Twenty years ago, I sat at a bench at a new job. The products were timers and controllers, and one day, I grabbed some dead units and started to evaluate them. In looking at the schematics, I found a rather bizarre situation -- several 10K resisters were labeled R1. I thought that this might be due to some lazy CAD driver, and that they were probably hand drawn. At Tektronix, we refer to PCB layout drawings as dolly sheets. I looked at the dolly sheets, as well as the silkscreen on the board, and I was horrified. All components with the same value had the same nomenclature.
I talked to the designer, and he told me this was done to make the hand-stuffed-through-the-hole parts easier on the assemblers. I guess he was assuming a high yield. However, reality says human error creeps in on monotonous and repetitious jobs like stuffing PCBs by hand day after day.
I started to work on the boards, but I had to trace every node as if there was no documentation available. Thankfully, these were only two-sided boards. Since 10K is probably the most used value of resistors, R1s were all over the place.
I kept to myself on this, since I was a new guy. I didn't want to ruffle any feathers. Over several months, I did a lot of trace following. The only benefit was that I didn't have to check the bill of materials when a part was missing. It turned out the parts were binned as R1, R2, C1, etc., as well. So all I did was check the silkscreen and fetch the part. Neat, right? No way.
One thing that is missing in our industry is standards. But even with standards, some folks feel autonomous enough to do really goofy things. Stories like this make this field of endeavor rather entertaining.
This entry was submitted by Steve Lindberg and edited by Rob Spiegel.
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Colorado Native--You have just indicated one huge problem in some manufacturing areas, at least in the appliance business;"beaners" are driving the bus. Cost accountants provide definite "value-added" but there are times when solid engineering must rule the day, especially when quality and safety are concerns and they are always concerns. One of the biggest problems we had a GE was substitution of parts when the part moved to low cost producers (LCCs). The qualification of vendors is difficult at best but when half way around the world it's really tough.
I have as most of us have, been the new guy. Sometimes a new perspective shines light on a bad practice. Keeping it to yourself, as I did and you did, does not always fair well. I know how it is to be the new guy and not rock the boat, but when things can be done better and safer, I wish it wasn't so hard to do. I finally did it and I got a lot of resentment for it. Was it worth it...not sure..I ended up quiting.
There are pros and cons for doing it any of the ways mentioned, all have drawbacks and advantages, it all depends on who's driving the bus (usually bean counters these days).
Obviously, these boards were labeled with assembly in mind and not repair, it was not mentioned whether or not these units were intended to be throw-aways or not, if they weren't, then this decision was not particularly wise.
As to the trouble shooting aspect, I have a VHS deck which is in need of recalibration, I have the full service manual and schematics, the calibration procedure is given in full, the problem being is that there are no test points on the board labeled and the calibration procedure does not indicate where to put your probes to monitor the signals for adjustment. This makes it very difficult to do the calibration. I've done this calibration procedure a great many times over the years with quite a few different types of video decks and this is the first one I've come across with this kind of stupid fowlup. Maybe the manufacturer had a test bed for this during manufacturing but nothing in the way of test fixtures are called out in the manual. This is just plain dumb from beginning to end. These decks require calibration every so often and not providing the proper information causes problems and expense at the consumer end.
Personally, I don't like tossing something that should be repairable and useable for a good long time, obviously a lot of manufacturers don't view this as a plus, our throw away culture that has developed over the last 20 years is going to come back and bite us in a very bad way in the future.
I've got a lot of tube equipment which was designed and built to last, something most of the junk being peddled today can't do. I have equipment still working just fine that is 40, 50, 60 years and more old that will probably still be in use while the junk yard fills up with today's cheap trash, no matter how the PCBs are labeled.
I think we've made a lot of bad decisions in the name of cost and profit, they will come back to haunt us in a bad way.
@takochip- Yes, understand the motivation and "requirement" that led to it. My point was that if, for example, a location marked as "10k" needs to be changed to a 15k value, the silkscreen is now wrong. That means modifiying each board or scrapping them. Special work instructions could be generated to pull from the 15k bin and install it at that location which is marked "10k". You can imagine the potential mistakes that will result !
Of course the best way is "R1, R2, etc...." but the article mentioned that the company did not want the assemblers looking at the drawings to find the correct values for insertion.
Another reason to use "R1, R2..." and not the component values on the PCB silkscreen. As soon as a design revision or a new configuration requires one of the component values to change the silkscreen will need to be changed. All the existing bare PCBs will need to be re-labeled or scrapped.
As component sizes shrink and physical density increases, silkscreening the reference designators becomes impractical. We were spending many hours re-arranging the CAD-generated text so it was not covered by components or superimposed over a solder pad. The result was almost unusable in crowded areas of the PCB. Everyone in the design/ manufactuing/ support chain agreed the pain exceeded the gain so most of the silkscreen was deleted. That said, we have online tools that link BOM, schematic, and assembly drawing. Click on one, and it highlights the item in the other two.
If a product is not considered to be worth repairing then all of that labelig is a waste, since boards that don't function correctly may not be repaired anyway. It certainly does come down to the manufacturer's attitude about the whole product being worth repairing. This applies not only to really cheap consumer items, but also to quite expensive automotive electronics as well.
My guess is the lack of silkscreen was not a money saving decision, but one to make reverse engineering more difficult. Working on a board like this is not difficult with the "dolly sheet" in hand.
In fact, it is much easier to generate the "dolly sheet" (wow, after using it a few times I really dislike that term) than place reference designators in locations that are easily read after placement.
I worked at a company that used no silkscreen and only placed part numbers on schematics. The idea was to keep the design proprietary... and it meant you needed the schematic, BOM and "dolly sheet" to do anything.
The best one I've seen so far is a large board with NO designators or markings of any kind! I've seen this on really old boards, but this was something under 5 years old. I guess they decided to leave the silkscreen off to lower board costs. That one was a pain to troubleshoot from a schematic.
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