Re: Analog Vecor Generator

>>
>> When I examine the current outputs of the DACS, I found that the working, but
>> distorted 'X' output was nice virtual ground, and after the current/voltage
>> convertor I get a waveform. BUT, in the middle of the sawtooth there is a big
>> triangular 'dip'. Could this be beause the DAC is bad, or is it more likely
the
>> DAC is getting wrong data? You can spot this dip in any test mode.
>

>Hope for wrong data. Fix the other output first and then see if this is still
bad.

Would that not be much harder to fix than a defective DAC or op-amp? I can
imagine it will be a lot of trouble fixing the mathbox or something... What do
you do to fix processor-related stuff, just check for activity around all logic
gates/ram/rom?

>> For the 'Y' current DAC output, which is not working at all, I measure a 5
volt
>> p-p random-like sawtooth (which does not resemble the one you should get
AFTER
>> the current/voltage convertor) in stead of a virtual ground.
>> So my guess is the DAC's bad, but I am not sure, because I cannot explain
what
>> the DAC08 is exactly doing (this one generates a 'BIPOLAR' signal, a current
>> added to that of the X-Y DACs).
>> AM6012 DAC's cost about $30 here in Holland, so I want to make sure before
>> buying and blowing them again. :)
>

>If you don't have the virtual ground it probably ISN'T the DAC, the opamp is
>probably bad. It's the output of the opamp, fed back through a resistor inside
the
>DAC, that gives the virtual ground. If the opamp is bad and has no output
there is
>no feedback and you get exactly as you describe.

You are probably right there. It's the Op-Amp providing the virtual ground
indeed. I've checked outputs and these are clipped to VCC, so it is the feedback
network or the amp itself...

>
>> I tried to find exact information on this AVG circuit on the net, but I
cannot
>> find a really good description of it's priciple of operation, and why the
analog
>> multipliers MC1495 are in the circuit.
>

>The multipliers are a form of pincushion correction needed by certain monitors.

With what signal do these multipliers multiply?

Thanks for your info!
Received on Wed Nov 3 04:42:34 1999