[sdiy] Re: Help! Fatman problems!

[John Goodall]

Thanks Scott,

I had fun making a more permanent line tracer with a bulldog clip and a
small broken screwdriver yesterday! I should be getting a Voltmeter on
Wednesday so I should be able to do some more tests on the
circuitry/components then.

I had a bit of a breakthrough yesterday. Previously I mentioned that the DAC
tuning pot has no effect on the pitch. When I turn the Fatman on and, using
the headphone probe, listen to R56 (VCOs 1, 2 and 1&2), rotating the DAC pot
has no effect UNTIL I send a note through to the Fatman via midi. After I've
done this the pitch can be tuned using this pot!

So, it appears that everything up to the VCO mix pot is working! I guess the
next thing is to check the VCF section and find out where the signal is
failing. I'll check the voltages around the Power Supply section and let you
know what the findings are.

Does this still sound like power supply problems, if the VCOs appear to be
working properly?

Many thanks, John


-----Original Message-----
From: Scott Gravenhorst [mailto:music.maker at gte.net]
Sent: 19 January 2002 04:58
To: John Goodall; synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Re: Help! Fatman problems!


Looking at some of this data, I see power supply
problems.  For example, IC 17 pin 6 is connected
to -V and is giving a "loud farty noise".  This
should not be if -V is putting out a steady voltage
as it ought to be.  Pin 11 is +V which is doing
the same thing and ought to be silent as well.

Do you have a DVM?  This is a pretty necessary
piece of equipment and even borrowing one for
this would really help.  

You need to ensure that your power supplies are
producing the correct voltages and that there's
no undue noise on them.  Check the construction
of the power supply section, making absolutely
sure that all parts, diodes, regulator ICs etc
are all properly oriented.  Check the board for
open etch traces and solder bridges.  I use a
magnifier like a gemologist's loupe (mine is
actually a telescope eyepiece) to do this sort
of examination.

John Goodall <jgoodall at rm.com> wrote:
>Hi, and thanks for all the suggestions. It seems common concensus that I
>should try troubleshooting as the problem could be anything!
>
>As I don't have an oscilloscope, or access to one, or a lot of available
>cash at the moment I've started with the signal tracing section in the
>fatman instructions, with a pait of old headphones. Here are my findings:
>
>VCO1 - Yes, everything appears to be working fine here.
>VCO2 - Again, everything appears to be working fine here.
>VCO1/VCO2 Mix (lug 2 on R56) - I hear the mix of the two VCOs but the
volume
>is half that of the individual VCOs
>
>VCF - Didn't hear the same tone at pin 9 on IC 17 so tested  IC17, IC13, Q8
>& Q9, here are the results of testing each pin:
>
>IC17:
>1 - Loud farty noise
>2 - Nothing
>3 - Nothing
>4 - Nothing
>5 - Nothing
>6 - Loud farty noise
>7 - Nothing
>8 - Nothing
>9 - Nothing
>10 - Very faint sound of the mix
>11 - Loud farty noise
>12 - Very faint mix
>13 - Very faint mix
>14 - Very faint mix
>15 - Nothing
>16 - Loud farty noise
>
>IC13
>1 - Very faint mix
>2 - Mix
>3 - Mix
>4 - Loud farty noise
>5 - Very faint mix
>6 - Nothing
>7 - Nothing
>8 - VCO1
>9 - VCO1
>10 - Nothing
>11 - Loud farty noise
>12 - Very faint mix
>13 - High noise
>14 - Low noise
>
>Q8 + Q9
>1 - Loud farty noise
>2 - Mix
>3 - Loud farty noise
>
>That's it! Unfortunately I've absolutely no idea how to interpret these
>results & don't know which noises should be coming from which pins - does
>any of this sound correct/incorrect? Does anyone have any suggestions based
>on these findings?
>
>Many thanks, John
>
>-----Original Message-----
>From: Scott Gravenhorst
>To: synth-diy at dropmix.xs4all.nl; John Goodall
>Sent: 18/01/02 18:01
>Subject: [sdiy] Re: Help! Fatman problems!
>
>John Goodall <jgoodall at rm.com> wrote:
>>Hi everyone,
>>
>>I've just plugged in my Paia Fatman having finished construction of it
>to
>>discover it doesn't work :0(
>>(It was to be expected really, it's the 1st synth I've built)
>>
>>Here's the problem. When I strike a key I get a very short noise coming
>out
>>but it's very brief and to my electronically untrained ear sounds like
>it
>>could be a really low bass note, maybe just 1 cycle of the waveform(?).
>>
>>Playing a higher or lower note on the keyboard makes no noticeable
>>difference to the pitch, neither does changing any of the 5 trimmer
>>resistors or the pitch control on the front.
>>
>>The 1800 ohm resistor that bridges R34(1) & R34(3) was missing from the
>kit
>>so I ordered one from RS, it's the same value but states it is 1%
>(R5%).
>>I've also used a blue led for the power light, I know these use
>slightly
>>more current but that couldn't be the problem could it..?
>
>I would doubt that it draws so much power as to cause a problem.
>That brings me to the first of my own trouble shooting techniques:
>First measure the +5, +8 and -12 volt supplies.  If you
>have a scope, look at them with the scope.  On DC make sure
>they are a flat line.  On AC, keep turning up the scope's 
>sensitivity until you see some noise or ripple and measure that.
>If you don't have a scope, you can still measure noise/ripple
>with a DVM set to AC, again, turn up the sensitivity until you
>can get some numbers.
>
>Let us/me know what you see.  I need to know if your
>supplies are right before we can go any further.
>
>>Please can someone help me? It would be great if you could advise me in
>>simple terms, I am a total novice!
>
>(c:  We *all* start there.
>
>>
>>Many thanks, John
>>
>>
>>Visit our website at http://www.rm.com 
>>
>>Standard Disclaimer:This message is confidential.  You should not copy
>it or
>>disclose its contents to anyone.  You may use and apply the information
>only
>>for the intended purpose.  Internet communications are not secure and
>>therefore RM does not accept legal responsibility for the contents of
>this
>>message.  Any views or opinions presented are only those of the author
>and
>>not those of RM.  If this email has come to you in error please delete
>it
>>and any attachments.  Please note that RM may intercept incoming and
>>outgoing e-mail communications.
>>
>>
>
>=========================================================  
>- Government: The other religion.
>- The media's credibility should always be questioned.
>- Lambs who lie down with lions are lunch.
>
>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>-- Linux Rex         | RedWebMail by RedStarWare
>-- FatMan: home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/index.html
>-- NonFatMan: home1.GTE.NET/res0658s/electronics/index.html
>
>
>
>Visit our website at http://www.rm.com 
>
>Standard Disclaimer:This message is confidential.  You should not copy it
or
>disclose its contents to anyone.  You may use and apply the information
only
>for the intended purpose.  Internet communications are not secure and
>therefore RM does not accept legal responsibility for the contents of this
>message.  Any views or opinions presented are only those of the author and
>not those of RM.  If this email has come to you in error please delete it
>and any attachments.  Please note that RM may intercept incoming and
>outgoing e-mail communications.
>
>

=========================================================  
- Government: The other religion.
- The media's credibility should always be questioned.
- Lambs who lie down with lions are lunch.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/index.html
-- NonFatMan: home1.GTE.NET/res0658s/electronics/index.html



Visit our website at http://www.rm.com 

Standard Disclaimer:This message is confidential.  You should not copy it or
disclose its contents to anyone.  You may use and apply the information only
for the intended purpose.  Internet communications are not secure and
therefore RM does not accept legal responsibility for the contents of this
message.  Any views or opinions presented are only those of the author and
not those of RM.  If this email has come to you in error please delete it
and any attachments.  Please note that RM may intercept incoming and
outgoing e-mail communications.