Hung Chang 5506 oscilloscope - HOLDOFF function - Page 1
Forum section: electronics / repair

author: Libas
author_rank: Regular Contributor
timestamp: February 21, 2024, 08:45:35 am
content: Hi,I have troubles with holdoff function on my Hung Chang oscilloscope. It seems to me like it doesnt work at all.Is here anybody who has similar scope?

author: Libas
author_rank: Regular Contributor
timestamp: February 21, 2024, 08:48:22 am
content: When I follow procedure mentioned in following video (time 7:45) I cant see any time delay.https://www.eevblog.com/2011/03/30/eevblog-159-oscilloscope-trigger-holdoff-tutorial/

author: CaptDon
author_rank: Super Contributor
timestamp: February 21, 2024, 01:33:25 pm
content: Holdoff does not provide the same function as a delayed timebase. Its most useful function is to delay the ability to retrigger until the intended start of the beginning of the next event. For instance if you display an RS232 signal triggering on the start bit and show the entire start / 8 bits / parity / and stop the scope will most likely jitter and retrigger on a data bit of the next word. So you set the holdoff long enough where you skip over the next part of the word where the scope has missed the start bit but after the holdoff delay it is exactly ready to catch the following start bit. Maybe a different way to picture what I'm saying is Display first word / Skip second word with holdoff / Trigger on third word / Skip forth word with holdoff / display fifth word......This is one example of using holdoff to provide a stable display. If you were triggering on a 60Hz line signal and viewing perhaps the 12vac output of a transformer you would observe with longer holdoff delays that you would only see every other event or every third event or every forth event depending on length of delay. I very seldom use the holdoff feature and you really need to anticipate how and when to use it. Most folks leave it at the minimum delay and never use it.

author: Libas
author_rank: Regular Contributor
timestamp: February 21, 2024, 09:27:23 pm
content: I just noticed that holdoff function actually works fine....just time delay on this Hung Chang scope is much much shorter than on scope in video by Dave and its only noticeable on faster sweeps.Is it possible to somehow easily increase this time delay internally? Could anybody explain how this function generally works internally on analog scopes?

author: CaptDon
author_rank: Super Contributor
timestamp: February 21, 2024, 09:47:49 pm
content: Very simple on analog scope, it can have one of two start triggers. One method the holdoff and timebase trigger at the same time, the holdoff must be adjusted to a longer total time than the trace (not very commonly seen). The second and more popular holdoff delay starts when the horizontal timebase (sweep) ends and prevents the timebase from retriggering until the holdoff timer has timed out.

author: Jwillis
author_rank: Super Contributor
timestamp: February 22, 2024, 12:41:10 am
content: You use the hold off for signals than are rather noisy or have over lapping signals . It tells the trigger circuit how long to ignore candidate trigger events after a valid trigger event is found.

author: Libas
author_rank: Regular Contributor
timestamp: February 22, 2024, 10:20:53 am
content: Quote from: CaptDon on February 21, 2024, 09:47:49 pmCould you describe please more in detail? Is it possible somehow to modify holdoff timer circuit to increase available delay?