Fidelity HF 45 primary transformer burnt out. - UK Vintage Radio Repair and Restoration Discussion Forum

leslie5555 · 17th Dec 2017, 12:49 pm

I have replaced the complete motor on this Fidelity HF 45 after the old one overheated and trashed the pri transformer.
All is working fine now but I am worried about what made the transformer overheat in the first place.
I have powered it up for about 15 mins and it is only slightly warm so it may be ok .
What should I check as a possible cause, it has already been suggested that the rectifier may be at fault and needs checking , but what is the voltage (18 V ?) And how do I check the voltage?

Station X · 17th Dec 2017, 12:59 pm

Is this the version with a TBA800 IC?

If so there is no "pri transformer". The amp is powered from an overwinding on the motor.

Bookman · 17th Dec 2017, 1:12 pm

Does the transformer have a rating plate that specifies its VA rating? If it does you can check the load current and compare it to the VA rating capacity.
Note that these are tests that are undertaken under normal conditions. This considers no damage to the transformer or connected load (motor).

Overloading of transformers normally results in damage to the wiring insulation which in turn affects the thermal capacity or VA loading capacity of the transformer. One would normally reduce the VA capacity (or ability to do work) of the transformer under such conditions.

When checking the motor loading it would be prudent to measure values at no load with shaft unattached and with attached.
No load current should be marginal but if this is not so then there are possible mechanical problems such as bearings or thermal damage to the motor windings.
Trust this helps
Joe

leslie5555 · 17th Dec 2017, 1:42 pm

this is the old motor with the burnt out transformer, if that helps.
Graham the IC is SN76013ND

Station X · 17th Dec 2017, 1:50 pm

That's an over winding on the motor, or to be more exact a split bobbin.

I'd check the rectifier for faulty diodes and the smoothing capacitor for electrical leakage.

Tractorfan · 17th Dec 2017, 2:19 pm

Hi,
That's the half of the bobbin with the most wire on it, so it looks like the input 'primary' half. I wonder if shorted turns have done for it?
Some motors had a 110volt tapping which, if connected in error to 240volts would soon burn it out, but I'm not sure if that one has the said tap.
Cheers, Pete.

Station X · 17th Dec 2017, 2:31 pm

Given that the complete motor has been changed, the obvious question is what voltages is the OP seeing when compared to the circuit in post #2.

leslie5555 · 17th Dec 2017, 3:03 pm

I have checked the smoothing cap and it's OK. I will check the voltages later. Thanks.

Bookman · 17th Dec 2017, 3:23 pm

It is possible that there may be confusion. The photograph is of a motor (not transformer) with what looks like a burnt out or over heated stator winding. A quick measurement with a multimeter will prove this.
You mention a primary transformer which would suggest the motor is a 110V a.c. hence the need for primary device. It is strange why only one coil has burnt out?

TonyDuell · 17th Dec 2017, 3:28 pm

I believe that in these players, the device is both a motor and a transformer. There is a coil (the one that has burnt out I think) connected to the mains. It's on a laminated core with copper shading rings, and forms the stator of the turntable motor. There is a second winding on the core, in which a voltage is induced to power the amplifier (thus the 2 windings act as a mains transformer).

Station X · 17th Dec 2017, 3:34 pm

I'm sure you're correct Tony.

A far as I know no circuit is available for the early version HF45's which used an SN76013ND. It can't be that dissimilar to the TBA800 version though.

Fidelitys were cheap and cheerful. I doubt they used a separate step down transformer.

leslie5555 · 17th Dec 2017, 4:10 pm

Just to confirm Tony's post the burnt out part is indeed connected to the mains and the other one goes to the amp via two white wires.
I'm no expert at electronics so I'm sorry if my previous posts have not been clear. But I can make basic checks etc with my multi meter and change components safely.

Herald1360 · 17th Dec 2017, 4:44 pm

It's most likely the burnout was just down to a faulty winding. Stalling the motor has little effect on total loading on the motor/transformer primary winding- most of the load is likely to be from the secondary (psu feed) winding and the shading coils in the magnetic circuit which are effectively shorted turns around part of the core.

Bookman · 17th Dec 2017, 7:27 pm

Quote:

Originally Posted by TonyDuell

I believe that in these players, the device is both a motor and a transformer. There is a coil (the one that has burnt out I think) connected to the mains. It's on a laminated core with copper shading rings, and forms the stator of the turntable motor. There is a second winding on the core, in which a voltage is induced to power the amplifier (thus the 2 windings act as a mains transformer).

I accept this as fact but strange in that the motor has to be energised before one can consider switching on the amp?

peter_sol · 17th Dec 2017, 7:40 pm

For those who were not around at the time
Those motors normally had 18volt secondary windings for transistor amps, as apposed to the 240/110 or using the 80v tap for the valves on the older type.
The motor spun all the time. no point in being picky about the actual wording IE motor or transformer.
We know what is meant.

Nuvistor · 17th Dec 2017, 7:41 pm

The motor is probably running as soon as the amp is turned on, the turntable /Automatic function will start when the idler wheel is engaged.

The other option is that there is a switch on the turntable, when that energises the motor it power the amplifier, the amp is IC so no warm up time.

Edit. Crossed post, 3 answers all the same.

ms660 · 17th Dec 2017, 7:42 pm

It's not a problem, the amplifier only needs to work when a record is playing.

EDIT: Post crossed.

Lawrence.

leslie5555 · 17th Dec 2017, 8:05 pm

Just to clarify the motor does indeed spin all the time the amp is on.

17th Dec 2017, 12:49 pm	#1
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Fidelity HF 45 primary transformer burnt out. I have replaced the complete motor on this Fidelity HF 45 after the old one overheated and trashed the pri transformer. All is working fine now but I am worried about what made the transformer overheat in the first place. I have powered it up for about 15 mins and it is only slightly warm so it may be ok . What should I check as a possible cause, it has already been suggested that the rectifier may be at fault and needs checking , but what is the voltage (18 V ?) And how do I check the voltage?

17th Dec 2017, 1:12 pm	#3
Bookman Hexode Join Date: Aug 2017 Location: Taunton, Somerset, UK. Posts: 318	Re: Fidelity HF 45 primary transformer burnt out. Does the transformer have a rating plate that specifies its VA rating? If it does you can check the load current and compare it to the VA rating capacity. Note that these are tests that are undertaken under normal conditions. This considers no damage to the transformer or connected load (motor). Overloading of transformers normally results in damage to the wiring insulation which in turn affects the thermal capacity or VA loading capacity of the transformer. One would normally reduce the VA capacity (or ability to do work) of the transformer under such conditions. When checking the motor loading it would be prudent to measure values at no load with shaft unattached and with attached. No load current should be marginal but if this is not so then there are possible mechanical problems such as bearings or thermal damage to the motor windings. Trust this helps Joe

17th Dec 2017, 1:42 pm	#4
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Fidelity HF 45 primary transformer burnt out. this is the old motor with the burnt out transformer, if that helps. Graham the IC is SN76013ND Attached Thumbnails

17th Dec 2017, 1:50 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Fidelity HF 45 primary transformer burnt out. That's an over winding on the motor, or to be more exact a split bobbin. I'd check the rectifier for faulty diodes and the smoothing capacitor for electrical leakage. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2017, 2:19 pm	#6
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: Fidelity HF 45 primary transformer burnt out. Hi, That's the half of the bobbin with the most wire on it, so it looks like the input 'primary' half. I wonder if shorted turns have done for it? Some motors had a 110volt tapping which, if connected in error to 240volts would soon burn it out, but I'm not sure if that one has the said tap. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

17th Dec 2017, 12:59 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Fidelity HF 45 primary transformer burnt out. Is this the version with a TBA800 IC? If so there is no "pri transformer". The amp is powered from an overwinding on the motor. Attached Thumbnails __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2017, 2:31 pm	#7
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Fidelity HF 45 primary transformer burnt out. Given that the complete motor has been changed, the obvious question is what voltages is the OP seeing when compared to the circuit in post #2. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2017, 3:03 pm	#8
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Fidelity HF 45 primary transformer burnt out. I have checked the smoothing cap and it's OK. I will check the voltages later. Thanks.

17th Dec 2017, 3:23 pm	#9
Bookman Hexode Join Date: Aug 2017 Location: Taunton, Somerset, UK. Posts: 318	Re: Fidelity HF 45 primary transformer burnt out. It is possible that there may be confusion. The photograph is of a motor (not transformer) with what looks like a burnt out or over heated stator winding. A quick measurement with a multimeter will prove this. You mention a primary transformer which would suggest the motor is a 110V a.c. hence the need for primary device. It is strange why only one coil has burnt out?

17th Dec 2017, 3:28 pm	#10
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Fidelity HF 45 primary transformer burnt out. I believe that in these players, the device is both a motor and a transformer. There is a coil (the one that has burnt out I think) connected to the mains. It's on a laminated core with copper shading rings, and forms the stator of the turntable motor. There is a second winding on the core, in which a voltage is induced to power the amplifier (thus the 2 windings act as a mains transformer).

17th Dec 2017, 3:34 pm	#11
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Fidelity HF 45 primary transformer burnt out. I'm sure you're correct Tony. A far as I know no circuit is available for the early version HF45's which used an SN76013ND. It can't be that dissimilar to the TBA800 version though. Fidelitys were cheap and cheerful. I doubt they used a separate step down transformer. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2017, 4:10 pm	#12
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Fidelity HF 45 primary transformer burnt out. Just to confirm Tony's post the burnt out part is indeed connected to the mains and the other one goes to the amp via two white wires. I'm no expert at electronics so I'm sorry if my previous posts have not been clear. But I can make basic checks etc with my multi meter and change components safely.

17th Dec 2017, 4:44 pm	#13
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Fidelity HF 45 primary transformer burnt out. It's most likely the burnout was just down to a faulty winding. Stalling the motor has little effect on total loading on the motor/transformer primary winding- most of the load is likely to be from the secondary (psu feed) winding and the shading coils in the magnetic circuit which are effectively shorted turns around part of the core. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

17th Dec 2017, 7:40 pm	#15
peter_sol Octode Join Date: Aug 2003 Location: Welwyn Garden City, Herts. UK. Posts: 1,906	Re: Fidelity HF 45 primary transformer burnt out. For those who were not around at the time Those motors normally had 18volt secondary windings for transistor amps, as apposed to the 240/110 or using the 80v tap for the valves on the older type. The motor spun all the time. no point in being picky about the actual wording IE motor or transformer. We know what is meant.

17th Dec 2017, 7:41 pm	#16
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: Fidelity HF 45 primary transformer burnt out. The motor is probably running as soon as the amp is turned on, the turntable /Automatic function will start when the idler wheel is engaged. The other option is that there is a switch on the turntable, when that energises the motor it power the amplifier, the amp is IC so no warm up time. Edit. Crossed post, 3 answers all the same. __________________ Frank

17th Dec 2017, 7:42 pm	#17
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Fidelity HF 45 primary transformer burnt out. It's not a problem, the amplifier only needs to work when a record is playing. EDIT: Post crossed. Lawrence.

17th Dec 2017, 8:05 pm	#18
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Fidelity HF 45 primary transformer burnt out. Just to clarify the motor does indeed spin all the time the amp is on.