Re: 7104 versions, and vertical amplifier issue


cmjones01
 

Good news: the scope now works. I cleaned and reseated the Y output hypcon
U862 a couple of times but nothing changed. Then I cleaned and reseated the
driver U842 and, for good measure, swapped its elastomer and plastic frame
with U862. Now I have full vertical sweep, and a usable scope.

There are lots of niggles remaining: both 7A29s have attenuator contact
problems (the attenuation factors are randomly wrong) as well as an odd
effect rounding the end of the leading edge of the calibrator waveform,
which I suspect is due to the feed-beside adjustments. The 7B15 is
reluctant to trigger and the plug-in connectors have various
intermittent issues, as I'd expect on a scope which has been stored for a
while.

Chris

On Wed, 16 Jun 2021, 16:57 Mark Vincent, <orangeglowaudio@gmail.com> wrote:

Chris,

The Hypcons are sensitive to being clean and the contacts being aligned
right. You should remove each and clean the contacts on the chip and
connector. Also do this to the other ICs and transistors. The square
mounting frames for the Hypcons should be put on with an even pressure on
all sides. The screws are tightened to snug in opposite corners at a time
as the lug nuts on the wheel of a vehicle. I did add good heatsink compound
to the Hypcons and the heatsinks. Roger is right about making sure the coax
connectors are also cleaned. It is possible the neck pins have oxidation on
them. Check the voltage at the input of the vertical if cleaning does not
fix the problem. It is possible the problem is earlier. One dirty contact
somewhere can cause headaches in finding it. Many here will agree to this
having seen it enough times.

IF yours looses sync in the readout, the 741 IC under the handle on the
horiz. board towards the rear will be bad. I had this happen in mine. It
will occur when it warms a little. This happened in mine after a minute
with the left side off. The trace will remain normal. This information is
only in case this happens to yours or anyone else's.

Jon is right about keeping the intensity low. When I use mine, the
intensity is enough to see the line and readout. When a trace is on the
screen, I turn the intensities up a little. The intensities I keep it at
are so that it is barely visible until I raise it enough to see a trace and
readout which is still low. The yellow LED will not come on the way I keep
the two set. It may be easier to use a lamp on the circuit while keeping
the screen in a low light level to ensure the trace seen is safe for the
MCP.

Mark





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