Re: Wong data for the Y DAC (Tempest)

The high bit determines which half of the screen, so take a look there to
see if it goes to both states or not. Also look at the output of the DAC
where it feeds the opamp. You should see zero volts there with maybe a
little noise, but you should NOT see anything swinging one side of zero.
That would indicate an opamp problem. Also check + and - power supplies
going to the DAC and opamp. Any of these missing will cause your problem.

Tek wrote:

> Hi guys,
>
> As you might have noticed, my Tempest board is still not functioning, so
> I'll Give it a try here again...
>
> Did anybody ever see that the XDAC was fed with the right data, but the
> Y DAC with completely wrong data? (for example, in the large '+' test
> screen, the X output shows correct,(a positive-negative going triangle
> wave), the Y shows only one big positive going sawtooth).
>
> I am sure the DAC's itself are OK, as well as the analog circuitry
> around them.
>
> My first guess is, that the cause could be the Vector Generator Data
> Shifer circuitry. I believe this piece of hardware 'grabs' the X and Y
> data from the databus, and thus could cause erratic Y data, and correct
> X data.
> Am I right here?
>
> If ths is not causing the trouble, the data on the bus itself should be
> wrong, but only for the 'Y' output. has anybody ever seen this before?
>
> Is there theory of operation somewhere on the net, which describes these
> digital circuits?
>
> Thanks a lot guys!
>
> Mendel
Received on Sat Nov 27 13:08:56 1999