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Help Reading Schematic on My Old Sony AM/FM Mono Radio (Leaked Battery Acid

Bluejets

Oct 5, 2014
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The second problem has been bugging me for over 10 years. The west side of my home does not get clear AM due to nearby factory(loud annoying buzz/hum). Read somewhere that I can filter the guilty frequency out. Last question I have is there a way to cheaply find this offending frequency and filter it out?

You may likely need access to their machinery which would hardly seem worth while.
Noise is usually suppressed at the source.
You could of course approach any government body who might investigate any "unlawful" rf noise.
 

whiteoutage

Jul 20, 2017
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You may likely need access to their machinery which would hardly seem worth while.
Noise is usually suppressed at the source.
You could of course approach any government body who might investigate any "unlawful" rf noise.

I like approaching gout. idea. - on my to do list , great suggestion - thanks again and again!
Any thoughts on re-claiming lost AM bandwidth?

Regarding the switch being more difficult due to suspected battery corrosion, here is a quote from Ian M of the EEVblog on repairing said switch:
"CAUTION: If this is the first time you're attempting to take a switch apart to service it I'd give better than even odds on you making it worse!

If that's the type with two open ends, it should be possible to desolder it and bend the sides out slightly to free the Paxolin base plate. You'll find two contacts in recesses in the bottom of the slide actuator, which will probably drop out of their slots, and may even stay on the fixed contacts staked through the baseplate. Beware of the spring detent mechanism jumping out - there may be a tiny ball bearing with a spring behind it in a hole in the side of the actuator.

Nothing can be done to service the contacts other than carefully cleaning them and possibly squeezing the moving contacts slightly if wear has made them too loose on the fixed contacts. The inside of the shell can be cleaned with a mild abrasive to remove corrosion.
Use PTFE dry lube on the inside of the shell and a trace of plastic compatible non-silicone dielectric grease on the contacts and detent mechanism. Reassemble carefully, checking the baseplate is fully seated and the slider slides, before nipping up the sides to retain the baseplate."

Pretty sweet advice. I will attempt it after I locate a working replacement - just in case.
 
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73's de Edd

Aug 21, 2015
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Sir whiteoutage . . . . .

" locate a working replacement "
THAT'S gotta be categorized as . . . . . a rats anal orfice chance in Hades !

Instead, don't "muck" with disassembling the switch(es) just RE-ADD some oil to their mechanically moving / sliding portions . . . .which your cleaner dissolved and BLEW AWAY / RAN OFF during the "cleaning " of its switch contact portions.

NOW, your no AM working situation , I would solely attribute to having / leaving/ placing the MEMORY switch in its ON position, if you have the main AM-FM band switch placed in its AM position. Move the FM MEMORY switch in its OFF position and the AM portion should then work. Detailed explanation to follow on another post.


Also the lost tuning range . . . in order to get that chassis to pull out and manipulate around in doing your initial repairs . . . . . I would attribute to your having had to unravel the linear dial scales dial cord from its large round pulley and the two smaller brass direction changing idler pulley, the dial pointer, and another medium size pulley ( not viewable here/this side) on the center of chassis main tuning condenser.
You then probably didn't get it replaced back correctly.
upload_2022-3-2_9-15-46.png
Notice this RED circled point is where one dial cords end comes into the pulley, for either a tie down or its connection to a tensioning spring..
There may be the other cord end at the bottom end of the RED circle area and not visible with this photo shot.
Or there might be another slot. BUT I believe that if you will watch the cords ends either feeding into or coming out of a / this / their slots.
As you watch, and slowly turn the tuning knob, that the point where they stop is where a slot lines up directly with the companion medium pulley on the center chassis main tuning condenser. Thus,you can then see that there needs to be another 1/2 wrap around of dial cord on one of the two pulleys in order for that stalled pulley to be able to rotate further.

Yet another fault can be the installation of the dial cord in the wrong direction around one pulley.
You know this by the stations reversing on the ends of the dial scale.
Another fault can be at the tuning knobs shaft with its dial cord wrap arounds, with a mis direction causing the dial pointer to move to the right, while the tuning knob is rotated to the right.
Both, dial pointer and tuning knob should move in the same direction.

A REINSTATEMENT OF YOUR ALREADY POSTED PHOTO FOR ITS POINTS OF INTEREST . . . .

img_3354a-jpg.54403


  • The large amber colored dial cords pulley at the bottom of picture and at very center chassis is the main tuning condenser and its intermediate pulley.
  • Running vertically along the right side of the chassis . . . . .the black Ferrite rod antenna used for AM reception, with its coil at its top.
That is what is going to permit you to ZERO in on your AM bands interference source

  • Chassis very top right corner is the "MEMORY" tuner condenser area and its round blue FM dial and just below its metal shielding, is the SCHADOW type of switch being used for S2 MEMORY ON-OFF .
An info fulfilling write up is to follow later . . . .with cartouche, hieroglyphs, UNITIZED schematic and cartoons !

For now, THAAAAAAAAAAAASSIT.

73's de Edd . . . . .

upload_2022-3-2_10-26-23.png
.
 
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whiteoutage

Jul 20, 2017
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Great stuff Ed, unfortunately I won't be able to delve into until this weekend - thank you!!!!!
 

whiteoutage

Jul 20, 2017
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Currently radio is in my car and I blissfully have been using it as intended, but will this weekend attempt restringing it. I do receive my two primary AM channels though it will be a most special treat to see what else I am missing!

Couldn't sleep. Offhand, I don't remember if AM tuning pointer turns in same direction as dial does. Don't know, but possibly someone else may have had a go at fixing this radio, and messed with the line cord. Fortunately string does not have to be removed on this radio to do circuit board repairs, I think, as the board is separate from the string and the string just attaches to the front chasis of radio? Since the channels are backwards (ie. my AM 620 is now 1700) I am guessing based on my interpretation of your analysis that someone put string "in the wrong direction around one pulley". But could that also account for losing 1/3 of its range? If not, maybe someone also cut out or lost some of the cord's length? Again, I am really clueless.
 
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whiteoutage

Jul 20, 2017
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Pointer does turn in same direction as knob or clockwise dial movement corresponds to pointer moving to the right. Attached is photo of entire string movement- it is taunt and moves freely. Hope you can see it - I now have limited photo editing capability since my computer just died.
 

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whiteoutage

Jul 20, 2017
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My personal computer is back on line - needs a refresh to start new again.

Back to the problem child. No clue why the AM radio channels are on wrong end of dial and why missing a large chunk of the AM band. Maybe someone else did attempt restringing because maybe it broke, and maybe strung it in reverse? Lots of maybes - eBay has a service manual but cost more than this radio is worth. Can someone smarter than me reverse engineer this string?
 
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whiteoutage

Jul 20, 2017
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No clue why the AM radio channels are on wrong end of dial and why missing a large chunk of the AM band. Maybe someone else did attempt restringing because maybe it broke, and maybe strung it in reverse? Lots of maybes - eBay has a service manual but cost more than this radio is worth. Can someone smarter than me reverse engineer this string?

Stroke of Luck! eBay seller was nice enough to provide some eye candy preview pics of Sony's Service Manual, one of which is the dial cord stringing procedure. From what I've read on eBay's picture copyright laws, I can share the picture but only if it links directly to the listing. So here it is: https://www.ebay.com/itm/144139858198?hash=item218f67b116:g:940AAOSwK7hhCscE
Not sure if conforms to eBay's photo laws, but I downloaded it to my PC and blew it up just enough so most of it is legible. I personally may have violated some laws by manipulating photo on my PC but, for sure have not subjected EP to any violations since above ebay link has not been altered. Also not sure, but there may be a page 2 of stringing procedure. Still, this is a sweet find.

UPDATE: Think I have an answer! Examination of the cords' knots tied and crimped appear to be factory done, or at least done professionally, BUT, based on the Manual, the stringing was done in reverse (strung clockwise, instead of counterclockwise!). As Ed proclaimed, reversal is the reason my channel is on wrong end of dial, and also for missing channels since an incorrect clockwise threading yields less string/travel. Ed, you were of course right about everything all along! Thanks also to BlueJets for schematic reading, soldering guidance, plus advice on reporting illegal radio interference.
UPDATE: I should be able to handle it from here but any advice would be appreciated on line replacement (ie., is fine fishing line ok as a replacement wire, and any other problems I may encounter while restringing)?
 
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whiteoutage

Jul 20, 2017
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Think I have an answer! Examination of the cords' knots tied and crimped appear to be factory done, or at least done professionally, BUT, based on the Manual, the stringing was done in reverse (strung clockwise, instead of counterclockwise!). As Ed proclaimed, reversal is the reason my channel is on wrong end of dial, and also for missing channels since an incorrect clockwise threading yields less string/travel.

I just renamed this thread "Comedy of Errors". What a joke I am.:(
Closer inspection of the large pulley wheel reveals proper winding - cord is actually wound in correct counterclockwise fashion, and I suspect wiring to be all original. So back to square one again, as usual for me. Now I am back to guessing again which is dangerous.
1.Last illustration in manual shows what is called a "dial drum holder" that fits inside the large pulley, aka the "dial drum". Maybe it got rotated a half turn somehow - though I am sure I never rotated it and am doubting if anyone else ever ventured inside here before.
2.Maybe the line is slipping, though my slip test was inconclusive?

Anyone know wtf is going on here?

UPDATE: AND FINALLY! AM is Golden (full range and not backwards). So while I did not move the dial drum holder, I did turn the exterior dial/drum while it was separated(taken apart) from the drum holder that is on the circuit board. Then when I put it back together the dial drum holder was not aligned with the dial drum so there was tuning slack(slippage) on either end of dial until holder caught on to drum. Ed, probably called this one too, but I am just too dense. Afraid to count all the user errors in this one simple thread - Oh well, carry on.
 
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whiteoutage

Jul 20, 2017
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even though I do receive my primary channel 620AM, it will be a most special treat to see what else I am missing!

Just went through AM's entire band using my headphones. Even on the bad end of my home with factory noise, I am amazed at the sheer number of channels. Maybe all this misery I put on myself was actually worth it.:D

Question: Do you think it would harm the radio to power it from a 18650 3.8V battery when it normally takes two D size @ 3V?
 
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73's de Edd

Aug 21, 2015
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Sir whiteoutage . . . . .

Can someone smarter than me reverse engineer this string?

Why "soitanly ! " . . . . but its now only being possible, with the aid of that photo of that . . . . actual SUNNY, dial cord drive mechanism.

Now, indeed, that SONYs viewed mechanical structuring, is certainly looking to be service friendly.
Usually on all other units . . . . . you need the dial cord to be loosened and set aside, to be able to pull the chassis and repair it and then figure out how to restring the dial cord . . . . . . BACK IN THE SAME MANNER. .
BUT, at least, it is ALREADY being of the proper length, with just the proper routing needed to be figured out.

NOW, The real clincher is that the central main tuning condenser seems to be snap-coupled into the LARGE pulley.
Now you did not show that aspect with another picture, but we might suspect that is going to be by the coupling between
them by a clip in bar that engages into the two GREEN clips, as is being marked in with the two GREEN rectangles..
So there could potentially be a 180 degree error in the clipping in of the two parts together.

DIAL CORD STRINGING's DRAW UP . . . . .
upload_2022-3-6_0-23-3.png


My draw up has REPLICATED RED dial cord paths . . . . but those are being spaced outwards a bit, so as to not block viewing of the original dial cord path from being additionally viewed..

In viewing the long linear dial scale we are seeing that both bands lowest frequencies are being at the left side of the scale.
CHECKS . . . .
In your minds eye, rotate the tuning knob clockwise and then visualize that cord is fed to the right on its rotation. Then, naturally the dial pointer, now at the mid scale point, is ALSO moving down towards the
lower frequencies.
CONFIRMED . . . . . . that the dial stringing is being correct . . . .up to this point.
NEXT . . . . use the tuning knob to run from one extreme end of the dial scale, and then back to the other extreme.
If all is in order and no stopping / lock down of the dial cord and pointer indicator, all is in order.
It is now just a matter of seeing what is not correct in your mechanically mating together the large off white pulley and its " mechanical coupling mate " on the center of the chassis variable tuning capacitor.
Looks like the dial cord also "drags" across a plastic support pillars groove. at left side routing up from second small idler pulley and then at mid span over to the incoming wrap into the LARGE pulley and its terminating tensioning spring.

TEST . . .
Grip that tuning condensers " mechanical coupling member " and then do duly note that it should be able to make a full 180 degrees rotation between its two extremes.
THE MYSTERY SITUATION . . . .
In ye olden tymes . . .tuning condensers had two sets if alum-i-ninny-yum-yum finned vanes that intermeshed and had insulated air spacing between alternate surfacing fins.
You could then see fully meshed fins that would be maximum capacitance in order to tune to the LOW frequency ends stations or totally unmeshed fins / vanes that would be at the extreme other HIGH frequency end of the dial.
NOT SO, on your mini sized tuning capacitor . . . . it uses mini sized vanes with thin poly sheet spacers between each set of vanes .
Thereby, no chance of bent / shorting fins . . . . . plus higher capacitance in small packaging by using poly as the dielectric insulator medium, vice air.
DISADVANTAGE . . . . .typically, you can't readily view the meshed / un meshed fins / vanes mechanical state.
Its quite glaring . . . on the olde cap styles.

This is all leading into your need now to couple the tuning condenser (? bar / rod ?).
Hopefully you might now expect to run the dial scale pointer to one extreme end ( say the low freq end) and rotate the tuning condensers (? bar / rod ?) to its PROPER maximum capacitance end setting .
Then you mate the two together . . . . .expecting the two to then snap together !
Then expect tuning to work properly, with proper, full unhindered tuning range.

OR if you made an incorrect extreme positioning of the tuning condenser , expect a limited tuning range, such as you WERE experiencing .

YET another LIKELY SCENARIO . . . . . was if you had the dial scale . . . . NOT . . . .at and end position and then just slapped the two parts together. With the bar then just being haphazardly engaged, to either side of either clip after some degree of rotation. This condition then would be giving you only partial coverage before binding up and stopping, as well as its mis- calibration to stations.

BUT NOW . . . .you apparently have stumbled . . .and that's being heav-eeeeeeeeeee on the STUMBLED aspect . . . back into the units correct re-assemblage.

YE OLDE TYMES . . . . . VIEWABLE TUNING CONDENSER . . . . VERSUS . . . . .NEW UNITS

upload_2022-3-6_0-24-11.png
THAAAAAAAAAAAAAAASIT !

73's de Edd . . . . .

upload_2022-3-6_0-26-24.png
.
 
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whiteoutage

Jul 20, 2017
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Sir whiteoutage . . . . .

Can someone smarter than me reverse engineer this string?

Why "soitanly ! " ......
........
NOW, The real clincher is that the central main tuning condenser seems to be snap-coupled into the LARGE pulley.

YET another LIKELY SCENARIO . . . . . was if you had the dial scale . . . . NOT . . . .at and end position and then just slapped the two parts together. With the bar then just being haphazardly engaged, to either side of either clip after some degree of rotation. This condition then would be giving you only partial coverage before binding up and stopping, as well as its mis- calibration to stations.

YE OLDE TYMES . . . . . VIEWABLE TUNING CONDENSER . . . . VERSUS . . . . .NEW UNITS

View attachment 54481
.

Fascinating! I once saw one of the old style condenser's by itself and wondered what the heck this cool looking precision moving device was used for - now I know. Just as this knob had no clue to the new style either - so did not understand the importance of condenser's dial having to be fitted/aligned into "the slot" of the big pulley, rather than just "slap happying" the two together(which accounted for the loss of bandwidth (from string turning at both ends but not turning condenser dial until engaged with slot)).

One very, very tiny correction - if you follow the eBay link that unfortunately will expire after manual is sold, you will see that there are three turns around the upper left pulley. I did confirm three turns when I looked at my pulley on the weekend. Everything else on your drawing is spot on.

Affectionately quoting my friend:
THAAAAAAAAAAAAAAASIT !
 
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