madison fielding 440 project.

First place I look for dropped inputs is the selector switch/push buttons... Then recheck anything that was changed or replaced... its easy to put a resistor on the wrong tab...
 
If no joy there, check for voltage in the tuners. If the schematic doesn't tell you what it should be, at least verify the plates of the various tubes all have B+.

got a copy of the schematic to post?
 
If no joy there, check for voltage in the tuners. If the schematic doesn't tell you what it should be, at least verify the plates of the various tubes all have B+.

got a copy of the schematic to post?

I have a paper copy of the schematic, will try to scan and post. I worked over the selection switches again and verified I have voltage at all the related am/fm tubes. When you say “check voltage in the tuners” do you mean to big comb-like capacitors?
 
no, the tubes that make up the tuner section of the unit. If there was a connection problem you'd find one or more tubes in the tuner with no plate voltage, and that would definitely make it not work.

Do you have a tube tester? Do your measured voltages jive reasonably well with the schematic, or does the schematic not give that info?
 
Yes I have tube tester and I guess I will retest all those tubes to be sure. Voltages were about 10% higher than specs called for..
 
Not unreasonable. They're probably higher everywhere. As long as none are completely out to lunch that gives a basic integrity check of all of the stuff between the tube and the power supply. When you get 5 volts someplace that you expect 100, that points to a problem.
 
https://www.dropbox.com/s/h5pb6ecwlpvfhyn/madison fielding 440.pdf?dl=0

finally got the schematic scanned. i probably should get it in the ak database, if I can figure how to do that. I emailed it in, hopefully will get into database. Again, my current issue is looking for things to check to get both the AM and FM working. They are both non responsive. So far, I have double checked the related tubes, rechecked my new cap connections, checked voltages to related tubes, cleaned and re-cleaned selectors switches. AUX works good with iphone music, so at least something is working. ANY THOUGHTS APPRECIATED, I am get cross eyed and confused when trying to fix radio issues.
 
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ok, no movement here.. I am stuck and have read all I can comprehend on the subject of am/fm troubleshooting. Still don't know my way around this subject. I would sure like to enroll in a workshop designed for the non electrical engineer and learn how to trouble shoot and align the am/fm radios on old tube gear. But, I am pretty sure that does not exist.
Can anyone recommend a tech in the Oklahoma Texas area?
 
ok, no movement here.. I am stuck and have read all I can comprehend on the subject of am/fm troubleshooting. Still don't know my way around this subject. I would sure like to enroll in a workshop designed for the non electrical engineer and learn how to trouble shoot and align the am/fm radios on old tube gear. But, I am pretty sure that does not exist.
Can anyone recommend a tech in the Oklahoma Texas area?

I've been wondering the same thing in regards to analog tuners. Who can give me the quick and dirty on how to align and troubleshoot them? I asked one guy who never came through. I'm considering meeting with my local ham radio club to mine that gray matter... I suppose that Murphys law dictates that as soon as I figure it out, the only local station worth listening to will transfer to online only digital format in under a week...
 
What test gear do you have? A lot of the troubleshooting will depend on what you've got to work with.

Alignment you really need a proper generator for. AM is easy, if its not totally out to lunch you can even do it by ear. FM needs a sweep generator or something like an ST1000A or the Sencore 165 if you want to do stereo multiplexer adjustments. There are ways to brute force it with a fixed frequency generator but its not going to work as well as the proper thing.

I actually need to spend some time with my own ST1000a to really learn how it works. Its different enough from the methods I've used in the past with not quite the proper gear that it will be a learning curve.
 
What test gear do you have? A lot of the troubleshooting will depend on what you've got to work with.

Alignment you really need a proper generator for. AM is easy, if its not totally out to lunch you can even do it by ear. FM needs a sweep generator or something like an ST1000A or the Sencore 165 if you want to do stereo multiplexer adjustments. There are ways to brute force it with a fixed frequency generator but its not going to work as well as the proper thing.

I actually need to spend some time with my own ST1000a to really learn how it works. Its different enough from the methods I've used in the past with not quite the proper gear that it will be a learning curve.
gadget - working on a deal for a sencore sg165, once I get it I might be ready to learn the ropes of alignment. I have an oscilliscope, though not too savy on it's use. I also have a tone generator, if that will be of some use. After I get the sencore, I REALLY would like to spend a day or two with someone that knows how to do this stuff, or a workshop put on by an organization like AK. Does AK ever organize workshops? never seen one.
 
ok, for now lets go with no generator troubleshooting. I'll make some assumptions here, but if the assumptions are wrong please feel free to correct

1) the amplifier itself works fine with external inputs
2) all tubes have been tested good
3) all tubes and tube sockets have been cleaned
3a) nothing has been cleaned with steel wool, bits of that stuck in the tuning fins will cause all manner of headaches
4) all tuner voltages have been confirmed in spec, schematic value +/- 15%

The last one is really important since the only part both tuners share is the power supply. They both run off the EZ80, and it looks like nothing else does so problems there will definitely kill the tuners.

If all that jives, lets start with checking the oscillator. You'll need a portable radio that you can get fairly near the reciever. Tube oscillators are pretty hot so it shouldn't need to be stuffed inside the unit, but it will need to be next to it.

On AM, set the M-F to 1000
On the portable radio, you should hear a whistle if you tune it around 1455 kc, and the whistle should move if you move the dial on the MF.


On FM, set the M-F to 90
On the portable, you should hear the white noise blank out around 100.7, and the point where it blanks out should move with the MF dial
if no joy, try reversing those numbers. Depends if its a high side oscillator or a low side. Most of them are high side, meaning the oscillator runs at a higher frequency than the station you're tuning in.


If the oscillators aren't working, none of the rest will either so may as well check that first.
 
gadget - GREAT info.. trying now to find a simple portable AM/FM radio. I guess I threw them all out years ago. Your assumptions are correct, I did all 1-4 items you list. I will say the tuning fins and the entire tuning capacitors were crazy dirty from smoke tar and dirt. I scrubbed them liberally with various cleaners and then faberlubed the rotating connections. As soon as my portable gets here I will follow your directions and report back. Also, ordered a VTVM as I have been reading how that can be used at some point. Thanks for helping the helpless!
 
Mouser site is a little tricky til you try it a few times... Its actually very easy and user friendly, once you get used to it,,,
Film cap will be good to replace the paper/wax ones (8uF and 25 uF will be electrolytic) in your list... Go to passive components>capacitors>film> then put in your values and voltage...
Or just order a paper catalog. They're issuing them again and they are free. Just call them.
 
Most of the time a digital voltmeter will stand in for a VTVM without any fuss. I do own one and once in a while I actually make use of it but mostly only when I need to adjust something to a peak or a null.
 
2350B7AA-EC16-4F70-8F23-A8EF660FEE41.jpeg Gadget
Finally got my hands on a cheapo portable and do the test, am and fm oscillators are confirmed as working. Also double checked voltages on rectifier tubes and all is well. I did receive my DTVM but it will need a rebuild, ancient battery within spilled acid everywhere. But I do have dvm of course and a friend gave me this pretty new audio generator.
 
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Neither of the eye tubes move. They stay about half engaged.

I rechecked rectifier tubes today, not the tuner section tubes , but they were fine a week ago.... that is if I am checking them correctly.
 
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