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7104, fixing a few minor things


@0culus
 

Hi all,

Hope everyone is well and avoiding cabin fever! Part of my cabin fever antidote is spending time in my lab. :o)

Anyway, some of you may remember that I picked up a very nice shape 7104 + plugins at a property auction a while back, for a cool $125. While the scope is ~99% in great working order, it's that final 1% that I'd like to see if I can deal with, pretty much minor things.

1) Readout intensity only works in the "pulsed" position, triggered by +gate. I can adjust the readout brightness fully using the pot in the "pulsed" position.

2) The readout disappears on a few timebase settings, mainly about midrange sec/div settings.

3) SIG OUT seems to not have usable output.

4) On certain faster timebase settings, the trigger point and some of the displayed waveform "disappears". Worth noting that my 7904A which also has a 7B15 in the delaying position also does this. Is it expected behavior?

I mainly want to ascertain if these are common issues with known solutions.

Thanks,

Sean


David DiGiacomo
 

On Thu, Mar 26, 2020 at 3:39 PM <sdturne@q.com> wrote:
1) Readout intensity only works in the "pulsed" position, triggered by +gate. I can adjust the readout brightness fully using the pot in the "pulsed" position.
This is quite a common issue on the 7104 and 7103. There has been
discussion of it here in the past, but I don't think anyone ever
tracked down the exact cause and cure.

On one of my 7104s I was able to sort of fix it by putting 1.2K in
parallel with R1922 and 1.1K in parallel with R1925, but I was never
exactly happy with that.

some of the previous threads:

https://groups.io/g/TekScopes/topic/7629541
https://groups.io/g/TekScopes/topic/7633990
https://groups.io/g/TekScopes/topic/7648866


@0culus
 

On Thu, Mar 26, 2020 at 03:17 PM, David DiGiacomo wrote:


This is quite a common issue on the 7104 and 7103. There has been
discussion of it here in the past, but I don't think anyone ever
tracked down the exact cause and cure.

On one of my 7104s I was able to sort of fix it by putting 1.2K in
parallel with R1922 and 1.1K in parallel with R1925, but I was never
exactly happy with that.
Hmmm, interesting that no one has pinpointed a cause. Maybe it's that U1714 going flaky?

Sean