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Sharp RT-3388a solenoid/plunger not working

Florida21

Jul 11, 2022
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Do all the physical switches (mechanical) all work? Are they all in their correct operating position? Have the contacts been cleaned? Still can't read the damned schematic! but the solenoid is essentially activated from two inputs at the base of Q804? There re two 10k resistors attached to the base of that transistor and if you ground the 'top' end of either of them then the solenoid should operate - is this the case?
Yes, all the switches(mechanical) work. I have also used deoxit to clean them. I have been able to get solenoid to operate by shorting Q802, however I will also try grounding the resisters. And of course I flipped the pick AGAIN!
 

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Florida21

Jul 11, 2022
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Yes, all the switches(mechanical) work. I have also used deoxit to clean them. I have been able to get solenoid to operate by shorting Q802, however I will also try grounding the resisters. And of course I flipped the pick AGAIN!
So I grounded both R821 & R823 and nothing. But just to clarify, took wire from ground and touched the other end to both top and bottom ends of resisters and no response from Solenoid. And just to remind, shorting Q802 does work the solenoid
 

Bluejets

Oct 5, 2014
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You WILL need to post a higher resolution photo of your entire circuit.
It is currently unreadable for detail.

Kellys_eye was referring to grounding the "TOP END" of R821 or R823, which are two 10K base resistors on the transistor number Q803.

Be careful grounding willy-nilly as you can damage circuitry unless you know what you are doing.

I'm not surprised grounding R821 or R823 resistor top end did nothing.
Again, with all respect to Kellys_eye, schematic is unreadable to a large degree.
Q803 needs to turn "ON" to turn on Q802 and hence the solenoid so therefore a voltage of the appropriate level would be required , not ground.
 

Florida21

Jul 11, 2022
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You WILL need to post a higher resolution photo of your entire circuit.
It is currently unreadable for detail.

Kellys_eye was referring to grounding the "TOP END" of R821 or R823, which are two 10K base resistors on the transistor number Q803.

Be careful grounding willy-nilly as you can damage circuitry unless you know what you are doing.

I'm not surprised grounding R821 or R823 resistor top end did nothing.
Again, with all respect to Kellys_eye, schematic is unreadable to a large degree.
Q803 needs to turn "ON" to turn on Q802 and hence the solenoid so therefore a voltage of the appropriate level would be required , not ground.
I’ll try to take better pics tomorrow. I’ll be sure to review them as well. Thank you as always for all the help.
 

Bluejets

Oct 5, 2014
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ok....if you have a link to say a pdf file for the circuit diagram, that would be ok also.
 

Florida21

Jul 11, 2022
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ok....if you have a link to say a pdf file for the circuit diagram, that would be ok also.
Here are a few that I scanned. I reviewed before posting. None upside down and was able to enlarge with much clarity. :)
 

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Florida21

Jul 11, 2022
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Here are a few that I scanned. I reviewed before posting. None upside down and was able to enlarge with much clarity. :)
Ok, so based on my very little technical knowledge I still wanted to test a few things at least to see if this would be helpful to you. Please bare with me. With the unit plugged in but power switch down/off position, here are the readings:
Q802 B=28.4v, C=.2mv, E=28.4v (shorted B&C and solenoid worked)
Q803 B=4.1mv, C=28.5v, E=0mv (shorted E&C and solenoid worked)
unfortunately I dont have technical equipment other than meter. Hope this helps.
 

Florida21

Jul 11, 2022
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Ok my helpful friends. Haven’t heard from anyone in a bit. I did attach addl copies of schematics which I hope were better. Before I put this project to bed, thought I’d reach out for any possible suggestions that I didn’t try based on my abilities. And as always, can’t thank you enough to all who have tried to help me diagnose the issues with the tape deck.
 

kellys_eye

Jun 25, 2010
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Check the collector of Q820. This transistor delays the functioning of the solenoid until the switch-on power levels have stabilised. It should be 'low'.
The solenoid is then otherwise controlled by one of two inputs on the base of Q803 - signals from the control unit or via SW10. These signals are pulses from F1 and R1 (pins 3 and 5) i.e. as detected when the tape reaches its fully forward or reverse positions OR when SW10 is operated.
Each pulse will take Q803 collector low and operate the solenoid. You can check the operation of the whole solenoid control circuit by applying a brief high voltage (5V or more) to the top of R821 or R823 (short those points to the emitter of Q802). If the application of a short duration voltage at those resistors doesn't activate the solenoid then Q820 may not be switched on i.e low. Q820 might not be 'on' if C812 is dodgy (ooo, it's an electrolytic.......)

At any other time the solenoid is NOT active and Q802 collector will be at 0V.

If the above checks prove ok then the signals from the control unit are missing - you can only check these with a pulse checker (stretcher) or a 'scope - they'll be too fast to see on a test meter.
 

Florida21

Jul 11, 2022
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Check the collector of Q820. This transistor delays the functioning of the solenoid until the switch-on power levels have stabilised. It should be 'low'.
The solenoid is then otherwise controlled by one of two inputs on the base of Q803 - signals from the control unit or via SW10. These signals are pulses from F1 and R1 (pins 3 and 5) i.e. as detected when the tape reaches its fully forward or reverse positions OR when SW10 is operated.
Each pulse will take Q803 collector low and operate the solenoid. You can check the operation of the whole solenoid control circuit by applying a brief high voltage (5V or more) to the top of R821 or R823 (short those points to the emitter of Q802). If the application of a short duration voltage at those resistors doesn't activate the solenoid then Q820 may not be switched on i.e low. Q820 might not be 'on' if C812 is dodgy (ooo, it's an electrolytic.......)

At any other time the solenoid is NOT active and Q802 collector will be at 0V.

If the above checks prove ok then the signals from the control unit are missing - you can only check these with a pulse checker (stretcher) or a 'scope - they'll be too fast to see on a test meter.
Kellys_eye Thank you thank you thank you. Sorry for the delay. By the time I want to look into this had to deal with the hurricane in Florida where I live. I ended up checking everything you stated (not including those signals since I don’t have a scope) and all checked good until just 10 minutes ago I checked Q820 and did not read to spec so I pulled it and thankfully I had another from the board I bought on eBay and it WORKED! Thank you also for all who added input And thank you for your patience with a guy who is a novice but continues to learn. Have a great weekend!
 
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