Re: 485 super weak brightness control

Ondrej Pavelka

Here are the observations on the A sweep.

Note the difference between free running and triggered

On Tue, 23 Mar 2021, 07:20 Ozan, <> wrote:
Your observations in the video look OK for B sweep:
1) There is no change in B sweep in 1n/div and 2n/div settings. 2x is
handled by the horizontal amp for 2n -> 1n setting.
2) Delay changing B gate position in INT setting is OK. As far as I
remember B internal trigger still waits for delay before waiting for
trigger. In "B runs after delay" it will run when delay expires without
waiting for trigger.

This shows your B sweep is working in 5/2/1n setting as you mentioned
before. Now we need to figure out why A sweep doesn't pick B sweep properly
in 5/2/1n mode.

There I could line up A B gate and A B sweeps. The problem is what comes
Which point are you measuring the output? All the nodes from emitter of
Q1318 and collector of Q1312 until you hit TP1364 are low impedance points
(this section is a transimpedance amp). TP1364 is the earliest node that
shows muxed sweeps.

I recommend this setup:
1) Scope is in 5ns/div and A sweep
2) Ch1 at left side of R1322 (B sweep)
3) Ch2 is at base of Q1318
4) Ch3 is at TP1364

We should see B sweep going through Q1318 and Q1358. In this state Q1356,
Q1312 and Q1338 should be off.

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