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[LD-S2] Power supply issue
https://forum.lddb.com/viewtopic.php?f=52&t=9575		 Page 1 of 1
Author:  ambroiseg [ 08 Jan 2021, 17:12 ]
Post subject:  [LD-S2] Power supply issue
Hi there, I'm Ambroise from Paris, and I had the chance to buy a not working LD S2 for a small price several days ago, and as I was suspecting, someone screwed up the transformers putting 230V instead of 110V...

Anyway I'd like to install new transformers that can work with 230V, so I'm looking for secondaries voltages info : there is nothing in the service manual so I tried to guess with the schematics :

VTT1075: 80VA (written on the transformer, confirmed by size) : 6-0-6V, 12-0-12V, 0-9V or 0-10V and 5-0-5V but not sure of the last two underlined parameters. I used the schematics but it's quite difficult to know.

VTT1076 :20VA (idem) seems to be 0-9V and 0-9V because the power-on voltage (5V) is adding to this voltage once regulated.

Could someone open his LD S2 and check the transformers secondaries voltages of these two transformers ? It can be done removing the bottom and you'll see 2 strips (CN311 & CN310) on a power board (with big capacitors : VWR1034) and one strip (CN405) on the board under the copper film near RCA audio outs.

Thank you so much, and I know it will help some other guys worldwide :)

Cheers !

Ambroise
Author:  krbahr [ 09 Jan 2021, 01:34 ]
Post subject:  Re: Power supply issue with a LD S2
If you view the actual power supply filtering schematic you will see the different secondary outputs produce the +5VDC, -5VDC, +7VDC, -7VDC, +14VDC, -14VDC and then the standard FL or display AC power. You just need a transformer that can output voltages a little higher than these so the regulator for each voltage can output a steady voltage as the load changes. You’ll also need to check the audio transformer that sends separate voltages to the digital audio board.
Author:  ambroiseg [ 09 Jan 2021, 11:24 ]
Post subject:  Re: Power supply issue with a LD S2
Thank you for your answer, I though secondary output had to be under the regulated value as diode bridge give a higher DC voltage than AC, am I wrong ?
I made a mistake because all my value have to be divided by 2 because of 0 connected to earth on symetrical supply :

VTT1075 :
CN310 : 3-0-3V=6Vac ->7Vdc 6-0-6V=12Vac->14Vdc
CN311 : 0-12Vac -> 14dc and 12Vdc once regulated with Q22
So would you recommand to use higher voltages : 4-0-4V, 7-0-7V and 0-15V for example with standard value ?

What could be FL ac voltage, I've no idea... that's a mystery and nothing is explained on the schematics...

VTT1076 (audio transformer) : schematics p.67 but I'm a bit lost : it seems to be 0-6Vac and 0-10Vac in 2 diode bridges and a sum is made, or 0-20Vac, 0-20Vac divided then in +/-5Vdc and +/-14Vdc but I'm not sure :
Attachment:
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The best would be someone measure it :)
Author:  krbahr [ 09 Jan 2021, 23:56 ]
Post subject:  Re: Power supply issue with a LD S2
The diode bridge will bring both halves of the sign waves to one side which makes filtering to the DC level easier. A 230 VAC is 115 V positive and 115V negative full wave to side you bias it to. You use the transformer to isolate the AC input power from the DC operating power. You have the number of turns in the secondary of the transformer to step up or down the input to the voltage you want to work with. If you put 7 Volts into a 5 Volt regulator it will output 5 Volts and sync out the rest. The higher the voltage going into the regulator the hotter it will get to sync out the extra voltage.

There is someone selling S2 parts on eBay. You need to check what parts are being sold.
Author:  ambroiseg [ 11 Jan 2021, 10:19 ]
Post subject:  Re: Power supply issue with a LD S2
Thank you,
I contacted him and he seems to have the two transformers : I'll buy them or get the voltage infos and I'll share it here ;)
Author:  ambroiseg [ 19 Jan 2021, 12:35 ]
Post subject:  Re: Power supply issue with a LD S2
Hi !


Good news : I received the two transformers : they seem to be the LD X1 versions because it's VTT1071 (audio) and VTT1077 (main). It is surely the same, anyway I took car because in Japan the mains voltage is 100V.

And so on a 100V transformers, without load :

VTT1071 : 17,7V & 17,7V

VTT1077:
CN310
orange-brown : 7,9V
brown-grey : 7,9V
So 16V symetrical
yellow-black : 13,7V
black-red: 13,7V
So nice 27V symetrical

CN311:
red-purple: 14,3V
green-white: 2,3V
white-blue : 2,3V
So 4,5V for FL AC

It couldn't be guessed easily !

Thank you for your help, I hope this can help someone to rebuild new transformers.
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