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texham
10-15-2005, 06:32 PM
I purchased an Icom OPC-254L power cable. It is not red and black wire as I'd hoped, only black and black with a white stripe. If I remember right, the one with the white stripe is negative, correct?

I want to make certain of this before I hook it up to my power supply.

KA9VQF
10-15-2005, 06:47 PM
Hummmm, usually when I build something that has similar colored wires but one has a stripe I use that one for the positive side. I try to always do that because sometimes it is years between the initial construct and service.

texham
10-15-2005, 07:25 PM
Thank you, you were correct. White stripe = positive.

I actually tried both ways. When they were reversed, my radio would not power up, so at least it did not short out the radio or anything.

KB2VXA
10-15-2005, 09:00 PM
2-R
11-WH/BK

At least that's how the IEEE color code goes, hmmmm. (;->)

Seriously:
"I actually tried both ways."

You're flirting with the devil, best run an ohm meter polarity check (R X100) first. 1.5V at low current won't pop it's corn, 12V backward and "The odds are fifty-fifty." if you like Zappa or "Are you feeling lucky, PUNK?" for the Eastwood fans.

W9GB
10-16-2005, 02:24 PM
Quote[/b] ] actually tried both ways. #When they were reversed, my radio would not power up, so at least it did not short out the radio or anything.

That is NOT a smart approach. #With many radios that approach would have destroyed internal components -- sending the radio to a repair center ($$) or time on your bench (both lost hours of enjoyment/usage). #
A cheap digital voltmeter (DVM) or analog volt-ohm-meter (VOM) is a basic tool for the radio amateur.
A basic DVM or VOM costs only $10 to $15 USD.
Harbor Freight and Buffalo Tools sold a Chinese import DVM for $2 earlier this year -- which my brother purchased at my insistence -- that regularly sells for $15.

w9gb

texham
10-16-2005, 05:27 PM
Yes, thank you I do understand that reversing the wires is not a smart approach. However, what would YOU have done?

I have some of the best test equipment from Fluke you can get your hands on, but that makes no difference if my test probes cannot fit into such a small hole for the power connector, and on top of the fact that I cannot disassemble the actual power connector itself to see which wire was connected in what way.

Bottom line, it's over and done with and now I know which wire is which. Icom also needs to take a hint and use a red wire instead of 2 black ones.

K9STH
10-16-2005, 07:22 PM
If your test probes won't fit then you use short pieces of wire to stick into the connector. Then touch the probes to the wires.

You were VERY lucky that you did not damage the equipment. Most equipment uses a reverse polarity diode across the input to short out the input voltage if the input polarity is reversed. Often this diode shorts out and, more often than not, takes some of the printed circuit with it.

A few units have a series diode which prevents the current from flowing if the input polarity is reversed. The drawback to this type of protection is that there is an average of around 0.7 volts dropped in the diode no matter what the current. Also, the diode has to be capable of handling the maximum current that is going to be drawn by the unit plus some safety margin. That is why most units use the reverse polarity diode. It doesn't have to carry as much current but will often short out when it is needed.

If the reverse polarity diode fails in the open mode (this doesn't happen that often, but it does happen) then you can cause all sorts of problems with the unit including blown transistors (especially the final amplifier transistors) which generally means a MAJOR repair bill if the unit can be economically repaired at all.

Glen, K9STH

WA9SVD
10-16-2005, 10:03 PM
Quote[/b] (texham @ Oct. 16 2005,10:27)]Yes, thank you I do understand that reversing the wires is not a smart approach. However, what would YOU have done?

I have some of the best test equipment from Fluke you can get your hands on, but that makes no difference if my test probes cannot fit into such a small hole for the power connector, and on top of the fact that I cannot disassemble the actual power connector itself to see which wire was connected in what way.

Bottom line, it's over and done with and now I know which wire is which. Icom also needs to take a hint and use a red wire instead of 2 black ones.
Well, if your test probes don't fit,

1. It's time to get an additional set of probes to fit such tight spaces

2. Use some ingenuity. I've used straightened paper clips, and even straight pins to serve as probes; you can use regular alligator clip leads to attach to probes that small.

3. The LAST thing I'd do is try connecting equipment if there's even a possibility of reversed polariy. As stated before, that could have caused almost instant, total annihilation of most (or all) of the solid state devices in a unit. As I see it, you had more luck than ...(you know, gray matter) by that stunt. The next time, you might not be so lucky. Having the best test equipment in the world doesn't mean much if you don't use it.

W9GB
10-16-2005, 10:06 PM
Quote[/b] ]I have some of the best test equipment from Fluke you can get your hands on, but that makes no difference --- if my test probes cannot fit into such a small hole for the power connector
All you need to establish is which conductor is ground - standard continuity test - fundamental experiental knowledge - this test can be perfromed with a buzzer or light bulb and battery. #
The outside (metal shell) of that plug is reachable by any test probe that Fluke makes - to establish which is the ground wire. #Any DVM can do this test, for the Fluke 77 or 87 you can use the diode or resistance test - either provide satisfactory results. #

w9gb

WA2ZDY
10-17-2005, 02:39 AM
The reverse polarity protection diode is INTENDED to pop the power line fuse in the event of the power being applied backwards. If you have no fuse in the power line - and lots of otherwise bright hams don't - a few things can go very wrong. First, the diode opens and as Glen said, the protection is gone and the rig gets the reversed polarity. Second, the diode can short and nuke your power supply. Or it can short and burn the house down if you're using something like a car battery for power.

Word to the wise, use a fuse, no matter what.

AG3Y
10-17-2005, 04:52 PM
Quote[/b] (texham @ Oct. 16 2005,13:27)]Yes, thank you I do understand that reversing the wires is not a smart approach. #However, what would YOU have done? #

I have some of the best test equipment from Fluke you can get your hands on, but that makes no difference if
Texham, you really need to watch your attitude. Admit that you did a really dumb thing, be thankful that no harm was done to your rig ( at least not THIS time ) and accept the words of advice that were offered to you in good faith.

I did not see anything posted that was out of line. There have been a lot of "elmers" in years past that would have given you a resounding "shoutdown" for the error in judgement you displayed. It may smart for a while, but hopefully you learned from your experience, and will be a little more cautious the next time you need to do such a thing.

BTW, the best test instruments in the world won't do you any good, if you don't use them properly !

73, Jim

WA7KKP
10-17-2005, 07:49 PM
I'd ALWAYS use an ohmmeter to determine which is positive and which is negative.

Now on the wall wart and similary supplies with the tiny coaxial plugs, the striped wire usually went to the outside, and the plug itself is either negative or positive on the shell, so I check them first before plugging in and praying . . . .

Gary WA7KKP

N0WVA
10-18-2005, 01:49 AM
Quote[/b] (texham @ Oct. 15 2005,11:32)]I purchased an Icom OPC-254L power cable. #It is not red and black wire as I'd hoped, only black and black with a white stripe. #If I remember right, the one with the white stripe is negative, correct?

I want to make certain of this before I hook it up to my power supply.
FYI, and in case you ever run into this problem again, not all power supplies have the white stripe as positive. I have run into a few that had the white stripe as negative.

Since then I always check with a VOM every time.

K9STH
10-18-2005, 02:59 AM
If the cable "follows" the NEC (NFPA National Electric Code) then the white stripe WILL be ground. Remember that in AC wiring that black is "hot" and white is "neutral" (which equates to ground where DC is concerned).

Glen, K9STH

N0WVA
10-19-2005, 01:50 AM
Quote[/b] (K9STH @ Oct. 17 2005,19:59)]If the cable "follows" the NEC (NFPA National Electric Code) then the white stripe WILL be ground. #Remember that in AC wiring that black is "hot" and white is "neutral" (which equates to ground where DC is concerned).

Glen, K9STH
Hmm. Well at the time I was thinking it was just wired up backwards. But on second thought, that may have been a 9v battery clip......

W4ASS
10-19-2005, 01:55 AM
Quote[/b] (texham @ Oct. 15 2005,14:32)]I purchased an Icom OPC-254L power cable. #It is not red and black wire as I'd hoped, only black and black with a white stripe. #If I remember right, the one with the white stripe is negative, correct?

I want to make certain of this before I hook it up to my power supply.
yes the black with white stripe is the hot, just like a rig with a red wire with a black stripe is hot , unless ur wireing a house then black is hot , lol





73's bob
ki4ltg

WA9SVD
10-19-2005, 06:19 AM
A word of caution on checking with an "Ohmmeter." If you check a circuit or connector that's either actively powered up, or still maintains a significant charge, your ohmmeter may not "live to measure another day." Better is to check with a voltmeter setting FIRST, (e.g. 20 V scale for typical 12-15 Volt sources) to make sure a circuit isn't energized or charged in any way. (And that may tell you what you need to know, even without the ohmmeter measurement.)

VE7NOT
10-19-2005, 07:30 AM
Quote[/b] (wa9svd @ Oct. 18 2005,23:19)]A word of caution on checking with an "Ohmmeter." If you check a circuit or connector that's either actively powered up, or still maintains a significant charge, your ohmmeter may not "live to measure another day." Better is to check with a voltmeter setting FIRST, (e.g. 20 V scale for typical 12-15 Volt sources) to make sure a circuit isn't energized or charged in any way. (And that may tell you what you need to know, even without the ohmmeter measurement.)
I heard of a guy that was measuring the ac power in his shop... he accidently put it on the ohm setting... the leads went in the plug and that battery inside blew up... That must have hurt

W6TMI
10-19-2005, 07:49 AM
Quote[/b] (K9STH @ Oct. 16 2005,12:22)]If your test probes won't fit then you use short pieces of wire to stick into the connector. #Then touch the probes to the wires.

You were VERY lucky that you did not damage the equipment. #Most equipment uses a reverse polarity diode across the input to short out the input voltage if the input polarity is reversed. #Often this diode shorts out and, more often than not, takes some of the printed circuit with it.

A few units have a series diode which prevents the current from flowing if the input polarity is reversed. #The drawback to this type of protection is that there is an average of around 0.7 volts dropped in the diode no matter what the current. #Also, the diode has to be capable of handling the maximum current that is going to be drawn by the unit plus some safety margin. #That is why most units use the reverse polarity diode. #It doesn't have to carry as much current but will often short out when it is needed.

If the reverse polarity diode fails in the open mode (this doesn't happen that often, but it does happen) then you can cause all sorts of problems with the unit including blown transistors (especially the final amplifier transistors) which generally means a MAJOR repair bill if the unit can be economically repaired at all.

Glen, K9STH
Have to add to the "he's lucky".

But then again, so am I.

I did the airhead routine with my yaehoo 847, it popped the overload protection on my power supply.

I was like, wtf? Ohhh... oops..

When I got done swearing at myself, I gingerly put a meter across the power leads expecting at the very least to have to change a prot diode. (My experience is 99.9% of the time they short).

They must use a serious diode.. Darn thing was fine after dumping 33 amps through it..

K8ERV
10-19-2005, 01:06 PM
I have over 300 wall-warts, from yard sales. I have a handy gadget that might be of interest. A dual-colored led (from shack) with a series resistor. Tells me if the wart is working, and the polarity. Very useful.---

TOM K8ERV Montrose Colo

KD6NIG
10-19-2005, 03:25 PM
A VOM is a good tool to keep around. I always check polarity before hooking things up, because knowing me, I would do it the wrong way.

Harbor Freight had some cheapo ones for $10 recently. I grabbed a pair and put them in my glove boxes. They are very handy tools.

But, just like when cutting wood for a project, measure twice, cut once-I always check twice before hooking up. Partially to make sure, partially because I usually forget I did it the first time and have to do it again to make sure.

Also, I got one of those label makers that prints with the white tape, and I like to label things after I check them. That helps with the old memory thing. I'll also strip one wire at a time, check polarity, hook up the proper wire, tape it up, then do the other one, so then I know I checked and got it right first. Most of the time I have had issues is when I have stripped all of the wires first then tried to 'remember' what was what http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

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