Author Topic: Zenith 5S-127  (Read 3311 times)

electra225

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Re: Zenith 5S-127
« Reply #15 on: September 14, 2018, 04:32:30 PM »
I really believe I am wasting my time working on this thing without changing the resistors.  A problem I'm having is identifying them.  The colors have mostly faded into nothingness.  Thank God for a schematic.  I'm going to change all the resistors and a couple micas in the oscillator circuit.  I kinda/sorta aligned the IF section this afternoon.  Had that part working well until I went in to get a sandwich.  Came back out and nothing would work.  Apparently, I need to clean the volume control and/or tone control.  Fiddling with them restored the output from the signal generator in the radio speaker.  The oscillator should really be working.  If it is out of alignment as much as the IF's were, I can see why it is not working. 
I don't need Google.  My wife says she knows everything.

ed from Baltimore

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Re: Zenith 5S-127
« Reply #16 on: November 08, 2018, 06:44:17 AM »
    I guess a lot of non-working radios you find these days once passed through the hands of someone who knew just enough to be dangerous and turned all the adjustments--and left them turned--- as if that's why a working radio suddenly stopped working---all the adjustments drifted several turns out  of alignment. Then it's advertised for sale "as is" implying a bad part or something cuz they're embarrassed  to tell what they did. It's like trying to tune a car that someone changed the plugs on and mixed up the plug wires by mistake, but doesn't tell you that.

electra225

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Re: Zenith 5S-127
« Reply #17 on: November 08, 2018, 09:13:55 PM »
I'm 1400 miles away from this radio right now, which may be good.  I'm going to regroup in the spring and change the resistors and take it from there. 
I don't need Google.  My wife says she knows everything.

hermitcrab

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Re: Zenith 5S-127
« Reply #18 on: December 01, 2018, 04:19:42 PM »
I've got a slightly older tombstone, a 6-S-27 from 1936.  It has  bad interstage audio transformer.  This was a gift from before the internet age so it got put into storage--a "one of these days" radio.  But maybe I should move it up in priority.

Chris Campbell

Chris , I just did a restore on that same model for a friend of mine , I forget is that 6-S-27 the battery set or electric? Like the looks of the curved front on that one.. had to make the dial pointer because his was missing, and the dial was gone ordered a replacement from radiodaze…. turned out nice.
Elton

TC Chris

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Re: Zenith 5S-127
« Reply #19 on: December 01, 2018, 04:46:57 PM »
Mine is in storage in Bay City.  I just looked up the schematic on Nostalgia Air and it shows AC power, but also no interstage audio transformer.  My recollection was that it was a battery set and I'm quite sure that I diagnosed the faulty transformer. Either my mind is frail (OK, yeah) or I wrote the number down wrong.

Chris Campbell 

hermitcrab

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Re: Zenith 5S-127
« Reply #20 on: December 01, 2018, 04:52:30 PM »
nice thing about the tube sets is you could throw just about anything in as long as the winding resistance was close , I have ordered generic replacements from antique radio supply , they worked fine ...
Elton

TC Chris

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Re: Zenith 5S-127
« Reply #21 on: December 01, 2018, 11:16:03 PM »
I acquired my Zenith before we had the internet.  In those days, you found a large paper catalog from one of the electronics-parts houses and searched for an appropriate part.  Or in Michigan, placed an ad in the MARC publication and hoped somebody had a parts set.  But there was a lot of sending envelopes back and forth.  So it got put in line for a some-day focus.  Then I moved, and it went into storage, and I bought what I called "the small house with the large price" and it has stayed in storage. 

I would vote for adding about 4 extra hours onto each day, and making it illegal to force anybody to work (at a job for pay) during them.  Then I could get caught up.

Chris Campbell

electra225

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Re: Zenith 5S-127
« Reply #22 on: February 10, 2019, 09:35:21 AM »
The rubber washers on the tuner for this radio has turned to goo and have disappeared years ago.  I read on another forum how, if these washers are not good, the oscillator section of the tuning cap can be shorted out, killing the radio.  I was not intending to replace this stuff until I got the radio working.  I may need to rethink that plan at this point.  Since I have a dead oscillator and since I need to replace this stuff at some point, I'll fix those grommets and restore the dial drive mechanism.
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Zenith 5S-127
« Reply #23 on: February 10, 2019, 11:56:40 AM »
Call me lazy, but I've always resisted undertaking one of those big tuning-cap disassemblies.  There are so many opportunities to mess other things up.  How about just stuffing paper or cardboard shims under the tuning cap until you see whether there are other issues with the radio. 

Chris Campbell

electra225

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Re: Zenith 5S-127
« Reply #24 on: February 10, 2019, 02:50:27 PM »
We are on the same page here, Chris, no doubt about that.  I avoid tuning caps and oscillators like the plague.  I have also tried the shim/kluge/cuss method and have made zero progress.  Those grommets will need to be replaced sooner or later.  The dial does not line up in the glass and it looks goofy.  The dial drive belt has been replaced with a rubber band and that needs to be put right.  My understanding is that if the grommets are bad, the tuning caps is not only in the wrong spot for the glass, but it can cause the cap to short, killing the oscillator, hence the radio.  Trust me, if there was any other method to line up the dial to the glass and to make this thing work, I'd take it.  I typically don't mess much with Zenith radios.  My wife thought this one was cute, so now I'm committed.
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Zenith 5S-127
« Reply #25 on: February 10, 2019, 08:33:59 PM »
Those grommets will need to be replaced sooner or later.  The dial does not line up in the glass and it looks goofy.  The dial drive belt has been replaced with a rubber band and that needs to be put right.  My understanding is that if the grommets are bad, the tuning caps is not only in the wrong spot for the glass, but it can cause the cap to short, killing the oscillator, hence the radio. 

Thicker cardboard under the cap & some cut-up soda straws or heat-shrink tubing to isolate the studs from the chassis... at least long enough to get it working.  Then if it's an all-star you can dig in to the mechanics.

Chris Campbell

electra225

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Re: Zenith 5S-127
« Reply #26 on: April 29, 2019, 05:32:23 PM »
Okay, all you Zenith gurus, I need you to bail me out on this one, I guess.  I'm beating my head against a stump with this one.   :-[ :-[

I went back over my previous work.  I found a couple of .05@200 volt caps I had not changed, since I had run out of that value.  I changed those, with no change in operation.  I rechecked the oscillator coil, and, by all I can tell, is okay.  I can get a signal all the way thru the set from the antenna terminal to the speaker, so that just shows the antenna coil and the IF transformers are okay.  There is actually a small positive voltage on the oscillator grid, which should be -1 volt negative, according to the schematic.  I tried to hear the oscillator squeal in another radio, a procedure I've had mixed results with.  I did not hear the oscillator in the other radio, my Hallicrafters SX-110.  There is a 49K resistor connected from the cathode, pin 8 to the grid, pin 5 of the 6A8.  It has drifted to 111K ohms, so it should be replaced.  R3, an 11k ohm resistor measures almost 19K ohms.  B+ for pin 6 of the 6A8 is given as 166 volts, but I'm only getting 140 volts.  R3 feeds B+ to pin 6 of the 6A8.  Pin 6 is the output of the oscillator, so if the voltage was low on it, would that stop the oscillator?  This and the grid of the oscillator are the only two voltages in this chassis that are low.  Others are actually higher than specified.  The schematic specifies 112 line volts and I'm sure mine is some higher than that, although I am powering the chassis on my Variac.  There is a 25pf mica from pin 5 to a trimmer.  I guess I'll replace it just because.  I know I need some new components in certain areas, but I'm trying to troubleshoot the converter section so I'll learn them better.  I'd sure appreciate any suggestion you might have.   :) :)

Oh, and one other point.  When I put the probe of my signal tracer or VTVM on pin 6, the second grid or output, of the 6A8, it would kill the station on my SX-110.  I read somewhere that this was a test of the oscillator, but I forget what the details were.   :-[ :-\
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Zenith 5S-127
« Reply #27 on: April 29, 2019, 07:11:31 PM »
So by changing the load on the oscillator plate, you're making it oscillate so furiously that  it's killing the signal on the other radio?  And if all the other voltages are way too high, but on the oscillator they're too low... so they're probably WAY too low as compared with the other tubes.  Just thinking out loud....
Chris Campbell

electra225

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Re: Zenith 5S-127
« Reply #28 on: April 29, 2019, 09:15:53 PM »
I understand (?!) that voltages and component values are critical in an oscillator circuit.  We have had considerable discussion about the tuning capacitor, so I checked it to make sure it was not shorted, and it appears to be okay.  The tuner is loaded with a spring that brings it back to completely meshed.  That is a pain to mess with, since I don't have any dial or tuner drive on this radio.  As best I can tell, the bandswitch is not a problem.  After I get thru Oscillator 101, I need to take Bandswitch 101.  They are never drawn the same, so I have to study each chassis and its schematic to figure out where I am.  I may have been on the right track to start with.  I'll probably replace all the dogbone resistors in this chassis, and have already replaced all the capacitors. 

The cathode grid capacitor in this chassis is listed as "25 MMFD", so in modern nomenclature that would be 25 pico-farad or 25 pf.  That would be .0025 numerically, would it not?  The mica capacitor is coded red-green-black.  Most I have seen are 100pf or even 250pf.  I need to make sure the 25 pf is not a misprint.
I don't need Google.  My wife says she knows everything.

electra225

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Re: Zenith 5S-127
« Reply #29 on: April 30, 2019, 05:06:24 PM »
It is raining here today, so can't mow or do anything outside.  The wife went shopping and I went to the garage.   ;) ;) :) :)

I started working on my Stromberg-Carlson radio/repopulate chassis project.  I messed up two patterns, so I decided that was enough for today.  I made the same mistake-twice.  I can't seem to get the opening for the pushbuttons straight.  The hole the bezel fits in is not perfectly flat, it has a little bow in it.  I can't get that bow right. 

I started working on connecting everything on the TV chassis in the ST, and did not get the "screen door spring" that grounds the 'dag coating so it makes a capacitor in the high voltage.  Horrible, silly idea, that.  Why not just put a capacitor in the high voltage and not have to use that kluge.  I got everything hooked up and all the bolts back in and realized I had forgotten the spring.  Now it has to come back apart partially to do that.  Another day..... :-[

Okay, how about something simple.  I have some radios probably destined for the parts pile.  I have a bad habit of fixing up my parts sets, then I have no parts.  I have a cute little RCA clock radio, model 1-RD-65 with that odd tube lineup, 18FX6, 18FY6, 34GD5 and 36AM3.  It has a dead oscillator.  I put a new filter cap in it because it hummed.  Now it is just dead.  I believe I'll print the diagram for it and see can I get it going.  I have an Airline AA6 with a "10"" speaker.  It might be ten inches long, but it is only about a couple inches wide.  It, too, hummed, and got new filter caps.  It, too, had a dead oscillator.  It is unusual enough, if it takes too much to get it going, it might be a shelf queen.  I got these radios in a box of junk and had not done anything with them.  I got my little Emerson 522 out and found it played weakly.  It has always been a robust performer.  It was still all original as far as I could tell.  I've had that radio since 1955.  I completely recapped it and found it a little better, but not much.  I found the 12SQ7 audio tube weak, and replacing it restored the volume.  The chassis is still on my radio bench.  I believe I'll do an alignment before I stick the chassis back in the cabinet.  I have a little Heathkit scope I got somewhere.  I had messed with it before and found I could not get a trace on the screen.  So I tinkered with it a bit, and found the probe to be wonky.  I have it partially apart, then I stopped to do a bit of research before I went too far.  I'm not sure it's the right probe, but it says Heathkit on it.  There is a switch that does who-knows-what and that switch is making poor contact.  If I fiddle with it, I can get a trace.  The trace seems pretty dim to me, probably because I don't know how bright it should be.  Maybe it needs tubes or caps or something.  I figured it would be simpler to get running and to operate than my old Tek 532.  Perhaps an operators' manual would answer some of my questions.  Then I started pitching things I saved because I would surely need them someday.  I can actually see the top of my bench now.  I found a Zenith 6-D-511 that has a busted cabinet.  I confirmed that it still worked, so I may fix the cabinet then hot rod it.  It is dull brown bakelite now and busted, so I have little to lose. 
I don't need Google.  My wife says she knows everything.