[sdiy] SCI Pro One 15+ power rail

[Csaba Zvekan]

Hi Guys,

So this morning I went to my local electronic store and got myself some LM7815 and replaced it later today and my voltages are all correct. Turns out the voltage regulator was only working when I was testing it on my breadboard before I put it in. This must have been some B- or D product from china as it would work when you do a quick test (as I did prior to installing). Then under load it would collapse. How weird is that ?
And this scenario for  two parts on the roll from the same batch. Well, lesson learned . No more cheap parts in a bulk from China for me.
As far as the synth goes there is  still no sound with the keyboard played or from the CV/Gate. So it needs more investigation on what's happening there. By the way all tantalum caps have been replaced with elco's a few years back when I got this synth.
Not sure what the problem is but I'm suspecting the DAC :(.  Which is probably a nightmare to find these. With the time machine I could probably jump back three decades in time and stock a few of these older DACs with some CEM and CA3080 hahahahahaha.
Thank you guys for your help

Csaba


On 28 Aug 2013, at 11:00, Tom Wiltshire <tom at electricdruid.net> wrote:

> Not a bad idea anyway. I replaced the regulators and power caps on my Pro-One as a preventative measure. The poor things are 30 years old - that's got to be the end of their designed lifespan.
> 
> On 28 Aug 2013, at 08:51, Stewart Pye <stewpye at optusnet.com.au> wrote:
> 
>> Csaba,
>> 
>> I thought you discovered there is no short on the +15V output???
>> Is the regulator getting hot?
>> 
>> In my experience most shorts on power supply lines will measure a short when tested with a multimeter on DC resistance. There has been the odd occasion when it has been within an IC and didn't show up until power was applied. It's cheap and easy to replace a 7815, rather than chasing ghosts.
>> 
>> Regards,
>> Stewart.
>> 
>> 
>> On 8/28/2013 7:38 AM, Csaba Zvekan wrote:
>>> Barry,
>>> 
>>> Could I be using my FOSCAM Baby monitor in infrared mode to find and see the possible bad cap ?
>>> 
>>> 
>>> On 27 Aug 2013, at 23:33, Barry Klein <Barry.L.Klein at wdc.com> wrote:
>>> 
>>>> Just found a shorted multilayer ceramic this way on a server board last week. Took 30 seconds.
>>>> What, you don't have an IR camera?  One coming on Indiegogo for $150....   :-)
>>>> 
>>>> -----Original Message-----
>>>> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Tony Kalomiris
>>>> Sent: Tuesday, August 27, 2013 1:53 PM
>>>> To: Synth DIY
>>>> Subject: Re: [sdiy] SCI Pro One 15+ power rail
>>>> 
>>>> You could try replacing the 15 V regulator, seeing you replaced the tantalums already.
>>>> Or isolate the PSU from the rest of the electronics to know if something is shorting out.
>>>> Touch the regulator to see if it's getting hot. is the +5 V ok, it's fed from the same full wave rectifier.
>>>> You didn't say what the input voltage was at.
>>>> 
>>>> I like Barry Klein's suggestion, for people with a well equipped bench.
>>>> IR camera eh ? hmm
>>>> 
>>>> Tony K
>>>> 
>>>> 
>>>>> On 8/28/2013 6:37 AM, Csaba Zvekan wrote:
>>>>>> HI John ,
>>>>>> 
>>>>>> All the tantalum caps have been replaced by electrolytics. I also removed all the socketed IC's hoping that the voltage comes back to +15V.  Now I will measure OP-AMPS power and see if I have a low resistance.
>>>>>> Can I do the same with the CEM3310 and CEM 3320. And most of all can I do it in circuit ? I could go ahead and socket and replace all new OP-AMPS I'm still guessing that's not my problem.
>>>>>> I'll double check the bypass caps again.
>>>>>> 
>>>>>> Csaba
>>>>>> 
>>>>>> 
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