Why is my right speaker channel failing?

This vintage analog integrated amp has an enjoyable sound, but for some reason the right speaker channel doesn't work all the time. (it's not the speaker itself, I checked)

Weird thing is, when I put pressure on the capacitators on the circuit board, slightly bending the circuit board, it usually works again…. only to stop working some time after.

Also sliding the volume control on the front panel to maximum for a brief moment sometimes does the trick.

I have no idea what is causing this.

I don't have the guarantee or puchase paper, sony won't help me.

And I'd like to fix it myself.

Any ideas?

I've added a picture of the inside and marked in red the capacitators I press

and a link to an image of the front panel on

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google image of the front panel

Update (01/25/2016)

Hey Jayeff,

Both sides of the board are accessible, but I didn't really find a dry joint.

No apologies needed, even if I did already know what it looks like :D.

Still not sure what the problem is.

I tried bending this part (red circle in pictures) , which is crooked. I'm nog sure if it's supposed to be crooked.

Also thought it was maybe this thing (green circle), unsoldered and resoldered that, but to no avail.

Also, when i there is alot of volume, usually it works again. (like, when a laptop goes into the TV via hdmi, then via minijack/cinch out of the TV's headphone socket into the amp, and all volumes are set high) But so this got me thinking that maybe it could be something else?

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Answered! View the answer I have this problem too

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@nemorinus just to help you and jayeff out you can get the service manual from the bottom of this page It may help to further identify your caps etc.

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Hi OT03,

Thanks for that much appreciated.

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jayeff, both caps are on the power supply side of the amp. The voltages are marked on the bottom. May be Nemo can check on those. I am wondering if the caps are failing or even the rectifier. Anyhow, great question/answers on your part. I'll keep my eyes open (fingers crossed) to see if you are getting anywhere with this. Good Luck.

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Deck the Halls
With tools and Fix Kits

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Hi,

By putting pressure on the capacitors you are making something come into contact again, as you say by flexing the board. It is more likely to be a dry joint or loose connection (even looks like there are wire wrap type connections - orange/red/black/red wires near capacitors- I may be wrong on that).

See if you can trace the wires from the right speaker channel output back to the board (and hopefully it is near to where you have been applying pressure) and then inspect with a strong light and a magnifying glass for dry solder joints or loose cable connections. Hopefully it is on the front of the board so that you don't have to remove it. Also make sure that the power is completely removed so that no 'accidental' probing will cause more problems.

If you have to remove the board because you need to inspect the back keep the picture you posted handy, take more if necessary so that you know where everything belongs when you go to put it back.

If you have to remove the board be careful when you handle it, you do not want to 'bend' any components causing possible s/c or o/c or break off any either.

Here is a link to show how to solder components on a pcb and a picture to show what a dry joint looks like. Apologies if you know this already.

https://www.youtube.com/watch?v=SD0Gtm5p...

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If it is a wire wrap type connection that is faulty - actually loose, (the wire is actually wrapped tightly around a post with a special tool, so that the post edges bite into the wire to make the connection) it is best just to solder the wire to the post as is.

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Hey Jayeff, I answered your suggestion below here, with pictures.

Thanks for the quick response!

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Hi Nemo,

Thanks for the pics. The 'works with max volume' seems to me to indicate that there is enough power (at max) to overcome a resistance problem, however briefly.

The cable being bent is no problem, as long as it is terminated correctly at both ends it makes no difference. It does look like it is one of the channel power supply cables though, given there is an identical cable at the other end of the connector.

What caught my eye though is what I hope is either a Speaker protection relay (or an anti 'thump' relay) just to the left of the 'green circled cable. It is in a clear plastic case. Next to the big capacitors which I hope were the ones that you were pressing originally.

If it is a relay, with changeover contacts, I'm wondering if (with the power removed - can't tell you how many times I caused more problems by investigating with the power on) you can remove the cover and clean the contacts. If you don't have a contact cleaner spray, just fold a piece of paper a few times to give it strength and then slip it between the contacts a few times. Also ensure that there is enough travel when the contacts make (either way when the armature is operated (pushed in) and released) the contacts should have follow through and follow back.

If that is not the problem, and you can still turn on the right channel by pressing on the board, then my other suggestion is that you power up the amp (yes I know) and with the plastic handle of a screwdriver or any other non metallic probe start gently tapping components and see if the right channels comes on. Without a schematic you could trace the circuitry but you don't know if it is a 'power'problem or an 'audio' one. There isn't any 'hum' in the speaker by any chance, indicating that the power is there but not the audio?

It is still looking like an intermittent open circuit problem which is usually either something loose or broken or not connected properly. Electronic components can go high resistance and then things don't work but it is very unusual that they restore back to normal.

Again apologies if you know a lot of what I've said.

Added comment:

Thanks to OldTurkey03 we now have a circuit diagram. See his 1st comment above.

Initially I suggest that you visually inspect the right channel path, starting at the right speaker + terminal on TM401 R+ connector point and working back thru headphones connector jack CNJ401 contact then to relay RY401 contact, R468, R463 and onto pin13 of IC401 on the Power IC board. (pin 1 is usually marked with a 'dot' on the IC case, then you count down that side then back up the other side to opposite where you started).

The volume control is a double potentiometer, one for each channel. You may also like to inspect from IC401 pin18, C452,R452, to volume pot RV401/2. This is the input path from the volume control.

After all this it may be that OT03 is right when he suggests that the Power capacitors may be failing. If you have a Voltmeter check that the voltages marked on the circuit for IC401 are correct e.g. -ve 31V on pin14. Just be careful when you measure that your Voltmeter probe doesn't slip and bridge 2 points, You might be looking at more problems. Also be careful yourself.

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Hi guys

- I tried cleaning the contacts of the plactic-cased-relay-thingy, but no effect.

- Not sure what you mean by "ensure there is enough travel" and " follow through and follow back"

- I have no technical background whatsoever so please describe in detail how to check certain things.

I have a basic volt tester but don't know how to use it

(sth like this http://www.conrad.be/medias/global/ce/10...)

So when you advise to check the voltages on the IC401, I have no idea on which points to place the test pins.

- Also no clue about reading a diagram, so I don't know what you mean by "inspecting"

- Sth else: The problem persists when plugging in the headphones.

- I tried tapping the components at full volume, but the only thing that genuinely works is pressing the board. The right channel then works again perfectly but the slightest tap makes it drop again.

Thanks for the patience!

and so no more apologizing, cuz it's ibvious I don't know any of it :D

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Hi,

OK. If you feel like doing this, this is what you need to do.

A visual inspection: "with the power removed", a magnifying glass and a good light so that you can see well.

You need to carefully look for loose connections, dry joints and breaks in the tracks. Also inspect the components themselves, actually try to move them (gently) especially the capacitors (C = capacitor, R = resistor) they will obviously bend but not feel loose. With the capacitors try gently pulling them up and down whilst observing their solder connection to the tracks. If there is a dry joint you may see movement

If any solder joint looks suspect re solder it.

One of the pictures you posted https://d3nevzfk7ii3be.cloudfront.net/ig... showed the terminal connections for the IC401 power board with the numbers written on the track side so you should be able to work out where pin 13 is, look at the cable wire that joins it to the mainboard (on the other side) then follow the track from there to get to R463 on the board. When you have finished looking at the solder connections and the track for this path go to the other side of R463 and follow the path to R468 then onto the relay contact, thru the contact (you pretend that you go up thru the contact then back down on the contact it makes onto and see where it connects to the track and then follow it from there) onto the track and on to where it leaves the board to get to the headphone jack board. Now do the same from pin 18 of the IC401 power board and follow it to C452, then to R452 and then to where it leaves the board to get to the volume control.

You should also check the connections of the following C551, C552, C501, C502, R551, R552, D502, Q502

With regard to follow thru on relay contacts. When a relay operates it pushes a set(s) of contacts so that they make or break away from another set(s) of contacts. When contacts are meant to make you want to make sure that the contacts are pushed far enough together so as to make good contact.(it doesn't have to be excessive, just enough so that good contact is maintained with the relay operated - that they don't bounce and cause problems). This is known as follow thru. The contacts make before the relay armature (operating lever if you like) has finished its movement. Therefore when the armature has finally come to its fully operated position the contacts have been pushed together a bit further. Follow back is the same in reverse. Contacts that were broken when the relay operated need to have good contact when the relay is released.

I feel that I should tell you now that I will not be advising you how to measure voltages in the circuit. Because you admit to little knowledge regarding electronic servicing, you can cause serious damage to the amplifier just by inadvertently making a slip with your test probes. For instance, just by short circuiting two points next to each other (by 'bridging' just one test probe across them) that are 'live' may destroy any number of components which will definitely be harder to find and more expensive to fix.

Secondly and more importantly, because the amplifier obviously has to be opened, there a lethal voltages present and again it doesn't take much to inadvertently touch the wrong thing.

If you haven't found the problem by visual inspection, take it to a professional for repair

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Haven't tried extensively yet to inspect using your instructions. Will defenitely do so at some point in the future.

Thanks in the meantime anyway for the guidance!

Cheers

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Nemo will be eternally grateful.
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