[sebhc] Question about testing the Z-89-37 controller

[William Elkins]

Typically measurements are made referenced to chassis ground. One lead
should go to ground point of the power feed on the card and the other
lead goes to the test point.

The 15.84KHz is the horizontal scan on the crt. As this freq is also
used to generate the hi voltage for the crt there is a lot it
available to be detected.

Bill Elkins

On 7/23/06, Mark Garlanger <garlanger at gmail.com> wrote:
> I bought up a DMM that has a frequency measurement (supports 10 Hz -
> 10 MHz). The Z-89-37 manual states that you should "connect the
> frequency counter to test point 2 on the board." Do I just put the
> positive lead on test point 2 and leave the negative lead floating? It
> doesn't state where the negative lead should be placed. I tested a
> power outlet and with only the positive lead inserted it read
> 59.97-60.02 but was jumping around (that small range) alot more than
> if I inserted the negative lead also.
>
> So if it's valid to only place the positive lead, then my reading is
> WAY off. It should be 2 MHz, but the DMM is reading 15.84 KHz. I
> haven't yet tried to turn/adjust R17 because I can not figure out how
> I'm supposed to get to it and wanted to make sure I was measuring it
> properly before adjusting. A screwdriver of ANY length will be blocked
> by the CRT, and I don't think I should have my hand that close to the
> CRT. Now that I think about it, I do remember my dad having long
> narrow plastic tool that would probably work good for this.
>
> Mark
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