Radiomobile 104 8 Track Player - Motor Starting Problems - UK Vintage Radio Repair and Restoration Discussion Forum

Magical · 12th Oct 2020, 12:12 am

Hello all, I'm after a bit of help please.

I'm refurbishing a Radiomobile 104 8 track player. I've got the radio working correctly. I've cleaned and lubricated all the mechanical parts, including the capstan shaft, making sure the capstan itself is clean, and it turns freely. I have a problem with the motor developing enough torque to start. Once it's going it's ok and the cartridge plays, but it does have problem starting. If I remove the belt it's the same. Once I give it some help the pinion will turn under power. If I connect 12v to the motor drive board without the drive belt I still have the same problem, the motor will start with some help. The motor spins freely with no power. Is there a component on the motor drive board that's shot or is it the motor?

Any help greatly appreciated,

Many thanks,

Nickthedentist · 12th Oct 2020, 10:59 am

It does sound awfully like a "dead spot" on the motor's commutator.

Can the motor be carefully dismantled?

N.

Magical · 12th Oct 2020, 3:36 pm

Thanks Nick,

I think you may be right. I have stripped it down and had a look, couldn’t see anything, put it back together and then reinstalled it. Same result I’m afraid. Before I “hand start” the motor and rotate very gently, I can feel the “electromagnetic force” of each segment. Once running, the motor’s great, but it really struggles with starting.

Cheers.

Fidelity Fan · 12th Oct 2020, 9:19 pm

This is similar to problems I have encountered with model train motors. It can mean that one of the armature windings is defective, one of the connections to the commutator has come adrift, there is a build up of carbon in the commutator slots or a breakdown in insulation.

If you have access to a multimeter, do a resistance check across each segment of the commutator, Each segment should give a similar resistance reading if the armature windings are okay.

Next check for any short to the armature body by touching each segment and the armature shaft in turn. A reading here indicates that the insulation has broken down. Make sure that the slots between the commutator segments are not clogged with carbon, if he motor uses carbon brushes.

Magical · 12th Oct 2020, 10:40 pm

Thanks Fidelity, will do.��

Magical · 13th Oct 2020, 9:38 pm

I’ve had a look at the motor and it is a permanent magnet unit so is driven by transistors firing and not brushes....could I have a dodgy transistor that’s causing this?

12th Oct 2020, 12:12 am	#1
Magical Triode Join Date: Jun 2020 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 33	Radiomobile 104 8 Track Player - Motor Starting Problems Hello all, I'm after a bit of help please. I'm refurbishing a Radiomobile 104 8 track player. I've got the radio working correctly. I've cleaned and lubricated all the mechanical parts, including the capstan shaft, making sure the capstan itself is clean, and it turns freely. I have a problem with the motor developing enough torque to start. Once it's going it's ok and the cartridge plays, but it does have problem starting. If I remove the belt it's the same. Once I give it some help the pinion will turn under power. If I connect 12v to the motor drive board without the drive belt I still have the same problem, the motor will start with some help. The motor spins freely with no power. Is there a component on the motor drive board that's shot or is it the motor? Any help greatly appreciated, Many thanks,

12th Oct 2020, 10:59 am	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,841	Re: Radiomobile 104 8 Track Player - Motor Starting Problems It does sound awfully like a "dead spot" on the motor's commutator. Can the motor be carefully dismantled? N.

12th Oct 2020, 3:36 pm	#3
Magical Triode Join Date: Jun 2020 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 33	Re: Radiomobile 104 8 Track Player - Motor Starting Problems Thanks Nick, I think you may be right. I have stripped it down and had a look, couldn’t see anything, put it back together and then reinstalled it. Same result I’m afraid. Before I “hand start” the motor and rotate very gently, I can feel the “electromagnetic force” of each segment. Once running, the motor’s great, but it really struggles with starting. Cheers.

12th Oct 2020, 9:19 pm	#4
Fidelity Fan Hexode Join Date: Jan 2013 Location: Wigan, Lancashire, UK. Posts: 372	Re: Radiomobile 104 8 Track Player - Motor Starting Problems This is similar to problems I have encountered with model train motors. It can mean that one of the armature windings is defective, one of the connections to the commutator has come adrift, there is a build up of carbon in the commutator slots or a breakdown in insulation. If you have access to a multimeter, do a resistance check across each segment of the commutator, Each segment should give a similar resistance reading if the armature windings are okay. Next check for any short to the armature body by touching each segment and the armature shaft in turn. A reading here indicates that the insulation has broken down. Make sure that the slots between the commutator segments are not clogged with carbon, if he motor uses carbon brushes.

12th Oct 2020, 10:40 pm	#5
Magical Triode Join Date: Jun 2020 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 33	Re: Radiomobile 104 8 Track Player - Motor Starting Problems Thanks Fidelity, will do.��

13th Oct 2020, 9:38 pm	#6
Magical Triode Join Date: Jun 2020 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 33	Re: Radiomobile 104 8 Track Player - Motor Starting Problems I’ve had a look at the motor and it is a permanent magnet unit so is driven by transistors firing and not brushes....could I have a dodgy transistor that’s causing this?