MOTM

I have a question about the troubleshooting guide in the back of the 
MOTM 300 instructions.

The third check box has several lettered steps.  Step (b) says to 
check the VX voltage, and make sure it is close to +4.8V, and mentions 
the right side of R3.

Looking at the schematics, it looks like R3 is involved in the fine 
tune voltage, whereas R37 is closer to where one might find VX.

Comments?

Oh yeah, I have an MOTM-300 that is not playing nice at the moment.  
All of the voltages seem to check correctly (with the exception of VX 
as noted above), now it is down to verifying that all of the 
components are in the right spot...

Part of me is wondering about O-Scopes and if that might help me find 
the trouble sooner.  There is no sound at all out of the module, 
except from the pulse jack, if I turn the coarse tune knob to just the 
right spot, it outputs noise that can be changed by moving the PWM 
pot.  8-)

Wahoo! (translation: this should keep me occupied for the next couple 
of nights)

Bruce

>
> Looking at the schematics, it looks like R3 is involved in the fine
> tune voltage, whereas R37 is closer to where one might find VX.
>
> Comments?

Manual typo. It's R37.


>
> Oh yeah, I have an MOTM-300 that is not playing nice at the moment.
> All of the voltages seem to check correctly (with the exception of VX
> as noted above), now it is down to verifying that all of the
> components are in the right spot...

If the SAW is not working, not much else works. For this you *need* a scope
:)

Just get a $100 Tek off eBay. There are usually 20-30 on there every day.
Search the MOTM
archives for my opinions about scopes.

Paul S.

Hey, this means I won't be alone in the next couple of nights of
troubleshooting *my* recently-built 300.

Mine seems fine except that the sine and tri wave outputs are weak and
buzzy; I haven't been able to calibrate it yet, so maybe that will put
things right. Life can really get in the way of building/calibrating
modules--what a pain! ;)

David.

> -----Original Message-----
> From: bruce@... [mailto:bruce@...]
> Sent: Thursday, February 22, 2001 1:47 AM
> To: motm@yahoogroups.com
> Subject: [motm] Question about MOTM-300 Troubleshooting guide
> 
> 
> I have a question about the troubleshooting guide in the back of the 
> MOTM 300 instructions.
> 
> The third check box has several lettered steps.  Step (b) says to 
> check the VX voltage, and make sure it is close to +4.8V, and 
> mentions 
> the right side of R3.
> 
> Looking at the schematics, it looks like R3 is involved in the fine 
> tune voltage, whereas R37 is closer to where one might find VX.
> 
> Comments?
> 
> Oh yeah, I have an MOTM-300 that is not playing nice at the moment.  
> All of the voltages seem to check correctly (with the exception of VX 
> as noted above), now it is down to verifying that all of the 
> components are in the right spot...
> 
> Part of me is wondering about O-Scopes and if that might help me find 
> the trouble sooner.  There is no sound at all out of the module, 
> except from the pulse jack, if I turn the coarse tune knob to 
> just the 
> right spot, it outputs noise that can be changed by moving the PWM 
> pot.  8-)
> 
> Wahoo! (translation: this should keep me occupied for the next couple 
> of nights)
> 
> Bruce
> 
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Take 10 seconds and a small screwdriver and twist the sine symmetry 
trimmer while listening to the waveform. It will definitely be buzzy 
if the sine is out of trim. I'm not sure what would cause the 
triangle to be buzzy, though.

Moe

--- In motm@y..., David Bivins <dbivins@f...> wrote:
> Mine seems fine except that the sine and tri wave outputs are weak 
and
> buzzy; I haven't been able to calibrate it yet, so maybe that will 
put
> things right. Life can really get in the way of building/calibrating
> modules--what a pain! ;)

Chances are greater than 50% that your problem is something simple 
like a bad solder joint, or IC in backwards. I had two modules that 
had completely dead outputs when I finished them. The problem? Too 
much heat had caused the coax insulation to melt just enough to short 
the output cable. I had to learn to modify my coax installation 
technique!

Moe

--- In motm@y..., bruce@s... wrote:
> I have a question about the troubleshooting guide in the back of 
the 
> MOTM 300 instructions.
> 
> The third check box has several lettered steps.  Step (b) says to 
> check the VX voltage, and make sure it is close to +4.8V, and 
mentions 
> the right side of R3.
> 
> Looking at the schematics, it looks like R3 is involved in the fine 
> tune voltage, whereas R37 is closer to where one might find VX.
> 
> Comments?
> 
> Oh yeah, I have an MOTM-300 that is not playing nice at the 
moment.  
> All of the voltages seem to check correctly (with the exception of 
VX 
> as noted above), now it is down to verifying that all of the 
> components are in the right spot...
> 
> Part of me is wondering about O-Scopes and if that might help me 
find 
> the trouble sooner.  There is no sound at all out of the module, 
> except from the pulse jack, if I turn the coarse tune knob to just 
the 
> right spot, it outputs noise that can be changed by moving the PWM 
> pot.  8-)
> 
> Wahoo! (translation: this should keep me occupied for the next 
couple 

> of nights)
> 
> Bruce

My thoughts were along the same lines, but the IC's are pretty easy 
(for me anyhow) as they were made to line up the same direction. I had 
some of the via holes had not been flowed all the way through last 
night, correcting that did not modify the behaviour.

I am going to run this thing the way I would as a crusty old avionics 
tech (hmm...)

But as Paul mentioned earlier the place to check things out would be 
the Sawtooth first, and I have this fear that I may have cooked one of 
the nice custom Q's that came with the kit.  The smaller one (Q2?) 
really did not want to get soldered in correctly, and I may have given 
it too much iron.  

That is the place where I will start anyhow.  Glad that the theory is 
in there too, makes it much easier to figure out.

Now to hunt ebay for an O-Scope

Bruce

--- In motm@y..., mate_stubb@y... wrote:
> Chances are greater than 50% that your problem is something simple 
> like a bad solder joint, or IC in backwards. I had two modules that 
> had completely dead outputs when I finished them. The problem? Too 
> much heat had caused the coax insulation to melt just enough to 
short 
> the output cable. I had to learn to modify my coax installation 
> technique!
> 
> Moe
> 
> --- In motm@y..., bruce@s... wrote:
> > I have a question about the troubleshooting guide in the back of 
> the 
> > MOTM 300 instructions.
> > 
> > The third check box has several lettered steps.  Step (b) says to 
> > check the VX voltage, and make sure it is close to +4.8V, and 
> mentions 
> > the right side of R3.
> > 
> > Looking at the schematics, it looks like R3 is involved in the 
fine 

> > tune voltage, whereas R37 is closer to where one might find VX.
> > 
> > Comments?
> > 
> > Oh yeah, I have an MOTM-300 that is not playing nice at the 
> moment.  
> > All of the voltages seem to check correctly (with the exception of 
> VX 
> > as noted above), now it is down to verifying that all of the 
> > components are in the right spot...
> > 
> > Part of me is wondering about O-Scopes and if that might help me 
> find 
> > the trouble sooner.  There is no sound at all out of the module, 
> > except from the pulse jack, if I turn the coarse tune knob to just 
> the 
> > right spot, it outputs noise that can be changed by moving the PWM 
> > pot.  8-)
> > 
> > Wahoo! (translation: this should keep me occupied for the next 
> couple 
> > of nights)
> > 
> > Bruce

Starting at the inputs/outputs (and the associated coax) can be a really
good idea (and are easily tested). I worked the other direction,
troubleshooting a problem on a module long ago, only to realize ultimately
that I hadn't completed soldering a jack (or something just as asinine).
What a kick in the pants after having disassembled the "sandwich" to inspect
solder points!

David.

> -----Original Message-----
> From: mate_stubb@... [mailto:mate_stubb@...]
> Sent: Thursday, February 22, 2001 10:36 AM
> To: motm@yahoogroups.com
> Subject: [motm] Re: Question about MOTM-300 Troubleshooting guide
> 
> 
> Chances are greater than 50% that your problem is something simple 
> like a bad solder joint, or IC in backwards. I had two modules that 
> had completely dead outputs when I finished them. The problem? Too 
> much heat had caused the coax insulation to melt just enough to short 
> the output cable. I had to learn to modify my coax installation 
> technique!
> 
> Moe