Comparator (LM393) not saturating at low frequencies

[floobydust]

I've never seen a scope have an issue at low frequencies when DC coupled. It's a DC path from input to the deflection plates, really. So even that doesn't make sense here.

[Gyro]

I've never seen a scope have an issue at low frequencies when DC coupled. It's a DC path from input to the deflection plates, really. So even that doesn't make sense here.

Read again. His AC/DC coupling switch was broken - didn't work in bypass the coupling cap in DC!

I don't know about the one on the channel next door though. I don't think he tried Ch2.

[nigelwright7557]

No decoupling wont help.
Yo u can use a speed up feedback capacitor from output to input (100pf )?
I have used this comparator in a LC meter and it worked up to 100KHZ fine.

Your waveform looks like the scope is on AC setting when it should be on DC.

One thing that hit but might not be a problem is your lower comparator input goes to ground which means other input has to go below zero which might latch it up. Might work or as is.

A slow moving input definitely needs hysteresis with a speed up capacitor.

Also any comparators I have used need pull ups on the output.

[Gyro]

No decoupling wont help.
Yo u can use a speed up feedback capacitor from output to input (100pf )?
I have used this comparator in a LC meter and it worked up to 100KHZ fine.

Your waveform looks like the scope is on AC setting when it should be on DC.

Is anyone reading the previous page? 

[StillTrying]

I've never seen a scope have an issue at low frequencies when DC coupled. It's a DC path from input to the deflection plates, really. So even that doesn't make sense here.

We've seen a few. I don't know about the OP's scope, but a scope's Y amp often has an AC coupled high frequency path and a parallel DC path. A lowish frequency square wave can show any mismatch between the Y amp's AC and DC paths.

Here's a bad one DC coupled @ 100 Hz, - now fixed.
https://www.eevblog.com/forum/testgear/siglent-sds1000x-series-oscilloscopes/msg1210795/#msg1210795

Nothing to do with the scope's AC/DC coupling switch, but switching to AC coupling can cause problems as well.
https://www.eevblog.com/forum/chat/scope-acdc-coupling-at-60hz/

[StillTrying]

Is anyone reading the previous page? 

The whole thread is surreal!

[ogden]

Is anyone reading the previous page? 

The whole thread is surreal!

Nothing wrong with this thread. We can learn alot about: 1) comparators 2) specifics of old analog scopes 3) people