[sdiy] burned, soda-soaked SH-101 (with pics)

[Steve Lenham]

The schematic shows that D8 is connected between switched +9V (battery) 
power and ground, normally reverse biassed. Looks like it is there to 
protect against batteries being inserted backwards or incorrect AC adaptors.

Interesting that the designers didn't put the diode in series with the 
supply - presumably they wanted to avoid the 0.6V loss and consequently 
reduced battery life (for people who did manage to fit them the right way 
round). It does mean that large currents could flow when there is a fault, 
limited only by the rather underwhelming 1 ohm series resistor R8. This 
might be why the diode got hot at some point, and I'd certainly check R8 for 
continuity as well.

To be honest, that scorch mark doesn't look too bad to me; if the diode 
hasn't gone short or open circuit I'd leave it there. If it does need 
replacing, anything you have rated at 1A or more should be fine.

On a side note, also interesting is that the circuitry around T1 looks like 
a small DC-DC converter to generate a split rail supply - who says switching 
supplies and synths don't mix? ;-)

Cheers,

Steve L.


----- Original Message ----- 
From: "John L Marshall" <j.l.marshall at comcast.net>
To: "Rude 66" <rude66 at xs4all.nl>; "Chad Coffman" <chadcoffman at comcast.net>; 
"diy synth" <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, June 07, 2005 2:56 PM
Subject: [Norton AntiSpam] Re: [sdiy] burned, soda-soaked SH-101 (with pics)


>From the size of the copper trace I would guess a 1N400x class rather than a 
1N4148, still cheap.

It should be okay to clean with soapy water.

Take care,
John

  ----- Original Message ----- 
  From: Rude 66
  To: Chad Coffman ; diy synth
  Sent: Tuesday, June 07, 2005 2:02 AM
  Subject: Re: [sdiy] burned, soda-soaked SH-101 (with pics)


  D8 looks like and probably is a diode.  doesn't it say on the schematic 
what kind it is? if you're lucky, it's just something like an 1n4148, which 
costs a few cents.
  the question is: what made it burn?

  first the cr, now this: you don't seem to have much luck with ebay 
purcheases.. or do you buy them cheap and broken to fix them up yourself?


  r./



    ----- Original Message ----- 
    From: Chad Coffman
    To: diy synth
    Sent: Tuesday, June 07, 2005 10:23 AM
    Subject: Re: [sdiy] burned, soda-soaked SH-101 (with pics)


    Excellent. Thanks for the response. Do I need to remove the ICs or 
anything? I imagine the socketed components should go, but what about those 
soldered to the PCB?

    Also, what do you make of the burn? It is labeled D8 on the schematics 
here:

    http://www.physicsenterprises.andrews.edu/diy_archive/manuals/roland/sh101/sh101_7.gif

    http://www.physicsenterprises.andrews.edu/diy_archive/manuals/roland/sh101/sh101_6.gif

    (lower left, both)

    Again, many thanks,


    Chad
      ----- Original Message ----- 
      From: Tim Curtis
      To: Chad Coffman
      Sent: Tuesday, June 07, 2005 1:01 AM
      Subject: Re: [sdiy] burned, soda-soaked SH-101 (with pics)


      If it's soda, then the best way to clean the PCBs is to totally remove 
them from the synth and run them under water.  Distilled water is best, but 
generally tap water works just fine.  You can just run them under the 
faucet, or use the shower in the case of larger PCBs.  You may want to 
follow this with a rinse of distilled water.

      After this, follow up with compressed air to dry it if possible.  You 
particularly don't want the water to stay in the pots and switches.

      Alcohol won't work too well with water based spills like soda or beer.

      Tim


      Chad Coffman wrote:
        I just received an SH-101 purchased over eBay, which was advertised 
as "not working". The problem, according to the seller, is that it simply 
does not power up. This was confirmed upon unpacking and plugging the unit 
in.

        So I take the unit apart. Look over everything. The first ominous 
sign is that the PCBs are soaked in soda (well, perhaps not soda, but 
something that was once a liquid but is now a sticky, brownish semi-solid). 
The second ominous sign is a burn near one of the most soda-soaked areas. 
Pics here:

        Front (80k) :

        http://home.comcast.net/~chadcoffman/sh101burn1.JPG

        Back (70k) :

        http://home.comcast.net/~chadcoffman/sh101burn2.jpg

        There are a few other curious-looking anomolies which could be 
causing problems, but these two issues appear to be most worthy of my 
immediate attention.

        Two questions:

        1: What is the easiest way to clean these PCBs? I tried isopropyl 
rubbing alcohol and q-tips, but this was proving to be a tireless endeavor. 
It would take about 20 hours at the rate I was going.

        2: What is that burnt part and where do I find a replacement?

        As always, many thanks in advance,


        Chad
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