With every plus there's a catch

pete246

Member (SA)
The catch of course being there's another problem waiting on my sharp vz3500.
Finally I got the record player to spin (yay) but it's spinning too fast kind of pinky and perky fast .
The variable resistors on the board do absolutely nothing and neither does the 45/33 button and there's no speed adjustment on the motor. All I can think of is the belt maybe wrong but I've tried two different ones .
If anyone has any ideas I'd be eternally grateful.
Pete
 

pete246

Member (SA)
The catch of course being there's another problem waiting on my sharp vz3500.
Finally I got the record player to spin (yay) but it's spinning too fast kind of pinky and perky fast .
The variable resistors on the board do absolutely nothing and neither does the 45/33 button and there's no speed adjustment on the motor. All I can think of is the belt maybe wrong but I've tried two different ones .
If anyone has any ideas I'd be eternally grateful.
Pete
I guess nobody else knows either.
 

BoomboxLover48

Boomus Fidelis
Never had that problem with my VZ3500. Belt can't be the issue here.
It could be running at a higher voltage due to a problem with the supply voltage.

Check the motor voltage and compare against what schematics show.

Normally when a DC motor runs at a higher voltage, it results in an increase in speed and output power. Motor speed is directly proportional to the applied voltage. Higher voltage means a higher torque and rotational speed when load and other conditions remain constant.

Our experts here can suggest more.
 
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Tinman

Member (SA)
I've never worked on a rp so I'm not sure if the motors are usually adjustable or not but are there any stickers on the end of the motor that may be covering a speed adjustment hole?
Some pics might help others help you.
 
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maxhifi

Member (SA)
Looking at the service manual, this record player has a motor which has a speed controller external to the motor itself. It gets direction (for the plays both side function) and speed logic signals from the logic IC, and speed feedback from a generator which is in the same package as the motor. I suggest to first check all the transistors and the electrolytic capacitors in this area, and then to check voltages during operation. Also, check the 33rpm and 45rpm speed preset pots to make sure they're in working order.
 
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pete246

Member (SA)
I've never worked on a rp so I'm not sure if the motors are usually adjustable or not but are there any stickers on the end of the motor that may be covering a speed adjustment hole?
Some pics might help others help you.
There is a hole in the back of the motor as you suggest but no adjustment screw I'm pretty sure adjustment has to be made via the variable resistors one the board one for 45rpm the other 33 rpm.
Will post pics thanks for your inputs.
 
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pete246

Member (SA)
Looking at the service manual, this record player has a motor which has a speed controller external to the motor itself. It gets direction (for the plays both side function) and speed logic signals from the logic IC, and speed feedback from a generator which is in the same package as the motor. I suggest to first check all the transistors and the electrolytic capacitors in this area, and then to check voltages during operation. Also, check the 33rpm and 45rpm speed preset pots to make sure they're in working order.
I have been testing capacitors randomly by removing ,testing and replacing with new so far they have all tested within tolerance.
I have not checked any transistors but now you mentioned it I will though I have been re soldering some dry joints on the back and I haven't tried it since .
I have also dismantled the 33/45 switches cleaned and tested for power all good.
Thanks for taking the time.
 

pete246

Member (SA)
Never had that problem with my VZ3500. Belt can't be the issue here.
It could be running at a higher voltage due to a problem with the supply voltage.

Check the motor voltage and compare against what schematics show.

Normally when a DC motor runs at a higher voltage, it results in an increase in speed and output power. Motor speed is directly proportional to the applied voltage. Higher voltage means a higher torque and rotational speed when load and other conditions remain constant.

Our experts here can suggest more.
Thanks for the input and I agree i don't think it's a belt problem. Testing the power at the plug to the motor is producing 8.6 volts which seems OK to me (though I'm no expert) certainly not excessive what are your thoughts?.
 

pete246

Member (SA)
Hi guys and thank you all for your contributions very much appreciated.
I'll post a couple of pics to show where I am at the moment I'm sure the answers lie on this board.
 

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maxhifi

Member (SA)
Hi guys and thank you all for your contributions very much appreciated.
I'll post a couple of pics to show where I am at the moment I'm sure the answers lie on this board.

It's a servo circuit where voltage from the generator slows down the motor until the circuit is in balance. Definitely test all the transistors within the speed control area (Q508-Q515). If the generator wasn't working it would also have the same effect, since the voltage coming from pin 5 of the motor is what causes the servo circuit to reduce the speed. So check that the wires from the motor are all intact and soldered properly on each end, because a loose wire here could also easily cause this problem.
 

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Tinman

Member (SA)
For future reference, that does look like a speed control on the motor.
You don't usually see the "screw" since they're usually set down inside of the motor and have a protective piece on the back of the housing covering the hole.
That protective cover usually has an X in it so you use a very small straight screwdriver inserted into the hole to turn the screw.
You twist the screwdriver slowly until it seats into the speed adjustment screw.

That said, I'd listen to maxhifi as it looks like he knows what he's talking about.
 

pete246

Member (SA)
Yes tinman it was my first port of call to be honest as I'd adjusted a few boombox cassette motors in the past however the screw is not there it looks like the mini board under the lid fills the whole top of it .
I'm taking note of maxhifi's comments he's very knowledgeable for total duffers like me and I'll look at the transistors when I get time Thanks for the suggestion though it's all good stuff .
 

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pete246

Member (SA)
It's a servo circuit where voltage from the generator slows down the motor until the circuit is in balance. Definitely test all the transistors within the speed control area (Q508-Q515). If the generator wasn't working it would also have the same effect, since the voltage coming from pin 5 of the motor is what causes the servo circuit to reduce the speed. So check that the wires from the motor are all intact and soldered properly on each end, because a loose wire here could also easily cause this problem.
Thanks for the heads up about the transistors I'll definitely check them out when I get time .
The wires are all intact and pretty solid to be fair I'm just hoping it's something simple rather than a motor strip which wouldn't be the first but not a nice job .
Many thanks maxhifi.
 

Nickeccles

Member (SA)
I don't think the motor has an internal pot, speed adjustment is on the FG servo board! Unusual I would say as Sharp electronics tend to be very reliable with mainly just mechanical issues & dirty switches to deal with! Having said that, these issues can be extremely frustrating when the cause can't be found!! Excellent tape decks on these too once rebelted!