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Teisco SX-400 Calibration
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Old 12th October 2012   #1
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Teisco SX-400 Calibration
Hi fellow Slutz,
I'm trying to tweak some trimmers in my SX-400 and there isn't much info about what I should be doing, in print, or in my head.

I've started by trying to get the voices to sound similar by flicking the 440hz switch on the back and trying to match each voice by ear.

There are some trimmers on the VCF board for Channel 1-4 Keyboard Feed Back Offset and Channel 1-4 Slope. There's some test points near by but I don't know what I should be measuring,and what I should be measuring with.

The test points are at the end of a CA3280/4558 circuit.

What is this offset I am measuring, how do I measure this offset?

I have a 100mhz Philips combiscope that I'm not all clued up on (user manual scares me) and I'm not sure how to see what's happening using this.
Maybe I'm just supposed to be measuring a voltage and am overcomplicating it by trying to learn how to use a scope.

Hopefully I can use any knowledge or tips I might learn here to help with the rest of the various trimmers, of which there is a great many inside the SX-400

Thanks
Martin

EDIT:
Just run some service tests from the test menu of my oscilloscope (Philips PM3365A)and I don't think that the triggering function is working correctly for DC input coupling,(AC works) so that might explain why I can't see anything particularly special while hooked up to the test points of my SX-400?

Will investigate further now I know I might have a problem.Looking forward to going through a 365 page service manual for a solution.

Or I could try to use Channel B instead. Triggering seems OK on that.
Last edited by apprenticemart2; 13th October 2012 at 12:56 PM.. Reason: Update
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Old 17th October 2012   #2
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Little bump.

OK. Nothing wrong with my scope after a 2 day strip down, just some poor connections on the odd cap.

No one with any experiences of the SX-400, more readable copy of the service manual maybe?

Cheers

Martin
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Old 19th October 2012   #3
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Check that the battery's not leaking while you're in there. If it's the original NiCd battery, you may want to remove it.
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Old 19th October 2012   #4
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I've already cleaned that mess up and it was a mess.
A previous owner managed to fry everything connected to the memory chips and beyond, some 14 chips. I just had to replace another chip this morning. It was leaky on one pin and the battery was discharging.

Hopefully I don't have any more problems on the CPU board. I installed a flash memory chip instead of the Eprom, and a lower power Z80 so hopefully that shaved a few 100 milliamps of the power supplies work.

I will just have to soldier on and calibrate it by ear.

Cheers.
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Old 25th November 2012   #5
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Anyone know how I can fix the aftertouch sensor? It's not particularly sensitive any more.
Cheers
Martin
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Old 1 Week Ago   #6
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^
I was able to take the touch sensor strip apart and clean it with some isopropyl alcohol. It works great now.
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