Hi Daniel,
Ha! Nice answer. I was asking for that really!
About the reading you took. There are some issues here definitely...
>> IC13 pin7 has a saw oscillation.
This is supposed to be the demuxed control voltage from the MG frequency
knob. You should have a voltage there which swings between 5 and +5v! 0v
when the control is in the centre. Check the your layout and connect very
carefully. Remove IC21 to prevent any damage and lift out one end of R18.
This will disconnect the mux from the oscillator. Q3 shorted shorted emitter
to base perhaps?
>> IC16 pin7 has a saw oscillation.
Looks right!
>> IC19 pin12 has a saw oscillation.
See the notes above! IC13 buffers the output of IC19!
Cheers,
Andy
On 24/08/2010 02:34, "Daniel A" <apophis93@yahoo.com> wrote:
>
> Andy,
>
>> > Now let me see... So you say you are getting just DC on TP5? Have you got
>> the scope in set for AC input? ;-)
>
> What!?! I shouldn't probe the outlet in my house as a 60Hz reference? ;)
>
>> > First, you should note whether the MG LED is on, off or pulsing. However,
>> in your case did we manage to get that blue wire back in place?
>
> Yes the loose blue wire is now reconnected to the PS +5v rail as it was before
> I found trace solder where it broke off. Light is currently holding steady ON.
> Hopefully this changes when the MG Freq is back online.
>
>> > Second we need to measure the a stable comprising IC16 and IC21 and see if
>> it is in oscillation. You know about oscillators, right? You present the
>> output as positive feedback to the input with a gain greater than 1 and the
>> whole thing starts to resonate. Only this circuit is current controlled by
>> pin 16 of IC21. The output of the mux (IC19), the buffer IC13 at pin 7 and
>> the long tail pair transistor are responsible for altering the current and
>> changing the speed of the MG. That is a very loose description of how it
>> works but it should give you some pointers. You should hook up your scope to
>> pin 12 of IC21, IC16 pin 7 and the drain of FET Q1 and see what you have. You
>> should have some nice slow running triangle waves if running.
>> >
>
> Here are my results I can give exact measurements if required:
>
> IC13 pin7 has a saw oscillation.
> IC16 pin7 has a saw oscillation.
> IC19 pin12 has a saw oscillation.
> IC21 no oscillation just DC shift
> (T1) FET Q1 no oscillation just DC shift
>
> - Daniel
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