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 Post subject: Reading Heathkit Switch Diagrams
PostPosted: Feb Wed 21, 2018 7:27 pm 
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Joined: Jun Fri 23, 2017 5:36 pm
Posts: 17
Can anyone offer a lesson on reading the rotary switch diagrams in their schematics? I have difficulty figuring out what is connected to what in the various positions, the diagrams seem very vague. Contacts are of varying "lengths" (does that tab make contact or not?), its not always clear which way the switch turns (some have arrows) , and how far the contacts move with each "click". Adding additional confusion, sometimes there is a connection from one side of the wafer to the other marked with some very small symbol. Surely it is easy if you know how. I wonder why they used these diagrams as opposed to the more understandable and standard technique for showing switches. Thanks for any help.


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 Post subject: Re: Reading Heathkit Switch Diagrams
PostPosted: Feb Wed 21, 2018 7:51 pm 
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Location: Costa Mesa, California
Unfortunately, schematics were not drawn such that understanding switch contacts is easy or sometimes even possible. But, first start with the notes on the side of the schematic diagram that tells you in which position the switch is drawn. A person then needs to understand the purpose of the switch. This can be helped by looking at the block diagram of the way the radio works and the manual discussion of the circuit description. Then a person can stare at the switch as it moves from position to position to see what it actually looks like and where the wires go. Finally assemble all of the above into an understanding of what the schematic is attempting to show.

Believe me trying to know if the drawing shows the back or front of a wafer, which wafer in the radio is which, and which position the drawing shows and which direction is the next position is not easy. That said, it is useful to dig in and try and figure it all out when the radio does not work right and indications are that the switch is involved.

Norm

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 Post subject: Re: Reading Heathkit Switch Diagrams
PostPosted: Feb Wed 21, 2018 8:12 pm 
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Heathkit actually does better than most and generally label front and rear on the switch wafers but that isn't always the case.

Usually the contacts will be one of two lengths with the longer one being the common wiper contact to the inner diameter of the rotating segment while the shorter contacts only make contact with the outer areas of the rotating segment. In complex switches the long common may also be used as a simple contact when the rotating center portion is broken into two or more insulated segments.

One hint to help you follow what is going on when rotating one of these complex switches is carefully sketch the rotating segment on a piece of transparency (clear plastic) material and then you can accurately rotate it and determine what parts are making contact at each position of rotation.

Note that the labeled contact numbers often don't reference the number of switch positions or a specific starting or stopping position but simply the number of contacts on a switch and you will have to figure out the starting and ending portions from the information on the schematic. Most specify the controls are either in a fully clockwise or CCW position but others specify specific control settings are depicted by the schematic.

Something else that often throws people is you will often see both switch contacts and/or wafer segments that are shorted through so that the front and back half of a switch wafer have common contacts and sometimes these are depicted in unusual ways on schematics. I think it might have been a Geloso receiver I was working on but one of the European models depicted a single wafer with parts of the front and back connected as consisting of a front, rear, and middle "sandwich" which threw me until I studied the schematic and realized what they were showing.

Rodger WQ9E


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 Post subject: Re: Reading Heathkit Switch Diagrams
PostPosted: Feb Thu 22, 2018 6:28 pm 
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Joined: Jun Fri 23, 2017 5:36 pm
Posts: 17
As always, thanks for taking time to post the replies. I was hoping that I was missing something but it doesn't sound like I was - its just difficult and probably best done with the actual switch in front of you. I like the idea of tracing the switch to plastic so you can rotate it on top of the diagram to simulate rotating the switch.

I guess I shouldn't feel too bad about the difficulty here because the newer radios use microprocessors to do the equivalent and those are totally impenetrable unless you have all the development tools and code which no one has. At least with switches you can figure it out, at least in theory.


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 Post subject: Re: Reading Heathkit Switch Diagrams
PostPosted: Feb Fri 23, 2018 7:29 pm 
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Joined: Oct Wed 01, 2014 1:20 pm
Posts: 106
Location: Wood River, Ill.
It is sure nice to hear that I am not the only one!!! It usually takes me hours of study and experimentation with an ohm meter to figure out some of these. All this time I thought I was just slow! :roll:

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 Post subject: Re: Reading Heathkit Switch Diagrams
PostPosted: Feb Sat 24, 2018 2:42 am 
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Joined: Feb Sat 15, 2014 5:59 am
Posts: 12
Location: College Station, Texas
This is a great topic! In all other respects I have no problem understanding schematics, but rotary switches are a complete mystery to me. I am almost never sure what the schematics for rotary switches are supposed to mean. It could all be made so simple if they would only depict them by an arrow coming out of central point, and a set of points on a circular arc, indicating a contact for each switch position. Instead, there is commonly a confusion of sliders, and unclear depictions of the actual switch geometry. All that is needed is a clear and unambiguous indication of what connects to what at each position of the switch. But only rarely is that made clear.

Chris


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