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Products => Test Equipment => Topic started by: Alex Eisenhut on February 02, 2020, 12:27:31 am

Title: Using a logic pulser
Post by: Alex Eisenhut on February 02, 2020, 12:27:31 am
For troubleshooting 1980s home computers. I have a logic probe and I prefer that to a scope or logic analzyer for vintage computers. The systems are so simple that all you really want to know is if there's a kind of signal or a stuck logic level.
However I never used a pulser. I understand it uses a "strong" transistor to force a very short pulse at some higher current level like 100mA to override whatever is driving the line.
But the pulse is so short how can I see anything on the probe? Now I see that pulsers go with the probe from the same company with a sync signal of some kind? The probe is synced to the pulser?
Not clear.
Worse are the eBay listings claiming to sell logic pulsers when they are simply selling logic probes with the word "pulse" on them. This isn't a pulser.
And why are these things still so expensive?
Title: Re: Using a logic pulser
Post by: TK on February 02, 2020, 01:46:36 am
The HP pulser I tested sends a train of pulses, not a single one

EDIT: Actually it works like oPossum said... single pulse or train of pulses
Title: Re: Using a logic pulser
Post by: oPossum on February 02, 2020, 01:58:15 am
Logic probes often have a memory feature that will catch brief pulses. The indicator LED for this may be labeled 'pulse'.

The HP 546A pulser I have can do a single pulse when the button is pressed or continuous repeating pulses when the button is held or locked.
Title: Re: Using a logic pulser
Post by: Shock on February 02, 2020, 04:09:29 am
Just to clarify, they come as separate tools or as combined logic probe and pulser. You still need two tools though if you want to transmit a pulse and use a probe elsewhere to detect it. At least without using another type of tool such as a logic analyzer or scope etc. It should state clearly if they are both tools in one and you would expect to see a pulse button on a tool that can pulse.

On some probes they have pulse or mem mode switch (which may be confusing), mem works like an auto hold on a multimeter and that is how you can detect single pulses if it's too fast to notice. Either that or as mentioned leave the probe in pulse mode and send a burst of pulses from your logic pulser.

They are fairly inexpensive unless you want the set of HP tools.
Title: Re: Using a logic pulser
Post by: Shock on February 02, 2020, 04:53:04 am
Some references of the HP logic tools which include a few troubleshooting tips.

HP journal
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1976-12.pdf (https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1976-12.pdf)
On page 13 it suggests what tool to use on what type of problem.

Manuals
http://kripton2035.free.fr/Resources/HP%20545A%20Logic%20Probe%20Manual.pdf (http://kripton2035.free.fr/Resources/HP%20545A%20Logic%20Probe%20Manual.pdf)
http://kripton2035.free.fr/Resources/HP%20546A%20Logic%20Pulser%20Manual.pdf (http://kripton2035.free.fr/Resources/HP%20546A%20Logic%20Pulser%20Manual.pdf)
http://kripton2035.free.fr/Resources/HP%20547A%20Current%20Tracer%20Manual.pdf (http://kripton2035.free.fr/Resources/HP%20547A%20Current%20Tracer%20Manual.pdf)

Demonstration of them
https://www.youtube.com/playlist?list=PL7K-x1E-x5j_XhmMCJg99_BhLusGDCUgT (https://www.youtube.com/playlist?list=PL7K-x1E-x5j_XhmMCJg99_BhLusGDCUgT)