Capacitor problem with Thorens TD 125 Mk2 - UK Vintage Radio Repair and Restoration Discussion Forum

Sixer-h · 18th Mar 2018, 10:43 pm

I'm an (enthusiastic) electronics novice, without much experience and have a problem with my newly acquired Thorens TD 125 Mk2, in that the motor throbs slightly when the deck on/off switch is turned off.

Reading on the internet about issues with irregular motor running with these decks, I understand that the speed control mother-board's power capacitors usually need replacing at some time. I therefore purchased two 1000uf 25v polarised caps and a new meter that can read capacitance values.

The new 1000uf caps have not arrived yet, but the meter has and so after some practise on old capacitors that I replaced from my Pye Record Maker, I thought I would start by checking the deck's switch electronics before looking at the mother board next week. I found a broken 47 Ohm resistor and have ordered replacements on-line, but, when I tried measuring the 0.1uf (250v) capacitor that the resistor was in series with it, first on and then off the board, and it read 0.208uf each time, more than double the marked value.

There are two stacked switches, each with a capacitor and resistor in series looping between the live to the switched terminals. The rectangular capacitors have the following markings: MP 85, 0.1uf, 250v alternating GPF, -40 + 85, 560-7, +S 6/74 (see photos). I checked both capacitors and they both read similar high values .

Is there something I'm missing (other than lack of experience)? I thought that when capacitors leak they lose value not gain it.

When the double switch is turned on, the power goes through a polarised tubular 0.1uf 250V cap (see photos), and a 100 Ohm resistor before reaching the transformer that feeds the Motherboard. The values are all correct according to the circuit diagram for the deck.

Can anyone help me understand why the switch capacitors show double the correct value and whether (after replacing the broken resistor), I should be looking elsewhere for the cause of original motor throbing issue? What voltage resistor value should I be buying (250V+)?

Some photos are with one capacitor removed the

Any help much appreciated.

Regards,

Richard

Michael Maurice · 18th Mar 2018, 10:58 pm

The capacitor/resistor is there to reduce clicks that occur when the switch contacts are closed. It looks like its been added by a third party, it does not affect the motor running, however the capacitor on the other board may well do.

Sixer-h · 18th Mar 2018, 11:04 pm

Oh OK, that makes sense. I will check the power capacitors on the mother board and probably change them anyway.

Thanks for the swift reply.

18th Mar 2018, 10:43 pm	#1
Sixer-h Triode Join Date: Dec 2017 Location: Congresbury, Somerset, UK. Posts: 21	Capacitor problem with Thorens TD 125 Mk2 I'm an (enthusiastic) electronics novice, without much experience and have a problem with my newly acquired Thorens TD 125 Mk2, in that the motor throbs slightly when the deck on/off switch is turned off. Reading on the internet about issues with irregular motor running with these decks, I understand that the speed control mother-board's power capacitors usually need replacing at some time. I therefore purchased two 1000uf 25v polarised caps and a new meter that can read capacitance values. The new 1000uf caps have not arrived yet, but the meter has and so after some practise on old capacitors that I replaced from my Pye Record Maker, I thought I would start by checking the deck's switch electronics before looking at the mother board next week. I found a broken 47 Ohm resistor and have ordered replacements on-line, but, when I tried measuring the 0.1uf (250v) capacitor that the resistor was in series with it, first on and then off the board, and it read 0.208uf each time, more than double the marked value. There are two stacked switches, each with a capacitor and resistor in series looping between the live to the switched terminals. The rectangular capacitors have the following markings: MP 85, 0.1uf, 250v alternating GPF, -40 + 85, 560-7, +S 6/74 (see photos). I checked both capacitors and they both read similar high values . Is there something I'm missing (other than lack of experience)? I thought that when capacitors leak they lose value not gain it. When the double switch is turned on, the power goes through a polarised tubular 0.1uf 250V cap (see photos), and a 100 Ohm resistor before reaching the transformer that feeds the Motherboard. The values are all correct according to the circuit diagram for the deck. Can anyone help me understand why the switch capacitors show double the correct value and whether (after replacing the broken resistor), I should be looking elsewhere for the cause of original motor throbing issue? What voltage resistor value should I be buying (250V+)? Some photos are with one capacitor removed the Any help much appreciated. Regards, Richard Attached Thumbnails

18th Mar 2018, 10:58 pm	#2
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Capacitor problem with Thorens TD 125 Mk2 The capacitor/resistor is there to reduce clicks that occur when the switch contacts are closed. It looks like its been added by a third party, it does not affect the motor running, however the capacitor on the other board may well do. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

18th Mar 2018, 11:04 pm	#3
Sixer-h Triode Join Date: Dec 2017 Location: Congresbury, Somerset, UK. Posts: 21	Re: Capacitor problem with Thorens TD 125 Mk2 Oh OK, that makes sense. I will check the power capacitors on the mother board and probably change them anyway. Thanks for the swift reply.