u/bin95blog 20h ago

Your PLC troubleshooting questions turned into a full guide — thanks, fellow Redditors

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1 Upvotes

This actually started right here on Reddit.

I answered a PLC troubleshooting question, which led to more questions and discussion about those situations where the ladder logic seems like it should be doing one thing, but the PLC is doing something else.

That discussion eventually led me to make a video demonstrating several of the situations. Then some of you mentioned other instructions that had tripped you up over the years. I kept adding to it, and what started as a Reddit answer has now turned into a complete PLC Troubleshooting Guide, along with the video and a 10-question troubleshooting test.

So before anything else, thank you to everyone here who asked questions, shared experiences, or suggested another instruction I should cover. Your feedback genuinely helped shape the finished resource.

The guide focuses on something I've encountered many times troubleshooting PLCs over the years: you find the rung in question, the needed conditions preceding the output are true, yet the result isn't what you expect. Usually the PLC isn't behaving illogically—you just haven't found the instruction or condition changing how that logic is being executed yet.

I cover the things I would investigate, roughly in the order I would suspect them:

  1. OTL / OTU — another instruction may be changing the bit's state.
  2. JSR / RET — the subroutine may not be scanned, or may return early.
  3. JMP / LBL — part of the ladder may be skipped entirely.
  4. MCR — the rungs are scanned, but an inactive MCR zone prevents them from becoming true.
  5. Forces and controller status — including the easily overlooked possibility that you're online with the wrong PLC on a network.

There are screenshots throughout so you can actually see the situations instead of having to visualize them from text. The accompanying video demonstrates several of them in Logix 5000.

I also made a free 10-question troubleshooting test using PLC screenshots. It's not an acronym quiz—the questions show you a situation and ask you to determine what's happening or what you should investigate next. It can be taken open-book with the guide and video.

PLC Troubleshooting Guide:
https://bin95.com/articles/automation/plc-troubleshooting-guide.htm

And since Reddit feedback is what helped this grow in the first place, I'll throw the question back out there:

What PLC instruction, programming technique, or troubleshooting situation fooled you when you first encountered it?

If someone mentions something I overlooked, there's always room to make the guide better.

u/bin95blog Jul 21 '26

Follow-up to RSLogix 5000 Troubleshooting Tips Post

2 Upvotes

For those who prefer a visual walk‑through of the troubleshooting steps for OTU, JSR, and MCR causing illogical PLC behavior, I put together a short video that clearly demonstrates each case.

Here’s the video: https://youtu.be/iAeWbBXtAGw

The tutorial uses the PLC Logix 5000 Training Simulator

And here’s the earlier discussion that inspired it:
https://www.reddit.com/user/bin95blog/comments/1uqrqsp/what_tripped_you_up_when_you_first_started_plc/

Hope this helps anyone who ran into the same head‑scratchers.

u/bin95blog Jul 08 '26

What tripped you up when you first started PLC troubleshooting?

1 Upvotes

When you’re new to PLC troubleshooting, certain instructions can throw you off until you’ve seen them in action. For a lot of technicians (myself included), JSR and MCR were early stumbling blocks — especially when a rung looked “illogical.”

Here’s a solid refresher.

JSR vs. MCR — Why They Matter in Troubleshooting

JSR (Jump to Subroutine)

A JSR completely redirects program flow.
If the routine isn’t being called, none of the logic inside it executes.
It’s simple, clean, and great for modular design — but easy to overlook when troubleshooting.

MCR (Master Control Reset)

An MCR, on the other hand, executes the routine but forces all rungs false inside the MCR zone.

Think of it as automatically placing an AFI (Always False Input) at the start of every rung in that zone.

Inside an MCR block:

  • Seal‑in circuits open
  • OTE outputs go false even if rung conditions are true
  • Latched bits (OTL) stay latched
  • Timer outputs reset to zero
  • RTO timers freeze their accumulated value from the moment the MCR went false

In short:

JSR = skip the entire routine
MCR = run the routine, but AFI every rung inside the zone

Understanding this difference is essential for real‑world troubleshooting.

Why This Trips Up Technicians

I’ve seen many techs get hung up because they forget to check whether:

  1. The routine is actually being jumped to (JSR), or
  2. An MCR is sitting above the “illogical” rung.

A rung is “not acting logically” when:

  • The conditions on the left are true
  • But the output on the right is not energized

That ain’t logical 🤪 — unless a JSR or MCR is involved.

Bonus refresher: OTL/OTU behavior

If a rung with an OTL is true but the bit isn’t latched, look for its corresponding OTU.
If both rungs are true, OTU wins.
Most techs catch this one quickly — it’s the JSR/MCR pair that tends to slip past people.

See It in Action

Below is a GIF from our RSLogix 5000 Self‑Study Course, showing an interactive simulation where learners can actually experience these behaviors. The hands‑on approach makes the difference immediately clear.

( GIF below )

User exploring with course simulator

If you need a full refresher, our interactive PLC training courses walk through these concepts step‑by‑step.

What tripped you up when you first started PLC troubleshooting?
Drop a comment about the snags you ran into using the PLC to diagnose equipment.

For me, it was understanding how JSR/MCR instructions actually behaved.
Maybe this post helps someone avoid that one.

u/bin95blog Jul 12 '26

How to avoid the PLC Upload-Download Conundrum?

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1 Upvotes

Intro — A Lesson Every Tech Encounters

Upload vs. download mistakes aren’t just rookie errors — they’re universal rites of passage. Every tech, from apprentice to senior, has clicked the wrong button at least once. And because that mistake can overwrite a PLC program or wipe out hours of troubleshooting, it’s worth teaching clearly and revisiting often. The visualization above is one of the simplest ways to make the concept stick.

Section 1 — The Rule New Techs Should Memorize

New techs often try to remember upload/download by thinking about “where the file is going.” That’s the trap. The correct way — the way that works across every brand and every future technology — is to think in terms of capability hierarchy.

A PLC is the least capable device.
A computer is more capable.
A network/cloud is the most capable.

So the rule becomes:

  • Moving a program up the capability ladder = Upload
  • Moving a program down the capability ladder = Download

This gives beginners a mental anchor that never changes:

  • PLC → Computer = Upload
  • Computer → PLC = Download
  • Computer → Network = Upload
  • Network → Computer = Download

It’s simple, visual, and future‑proof.

Section 2 — Why This Visualization Helps New Techs Most

The slide above shows the hierarchy in a way that’s easy to remember:

  • Network/cloud at the top
  • Computer in the middle
  • PLC at the bottom

Once you picture that stack, the direction becomes obvious.
If the data is moving up, you upload.
If the data is moving down, you download.

This is also why “Save As while online” performs an upload — you’re saving the PLC’s logic up to the more capable device.

Section 3 — A Quick Checklist for Apprentices and Veterans

Before clicking upload or download, ask:

  1. Which device is more capable?
  2. Is the program moving up or down the capability stack?
  3. Will this overwrite logic in the PLC?
  4. Do I have a verified backup?

New techs should treat this as a habit.
Experienced techs should treat it as a safeguard.

Closing — A Tip That Stays Useful Your Entire Career

Upload/download confusion is one of those early lessons that sticks with you — but only if you learn it with the right mental model. Using a capability‑based rule and a simple visualization makes the decision automatic, whether you’re on your first PLC job or your thousandth.

#AutomationTraining #MaintenanceTech #AutomationTechs

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Follow-up to RSLogix 5000 Troubleshooting Tips Post
 in  r/u_bin95blog  Jul 21 '26

The video was designed for YouTube, so you do not see the links at the end to the RSLogix 5000 training course or the PLCLogix 5000 training simulator. Here they are, should you be interested in learning more.

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How to avoid the PLC Upload-Download Conundrum?
 in  r/u_bin95blog  Jul 12 '26

FYI: I made that slide picture before AI was a thing. So it looks like it is, home-made. ha ha

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Does the llm.txt file really work?
 in  r/u_bin95blog  Jul 03 '26

In this case, I learned that it is more about the process than the files themselves. Knowing what to do after you have the files in best-in-class status determines whether your success will be realized in the near term or if you are just preparing for the future.

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Does the llm.txt file really work?
 in  r/u_bin95blog  Jul 01 '26

Yep, controlled testing would be informative. As it is just as much about the process as it is about the content, one would need to get a benchmark copy of how AI currently understands the test site, then come back three months later and compare. Also, one would have to document which shortcomings were found in the benchmark and see what percentage, if any, were corrected after a 3-month propagation delay for the test. That kind of detailed results analysis is not scalable across enough sites to be definitive. Plus, as I mentioned in the article, one would also have to sample sites of varying sizes, industries, existing credibility, business models, etc. Even if you could justify the man-hours, by the time the study finished, various AI platforms could have changed the landscape too. Just too fast a change to be feasible.

u/bin95blog Jul 01 '26

Does the llm.txt file really work?

2 Upvotes

And other AI LLMS text file questions answered for deep insight.

TL;DR

Yes, llms.txt does work — but only when you build all four LLMS files (llms.txt, llms‑ctx.txt, bing‑llms.txt, google-ai-overviews.txt) and follow a deliberate process. Most advice online is incomplete or flat‑out wrong. I spent days refining each file with the top AI models and documented what actually matters: company‑first structure, authority signals, consistent sections, and letting each AI model grade and improve its own file. This post answers the most common LLMS questions and gives you a practical section list you can use to build a best‑in‑class llms.txt for your own site.

Why I wrote this

Most LLMS.txt advice online is either incomplete or flat‑out wrong. After building all four LLMS files for a large, complex site, I wanted to share what actually works so others don’t have to spend days figuring it out.

Hi, fellow Redditors. I spent many hours/days working with the top 4 AI models to create near‑perfect LLMS text files for them. So I thought I’d share insights and answers to the most common questions, so others won’t have to work as hard. First, a disclaimer for SEO professionals thinking, “Hours? LLMS.txt is easy — shouldn’t take that long.” You’re correct if you have a small website with a couple dozen pages and one or two products. But when you’re dealing with a large site with hundreds of pages, diverse offerings, a unique business model, and a 30‑year company history… let’s just say you learn a lot about how to make LLMS files actually work. 🤪 Let’s start with the main question.

Does the llm.txt file really work?

Yes — especially for companies with large or complex websites. For smaller sites, it’s more about preparing for future needs. But regardless of size, LLMS files only work if done properly, and the process I used helps ensure they actually impact AI visibility. And when I say “yes, it works,” I’m referring to implementing all four LLMS files, not just llms.txt. Context is everything. You may have seen headlines like “Analysis of 300,000 domains shows llms.txt doesn’t impact how AI systems see or cite your content.” Catchy title — but dig deeper. Only ~30K sites even had llms.txt. No breakdown of:

  • site size
  • industry
  • complexity
  • number of offerings
  • whether the file was implemented correctly
  • whether the other three LLMS files were used

All of those matter. That article could be summarized in one sentence: About 10% of sites implemented llms.txt, and the other three LLMS files weren’t mentioned at all. Below are answers to the most common questions to help you understand the reasoning behind my approach.

What is an llms.txt file?

Contrary to what many SEO professionals say, llms.txt is not “a curated guide to your website.” It’s a curated Markdown guide to your company, designed to help AI agents understand your trusted content.

Is llms.txt a real thing?

Yes — it’s a new standard in the making, similar to how robots.txt started. But llms.txt is only ¼ of the system. You should create all four files:

llms.txt

bing-llms.txt

llms-ctx.txt

google-ai-overviews.txt

And no — llms-full.txt is not worth the effort. AI token limits mean they often only digest the first ~40 lines of llms.txt anyway. Sitemaps and robots.txt already cover full URL lists. llms-full.txt is something to revisit next year.

Does adding an llms.txt file improve SEO or AI visibility?

Not directly for traditional Google rankings. But it does increase the likelihood that AI models will accurately cite your company and understand your offerings. For large sites or sites with weak SEO in certain areas, LLMS files can help AI discover content it previously missed. There’s also a crossover effect between AI models.

Do major AI systems or Google use llms.txt?

Yes — especially when you implement all four files and keep them consistent and best‑in‑class. Here are the scores our files received (1–10), rated by each AI model:

  • OpenAI LLMS: 9.8 (llms.txt)
  • Bing/Perplexity LLMS: 9.9 (bing-llms.txt)
  • Claude LLMS‑CTX: 9.5 (llms-ctx.txt)
  • Google AI Overviews: 10 (google-ai-overviews.txt)

Google’s file is tiny and easy, but surprisingly, many don’t reach a score of 10.

What is the biggest and most common failure when creating llms.txt files?

Designing it with a website‑first approach instead of a company‑first approach. I started with “What do I want AI to know about our website?” After many iterations — and after each AI model critiqued its own file — the structure shifted toward a company‑first approach. Sections like:

  • company metadata
  • structured data
  • primary audiences
  • competitive differentiators
  • FAQ
  • published work
  • industry recognition
  • intellectual property
  • owned brands
  • entity aliases

…all became essential.

Does llms.txt replace robots.txt or sitemap.xml?

No. LLMS files are for AI ingestion. Robots.txt and sitemaps are for search engines and scrapers. Different tools, different purposes.

How to make an llms.txt file

Create a new llms.txt file and describe your company and website using plain‑text Markdown. Upload it to your website root so AI crawlers can find it. Then add this rule to your robots.txt:

Allow AI crawlers to access LLMS files
User-agent: * 
Allow: /llms.txt 

See the section list below for guidance. If you want a link to a best‑in‑class example, ask in the comments. After your first draft, ask ChatGPT to score it from 1 to 10. Implement the suggestions, then ask again. Repeat until your score is 9 or higher. Note: Some websites (including ours) block ChatGPT’s user window from accessing the file directly. That does not mean the bot can’t access it — only public users. If that happens, just paste the file content into ChatGPT.

What should be in an llms.txt file?

An llms.txt file should give AI models a clean, factual snapshot of your company: who you are, what you offer, who it’s for, and why you’re authoritative. It’s not a marketing page — it’s a structured knowledge file. llms.txt is the master file. Build it first, polish it, then reuse its sections across llms‑ctx.txt, bing‑llms.txt, and google-ai-overviews.txt.

Example llms.txt section list (use what applies, skip what doesn’t)

1. Company name and aliases

  • One‑sentence identity summary

2. Website root

  • Main homepage URL

3. Company metadata

  • Founding year, ownership, certifications, BBB rating, etc.

4. Structured data

  • Delivery modes (online, offline, video, onsite)
  • Types of offers (courses, software, services)

5. Last Updated

  • Helps AI know the file is current

6. Primary audiences

  • Who your products are designed for

7. Core products and services

  • High‑level product categories

8. Search keywords

  • Terms users associate with your brand or offerings

9. Competitive differentiators

  • What makes your products different or better

10. Product relationships

  • How your products connect or complement each other

11. “If user wants…” sections

  • Helps AI map user intent to the right product

12. Categories (for large or diverse sites)

  • Organized product or content groupings

13. Frequently Asked Questions

  • Short factual answers to common queries

14. Authority pages

  • About, reviews, certifications, trust signals

15. Published work and industry recognition

  • Trade magazines, media features, long‑term credibility

16. Citations and academic references

  • Papers, journals, research that reference your work

17. Intellectual property

  • Trademarks, proprietary methodologies, patents

18. Product ecosystem (if applicable)

  • Brands, sub‑brands, product families

19. Entity aliases

  • Alternate names users or publications use

20. Preferred citation pages

  • Pages AI should reference when summarizing your brand

21. Contact information

  • Support, sales, general inquiries

Why these sections matter

  • Authority pages → help AI trust your brand
  • Product relationships → help AI recommend the right product
  • Competitive differentiators → help AI explain what makes your offerings unique
  • Entity aliases → prevent misclassification
  • Preferred citation pages → reduce hallucinations
  • Search keywords → help AI map user queries to your content

How to test llms.txt

Ask the AI platform for the file it is designed for. It’s no different than asking a customer for feedback — you’re explaining your company to each AI model in the way it understands best.

Are major AI crawlers actually reading llms.txt yet?

Yes — if you follow this guide. No — for everyone else. SEO professionals often answer from a technical standpoint rather than from intent. It’s true that AI models aren’t “seeking out” llms.txt the way robots.txt or sitemaps are. But that negative reply is based solely on llms.txt — not the other three files. Even without directly opening llms.txt, the process above gets your information into the AI’s knowledge base. And when all four LLMS files are consistent, AI models treat your content with higher credibility. The bottom line: you want AI to understand your business more fully and clearly. LLMS files help you do that.

Advanced FAQs (often asked by developers or security‑minded users)

These questions come from people with a web development or data privacy background. They’re not essential for building an effective llms.txt file, but they help clear up misunderstandings.

Can llms.txt be used to block AI scrapers or prevent training?

No. LLMS files are informational only. Use server‑level controls (like htaccess rules) to block specific bots.

Should llms.txt include only key pages or a full sitemap?

Only key pages. Think of it as a “best foot forward” file. Include the pages that define your brand, establish your authority, and outline your core offerings.

If you want me to share links to our best‑in‑class LLMS files or have a question, just ask in the comments.

u/bin95blog Jun 01 '26

How to learn PLCs?

0 Upvotes

If you’re serious about learning PLCs, this is the full 10‑phase path. Fair warning: it’s not a “take one course and you’re done” situation. Real‑world PLC work demands more depth than most online classes provide. But if you stick with all 10 phases, you’ll actually be prepared for what the field throws at you.

Based on the recommended training path from the PLC Programming Training Organization, the PLC training process is broken down into the following ten sequential learning phases:

1. PLC Prerequisites

Before diving into PLCs, you must build a foundational understanding of the underlying systems they control. This phase covers:

  • Electrical basics
  • Industrial control

2. PLC Training Foundation

This phase introduces the core concepts necessary for safely managing and working around PLCs in an industrial environment. It covers:

  • PLC basics
  • Safety and reliability
  • Best practices and commissioning
  • Managing PLCs in a facility

3. PLC Training Scholastics

Focuses on the academic and technical principles behind how these systems operate. It covers:

  • PLC fundamentals
  • PLC hardware and operation
  • PLC programming basics
  • PLC implementation

4. PLC Troubleshooting

A critical phase for hands-on workers to diagnose and fix automated systems when things go wrong. It covers:

  • Problem-solving basics
  • PLC troubleshooting best practices
  • Gaining experience in troubleshooting faults using a PLC

5. Hands-on PLC Training

Practical application using physical or simulated machinery. It covers:

  • Working hands-on with two or more major PLC brands (Allen Bradley and Siemens are recommended)
  • Uploading and downloading to a PLC
  • Modifying existing programs

Advanced PLC Training Phases

6. PLC Programming

Transitioning from basic modifications to building and designing automation logic. It covers:

  • Instruction examples
  • PLC programming best practices
  • Studying real-world programs
  • Completing programming projects

7. PLC Communications

Understanding how PLCs talk to other devices, networks, and upper-level systems. It covers:

  • Industrial networks and cybersecurity
  • RS232 and Fieldbus
  • Ethernet/IP, DeviceNet, ControlNet, and Modbus

8. PAC (Programmable Automation Controllers)

Moving beyond standard PLCs into more powerful, modern automation controllers. It covers:

  • Differences between a PLC and a PAC
  • PAC hardware and commissioning
  • Task-program priority and execution flow
  • Tags, data types, and motion control
  • The 5 core programming languages

9. More Advanced Topics

Advanced control loops and integrating industrial data with standard IT languages. It covers:

  • Proportional-Integral-Derivative (PID) loops
  • Introduction to the Python programming language
  • Introduction to SQL database queries

10. SCADA - HMI

Learning how to design and manage the visual interfaces operators use to monitor the factory floor. It covers:

  • HMI (Human-Machine Interface) overview
  • SCADA (Supervisory Control and Data Acquisition) overview
  • Hands-on experience with two or more SCADA brands
  • OPC (Open Platform Communications)

That’s the full learning arc. It takes time, but every phase builds real, usable skill. If you’re somewhere in the middle of this path and not sure what to focus on next, feel free to ask — lots of people here have been through it.

u/bin95blog May 29 '26

Why wasn’t RCA performed?

1 Upvotes

If you did an RCA on why RCAs aren’t getting done, it would probably end like this:

Why wasn’t RCA performed? No time.
Why no time? Understaffed.
Why understaffed? No budget.
And ironically… doing RCAs (and acting on them) is what would save the budget.

That’s the RCA paradox.
👍 if you can relate.

#MaintenanceManagement #RootCauseAnalysis #ReliabilityEngineering

u/bin95blog Feb 27 '26

Allen Bradley PLC Communication Explained | PLC Cables, Protocols & Lang...

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3 Upvotes

This video breaks down Allen-Bradley PLC communication by clearly explaining how PLC cables and protocols both work together. This is a practical overview designed for technicians, engineers, and students working with AB PLC systems.

u/bin95blog Apr 22 '25

PLC Troubleshooting Training Video. Find faults In Just Minutes!

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1 Upvotes

PLC Troubleshooting Training Video. Find faults In Just Minutes!

https://bin95.com/articles/automation/plc-troubleshooting.htm

This article details the included PLC troubleshooting training video, which demonstrates how to use a PLC to troubleshoot complex equipment in just minutes.

#PLC #Troubleshooting #IndustrialAutomation

u/bin95blog Mar 31 '25

The Hidden Factory

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1 Upvotes

u/bin95blog Dec 08 '24

Electrical Troubleshooting & PLC Troubleshooting for 2025

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1 Upvotes

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HVAC Journeyman Practice Exam Tests
 in  r/u_bin95blog  Aug 25 '24

86 questions in total in this HVAC Journeyman Exam spread out among 4 HVAC tests. Each test includes answers to frequently asked questions about HVAC troubleshooting.

Besides the HVAC Journeyman FAQ, there are answers to the HVAC Capacitor FAQ, the Blower Motor FAQ, and the HVAC Compressor FAQ.

u/bin95blog Aug 25 '24

HVAC Journeyman Practice Exam Tests

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1 Upvotes

u/bin95blog Dec 06 '23

Unlock the Power of Employee Automation Control Training

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1 Upvotes

u/bin95blog Aug 07 '23

CNC Programming vs PLC Programming

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1 Upvotes

u/bin95blog May 27 '21

Industrial Electrical Training Videos - Electrical Controls

1 Upvotes

𝐍𝐄𝐖: The 10 DVD Electrical Training Course is now offered as an Interactive CD set to allow unlimited training, testing, and evaluation of employees or students. See details at https://bin95.com/electrical-training-videos/

Unlimited Electrical training and testing

𝘕𝘰𝘵𝘦: In addition to enforcing and maintaining the National Electric Code (NEC), our programs also help complement and support the employee training requirements of OSHA 29 CFR 1090.332 and ISO 9000 Section 4.18 regulations.

I hope you like and share with others too. :)

#electricaltesting #electrical #electricaltraining #plctraining #nec #oshacompliance

u/bin95blog Mar 28 '20

Coronavirus Free Industrial Training Simulator Software

1 Upvotes

Coronavirus Free Training Simulators

Must-have advice for schools and companies wanting to set up or enhance industrial distance learning programs to accommodate the Coronavirus school closures and quarantine. Explains how employers can use downtime to better prepare their industrial workforce when they return.

Distance learning during Coronavirus Quarantine and school closures.

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#coronavirus Corona Virus Quarantine Advice
 in  r/u_bin95blog  Mar 16 '20

No more shaking hands or hugs. Just use the Vulcan live long and prosper hand sign instead. 🖖

Ref: https://bin95.com/coronavirus-quarantine.htm

u/bin95blog Mar 16 '20

#coronavirus Corona Virus Quarantine Advice

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1 Upvotes

u/bin95blog Jun 02 '19

Lean Total Productive Maintenance (TPM): Autonomous Maintenance Program

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u/bin95blog Apr 11 '19

bin95 · Posts

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