Animation of the Fisher 500C selector switch function - w/ seven drawings

[daylite]

I was facing a job involving rewiring of the 500C’s 7-position 5-section selector switch and realized I did not have near the understanding I needed to feel good starting. To help myself get there I put together 7 drawings to show the state of the network and signal path for each switch position. I’m sharing them here.

The drawings show the signal path highlighted in blue and at the same time illustrate what nets are grounded in the various states. Grounded nets are highlighted in red, though in some cases I didn’t highlight a grounded net because it was an obvious dead end, or it just didn’t look relevant to the main function selected.

I have attached the drawings to this post. The drawings also make a nice animation shown here. It’s set to go pretty fast. Nevertheless, I found it instructive when watched for several cycles while focusing on subregions. If you download the animation and open it in a program that does not play it automatically you can step through at your own pace. You can also click on the gif in the attachment area to step through it. -d [EDIT: DG explains below that the source schematic from Fisher is wrong around Section 3, The frame files and animation here have all been updated with the correction he recommended. New files have 'Corrected-Section-3' in the filenames. -d ........Dec 24, 2021 9:22 AM ]

 

[notdigital]

Dayliteful!!!!

 

[gadget73]

Tracing through these rotary selectors is a massive headache. Extra bad when you have to imagine where each wafer is going to be at each position when its not drawn and there are multiples that gang together.

Nice job, this will surely help someone in the future.

 

[Dave451]

Awesome work! "Massive Headache" is right on. Pulled my hair out many times trying to trace through input circuits, matching up wafers, front/back, and element positions and trying to match the schematic to the physical switching. Appreciate the effort--going into the "500C" file.

 

[Tim D]

Nice work and very cool animation!

 

[grindfix]

What an effort!!!
I had a "pretzel" brain following switches while diagnosing the problem in my Hickok 533.
Thanks for sharing

 

[ncwalz]

Very nice!

 

[dcgillespie]

Day -- If I may, may I offer an opportunity of correction -- not of your work, but of the original schematic that you worked from? In that way, it ultimately does affect your work.

The errors on the schematic involve the wiring and makeup of Section 3 which is for the Right Channel of the Input Selector switch. The first error is that terminal 12 in Section 3 -- which appears on both the front and rear sides of the Section 3 wafer -- are electrically connected by virtue of the switch's construction: the same through rivet is used to mount both terminals, so the rivet ties them together electrically. But the schematic shows terminal 12 on the rear of Section 3 being tied to terminal 11 on the front side of Section 3. That's the first error. The second error is that the schematic shows the outputs of R29 and R30 permanently connected together (among other things). The third error is that the schematic shows terminal 11 and 12 permanently connected together on front side of Section 3 as well.

Shown correctly on the schematic:

1. On Section 3, terminal 12 Rear connects to terminal 12 Front (as explained above, to effectively draw the switch itself correctly), and to the output of R30 -- the same way as shown for terminal 12 and R29 of Section 1 for the Left Channel. That's it -- there are no other connections to terminal 12 of Section 3 (front or rear) -- just R30.

2. There is also a jumper connection between terminal 12 of Section 1 (front or rear) to terminal 11 of Section 3 Front. There are no other connections to terminal 11 of Section 3, other than this jumper. The jumper allows for the outputs of the two phono preamps to be connected together when the Input Selector switch is set to the Phono Mono setting for mono phono operation.

If you can make these corrections first, and then apply your superb signal flow indications, it will help achieve the ultimate clarity your work produces.

Super job!!

Dave

 

[daylite]

Dave - I'll enjoy making this more accurate with your help. May I PM you so we can work this out offline? Thanks
EDIT: I took a look at things and it really seems like this is pretty simple (famous last words!).
Please look at the attached and let me know what might still need to be fixed.
Thanks again -d

 

[dcgillespie]

Bingo! That's perfect, and with that, it's pretty easy to see that it also makes a whole lot more sense than the way it was originally drawn -- which was nothing short of goofy......

Dave

 

[daylite]

Great - I'll substitute corrected files in my original post asap - probably before Santa arrives. It was certainly obvious something was wrong with the schematic as published. I tried to deduce what the right drawing would be by looking at the bad schematic and imagining what would work. In this case of multiple errors, and probably in every case of such questions, a better approach would have been to simply get up, go to the bench, and measure what's right in front of me. Nothing like direct experience and observation. (I have deleted the thread "500C Schematic Error" I posted earlier.)
Many thanks to readers who have written notes of appreciation about this project! -d

 

[daylite]

Just replaced all files in the original post with corrected versions. New names are "Framed-v2.0-Corrected-Section-3-500C-7-Paths-STR.gif" and "Switch POSITION [#] v2 Corrected Section 3.png". A note on this was added to the original post. Glad to have had your help! -d

 

[Greg Nal]

This community is such a treasure! I am in awe of the contributions and sharing of work that took much time and effort, just to increase the body of knowledge and make life easier for others.

Keep it up and Merry Christmas.

 

[JamesML]

Love the Selector Switch Diagrams - Fantastic!

 

[baconbadge]

Most excellent, thank you!