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

[Mark Garlanger]

I got 0.000 Hz again when using either of the metal frame brackets. I
looked at the schematic, it looks like either U17 is bad, or it's not
getting the right signals to generate the frequency. I do have another
controller board that I haven't been able to install because the
connectors are loose, I may try to swap the chip in U17 to see if that
helps.

Mark



On 7/23/06, Barry Watzman <Watzman at neo.rr.com> wrote:
> Ground is ground; chassis ground, the big metal frame brackets at the top of
> both the TLB and H-89's CPU board.  Or the bracket holding the expansion
> cards in place.
>
>
>
> -----Original Message-----
> From: sebhc-bounces at sebhc.org [mailto:sebhc-bounces at sebhc.org] On Behalf Of
> Mark Garlanger
> Sent: Sunday, July 23, 2006 3:04 AM
> To: sebhc at sebhc.org
> Subject: Re: [sebhc] Question about testing the Z-89-37 controller
>
> I'm not sure where the controller's ground is, but I used the Black on
> connect P516 on the CPU board. It seems good since it's the same
> ground I used to test the VCO Bias Voltage - got 1.418 V, manual wants
> 1.42 V. Now with the negative lead on ground, the DMM shows 0.000 Hz.
> For the heck of it I measured the voltage on Test Point 2, and saw
> 2.013 V. Anyone have any ideas why the VCO center frequency would be
> zero?
>
> Mark
>
> On 7/23/06, William Elkins <bill at elkcomm.com> wrote:
> > 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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> > >
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