Re: 485 super weak brightness control


Ondrej Pavelka
 

On Sat, 20 Mar 2021, 03:16 Ozan, <ozan_g@erdogan.us> wrote:


This is exactly what I observed on A gate and A sweep, I haven't checked
the B sweep connector
I attached expected waveform here:
https://groups.io/g/TekScopes/photo/262059/0?p=Created,,,20,2,0,0
If it looks similar then B gate delay is OK, if B gate is delayed issue is
around U910/Q902.

This snap is extremely helpful. I will upload some of my pictures as well,
it makes the troubleshooting easier.
Really appreciate your help!



In the last paragraph you mentioned 2x multiplier but what we observe is
10x, does it still make sense to look in this part of the circuit?
You are right. However, I can't think of a simple reason why 0.2us-10us
range could be 10x slower in B sweep while 1ns-0.1us is OK (please confirm
this range is OK). K1242 switches at 0.2us step. Perhaps time to look at
that relay and measure cap C1443.

Are you sure B sweep shaft is not rotated out of alignment? You can look
at J1 (relay signal) and check it switches at .1us/.2us boundary.

If the gate signal matches the waveform I sent and you still see trace
shifted right, checking B18,B20, B22 can tell if anything is wrong with B
sweep horizontal shift circuit. These switches should make contact in
1/2/5n so if they are dirty you could see horizontal shift issues.

Ozan





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