Help!!!

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Re: Help!!!

Post by frank1956 on Sat Jun 28, 2014 12:57 pm

WC,
How do I lift one of the wire off the speaker without breaking or damaging it ???
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Re: Help!!!

Post by Wildcat445 on Sat Jun 28, 2014 7:01 pm

Let us consider where we are. We know that we have B+ from the rectifier. About ten volts high. Thru the filter caps that are correctly wired. We have B+ on the screen, also a tad high in voltage. We have B+ on the plate of the 50L6, also a tad high in voltage. Now we need to check out the secondary of the output transformer and the speaker voice coil. The resistor, R9 measures about 1800 ohms, give or take, which is also a little high. My suggestion is that, although R9 is out of range, it should not affect the operation of the audio stage. Again I suggest lifting one of the speaker wires by unsoldering it where the transformer wires are soldered to the speaker. This will clear these items of suspicion if they check okay. We should then have a known working audio stage, after we inject a tone into the volume control. We can address R9 later, if you want to. If you are still unsure of how to do this, post a picture of the rear of the speaker where the wires connect and we can talk you thru it.

WC

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Re: Help!!!

Post by frank1956 on Sat Jun 28, 2014 8:05 pm

WC,
Attached is a pic of the wire removed from the speaker. Which side of the wire do I need to take the reading from? I assume it did not matter which side of the wires I removed from the speaker.

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Re: Help!!!

Post by Wildcat445 on Sat Jun 28, 2014 9:23 pm

You measure across the voice coil (speaker) and you measure across the secondary of the output transformer. You measure across the one you disconnected and its mate, then across the two to the transformer secondary that are still connected. I gave you the readings you could expect earlier. If these two components test good, then we will move to the volume control. You are learning a lot, and should be given a pat on the back for being so diligent. Let us know what you find, and good luck.

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Re: Help!!!

Post by frank1956 on Sat Jun 28, 2014 10:01 pm

WC,
Took the two measurements. The one disconnected reads zero, the one connected reads zero as well. Did this several times to make sure of my reading.
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Re: Help!!!

Post by Wildcat445 on Sat Jun 28, 2014 10:33 pm

Make sure your meter was "zeroed". This is an important step, particularly when reading only a few ohms of resistance.  You will only be looking at 3 to 8 ohms on either, so if your meter was not accurately "zeroed", it might read zero.  Had it read infinity, or very high ohms, that would have been bad. Zero the meter and take the measurements again.  We do not want a zero reading, since that indicates a short.  If you  get a proper reading, restore the speaker connection.  I forgot to mention this, so I may have messed you up. Measure these two components on the R X 1 or lowest range on your ohm meter.

We will be happy to answer any questions you may have on this step.  You are doing great, Frank.

WC

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Re: Help!!!

Post by frank1956 on Sat Jun 28, 2014 11:15 pm

Meter "zeroed out" and both reading were still zero. When reading were taken R X 1 needle went all the way to zero. Reading was taken with an analog meter.
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Re: Help!!!

Post by Wildcat445 on Sat Jun 28, 2014 11:45 pm

I am not satisfied with a zero reading, so let's try something else.  Restore the connection to the speaker.  Find the volume control, R3 on the schematic, a 500K ohm pot.  This component should be a part of the volume control/power switch assembly.  You know where the power switch is.  There are three terminals sticking up out of the volume control.  We will concern ourselves with the center terminal.  Plug the radio in, turn it on, and allow it to warm up for a couple minutes.  Turn the volume up to nearly full volume.  Place the tip of your plugged in soldering iron on the center terminal of the volume control.  You should hear a loud hum or buzz from the speaker if all is well so far.  No buzz out of the speaker, or not a LOUD buzz, will indicate that we have not adequately checked a component thus far.  Do not be alarmed when you hear this buzz, as that is the response we want.  The soldering iron need not be hot for this test, and you only need to leave it on the volume control terminal for a second.  Use caution when performing this test, as you may jump or jerk your arm when you hear the noise, and you are working in close proximety to high voltage.  What we are attempting to do is to couple the 60 cycle hum from the iron heater into the audio section of your radio.  Do this and let us know what happened.  

Another word of caution. This radio is an AC/DC set with a potential "hot" chassis. Do not allow the soldering iron to come into contact with ANY other component other than the volume control terminal I specified. There is a potential of causing a short if the iron comes into contact with the metal radio chassis. BE CAREFUL and good luck.

WC

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Re: Help!!!

Post by frank1956 on Sun Jun 29, 2014 12:10 am

Reconnected speaker wires and turned radio on, alouded it to warm up. Located the center terminals on the volume control and proceed with the test no luck, no hum or loud buzz.
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Re: Help!!!

Post by 35Z5 on Sun Jun 29, 2014 12:14 am

frank1956 wrote:Reconnected speaker wires and turned radio on, alouded it to warm up. Located the center terminals on the volume control and proceed with the test no luck, no hum or loud buzz.

Won't buzz unless control is set at least 1/4 way or higher up...
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Re: Help!!!

Post by Wildcat445 on Sun Jun 29, 2014 12:20 am

Okay. If touching the tip of your plugged-in iron to the center terminal of the volume control did not produce a buzz in the speaker, we have a problem in either the speaker voice coil, or the secondary of the output transformer.

Unfortunately, you are going to have to disconnect the speaker again. This time, please disconnect the transformer secondary wires from the speaker, do not disconnect the speaker wires. We need to completely isolate these two components and check their resistance again. One of them appears to be shorted. I have never seen a shorted voice coil, although it is theoretically possible. You have checked and rechecked and you got zero ohms both times. I will be more satisfied with even 2 or 3 ohms, but zero will not do. Do this and let us know what happens. You are certainly hanging in there. Hopefully you are learning something along this journey. You are doing great, Frank.

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Re: Help!!!

Post by frank1956 on Sun Jun 29, 2014 9:45 am

WC,
I am learning a lot, more then I knew when I jumped into this. Before disconnecting the transformer secondary wire I rechecked the volume control test, but no hum or loud buzz. I disconnected the transformer secondary wire photo attached. Insured meter was zeroed out and took reading photo attached. Reading were taken mate to mate with same results zero ohms.



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Re: Help!!!

Post by Wildcat445 on Sun Jun 29, 2014 10:01 am

You are doing absolutely great, Frank. Frequently, posters get frustrated, especially when they are having a problem, and just give up, You are hanging in there. This thread will be a great resource for someone else just starting out. I salute you, sir.

Do you have another speaker laying around that you can sub for that one temporarily? I have never run into an apparently shorted speaker. Does anyone out there have a suggestion here? If you could test another speaker in this radio, or sub that speaker into another radio, that would be a definite test. How did the secondary of the output transformer test? Something out of the ordinary is going on here, and, I feel confident that with you hanging in there we will get to the bottom of it. We may end up changing both the speaker and the output transformer. We need at least a few ohms of resistance on the secondary of the output transformer.

Frank, just for review, and following the schematic, you have now checked every component in the radio from the volume control to the speaker. You have found a fairly certain fault. You have learned something. Several folks have pitched in to help. You could not have picked a better radio to go thru, piece by piece. Thank you for that experience.

WC

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Re: Help!!!

Post by frank1956 on Sun Jun 29, 2014 10:34 am

WC,
I do have another speaker we can check. Will located it and proceed from there. It me who should be thanking you, Tom and everyone else that has giving there advice and or opinions on this radio.
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Re: Help!!!

Post by 35Z5 on Sun Jun 29, 2014 11:04 am

frank1956 wrote:WC,
I am learning a lot, more then I knew when I jumped into this. Before disconnecting the transformer secondary wire I rechecked the volume control test, but no hum or loud buzz. I disconnected the transformer secondary wire photo attached. Insured meter was zeroed out and took reading photo attached. Reading were taken mate to mate with same results zero ohms.




That reading was taken on Rx1 correct??? Any other resistance setting & two or three ohms will read as zero ohms...
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Re: Help!!!

Post by frank1956 on Sun Jun 29, 2014 11:38 am

RX1 is correct.
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Re: Help!!!

Post by frank1956 on Sun Jun 29, 2014 11:41 am

I will be out of commission for awhile one of my Electrolytic Capacitor end broke off. Just ordered another, hopefully a day or two  Sad
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Re: Help!!!

Post by 35Z5 on Sun Jun 29, 2014 11:51 pm

I was poking around with some junk radios this evening and started checking OPT secondaries, not one read more than .5 ohm and a couple were as low as .25... I think you're probably chasin' snakes on the transformer...
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Re: Help!!!

Post by 75X11 on Mon Jun 30, 2014 6:32 am

I am following along and wanted to make certain of whether the suspect portion at this time is either the transformer secondary or the voice coil?
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Re: Help!!!

Post by Wildcat445 on Mon Jun 30, 2014 11:16 am

Tom, we are on the same page on the transformer. I have never seen a shorted voice coil in a speaker, Open, maybe. Dragging, maybe. Never shorted. I still wonder about reading such low ohmage and his meter. We have the problem cornered. This is one of those times that it is especially difficult to diagnose over cyberspace. He does not have any output when he put his soldering iron on the volume control. There is a problem somewhere, obviously, and we have guided him part by part thru the power supply and the audio section. I suggested he sub his speaker. What do you guys think about this? In one of Frank's earlier posts he mentioned static out of the speaker. It should be working, that being the case. I wonder if we are missing something simple.

This thing should really be working. I appreciate your helping Frank on this, Tom and 75, as he has learned a lot. He needs to be given lots of credit for hanging in there.

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Re: Help!!!

Post by 75X11 on Mon Jun 30, 2014 11:52 am

Frank said he had a speaker to sub. at least that would eliminate that area from consideration. I don't know if that size of meter would show such a fine degree of difference in a driver short. That is why I use a Simpson 269 as a bench analog meter. If this is not the area, move back and bracket again. That's about all there is.
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Re: Help!!!

Post by 35Z5 on Mon Jun 30, 2014 12:23 pm

75X11 wrote:Frank said he had a speaker to sub.  at least that would eliminate that area from consideration.  I don't know if that size of meter would show such a fine degree of difference in a driver short.  That is why I use a Simpson 269 as a bench analog meter.  If this is not the area,  move back and bracket again.  That's about all there is.

This is why I love digital meters, will show you a speck on a gnat's ass... Speakers are easy enough to test with a 1.5v battery...

BTW the speakers in said radios were all in the 2-3 ohm range, while again none of the OPT read over .5 ohm... I have a 757 source Silvertone radio similar to what were are trouble shooting, 50L6, three lead hum-buck xfomer and all, I'll check that OPT later today...
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Re: Help!!!

Post by Wildcat445 on Mon Jun 30, 2014 12:25 pm

75, you are right on the nose about the meter.  I use a VTVM on such small resistance, due to meter loading.  We are at a distinct disadvantage trying to talk Frank thru speaker testing, when we are not there to put our hands on it.  If a speaker sub does not do anything, I'm not sure what the next step will be.  We need a known working audio section, or we will be spinning our wheels and confusing Frank going any further.  I appreciate your input.

(Edit)   Tom, you and I were posting at the same time.  I appreciate your doing that.  When Frank gets his cap fixed, suggest that he try the battery test.  I overlooked that possibility.  Thanks for that suggestion.  We are getting close. Frank has a digital meter, does he not? Let us suggest that he measure the speaker with it.

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Re: Help!!!

Post by 75X11 on Mon Jun 30, 2014 1:17 pm

I would do the battery test on the driver and do a continuity and resistance check on the primary and secondary of the output xfmr, and pri to sec and each to core, just to eliminate it. then it is back to the signal handling sections, isolating to the first faulty reading.
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Re: Help!!!

Post by Wildcat445 on Mon Jun 30, 2014 2:55 pm

That's a good plan, 75. The primary of the OT should be okay, witness B+ on the plate of the 50L6. A short from primary to secondary was not something I considered. Good idea!

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Re: Help!!!

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