Re: 465 with V scale issue

Fabio Trevisan
 

Hello Nick
If the serial number is missing on the front panel, there's a chance that
the same is marked (with sharpie pen) on the back of the aluminum chassis,
behind the back plastic panel (that covers the FAN and supports the rear
BNC plugs).
On mine (a 464, not exactly same model as yours), I found recently the
serial number hand-written there, in big numbers (you can't miss it,
although part of it may be covered by the fan rotor itself).
Rgrds,
Fabio

2017-05-25 0:25 GMT-03:00 Nicholas Scalfaro nwscalfaro@...
[TekScopes] <TekScopes@...>:



Dave,

The Oscope loses the trigger on the 300 mv calibrator signal when the
entire trace is in the bottom third of the CRT. It can show an AC signal
across the full display. The waveforms do not distort vertically.

Serial number has been lost to history unless it's inside somewhere as
well. The 2 white boxes on the rear panel that presumably are supposed to
have the model and SN info are completely blank.

Dunno if it's integrated or discrete yet. Three kids and work have kept me
from opening it up to do any diagnostic work.

On May 24, 2017 2:21 PM, "David @DWH [TekScopes]" <
TekScopes@...> wrote:



It is a good idea to start by checking the low voltage power supply
outputs for level and ripple which can be done with just a voltmeter
but I suspect the problem is in the vertical amplifier chain after the
vertical channel switch.

Albert posted a great detailed suggestion for how to proceed.

Do the vertical position controls move the traces over the full
vertical range of the CRT?

When the calibrator waveform is displayed, does changing the vertical
position cause the displayed trace to compress toward the top and
bottom of the screen?

What serial number is your 465 and is the vertical CRT amplifier board
discrete or integrated?

My guess is that you will find an open resistor between the emitters
of one of the transconductance stages which should be easy to repair.
Albert's directions should lead you right to it.

On Tue, 23 May 2017 22:28:26 -0400, you wrote:

My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about
22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't
correct
that much. But I tried. I've learned a lot in the past week. The Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x Tek
probe installed. Since that doesn't affect anything other than which
light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference voltage
coming out of the PSU?

Nick
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