Help!!!

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Re: Help!!!

Post by 35Z5 on Thu Jun 26, 2014 10:06 am

75X11 wrote:If that is an x1 scale, it looks like 25 ohms to me. I'll defer to Warco as it will keep the number of cooks to a minimum.

Jump in the water's fine... Laughing 

Problem with the analogue pict is we don't know what scale is being used(this is important, without basic info it'd be like putting $20 worth of gas in your car while blindfolded)... We need to know meter setting, something higher will give more meter deflection making it easier to read...

I probably confused the issue on the resistance scales of the digital, generally these days they are 200, 2K, 20K, 200K, etc... Use the scale that's closest matches the value of resistor you're measuring... For 1500 you'd use 2K or maybe 20K, moving to a higher scale if there is no reading(meaning resistor is at least 2000 which is bad, no need to move beyond 20K if a 1.5 K resistor isn't giving a reading, it's history)... On the 2K scale, 2000 ohms is highest meter will read, 20,000 ohms for 20K etc...


Tom
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Re: Help!!!

Post by 75X11 on Thu Jun 26, 2014 10:20 am

The analog meters Are relatively safe for resistance readings for beginners, but are less forgiving on voltage measurements for the unfamiliar. I have seen too many meters get their needles well bent from reversed polarities or voltage measurements in the wrong scale. It looks like Frank is getting plenty of practical experience with his meters. It also makes a nice saga everyone can follow.
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Re: Help!!!

Post by Wildcat445 on Thu Jun 26, 2014 10:43 am

Frank, what progress have you made with your radio?

WC

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Re: Help!!!

Post by frank1956 on Thu Jun 26, 2014 12:45 pm

I have two meter one digital the other analog. The digital has the following scales for ohm reading 2000K,200K,20K, 2000 and 200. The analog has the following X1K, X100 an X10. The pic I posted was with the analog at X1K.

No progress has been made with the radio, maybe I need to change out the on/off switch, but can't figure how to get it off. Pic attached. As you can tell by the scratches I have made several attempts to remove it. Is there a special tool I need or just a little bit of elbow grease?

Again thanks for everyones help. I know it is probably frustration for you not having the radio right there for you to see and touch.

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Re: Help!!!

Post by 75X11 on Thu Jun 26, 2014 1:34 pm

That would make the reading shown in your picture 25K ohms. I wouldn't worry too much about the on/off volume control just yet. Let WC and 35Z5 offer some more advice. It is tempting to try a number of things at once, but that can get you too far astray.
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Re: Help!!!

Post by 35Z5 on Thu Jun 26, 2014 2:29 pm

frank1956 wrote:
No progress has been made with the radio, maybe I need to change out the on/off switch, but can't figure how to get it off. Pic attached. As you can tell by the scratches I have made several attempts to remove it. Is there a special tool I need or just a little bit of elbow grease?

Deep well 3/8" drive socket(should be 1/2" or maybe 9/16")... Six point if it's really tough, though a 12 should do the job...


BUT if switch is turning on then it has nothing to do with voltage readings, something else is wrong... Every time a change is made there is a chance for error
...
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Re: Help!!!

Post by Wildcat445 on Thu Jun 26, 2014 2:44 pm

I'm confused. What did you measure that is 25K ohms, according to the analog meter? Why do you need to change the switch?

Not to be abrupt here, but if there is not a disciplined troubleshooting procedure employed fairly soon, both the OP and those trying to help will be so confused nothing is going to work. Just taking haphazard stabs in the dark to see what sticks is not going to get us anywhere but frustrated.

Please, do this. Plug the radio in and turn it on. With your voltmeter set on DC volts, place the black (-) probe on one terminal of the on-off switch, and the red probe (+) on pin 7 of the 35W4 rectifier. Verify that the 35W4 is in its correct socket. You should have 125 volts DC, give or take, on that pin. What does this read? Let's do this a step at a time.

WC


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Re: Help!!!

Post by frank1956 on Thu Jun 26, 2014 4:57 pm

The switch was brought up in previous post. When I mess with it it seem to make the statics worth, was just throwing it out there as it was suggested to change it out. The reading for DC volt on 35W4 is between 133-134 on the 7th pin. The 35W4 is in the correct socket.
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Re: Help!!!

Post by Wildcat445 on Thu Jun 26, 2014 5:28 pm

Okay.  That is close enough for now.  Forget about the switch for now.  We know that the rectifier is in the proper socket, there is AC to it, so the switch is working and there is DC out of the rectifier.  Your reading is a tad higher than specified, but that could be due to variations in line voltage.  Next, please re-check the wiring of both filter capacitors to make absolutely sure they are wired correctly.  The negatives should go to one side of the power switch (B-).  If they are wired correctly, with your meter set to measure DC voltage, leave the black(-) lead of your meter on the power switch and put the red lead (+) on pin 4 of the 50L6, which is the screen.  There should be 94 volts DC, give or take on this pin.  What does this read?  I have to leave just now, and will be home later.  It may be morning before I can read your response.  We are taking this pin by pin thru the radio.  This will be a disciplined approach and will involve known successful diagnostic procedures.  You are doing great so far.  This baby will be playing before you know it.  

WC

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Re: Help!!!

Post by frank1956 on Thu Jun 26, 2014 8:14 pm

The wiring on the filter capacitors are correct, the neg is attached to one side of the power switch (B-). The DC voltage for pin 4 on tube 5OL6 is between 113-114. Thanks again.
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Re: Help!!!

Post by 35Z5 on Thu Jun 26, 2014 9:41 pm

WC has the correct method and from here he can run the show, but I want to post this so maybe you'll get the idea of how voltages are distributed through the set and better understand why you get a particular voltage reading... I left out 50L6 cathode voltage(Pin #8 ), and a couple other items, these are the basics that must be there or it probably isn't going to operate... Likely none of these will help isolate the constant crackle you mentioned but again must be there or the set isn't going to operate...

It's a little crude but should help...

Good Luck

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Re: Help!!!

Post by frank1956 on Thu Jun 26, 2014 10:28 pm

Thanks 35Z5
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Re: Help!!!

Post by Wildcat445 on Fri Jun 27, 2014 8:56 am

Thanks for the diagram, Tom. We both need to guide Frank thru his radio. I would appreciate your help here as well. We work together on TRF. i am going to need your help before this is over. You are well-experienced and we need all the help we can get.

Frank, the screen voltage is high. This may your first indication of trouble. Before we jump to conclusions, we need to follow the other branch of B+ and see what we find there.

Again, with the radio plugged in and turned on, with your meter set to measure DC volts on the 150 volts scale, with the black (-) probe of your meter on one terminal of the power switch, place the red probe (+) on pin 3 of the 50L6 audio output tube. This is the plate. There should be 117 volts DC, give or take, on this pin. Do this and let us know what you found. You are doing just fine. You have just found a potential area of concern. We are getting warmer.

WC


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Re: Help!!!

Post by frank1956 on Fri Jun 27, 2014 9:33 am

WC my meter does not have 150 volt scale the next best thing is 200. The DC Volts on pin 3 tube 50L6 is between 123-124
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Re: Help!!!

Post by 35Z5 on Fri Jun 27, 2014 4:10 pm

OK the next thing would be to check pin 8 of the 50L6 to see if it actually drawing current... With set on measure that pin, should be a small voltage in the range of 5-7 volts, use 20v scale...
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Re: Help!!!

Post by frank1956 on Fri Jun 27, 2014 7:22 pm

Pin 8 on 50L6 is between 7.4-7.5 volts.
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Re: Help!!!

Post by 35Z5 on Fri Jun 27, 2014 9:10 pm

frank1956 wrote:Pin 8 on 50L6 is between 7.4-7.5 volts.

OK that's good, but Pin 4 is approx 20v high, either something is wired incorrectly or the 1.5K ohm resistor is low in value... From it's looks it appears OK and usually on a film resistor it's good or open, don't often change value... With the set disconnected measure R9 again, use 2K ohms setting... If you get significantly less than 1.5K, disconnect one of it's ends and measure resistor again... If it's now OK, take a pict of the general 35W4 & 50L6 area so we can determine if it's wired correctly...

A high voltage won't keep it from operating but something isn't correct... On my schematic, voltage should be approx 20v less on the blue/green end (vs yellow)of R9, which is same point as pin 4 of 50L6...


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Re: Help!!!

Post by frank1956 on Fri Jun 27, 2014 10:09 pm

Tom,
Neither of my meters have 2K ohm setting. I used the analog with 1X ohm setting. Pic's attached with reading and pic's of 35W4 & 50L6.





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Re: Help!!!

Post by 35Z5 on Fri Jun 27, 2014 10:33 pm

Rx1 means you have a 25 ohm reading, you're 1475 short... I assume the red wire snaking in from the right connects to pin 4 of 50L6? The green wire to filter cap and no other wires on pin 4? If that's the case disconnect R9 and measure it...

Post picts of meter selectors so we'll understand what you have...
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Re: Help!!!

Post by frank1956 on Sat Jun 28, 2014 8:21 am

Tom,
Attached are pic's of the R9 disconnect with reading. Also a pic's of the entire underside of chassis. The meter selection pic's is kind of hard to see the, but it is set on x1k setting.



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Re: Help!!!

Post by Wildcat445 on Sat Jun 28, 2014 9:06 am

I have a house full of people this weekend.  I appreciate Tom taking over to help out.  Frank, looks like you have made progress.  The voltage on the plate, if I read correctly, is 123 volts.  We have voltage on the screen.  Both the screen and plate voltages are a tad high.  But, please remember, it was high at the rectifier cathode as well.  This tells me that the power cord, switch, R10, rectifier, both filter caps and the primary of the output transformer are probably okay.  The resistance on R9 checks somewhat strange, but it is not enough to kill B+ to the 50L6.  Now turn off the radio, unplug the power cord, with your meter set for ohms on the RX1 or lowest scale, then measure resistance on the secondary winding of the output transformer?  This will be the two wires going to the speaker.  You will need to lift one wire off the speaker to make this measurement.  You should see from 3 to 8 ohms.  Then measure similarly the voice coil of the speaker.  Same resistance as the output transformer secondary.  If this checks out, we will have cleared any suspicion of trouble in the power supply and audio stages in this radio.  Hang in there, Frank, and thank you Tom, for co-directing Frank's efforts.

WC

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Re: Help!!!

Post by 35Z5 on Sat Jun 28, 2014 9:57 am

The resistor you are measuring is across the osc coil and is on  totally wrong end of set, no wonder you're getting a 25 ohm reading...

R9 is the brown, green red resistor connected between pin 6 & 4 of 50L6...

Before we go much farther you at least need to get a resistor color code chart for reference, plenty of them out there on the net for D/L...
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Re: Help!!!

Post by Wildcat445 on Sat Jun 28, 2014 10:14 am

I missed that picture, Tom.  I had not seen it until you posted.  I think if we get the secondary of the output transformer and the speaker checked out, we can do the "center terminal of the VC buzz test" and then get to the front end of the set.  We need to finish that up before we get too far off course again.  It looks like we may have an issue in the front end anyway.

Frank, read this, as it may help you:

http://www.tuberadioforum.com/t2953-radio-repair-safety

WC

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Re: Help!!!

Post by 35Z5 on Sat Jun 28, 2014 11:06 am

Voltage is close on plate of 50L6 but high on screen, we were trying to find out if R9 is the reason for the high screen voltage or maybe a wiring issue, at any rate R9 apparently isn't dropping voltage...I doubt there is a problem with the OPT...
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Re: Help!!!

Post by frank1956 on Sat Jun 28, 2014 12:50 pm

My apologies, not sure what I was looking at  confused I am back on track and have updated the pic's to correspond to R9.

WC thanks for the link, will come in very handy!!!!




Last edited by frank1956 on Sat Jun 28, 2014 1:01 pm; edited 1 time in total
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Re: Help!!!

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