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 Post subject: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Tue 15, 2013 7:49 pm 
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Any newcomer to any craft is faced with the necessity of developing skill and technique. Hopefully this offering will help the novice in vintage electronics repair develop his (or hers).

Unfortunately, Murphy’s Law is omnipotent. If any wiring error can be made, then sooner or later it will be made, and even the most experienced of us never get away from mistakes (including the simplest of mistakes).

On the other hand, some kinds of wiring mistakes are far more likely, thus far more common, than others. This article deals with eight errors or pitfalls that every “noob” should know and guard against.

ONE: ERRORS DUE TO WORKING WITHOUT THE SCHEMATIC. This issue all but speaks for itself. Despite such experience as we may have, few (if any) of us can afford to grope around on any repair job without the road map, the novice least of all. To the novice, the arrangement of parts and wires under the chassis is apt to be no more than a bewildering maze, even with a schematic to help. If the “noob” tries to do without it, wiring errors are foreordained.

Make it a rule to never work without a schematic, and preferably a pictorial as well.


TWO: ELECTROLYTIC CAP POLARITY REVERSAL. This is one of the most common wiring errors, and is among the most potentially dangerous and costly ones. At the same time, it is one of the most easily avoided errors. Polarity markings on lytic caps may not always be obvious, but they always exist, and proper attention to them is the way to avoid miswiring lytic caps in circuits.

Lytic caps are always meant to be used across a DC potential that may vary, but never reverses. Even a brief reversed potential can result in a compromised lytic cap. If wired backward, lytic caps will quickly fail, and in many cases, they may overheat and explode.

Don’t pull a lytic cap for replacement until you are dead certain of its polarity orientation. If you have trouble remembering it, then make a sketch or take a photo before you pull the cap.


THREE: OUTSIDE FOIL CONNECTION REVERSAL. This applies to so-called “tubular caps” (originally paper, wax etc. and lately the various forms of film caps). In these caps, two long sheets of metal foil, separated by dielectric (paper/mylar/film etc), are rolled into tubular form. One of the foil sheets ends up on the outside of the finished roll. The terminal connected to this foil sheet is almost always marked by a black stripe or by the words, “outside foil.”

If the terminal connected to the outside foil is grounded (or is at least referenced to ground), the sheet acts as a shield to the remainder of the cap, a desirable condition in many circuits. If the outside foil connection is reversed, hum and noise often result; the cap may also link electrostatically to neighboring caps and cause interference or even oscillation. Pay as much attention to outside foil markings as you would pay to polarity markings on lytic caps, and you may spare yourself a great deal of nuisance.


FOUR: SHORTS IN TIGHT QUARTERS. This probably happens most often around tube sockets, especially miniature sockets, but it is possible wherever bare wires (resistor/cap leads etc) are near enough to touch. You must especially look out for this whenever parts in tight quarters are being replaced. Wires/leads are often inadvertently bent into contact with each other while the repair tech is making room to work. It is worth noting, also, that while leads and wires in close proximity may not touch now, they may be stressed or strained into doing so later on, due to a variety of factors.

This problem is best avoided by keeping all leads and wires as short as possible (desirable in any case, especially in RF circuits), and by sleeving each bare lead and wire with “spaghetti” tubing when tight quarters cannot be avoided. When parts or wires must be moved to allow access to other parts or wires, be sure to move them back into their original places before moving on to the next step of your work.


FIVE: MULTIPLE LUG MISWIRE. This usually involves replacement of such things as tube sockets, complex switches, multi-section can-type lytic caps, etc. Multiple wires and parts are always involved in such a job. A multi-section lytic can (or a complex rotary switch) is very apt to have a number of small parts festooned onto its lugs. And it’s very easy to scramble things up (or leave things out altogether) while reconnecting them.

It isn’t wise to rely on memory in this situation. The schematic, for that matter, may not be enough. The more complicated the scenario, the more likely you are to need pictorial drawings or photos in order to get things back right. Get in the habit of making them whenever you face complicated wiring situations in any repair job.


SIX: FAULTY INSULATION PITFALLS. In vintage gear, the wiring insulation is prone to deteriorate along with the parts. Some kinds of insulation deteriorate worse than others; in many antique sets, you’ll find wires with rubber insulation that is simply crumbling away (or has already done so). The error in this case lies in failure to properly inspect, find, and replace wires with faulty insulation.

You cannot afford to ignore any insulation that shows the slightest sign of deterioration. Many of these wires carry dangerous voltages. In many cases, these wires touch the chassis or pass through areas congested with small parts; there is danger in any such case. Inspect every wire carefully, large and small, short and long. Don’t mince around about it. Where deteriorated insulation exists, replace the wires. Size and route replacement wires exactly as the old ones were sized and routed, particularly in RF circuits.

NOTE: Deteriorated insulation on the leads of major power-carrying parts (power and output transformers, chokes etc) constitute a likewise major danger and service issue that MUST be properly addressed before you attempt to turn on the set.


SEVEN: ERRORS OF HASTE. There are several of these. The two most common (and important) ones are closely related. One involves removing several parts before trying to replace any of them. It’s very easy to forget one part and leave it out. It’s just as easy to confuse two or more parts and substitute them for one another. It’s also just as easy to connect them incorrectly when you do get around to replacing them.

The other error involves only half-completing some step of your job (replacing a part, for example) and moving on to the next step, while thinking you’ll come back later and finish this step. Then you forget it, and don’t come back.

Both of these errors (and all other related ones) can be avoided simply by working one step at a time. Don’t reach ahead of yourself, however tempting (or seemingly justified) it may seem to be. Complete and verify each step of your job at the time you face it.


EIGHT: SOLDER DEBRIS ERRORS. Although these properly belong under the heading of soldering technique errors instead of wiring errors, I include them here because they are both common and dangerous.

Even the best of us occasionally lose blobs of molten solder into the chassis of whatever gear we’re working on. These blobs often run into places where they can cause trouble. They may bridge two tube pins, for example, or two lugs on a terminal strip. For another example, they may short tube pins or terminal lugs to chassis ground. This could cause problems up to and including a high-voltage DC short to ground, with concomitant damage.

Prevention (proper soldering) is the cure here; solder debris usually means too much solder in the first place. Proper soldering technique will largely prevent spillage and debris. When solder does get away from you, as sometimes it will, the debris must be traced and dealt with then and there. Don’t let it wait, or you may forget about it, only to be unpleasantly surprised later. Pay close attention to your soldering and carefully observe its results; solder usually doesn’t make any noise when it gets away from you and runs into places where it isn’t supposed to be. It must fall at least a few inches before it makes any significant impact noise.

As with fugitive screws, nuts, washers etc, loose solder debris can usually be shaken out of a chassis or blown out with compressed air or gas. Attached and/or wedged hardware and debris, on the other hand, must be removed with tools.

Hope this helps, and happy hobbying!

:wink: Larry

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Thu 17, 2013 8:23 pm 
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Very nicely said...well thought out. I have made some of those mistakes in the past, and learned not to.....but it's been more than ten years since I worked on a radio....printed and saved your advice as part of a refresher course one can get for free on here. It's amazing how much you need to re-learn after you've been out of practice for a while.


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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Thu 17, 2013 9:38 pm 
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Yes, it is amazing how things can get away from you, and sometimes you don't need to get too far out of practice before they do. Been there, seen that, over and over again... :?

Thank you for responding. I'm grateful that the writeup was of help to you. I selected these errors because they were the ones I was most often prone to make as a noob. As if that wasn't bad enough, they're the ones I've been most prone to make since, especially if there are distractions around when I'm trying to work, or if I'm working under any kind of time pressure. It's nice if we don't have to do that, but that's not the way of the world, unfortunately.

Good fortune, best regards, and thank you again,

:wink: Larry

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Fri 18, 2013 4:00 pm 
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Whether as a separate item or inserted into one of your points, I would add this:

DON'T BE THROWN OFF BY TUBE SOCKET LUGS USED AS TIEPOINTS. In a communications receiver I'm in the process of checking over for a friend, many components go to a tube socket lug with no connection to an active tube element. That's just the way the unit was engineered. Often it results in shorter leads than if a separate tiepoint next to the socket was used instead, and accomplishes the same purpose of interconnecting different components. It can momentarily confuse even old hands when they don't see a pin number called out on the schematic (because there's no tube element for that lug). Having a tube manual is essential for quick verification that the lug isn't connected to an active tube element.

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Fri 18, 2013 5:23 pm 
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Excellent, Avery, and many thanks for contributing this.

:wink: Larry

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sat 19, 2013 3:28 am 
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Great writeup Larry!...& some of your soldering advice can also be found in the old glossy-color pictured how-to-solder pamphlets that Heathkit included years ago. It also helps if one can help mentor/teach "noobs", including the electrical safety involved. Here in the college chem dept, I have always required our majors to (often on Work-Study or TempServices work assignments) learn and practice soldering & some circuit repairs (on chem equipment or instruments w/ my supervision....it's surprising how often that skill listed on the resume can help a newly degreed chemist land their starter jobs. A possible minor addition to your tube socket tie points: if one substitutes another tube type (say, a 1R5 for a 1L6, etc.) in an original socket having a tie point not connected to a tube element; be certain that this tie point is not connected to an element or grounded shield on the new replacement tube.


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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sat 19, 2013 8:18 am 
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Quote:
This article deals with eight errors or pitfalls that every “noob” should know and guard against.

I'm hardly a noob, but I can mis-wire or blow the polarity orientation with the best of 'em! :wink:

Nice write-up!

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sat 19, 2013 1:52 pm 
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Many thanks, guys, and another excellent piece of advice, Fred, concerning tube socket pins used as tie points. Thank you for offering it :wink:. As soon as I can work up a consolidation of this point and the one Avery offered, I'll modify my exposition... (done as new thread).

50's, I've blown the polarity orientation on lytics myself, altogether too often. If you get careless or distracted, as I often do, it's an incredibly easy mistake to make. I suspect that most of us have made it more often than we care to admit...

Best regards,

:wink: Larry

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Last edited by BigBandsMan on Jan Sat 19, 2013 8:38 pm, edited 1 time in total.

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sat 19, 2013 2:01 pm 
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BigBandsMan wrote:
...50's, I've blown the polarity orientation on lytics myself, altogether too often. If you get careless or distracted, as I often do, it's an incredibly easy mistake to make. I suspect that most of us have made it more often than we care to admit...
Larry


Yes, and it's easier to screw up now than it used to be. When did manufacturers stop putting a nice obvious ring of ++++++++ signs around the positive end of axial-lead electrolytics, and why would they do that?

I have to keep reminding myself to look to see which lead is anchored to the case so I know it's the negative end. I can never remember whether the grooved end of the capacitor is the positive or negative end.

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sat 19, 2013 8:48 pm 
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Thread on Unused Tube Pin Pitfall added as supplement to this thread.

Thanks again to Avery and Fred for their suggestions!

:wink: Larry

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sat 19, 2013 10:57 pm 
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Avery wrote:
BigBandsMan wrote:
...50's, I've blown the polarity orientation on lytics myself, altogether too often. If you get careless or distracted, as I often do, it's an incredibly easy mistake to make. I suspect that most of us have made it more often than we care to admit...
Larry


Yes, and it's easier to screw up now than it used to be. When did manufacturers stop putting a nice obvious ring of ++++++++ signs around the positive end of axial-lead electrolytics, and why would they do that?

I have to keep reminding myself to look to see which lead is anchored to the case so I know it's the negative end. I can never remember whether the grooved end of the capacitor is the positive or negative end.

Heh, wait'll you try re-capping certain Japanese radios, whose radial E-caps use only a black dot to signify...The negative terminal.

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sun 20, 2013 2:35 am 
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A suggestion for those concerned about __correctly__ wiring replacement parts into a radio:

1) Make sure you know which original part is being replaced and it's correct polarity, if any.
2) Match the replacement to the original (value, voltage, tolerance, etc).

Then:
1) Clip the leads of the original part right at the body.
2) Twist each lead of the new part together with the corresponding original lead.
3) Unsolder the terminating end of one lead, remove it, and connect the new lead in its place.
4) Make a good mechanical joint.
5) Solder immediately unless there are other part(s) going to the same location.
6) Repeat for the second lead of the replacement.

This technique should survive phone calls, SWMBO calls, nature calls, coffee calls, cat calls, etc.

- Leigh

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Jan Sun 20, 2013 4:42 pm 
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+1

:wink: Larry

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Feb Thu 28, 2013 4:44 am 
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One thing I found is that many of the Rider schematics are too small and without tube pin numbers and component values (I have Riders on computer file). It is a tremendous help to enlarge it and then write pin numbers (just google tube) and component values. I used print software to enlarge and break print into four 8x11's that are taped together to make one large schematic. So much easier without eyestrain! Bill


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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Feb Thu 28, 2013 2:33 pm 
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Quote:
One thing I found is that many of the Rider schematics are too small...


Too true! The originals were often bad enough, let alone scans of the originals.

:wink: Larry

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Mar Fri 01, 2013 3:10 pm 
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Leigh wrote:
A suggestion for those concerned about __correctly__ wiring replacement parts into a radio:
1) Clip the leads of the original part right at the body.
2) Twist each lead of the new part together with the corresponding original lead.
3) Unsolder the terminating end of one lead, remove it, and connect the new lead in its place.
4) Make a good mechanical joint.
5) Solder immediately unless there are other part(s) going to the same location.
6) Repeat for the second lead of the replacement.
This technique should survive phone calls, SWMBO calls, nature calls, coffee calls, cat calls, etc.
- Leigh


Leigh, I'm not sure what's going on in step 3. I gather that you are NOT suggesting soldering the twisted-together connection of the replacement component and the pigtail of the original? That the reason you're suggesting twisting them together is to make sure that if you're interrupted you have the right component and right leads in the right place?

The downside (assuming I do understand the description) is that you're unsoldering and removing the original lead while the other end is hooked to the replacement. It's often hard enough to get an old lead out of a lug without scorching adjacent insulation or destroying the lug without also having to do it with the new part taking up space.

At least it is for me--maybe others have the skill to do it effortlessly. But I did learn milspec soldering techniques during two summers on the assembly line at Weinschel Engineering back in '61 and '62, and I'd rather clip out the old part (step 1) and then consider various options for soldering in the new one depending on space, what's connected there already, etc.

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Mar Fri 01, 2013 3:31 pm 
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BigBandsMan wrote:
Quote:
One thing I found is that many of the Rider schematics are too small...


Too true! The originals were often bad enough, let alone scans of the originals.

:wink: Larry


And, at least with Philco info Riders received, not all later chassis and schematic changes were documented.
I would hazard a guess and tend to believe this happened with other mfrs as well.

Chuck

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Mar Fri 01, 2013 4:00 pm 
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Since the Riders are often so hard to read, I stay away from them as much as I can, so I don't have the experience with them that I might have. It seems logical to me, however, that if they failed to update Philco schematics, they wouldn't be too intent on updating others.

:? Larry

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Mar Wed 06, 2013 8:42 pm 
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Avery wrote:
Leigh, I'm not sure what's going on in step 3. I gather that you are NOT suggesting soldering the twisted-together connection of the replacement component and the pigtail of the original? That the reason you're suggesting twisting them together is to make sure that if you're interrupted you have the right component and right leads in the right place?
Hi Avery,

Twisting the leads together is just to maintain the association with the terminus until you start working on it.

For any individual lead, you untwist the two, remove the original lead and replace it with the lead from the new part.

Some people advocate soldering the new lead to the cut-off original lead. I don't do that, nor do I recommend it.

- Leigh

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 Post subject: Re: For the Noob: Wiring Errors and Pitfalls to Avoid
PostPosted: Mar Wed 06, 2013 10:56 pm 
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Leigh wrote:

Some people advocate soldering the new lead to the cut-off original lead. I don't do that, nor do I recommend it.

I see nothing wrong with doing it that way, esp if the original seems to be correctly soldered at it's other end, and it's difficult to get to. Very often those leads are simply going to circuit ground and/or the chassis. I've never had a problem with this procedure.

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