[sdiy] Siel OR400 power supply busted

[M Maeghan Skala]

Hi Steve,

Yes, I have learned an enormous amount over the past week troubleshooting the orchestra. I was thinking of replacing all the IC's starting with the PCB that was closest to the point where the short circuit occurred. I will mention, when this happened I saw an arc/light/s[arks go across the whole synth panel.

I've learned that CMOS chips are super sensitive so I'm just going to  order replacements for all the CMOS chips.

I've even made a spreadsheet to help keep things organized and know what IC"s are on what board.

As for the tools; yes! I am equipped with an Oscilloscope. Last year for christmas my husband got me a Weller WES51 soldering station and a 50's era scope, an EICO 460 … let's hope it works cause I haven't and a need to use it till now. (it does look fancy in my studio though).

As for the synth and what's doing, it hasn't once talked back to me…

When I turn it on I hear nothing through the Low output, i hear what sounds like some white noise maybe on the High output; also, when I press a key I hear a very faint clicking sound.

As for the LEDs, the LED's that are not mounted on a switch (Animator,LFO, Brass, Piano, Reed, Strings) are very faint.

The LEDs that are on the switches: Equalizer, Oct. Down, Animator, and LFO are bright.

When I turn the Equalizer on, the white noise increases in dynamics.

The power supply, when it is unloaded and not powering the synths circuit, it gives off the proper power/voltage.

When it is loaded the positive 12 signal jumps up to 15 and the negative jumps down a bit.

I hope this helps. I'm gonna go make some probes for my silly scope. Hopefully, these details are helpful. 

cheers ~ maeghan




On Aug 6, 2013, at 4:06 AM, Steve Lenham <steve at bendentech.co.uk> wrote:

> Hi Maeghan,
> 
>> I got the power supply working :)
>> 
>> But the synth isn't working. I'm gonna guess that even though the
>> power wasn't being distributed to the rest of the circuitry, that
>> when the short circuit happened … it arced and friend some
>> components.
>> 
>> THe synth is now turning on, and getting the proper voltages (not
>> perfect but .1 off on some of the leads) … no sound. One of the
>> chips, the LM13700 has a broken leg but according to Bob Wiegel over
>> on sounddoctorin, that would take out the brass section.
>> 
>> Here's my question: should I consider the synth dead?  or is this
>> something that can be fixed?
> 
> It can certainly be fixed. The question is, are you equipped to fix it? There are several things in your favour - the schematics are available, the synth in question is relatively simple and you have some experienced people here on the list willing to help.
> 
> In a way, painful as it might be, you are getting the best crash course in synth repair that you could wish for. You have already come a long way and must have learnt quite a bit - why not keep going?
> 
> However, the key question for me is whether you have, or can get access to, an oscilloscope of some sort. Do you? Without one the next stage will be all but impossible, because we need to check whether signals are present at various points in the circuit and they are signals that a DMM can't effectively see.
> 
> The scope really does not need to be anything special - I fixed a lot of synths using an ancient 10MHz Telequipment scope bought secondhand for £50 ($75). Most of the time we just need to see whether signal is present or not, and that it is roughly the right shape.
> 
> Let us know where you are at tool-wise and we'll see where to go next. In the meantime, what EXACTLY does the unit do? You say no sound, but do the selectors and panel LEDs work as expected?
> 
> Cheers,
> 
> Steve L.
> 
> Steve Lenham
> Benden Sound Technology
> www.bendensound.co.uk
> 
> 
> 
> 
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