Why is my right speaker channel failing?

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.

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