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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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17th May 2018, 10:28 am | #1 |
Retired Dormant Member
Join Date: May 2018
Location: Stoke On Trent, Staffordshire, UK.
Posts: 3
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Thorens TD 126 Mk 3 - problem with Speed Switches/lamps
Hi, i'm new to this forum, hope someone can Help with my weired issue ..
I have owned the deck for over 40 years, but it's spent the last 20 or so boxed. It's in great condition just needed a good looking over. So the turntable works and maintain's speed well, The motor nice and quiet but I had some issues with a bulb not working at first in one of the speed switch's so I have replaced all the bulbs in the switch's, but I have this strange problem If there is a bulb in place then the switch dosent hold contact .. Example, there are 4 switch's (Buttons) 78, 45, 33 and stop, if I take all the bulbs out then they all work fine, I press the button and release and the turntable gets up to speed and everything is ok. But If I put a bulb in any of the positions, then when I press the button, it lights and the motor starts but stops when I let go ... Another example, I take the speed switch bulbs out (all 3) I select one of the speed buttons (works the same for all) I press it briefly and the turntable spins up to speed ... great .. but then if I place a bulb in the circuit board (for the speed I have running) then the stop switch lights and the motor stops. i'd be very grateful for any Help. Cheers Paul |
17th May 2018, 11:25 am | #2 |
Hexode
Join Date: Jul 2009
Location: Wokingham, Berkshire, UK.
Posts: 437
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Re: Thorens TD 126 Mk 3 - problem with Speed Switches/lamps
Hi Paul,
First of all check the power supply voltages as often one half of the power transformer secondary or primary fails due to it being run on 240V. I have also had quite a few problems with this T/T caused by the switch pins on the PCB, which are silver plated, getting oxidised (sulphided) and turning black. The only solution I have found is to dismantle the PCB, unsolder and remove the pins and suspend in "Goddards Silver Clean" for about 5 mins. Then refit them with a smear of contact lube of some sort. The contacts in the push buttons may themselves need a clean with IPA or the like. John |
17th May 2018, 11:45 am | #3 |
Retired Dormant Member
Join Date: May 2018
Location: Stoke On Trent, Staffordshire, UK.
Posts: 3
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Re: Thorens TD 126 Mk 3 - problem with Speed Switches/lamps
Thanks for your reply john ...
I have in fact cleaned the switch pins which as you said had blackened, but I feel the problem is not there as the switch works well enough, just not when there is a bulb in the circuit .. Seems that with the bulbs in the "latching" part of the electronics is not working .. (that's well over my head) I don't know how that is achieved in the circuit, is that done by the chip ? I'll have a look at the power supply as you said ... I think I can at least manage that. Thanks again Paul |
17th May 2018, 3:05 pm | #4 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: Thorens TD 126 Mk 3 - problem with Speed Switches/lamps
It could be a power supply problem; if there is not quite enough juice in the PSU to light a bulb and maintain the logic state, it will switch off.
Alternatively, if incorrect bulbs have been fitted which draw too much current, this would also stop it from working. As a first quick test, does it work properly if you put the original bulbs back? And do you have, or can you borrow, a digital storage oscilloscope?
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17th May 2018, 4:46 pm | #5 |
Hexode
Join Date: Jul 2009
Location: Wokingham, Berkshire, UK.
Posts: 437
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Re: Thorens TD 126 Mk 3 - problem with Speed Switches/lamps
Hi Paul,
Then it look as though you need to turn your attention to the speed select chip (Z105 - SAS 670) as both the speed switching and lamp are controlled through this chip. I would suggest downloading the schematic from this website's library, then checking the voltages around this chip. There should be at least ±15V available. julie_m's idea is a good one - lamps should be 12V 0.03A (30mA). John |
17th May 2018, 5:42 pm | #6 |
Retired Dormant Member
Join Date: May 2018
Location: Stoke On Trent, Staffordshire, UK.
Posts: 3
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Re: Thorens TD 126 Mk 3 - problem with Speed Switches/lamps
Thanks to both of you ... I have played around with old and new bulbs as I only needed one but purchased 6 and so have some of each to play with, and I'm convinced it's not a bulb issue ..
Thanks again, I'll post if I find anything Best regards Paul |