Roland SH1000 ADSR problem

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Roland SH1000 ADSR problem

Postby jeferson » Fri Jun 15, 2007 5:48 am

Hi, New poster here :) .

Okay I was wandering if anyone knows what kills the attack in the envelope generator in these synths. The attack in mine is dead, the decay and sustain are still doing something (but not quite right) and the release is working fine.

any ideas?
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Postby mistercooper » Fri Jun 15, 2007 7:30 am

Find a service manual?

If you feel confident enough to test and solder components, figure out which transistors/caps/ics control those stages and replace them.

Old stuff that typically goes bad:
-electrolytic capacitors
-4000 series CMOS
-pretty much everything
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Postby Mutronix » Fri Jun 15, 2007 2:36 pm

My bet is the electrolytic capacitors.

A capacimeter will tell you exactly the capacitance of the cap, thus if it's way below it's nominal value. Note that a 10%-20% margin is normal. Below that, it's suggested to replace them with exact value. Or as close as possible (in case the exact value is unavailable). It's recommended to desolder them before testing.

Most of the electrolytic caps used are polarized. Pay attention to the - and + leads. And resolder the same way.

Discharge the capacitors before proceeding to the test. To safely do so, use a 100K resistor and short the leads for a few seconds.

You can test them with a multimeter too. There must be some websites telling you how to proceed.

If you're not knowledgeable in electronics, do not try to test any ICs. You risk to inflict damages to your synth. And you must have the datasheet of those ICs to know the pin configuration.
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Postby jeferson » Sat Jun 16, 2007 2:49 am

oops maybe I should have said I've been involved in electronics yor years and years (studying to be an EE) :D.

Someone had posted a link to the schematics in these forums before but not the full service manual.

The actual circuit for the ADSR generator is pretty complicated. It seems to use a single tantalum capacitor to generate the slopes by a complicated switching arrangement. There aren't any electrolytic caps involved unfortunately.

I've tested every component on the board and they seem okay.

I guess the next step will be to start replacing components one by one :( .
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Postby jeferson » Sat Jun 16, 2007 2:56 am

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Postby Mutronix » Sat Jun 16, 2007 5:31 am

I should have been more specific too.

There will be no electrolytic capacitors in the ADSR. What I was preoccupied with are the PSU, VCO & VCF. And you can see why.

Strictly speaking, have a look first at the ADSR potentiometers. Seems obvious but it happens. Also check the 555 timmer.
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