What happened to logic probes and pulsers? - Page 1
Forum section: electronics / testgear

author: MultiMike
author_rank: Contributor
timestamp: September 11, 2021, 08:55:01 pm
content: When I was young and working at Radio Shack trying to sell 5-pound mobile phones to people who didn't really want to spend thousands of 1987 dollars for them, a seemingly common method of finding faults in circuit boards was the 'logic probe and pulser.' I even bought a pair, myself, way back then. I don't know where they are now. They might be in a box in my mom's basement somewhere. Regardless, probes and pulsers don't seem to be 'a thing' any more. Nobody mentions them.What happened?Mike

author: james_s
author_rank: Super Contributor
timestamp: September 11, 2021, 09:03:47 pm
content: Integration happened. Back in those days it was common to see boards full of discrete TTL or CMOS logic ICs. Have you looked at modern hardware? Often the only digital part is a microcontroller, more advanced stuff is full of serial interfaces and high speed LVDS buses. A logic probe and pulser are simply not very useful with the majority of modern devices. I still use them when troubleshooting vintage hardware but that's a niche application.

author: rfclown
author_rank: Frequent Contributor
timestamp: September 13, 2021, 12:13:31 am
content: When I was young and buying parts at Radio Shack I built a very simple logic probe with a gutted pen, a nail, an LED, a resistor, a piece of wire and an aligator clip. I used it to figure out that the problem with my TRS-80 video was a bad inverter. I was really happy with that, so I then built a fancier logic probe (which I never used). The only other test equipment I had back then was a Radio Shack analog multimeter and some power supplies. High school days. Haven't used a logic probe since then. I now have an oscilloscope. A logic probe is only good if you have nothing else (IMO).

author: james_s
author_rank: Super Contributor
timestamp: September 13, 2021, 02:21:56 am
content: I still use a logic probe when I work on old arcade game boards. It's a lot more compact than a scope and most of them have a beeper so I don't even have to take my eyes off the probe tip. It can be powered off the DUT and doesn't require any external power source and I can carry it in my pocket.

author: wilfred
author_rank: Super Contributor
timestamp: September 13, 2021, 03:35:52 am
content: At least three things have changed. Oscilloscopes are much cheaper. Circuit boards are much more highly dependent on tiny SMT components and highly integrated special function IC's. The available probe points on a modern PCB is more likely to be a bus that carries a datastream and a logic analyser is preferred. The Logic probe and pulser have become of marginal utility in contemporary repair.I'd expect that as a previous poster said the logic probe will find use in the older technology like arcade games.

author: David Hess
author_rank: Super Contributor
timestamp: September 13, 2021, 04:23:38 am
content: Increased integration removes the nodes to probe and surface mount construction makes repairs more difficult.

author: james_s
author_rank: Super Contributor
timestamp: September 13, 2021, 06:07:19 am
content: Surface mount construction doesn't really make it any more difficult, it just requires different tools. Removing a large DIP from a board with PTH was always a pain, removing a large surface mount IC is a piece of cake with a hot air tool. BGA and similar is another matter though.

author: johnh
author_rank: Regular Contributor
timestamp: September 13, 2021, 08:26:26 am
content: Talking about logic probesdigging through a box stuff I found this old logic probe Date codes for some IC's are 1978

author: james_s
author_rank: Super Contributor
timestamp: September 13, 2021, 07:40:14 pm
content: That's neat, big chunky thing. Quite a lot going on in there too it looks like.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 14, 2021, 11:50:16 am
content: What happened? The last 30 years happened. What possible use could you get out of a few Hz of LED flashing or audio beeping on a DDR3 bus? Logic levels and rates are so different now. There are no parallel buses anymore. Just probing with your giant logic probe is probably adding 20pF to a bus that will not like it one bit and probably fail.How do you logic probe a differential bus?Most large modern logic systems have JTAG or boundary scan and effectively have a logic analyzer already built in. It's software, baby!Modern logic with its adaptive-equalized multi-gigabit data lanes and thousands of bits of configuration data aren't amenable to being troubleshooted with some manual poking about. Take a look at the size of the probe tip, now look at a modern PCB.Plus it's so cheap... If it doesn't work, well, there's always a newer and cheaper model.That said, when it comes to slow 5V logic like a Commodore 64 or even an original Amiga, it's my preferred tool. You have separate data and address lines, chip select lines, write enable, etc. Simple logic can use simple tools. As a matter of fact, a scope just adds needless hassle IMO. I recently helped a user repair their 64 through text posts on a forum... with a multimeter.It worked.

author: johnh
author_rank: Regular Contributor
timestamp: September 15, 2021, 06:58:15 am
content: That logic probe from Ericsson from when the main memory in the AXE APZ central processor memory was made from 64K x 1 dynamic ram chipsThe microprogram was stored in fuse link proms and the board were all wire wrappedyes , thing operated a lot slower back in those daysThe memory PS(program store) DS (data store) and RS (Reference Store), The PS and DS went from the floor to the ceilingI have attached a picture of one the processor card and the other photo give some idea of height of the suiteCan't find a photo of the central processor

author: Shock
author_rank: Super Contributor
timestamp: September 15, 2021, 08:07:29 am
content: With vintage computing and electronics gaining in popularity they have made a bit of a comeback.Here are some of the vintage HP logic tools, well worth watching.https://www.youtube.com/playlist?list=PL7K-x1E-x5j_XhmMCJg99_BhLusGDCUgT

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 15, 2021, 10:58:23 am
content: An affordable HP Logic Dart would be great. HP 10000-series sub-miniature probes with the DIP clip accessory are great too.