You may need to get back to me to help fault find the circuit. I got a schematic at http://www.eserviceinfo.com/download.php?fileid=6302 Get back to me here if you can/cant get the 24v reg back up and we'll attack the speed problem:)

Posted on Jan 26, 2008

  • Graeme Ross
    Graeme Ross Jan 27, 2008

    how is the speed control?

    I have some some probable causes for that too if you are interested?



    regards

    Graeme

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  • 395 Answers

Check for pico fuses on the 12v motor line or protection fuses that look like transistors but infact are fuses. they may have board location numbers like PSxxx, or PRxxx.

Posted on Jan 25, 2008

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  • Master
  • 790 Answers

Simple! just follow the lead Voltage!

Posted on Dec 16, 2007

  • carlos fernandez Jr.
    carlos fernandez Jr. Dec 16, 2007

    then follow the path! at this time dont use the scope use an ohmmeter tester! like a broken bridge you can not pass your car at the bridge!

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