Hello Stefano,

Sorry that did not fix it. If you could lay your hands on a voltmeter I would check the power supply voltages in the voice with problems. You could have a bypass capacitor in that circuit which is dragging down the power supply.? Be very careful not to short against any nearby pins.

I am concentrating on the electrolytic capacitors because given the +30 year age of these synths they are the most likely to fail. Caution : There are additional polypropylene caps in each voice circuit which should not be replaced as they last forever and are near impossible to find.

You could just replace all the electrolytic capacitors in the failing circuit. The tech will probably recommend an entire re-capping of the voice board. ?This would not be a bad idea but is expensive for the whole voice board.

If that does not fix it, the most likely suspect would be the many analog switch chips in the voice circuit.? To really narrow it down an oscilloscope would be very useful.

If you want to continue working on it ( not many techs will work on these anymore) I will be glad to help.

Best Regards

Karl

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Sent from for Windows 10

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From: Stefano via Groups.Io
Sent: Saturday, January 11, 2020 6:47 AM
To: [email protected]
Subject: Re: [xpantastic] Tuning fail

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Hi Karl,?

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I’ve finally replaced the C249, unfortunately the problem is still present. Every test on voice 6 fails. The FAIL label appear just after my Xpander start to test this voice, for each section (VCO, PW, ecc). I think it’s a problem in the first part of the voice path. Maybe a multiplexer, or the cap on the top of the PCB or a missing tension on that voice strip... I will try the latest test, then I will bring my Xpander to an experienced tech.

Thank you!

Stefano?

Il giorno 24 dic 2019, alle ore 06:58, Karl Schmeer <shire03@...> ha scritto:

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Hi Stefano,

Yes your right, I could not remember the voltage rating and looked it up in the service manual. It is listed there as 25V

But actual production values are 50V Which is fine. A 50 Volt will last longer and does not change the frequency

response. ( All the signal from the voice goes through this cap to be mixed before final output.)

Have a great holiday!!

• Karl

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Sent from for Windows 10

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From: Stefano via Groups.Io
Sent: Monday, December 23, 2019 8:17 AM
To: [email protected]
Subject: Re: [xpantastic] Tuning fail

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Hello Karl! Thank you for your kind reply and you detailed description. My Xpander was never serviced so I think that the problem could be a capacitor.?

I’m quite expert in soldering, so I can proceed by myself.?

Only a question: the 2,2 uf capacitor has a 50 voltage, not 25. But I think we are talking about the same component.?

I think I will replace this capacitor in the Xmas Holidays.?

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Best regards,?

Stefano

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Il giorno 22 dic 2019, alle ore 17:31, Karl Schmeer <shire03@...> ha scritto:

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Hello Stefano,

The good news is, it’s probably just a capacitor, the bad news is you must unsolder and replace a component on the voice circuit board. If you don’t feel comfortable soldering on a circuit board you might want to find an experienced tech.

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The following notes are in reference to the Xpander Service Manual available on the Xpantastic

forum.

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The most common part to fail /replace is Cx49.? This fail happens so often I have written a small service note for it.

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It is a 2.2 uF ?25V electrolytic capacitor.

The schematic is on page 27 of the Xpander Service Manual.

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Your looking for part number Cx49

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There is one each of these parts for each voice

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the x in the designation will be one of a 2 - 7 number. However, The numbers are not

the same as the voice number.?

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??????????? Voice 6 = C249 *?? Replace this one

??????????? Voice 5 = C349?????????

??????????? Voice 4 = C449?????????

??????????? Voice 3 = C549

??????????? Voice 2 = C649 ????????

??????????? Voice 1 = C749

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Note that each part in that voice will have the same prefix ex.?? C2xx? or U2xx for voice 6

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Parts Placement Drawing = Page 77 and 78

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Notice the parts for each voice are located in a strip which runs verticle down the circuit board.?

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Look to the bottom lefthand corner of the circuit board.

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Inside the Voice circuit notice an 8 pin chip with a designation of Ux16

The capacitor is located right next to the bottom lefthand corner of this chip.

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You can recognize them as a small electrolytic capacitor. The part designation

is printed right next to it.

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Polarity must be observed. but you probobly knew that.

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Best Luck

• Karl

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Sent from for Windows 10

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From: Stefano via Groups.Io
Sent: Sunday, December 22, 2019 9:04 AM
To: [email protected]
Subject: [xpantastic] Tuning fail

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Hi everyone! Unfortunately I’m writing here because my Xpander has some problem. Every test on voice 6 fails. VCO, PW, RES, VCF and VCA. So I suppose it’s not a CEM problem because it would fail only 1-2 test, or a power supply problem, because in this case it would affect all the voices.

I’ve swapped some IC, but the problems remain on the same voice. Please could you tell me and confirm me the the first one on the left is the voice 6 and the last one on the right the voice 1?

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Thank you very much,

Stefano

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