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

whiteoutage

Jul 20, 2017
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Very unfortunately, I left the batteries in my radio and it's now in need of repair. A smaller circuit board had just a dusting of corrosion. After thoroughly cleaning the small board all channels now come in, but volume is only audible and sound is somewhat distorted (not scratchy, just not quite right). So I peaked under the large circuit board and found significant green corrosion in one smallish area. Some of the traces/pads is this area seam to be missing, however all components test good.
I found the schematic of the radio but don't know how to properly read it. I can use hook-up wire but not sure where to place it.

Here are some current questions hoping for help with:
1. Should the emitters of Q9 & Q10 be connected? (currently there is no continuity)
2. Looks like R41's lead towards the middle of bad area should connect to Q9/Q10 emitters? Currently, that resistor pad is lifted and rocks in place with no continuity to emitters?
3. Other connection concerns in circled area include all 7 components in suspect area. ((2 transistors, 2 resistors, 2 ceramic caps, and the three legs on one side of a connecting transformer). Specifically, what continuity tests should I do - between all these pads?
4. Both the radio's speaker and headphone were working at a low volume, but did not sound the best. Cleaning the green corrosion, and my attempted feeble repair may have changed something so I am reluctant to test radio's sound again for fear of blowing a component(s). The battery compartment is not currently useable so all prior tests were on the AC switch.

I already tried bridging one emitter to suspect resistor but that fell off when I also tried to bridge the two emitters -- so I just removed them both, and back to square one. Plan 2 was to lasso the 2 emitter pins to the lifted resistor pin. But, truthfully I'm an electronics knob, and rather than chasing uneducated hunches, I was really hoping for assistance with a better thought-out overall plan for returning this corroded area back to working correctly again, and hopefully having a nice radio one again.
Thank you in advance!
 

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Bluejets

Oct 5, 2014
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1. Yes, and then to R41
2. as above
3. you started of great with specifics so suggest same for this query.
4. not sure what you need here.......
 

whiteoutage

Jul 20, 2017
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Ok, I will attempt 1&2 and go from there. Thank you.
1. Yes, and then to R41
2. as above
3. you started of great with specifics so suggest same for this query.
4. not sure what you need here.......

Picture of my attempt at joining 2 transistors and 1 resistor. Think it will work, and do you notice any other possible issues?
 

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whiteoutage

Jul 20, 2017
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No comment....:)
OK, so my solder joints don't shine like silver. Considering I use a 40 watt 2 buck special iron and just yesterday that whole area was all just a blue green poison rust mess, I'd say they are not too bad. Though just for the tough internet crowd I did put a shine on two of the possible ones that could of been cold soldered.
Anyhow, radio is now working full blast and sounds great - though mono is still mono. I have been without a car radio for 2 years since I charged the battery overnight, in reverse polarity! Great news is, now I can listen to basketball and NPR in my car - Super Sweet Deal!!!!! The only thing I really did was clean up all the battery acid and corrosion it left, plus make a loop de loop solder bridge. So glad it didn't require any EE smarts or I would have been doomed. Also was very fortunate to find the schematic for free online. Lesson learned though -- before mothballing anything with batteries - TAKE EM OUT FIRST.
Of course, any other comments, suggestions, rebuttals, or thoughts on like recapping an old radio, etc. greatly appreciated - not really interested in show room quality, just good-working.
Lastly, attached is the full schematic of the Sony ICF-7740W radio I forgot to include .

Addendum: Just noticed that the speakers attach to circuit board with jumper wires that are aluminum. I got it to stick but not very well. Do I use a some sort of zinc solder for a good connection?
 

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73's de Edd

Aug 21, 2015
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Sir whiteoutage . . . . .

Why for ?. . . . .you no give us . . .most honnable . . . Sony . . . . units model number, as their OFF-FISH-ULL complete service info may also give a chassis, parts mounted PCB drawing additionally . . . plus the Xstrs and part numbers . . .particularly for the transistors being used.
From what I can make out from supplied pics . . . . . the two output transistors emitters and their shared companion R41 . . .1 ohm emitter resistor. . . . . . . . are having the emitters foil lands being side by side and then you extend the foil path being between them to go out and form a triangle with that 1 ohm resistor being connected, so that the three make a foil triad and the other end of the 1 ohm resistor goes to ground.

So o o o o o o o . . . for a repair, au max simplicity, you can take a single strand of bare copper wire from an end piece of an AC line cord and form a triad / triangle wrap around the two emitter leads and the 1 ohm resistor and solder to make a triple joining.
THEN . . . . I BELIEVE . . . . that your other audio inadequacies will be attributed to aged /atrophy declined E-caps.
The originating detected audio of the radio comes in from the very top, as the faded large black arrow paths, to initially pass into C51 . ..3.3 ufd, then to pass on to C53 . . .3.3 ufd . . . to then get amplified by Q8 to driver transformer T1.

BUT . . . B U T T T T T T T T . . . . that Q8 transistor has to have good bypassing to ground via the C54 secondary filter AND bypass E-capacitor.
Or else, you will have DIMINISHED gain in that stage, to be able to go on and FULLY power drive the Q8 and Q9 power output transistors.

So o o o o o o o . . . get that triad connection made and then you can operationally test the three mentioned E-caps . . .one at a time . . . . for any associated curative affect . . . . by your merely holding the leads of a properly polarity oriented substitute E-cap across each individual one to be tested.
A 4.7 thru 10ufd can sub for those odd value 3.3's . And a 470ufd ( or two) will sub for the full 1000 ufd unit.

An operating listening test will confirm volume increase or audio quality improvement, SINCE a decline of capacitance in the C '51 or '54 can cause a tinny / loss of bass sound discoloration.

FACTOID . . . .Would really like to see the FM portion, as the FM section working on a 3VDC supply, as in that technological time frame, was like walking on water . . .
ADDENDA . . . . after your add on of the schematic in the interim . . . . .less the blocked out 1/2 model and chassis # . . . .figured out.


Know thuts ? . . . . . . Thaaaaaaaassit !

73's de Edd . . . . .

upload_2022-2-26_7-16-18.png


.
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whiteoutage

Jul 20, 2017
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Thanks again Ed,

The transistors in question were both 2SC2001s, and as mentioned all components in suspect area tested good out of circuit. Also after touching up some of my rougher solder joints and cleaning it up again, I decided the damaged area looked good enough to test, and fortunately was correct -still very excited that I fixed the AC side, it sounds so sweet! Model number was mentioned in post #6 along with the basic schematic being freely available on-line. Special thanks for explaining technically what is going on. It is so fascinating - one day I hope to understand.
The last thing I have to do before reassembling it is getting the DC battery side working since portability will be its intended use(though I could use my cheapo inverter to power it in the car, I suppose. This morning I laboriously filed the large battery spring that was very badly rusted, and noticed that the metal connector opposite the spring appears to be missing. Further investigation required?

Update: Love your detailed tip on the quick cap substitution method though turns out I did not need it. Still curious though - is it OK to hold a 1000uF 25V cap in your hand while touching it to a suspected cap, in a live circuit? Also, still curious how to best solder the two aluminum jumper wires that go from board to 8 ohm speaker. Finally, for posterity, I will post pics of the Sony's front and back circuit boards. The radio's outer case is beat to hell so no one want to see that.
 
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whiteoutage

Jul 20, 2017
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For posterity, I will post pics of the Sony's front and back circuit boards. The radio's outer case is beat to hell so no one want to see that.

Glad to report 3V battery DC mode works just as good as AC mode. Still tickled pink I am getting crystal clear radio waves over this beat up old relic.

Front and back side of circuit board pics attached.
 

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Bluejets

Oct 5, 2014
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Bit of an old relic myself but still hear me ok and sharp as a pin....remember radios like those from when I was an apprentice....made my own valve amp set way back then too....Elvis never sounded so good.
Soldering much better though....
 
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whiteoutage

Jul 20, 2017
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Bit of an old relic myself but still hear me ok and sharp as a pin....remember radios like those from when I was an apprentice....made my own valve amp set way back then too....Elvis never sounded so good.
Soldering much better though....

Never been a huge Elvis fan (70s rock was my generation), though we certainly share and appreciate good quality sound. I've said it before and will continue saying that I think it is so wonderful that all you experts come together here and selflessly help all us knobs out. Words can't do justice for how grateful I am for all your time and expertise - thank you all, over and over a million times.

Back to my sorry saga - so I listened to the radio for an hour, no problem on either AC or DC. Just turned it back on to brag to my wife and of course it would not tune a dam thing. Has sound and volume levels work fine. So will try Ed's cap suggestions and go from there.
 
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whiteoutage

Jul 20, 2017
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Back to my sorry saga - so I listened to the radio for an hour, no problem on either AC or DC. Just turned it back on to brag to my wife and of course it would not tune a dam thing. Has sound and volume levels work fine. So will try Ed's cap suggestions and go from there.

Well, she's working fine once again this morning so not sure what to think. Guess, I will just monitor for now.
At least I got a chance to try out a new alternative capacitor test method on all three suspected CAPs - all were good.
Also noticed, as Ed predicted, that DC does not tune channels quite as well, but is pretty close to AC.
 
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73's de Edd

Aug 21, 2015
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Sir whiteoutage . . . . .

is it OK to hold a 1000uF 25V cap in your hand while touching it to a suspected cap

Why shore . . . since its only being at a 3v DC potential from that power supply point.


I don't expect your INTERMITTENT problem to be with those caps, after your confirming no improvement in shunting them . . . .therefore no massive decline in capacitance.
PLUS . . . with this unit using those 2N2001's transistors, you told me of , it is not as old as I was initially expecting it to be.
Does the unit work on AC power, if it works on AC mode of operation, I would be heavier suspect of still having a fault in the connectivity of your battery wiring and connections

On that speaker wiring if being the yellow and black ones to the speaker. My experience would be, is that wire that they are using, is so meager in numbers of wire strands count and has a low quality of tinning that it is HIGHLY prone to heavy surfactal oxidation. Thus, you just might THINK that you are dealing with alum-i-in-ninny-yum-yum wire.
Just round up some, same or greater gauge good stranded wire to replace it with. They DEFINITELY were not specifically using any aluminum wire just for that run !
On the PCB, there just might still be a floating component wire lead with a solder ring around it, causing intermittent connection.
Get the unit in play position with PCB facing up and use a STIFF toothbrush and do fine round rotations to eventually cover all of the surface of the pcb, encompassing a quarter of an inch at each circle.
A loose connection should show up when being coaxed around in a 360 degree circle and thereby make the unit respond, or fail, if the unit was non working / working when you tried this flexing procedure.
Thaaaaaaaassit . . . . .

73's de Edd . . . . .


upload_2022-2-27_8-27-22.png


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whiteoutage

Jul 20, 2017
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Sir whiteoutage . . . . .

is it OK to hold a 1000uF 25V cap in your hand while touching it to a suspected cap

Why shore . . . since its only being at a 3v DC potential from that power supply point.


I don't expect your INTERMITTENT problem to be with those caps, after your confirming no improvement in shunting them . . . .therefore no massive decline in capacitance.
PLUS . . . with this unit using those 2N2001's transistors, you told me of , it is not as old as I was initially expecting it to be.
Does the unit work on AC power, if it works on AC mode of operation, I would be heavier suspect of still having a fault in the connectivity of your battery wiring and connections

On that speaker wiring if being the yellow and black ones to the speaker. My experience would be, is that wire that they are using, is so meager in numbers of wire strands count and has a low quality of tinning that it is HIGHLY prone to heavy surfactal oxidation. Thus, you just might THINK that you are dealing with alum-i-in-ninny-yum-yum wire
Just round up some, same or greater gauge good stranded wire to replace it with. They DEFINITELY were not specifically using any aluminum wire just for that run !
On the PCB, there just might still be a floating component wire lead with a solder ring around it, causing intermittent connection.
Get the unit in play position with PCB facing up and use a STIFF toothbrush and do fine round rotations to eventually cover all of the surface of the pcb, encompassing a quarter of an inch at each circle.
A loose connection should show up when being coaxed around in a 360 degree circle and thereby make the unit respond, or fail, if the unit was non working / working when you tried this flexing procedure.
Thaaaaaaaassit . . . . .

73's de Edd . . . . .


View attachment 54414


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Your diagnosis is spot on correct again, and thank you for answering aluminum and cap checking questions. :)

Problems were of course user errors, double doh again.)-:
Battery in one instance and mode error in second. Battery was simple contact issue.
This radio has a feature called FM Memory Station and it was inadvertently selected - when selected, outputs static only. Not sure what this feature is. Another feature, maybe related to it, is tuning channels (the previous picture shows the blue dial that I use to find channels. But, there is also a large dial in front that controls finer channel movement to a larger display. Oddly, it does not tune or find and channels, whatever channel is currently selected from blue dial stays put. Also it only has about 66% range (starts on 93.8FM left side goes to end of right side, or 108FM.
Since my radio is working great, I am more curious as to what functions are rather than trying to fix em, especially if it requires special equipment/expertise. Plus I feel I have already taken up too much of everyone's valuable time.
 
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whiteoutage

Jul 20, 2017
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Noticed nothing happens when i switch from AM to FM - just stays on current FM band. Physical switch does slide - will clean contacts tomorrow and hope that gets me AM.
 
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whiteoutage

Jul 20, 2017
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Noticed nothing happens when i switch from AM to FM - just stays on current FM band. Physical switch does slide - will clean contacts tomorrow and hope that gets me AM.

Dousing switch in 95% iso-alcohol a few times while switching rapidly between am/fm had no effect. Maybe needs a new switch or maybe I could take slider type switch apart, try to disassemble, and see if has any nasty battery acid remaining. Is there a quick test to rule out switch? (the switch is on the lower left part of the little green circuit board and has 10 pinouts? (see picture)

UPDATE: just ohm'd out the switch. All four outer switch posts are connected. Not so on the inner six (the left vertical row of three, are all connected -- on the right row only the top two are connected, no continuity between 2nd and 3rd pins - no continuity between outer posts, and inner pins). So thinking alternatives are:
0.switch is ok and i need to look elsewhere.
1.spray with a stronger cleaner - maybe carb cleaner, the same stuff I use for my car?
2.take switch apart and physically clean
3. take switch apart and repair.
4. replace switch with same pinouts/size/ratings,etc.?
5.jury rig an alternate switch in somehow?
6.short/bridge bad pin somehow?
7.multiple issues (switch and/or problems further down the line).

Picture of switch attached.

Suggestions/Help? Without AM radio I won't be able to cheer on my beloved NBA champions ---- THE Milwaukee BUUUCCCKKKSSS !!!!!
 

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whiteoutage

Jul 20, 2017
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Noticed the switch is noticeably harder to move than the off/ac/dc switch is. Found anatomy of a switch. Do you think the link's switch is same as mine - if so, maybe one of the silver contacts is carboned up and needs a good filing, or maybe dissolve carbon in some cleaner without having to dissemble?
https://www.engineersgarage.com/insight-how-slide-switch-works/

UPDATE: JUST NOTICED THAT THE SECOND ROW's CONTINUITY IS DEPENDANT ON SWITCH POSITION (not sure it matters, but if switch is in up position on row 2 with FM selected, then continuity is between pins 1&2 only, and if down in AM then continuity is between 2&3 only).
Also, read something that this switch may be a DPDT type, configured as an on/on type. So maybe the left row with continuity on all three pins in any position is the problem? Double throw double pole is too complicated for me, anyone?
 
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whiteoutage

Jul 20, 2017
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Noticed the switch is noticeably harder to move than the off/ac/dc switch is.
UPDATE: JUST NOTICED THAT THE SECOND ROW's CONTINUITY IS DEPENDANT ON SWITCH POSITION (not sure it matters, but if switch is in up position on row 2 with FM selected, then continuity is between pins 1&2 only, and if down in AM then continuity is between 2&3 only).
Also, read something that this switch may be a DPDT type, configured as an on/on type. So maybe the left row with continuity on all three pins in any position is the problem? Double throw double pole is too complicated for me, anyone?

Maybe someone who can read a schematic can tell if switch is working properly (please see attached picture). Again, I can't read schematics, but if I had to guess I would say electronically the switch is fine (base on my ohm readings of switch, and my uneducated interpretation of the schematic). If so, that suggests something is messed up somewhere else?

Anyone?
 

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whiteoutage

Jul 20, 2017
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Mysteries solved. Though AM switch is a little difficult to move, the switch does work electronically, and the AM radio is working, mostly. Someone in another forum suggested I look at the switch’s schematic shown in previous post. Ohm readings I measured on the switch are what you’d expect from schematic’s AM/FM switch detail.
So why no AM? Turns out this radio has separate tuning dials for AM and FM, and my earlier unknown mystery button selects which band/dial to use. AM tuning gets the big dial with the finer threaded large analog display and FM uses smaller blue thumb wheel.
All is not golden however. Now I have two new questions. First issue was briefly mentioned before. The big AM dial only travels 2/3 of its range. The primary channel I listen to WTMJ AM 620 does tune so I can listen to my Bucks - fantastic! Problem is the dial says 1600, not 620 AM and of course range is missing 33%(left side stops at 700, not 520). Do you think we can fix this?
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?
 
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