With every plus there's a catch

[pete246]

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]

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]

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.

 

[Tinman]

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.

 

[maxhifi]

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.

 

[pete246]

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.

 

[dubout]

I know that the function buttons on my VZ2500 like to act up. Try to click them trough all functions multiple times (read: endlessly )

 

[pete246]

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]

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]

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.

 

[maxhifi]

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.

 

[Tinman]

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]

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 .

 

[pete246]

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]

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!

 

[pete246]

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!

Sorry for the late reply I've changed many capacitors and just received some new transistors to change on the board to at least eliminate some of the maybe this maybe that issues. But on the plus side the radio works fine and now the cassette plays really good after belt change and pinch roller it's just this frustration with the platter speed.
Thanks for contributing.

 

[pete246]

Could this tiny transistor be the cause of my speeding platter?
Upon removal it is totally dead no reading from any pins on the multimeter.
I know it needs replacing whether or not it cures my problem is another matter.

 

[maxhifi]

That transistor could definitely be the problem, if it is bad. It's how the generator gets power, if it is open, the servo will "think" the speed is too slow and try to increase it as much as possible. Check that diode too.

Note: any small signal NPN silicon transistor can be tried as a substitute, don't worry too much about the part number. Just make sure you get E B and C in the correct holes, keeping in mind that the replacement may not have the same pinout as what's in there now.

 

[pete246]

That transistor could definitely be the problem, if it is bad. It's how the generator gets power, if it is open, the servo will "think" the speed is too slow and try to increase it as much as possible. Check that diode too.

Note: any small signal NPN silicon transistor can be tried as a substitute, don't worry too much about the part number. Just make sure you get E B and C in the correct holes, keeping in mind that the replacement may not have the same pinout as what's in there now.

Thanks for your answer it's given me hope after weeks of frustration.
I was dreading taking the motor to pieces as you know the caps are extremely tight ,trying not to damage the board underneath.
I have like for like on order regarding the transistors so I'll wait till it arrives hopefully that might be the answer

 

[pete246]

At last she's done and paired with vintage mission 700 speakers my grin stretching from ear to ear she sounds fantastic.
Many problems drove me to the edge of sanity from capacitors, transistors motors not working then working too fast .
The cassette was seized up and refused point blank to do anything.
Side a on the record deck wouldn't work so I ended up replacing the complete mechanism including all those cotton thin wires (grrrrrr) what a nightmare.
Many thanks to everyone that contributed and commented a merry Christmas to all.