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

Barry Watzman Watzman at neo.rr.com
Sun Jul 23 04:22:53 CDT 2006

The negative lead is always understood to go to ground unless otherwise

-----Original Message-----
From: sebhc-bounces at sebhc.org [mailto:sebhc-bounces at sebhc.org] On Behalf Of
Mark Garlanger
Sent: Sunday, July 23, 2006 1:01 AM
To: sebhc
Subject: [sebhc] Question about testing the Z-89-37 controller

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.

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