Evergreen Troubleshooting Lesson: Assume Nothing

[desertrout]

More of a general troubleshooting aside rather than anything Commodore specific, but: I recently acquired an early-model VIC-20 in its box with all the bits (manuals, transformer, composite cable, as well a datasette for good measure), but sold as powering on but having no video. Got it for cheap, thought it would be a easy restoration project as no video / black screen appears to be a common, fixable issue.

The machine arrived exactly as described. After some troubleshooting, including that the system was getting sufficient power in the right places, CPU was going into reset, activity on D/A lines, and of course that the video cable had continuity, I figured the Kernal ROM and/or VIC chip could be faulty (as per other sources).

To narrow it down, I borrowed a couple known-working, similar-model VIC's from a friend to swap chips. But when I plugged them in, they did exactly the same thing as mine - power on, no video.

What I didn't think to do was verify that the composite cable was the correct one for VIC's. Sure, it had continuity, but ON THE WRONG PINS. I rewired the cable and bingo-bango the machine works perfectly fine.

If I'd had another VIC-20 or C-64 video cable around (which I don't) I would have of course tested the machine with it and discovered the issue early on. But for some reason I decided that it was unlikely the cable that came with the machine was the incorrect one and moved on. I was on the verge of buying a Kernal ROM or Jiffy DOS, and it would have been for naught.

Lesson learned / reinforced!

 

[robert_sissco]

Welcome to the wrong rabbit hole club, you are in good company.

 

[br44]

When I first assembled a cable for my c64, I got all the pins mirrored and rotated. My only clue was my TV squealed like a disemboweled rabbit when I plugged everything in (composite video going into audio).

Yeah, not one of my finest moments.

 

[desertrout]

When I first assembled a cable for my c64, I got all the pins mirrored and rotated. My only clue was my TV squealed like a disemboweled rabbit when I plugged everything in (composite video going into audio).

Yeah, not one of my finest moments.

I'm not too proud to admit that I always have to refer to several pinout diagrams (with both male and female shown) to make sure I'm wiring connectors up properly. Every single time.

 

[daver2]

Well, If you never make a mistake, you aren't doing anything ar all!

Dave

 

[Hugo Holden]

Well, If you never make a mistake, you aren't doing anything ar all!

Dave

This notion once came up in a job application setting. It was ultimately concluded that an applicant who had an immaculate track record and had never made any mistakes was an inept and ineffectual decision maker, only able to sit superglued to the top of a fence and unable to make a solid commitment to either side.

 

[robert_sissco]

This notion once came up in a job application setting. It was ultimately concluded that an applicant who had an immaculate track record and had never made any mistakes was an inept and ineffectual decision maker, only able to sit superglued to the top of a fence and unable to make a solid commitment to either side.

Or lying through their teeth. At my current job I impressed my interviewer/boss by admitting when he asked if I ever made a mistake that I had accidently deleted a SQL table on a customer's database. Thankfully I made a backup of the table before I did anything (CYA people) and was able to restore it without issue, but still, if you are squeeky clean in IT, you aren't in IT.

 

[Hugo Holden]

Or lying through their teeth. At my current job I impressed my interviewer/boss by admitting when he asked if I ever made a mistake that I had accidently deleted a SQL table on a customer's database. Thankfully I made a backup of the table before I did anything (CYA people) and was able to restore it without issue, but still, if you are squeeky clean in IT, you aren't in IT.

Many years ago, way back in the early 1980's I was conducting job interviews for technicians to repair video equipment.

The interesting thing was that the applicants who put themselves forward as "geniuses in the field" turned out to be the worst of all.

I decided to conduct an experiment to find the applicants who had the technical knowledge and practical experience and who was faking it.

It was not complicated at all. I set up a series of practical testing stations. The tasks were things like; check, using this analog meter, from this pile of unmarked transistors which ones are npn and which are pnp. Sort them into a pile of each type. A diode was provided so the person could check the polarity of the voltage at the meter terminals.

Another was a simple single transistor stage with the transistor biased into class A as an audio amplifier with a 10V supply voltage, with a question like, "what collector voltage would you expect". Another with a simple multi-vibrator, with a question like "what would you expect this circuit to be doing?"

Also, a very good question; have you designed any circuits yourself, can you show us a schematic ?

It always seemed to be the most unassuming candidates who answered the questions correctly.

One guy claimed to be an expert in all things electronic and to be the co-inventor of some specialized technology, but he failed dismally at all the practical tasks and looked like a Deer in the headlights when asked to do them.

One of the better candidates, not even 20 years old, produced the design of an electronically controlled irrigation system that he had designed using 74 series TTL's. He got the job.

It seemed to me, to be more about what a person could do, than the School they had been to, or what they claimed they could do.

Later when the Pirates of the Caribbean movies came out, Jack Sparrow's remark reminded me of this:

Jack Sparrow : The only rules that really matter are these: what a man can do and what a man can't do. For instance, you can accept that your father was a pirate and a good man or you can't. But pirate is in your blood, boy, so you'll have to square with that some day.

 

[daver2]

I had a similar interview 'task' for software engineers. A simple piece of source code converting Centigrade to Fahrenheit (or vice versa - I can't remember which now). The task was to find the errors and issues that I had 'deliberately' introduced into the code.

This was a 'C' example. The number of my own programmers that missed some of the more 'esoteric nasties' I included... However, the errors were 'graded' from "everyone should be able to see these", to "the more knowledgeable will be able to see these", to "only experts will be able to see these".

I have had candidates say that they are not proficient in 'C' when given the task - so I have some other files coded in a language that I know they are proficient in (from their submitted CV). I have also had candidates that just walked out of the interview at that point! Needless to say we didn't employ those...

Some of the errors would have been caught by the compiler. However, some of them were errors in the conversion formula, and others were not strictly errors but things like poor commenting, incorrect comments vs the code and poor code structure.

Of course, these would always lead to further questions during the interview as to what a candidate would do differently...

Dave

 

[desertrout]

It seemed to me, to be more about what a person could do, than the School they had been to, or what they claimed they could do.

Yep. I teach in an interactive media development program (we produce front-end developers, UX designers, VFX designers, and the like). We intentionally don't 'teach to the portfolio' as many similar programs tend to do, instead we teach process, project diversity, resourcefulness, and persistence. Employer and graduate feedback is pretty consistent: our grads do well because they can get the job done and adapt to a rapidly evolving environment, whereas 'portfolio divas' can only do the one shiny thing (sometimes not even that), and it takes them forever.