[sdiy] Arp Omni PSU question

mark verbos mverbos at earthlink.net
Tue May 19 18:47:18 CEST 2015


You can assume that all of those 1uF tantalum caps are bad.ARP got a bad batch or something.
You will likely be replacing them in an Omni for many hours. There's one on each key.


Mark

On May 19, 2015, at 11:52 AM, Travis Thatcher wrote:

> Yeah - I found that one of the tantalum caps had shorted on the
> negative rail which I figured caused those resistors to blow.
> 
> On Tue, May 19, 2015 at 11:45 AM, Terje Winther
> <terje.winther at wintherstormer.no> wrote:
>> The burn mark under the resistor is not because someone did some surgery: it
>> is because the original resistor was blown because of a short circuit.
>> You need to swap the resistor for the right value, and then you need to swap
>> out the power transistors.
>> 
>> 
>> Den 19. mai. 2015 kl. 04.15 skrev Travis Thatcher:
>> 
>> I've got an Omni MK I with a power supply that has me stumped. I
>> replaced the 2 1000uF and 250uF caps, the 2 10uFs as well as the 1uF
>> tants and replaced both the lm301 and the 723 as well as all the 4001
>> diodes.  Still, I'm getting about 36v on the v+ and -6 on v- with the
>> trimmers doing very little. Someone else has already done some surgery
>> on this synth before me - you can see the burn marks under the 4.7k
>> resistors. I checked and I'm getting a healthy +- 36v out of the
>> transformer. The power tansistors aren't heating up - would that be
>> the next place to look or does anyone have any suggestions for
>> troubleshooting. I have a power one supply that I can stick in but was
>> hoping to save the original. If I go the power one route - I'm
>> assuming I can just wire v+, gnd and v- from the power one to the
>> appropriate inputs on the lower voice boards and ignore the V/gnd
>> sense lines?
>> 
>> Image of the current PSU is here: http://recompas.com/xfer/omnipsu.jpg
>> 
>> Thanks in advance for any help!
>> 
>> --
>> http://www.travisthatcher.com
>> http://www.soundcloud.com/thevoiceofsaturn
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>> 
>> 
>> Terje Winther
>> terje.winther at wintherstormer.no
>> http://wintherstormer.no/
>> 
>> 
>> 
>> 
>> 
> 
> 
> 
> -- 
> http://www.travisthatcher.com
> http://www.soundcloud.com/thevoiceofsaturn
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