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Vintage Sharp RT-3388a digital tape counter not counting

Florida21

Jul 11, 2022
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Hello, new to the forum. Hope this is the right place to post. Bought this unit months ago…had one when I was younger and loved it. Tape player works great since I have been fixing it. The digital control section with the clock works, second counter works, however when selecting tape counter this stays on “0”. Does not count. Any help on this much appreciated. Unfortunately I’m not that technical from an electronics point but can fight thru it. I do have the schematics on this unit!
 

kellys_eye

Jun 25, 2010
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Presumably the tape is actually running when the counter isn't clocking??

If this is the case then check the sensor(s) that will be coupled to the tape motor drive mechanism. Quite likely they are optical (dirty) but may eve be mechanical (again, dirty contacts).

Post a link to the schematic and/or upload it here.
 

Florida21

Jul 11, 2022
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Thank you for the feedback. I didn’t see anything on the schematic regarding sensors. I’ll check it out. I’m also going thru the troubleshooting on the schematic which doesn’t state anything on sensors. I’m also going thru and checking connectors that are related. I’ll try to post pics of the schematic too. And yes, as the tape plays, the arrow or whatever you call it on the display is lit up but the number counter is at “0”
 

kellys_eye

Jun 25, 2010
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The turns counter is a hall effect device (IC5) fitted to the back of the tape motor. Its output switches Q808 to send a pulse to the control unit via its pin#2.

Check the voltage at the collector of Q808 and look for the pulsing as the motor runs. The Hall effect IC detects the N-S-N-S magnetic pole changes of either the motor itself or a magnet attached to the rear of it - dunno, I don't have the equipment here! The magnet may have fallen off??? the hall effect device may be dud??? or Q808 is dud???? and/or the components on the base of that transistor - specifically C818 or C401 that may have suffered 'old age' as this type of capacitor often does.
 

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kellys_eye

Jun 25, 2010
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Extra - check the belt between the pulley and magnet (item 6 and 12 on page 11) - it might be snapped.
 

Florida21

Jul 11, 2022
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I did see earlier today IC5 and the magnet is still there. Also the belt is there as well. I’ve had it all taken apart a month ago since I had the issue of no reverse and replace a gear. I’ll be checking the other items you mention. Can’t thank you enough for your help. I’ll try my best and I will update with info and addl questions.
 

Florida21

Jul 11, 2022
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Thank you again kellys_eye. It was Q808. Being a novice at this I can’t thank you enough!
 
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