Hi. I have been using a late 1970's Toshiba Toshiba 330 separates for the past few years. When I got the the amp it needed a pair of transistors replacing which I did myself. It has worked faultlessly ever since.
Recently I have noticed that the right channel has been 'dropping out'. I get hardly anything from the right side speaker, just a very quiet distorted playback. After trying lots of things to try and find whats wrong I realised that If I turn the power off and turn it back on the problem goes away. The amount of time it takes to 'drop out' again is varied, but as soon as I touch the power toggle switch I get the sound back in the right channel. It takes a few seconds on this amp before the sound gradually fades to nothing which is how I discovered that cutting the power 'fixes' the issue (temporarily).
My knowledge of electronics is limited but I understand the basics and I'm reasonably handy with a soldering iron.
I a guessing that this is something to do with a dodgy capacitor?
I'd be really greatfull if anyone can advise further, I love my old HiFi setup and would really like to keep it going for as long as I can!
Thanks for reading my post, thanks very much in advance for any help
Recently I have noticed that the right channel has been 'dropping out'. I get hardly anything from the right side speaker, just a very quiet distorted playback. After trying lots of things to try and find whats wrong I realised that If I turn the power off and turn it back on the problem goes away. The amount of time it takes to 'drop out' again is varied, but as soon as I touch the power toggle switch I get the sound back in the right channel. It takes a few seconds on this amp before the sound gradually fades to nothing which is how I discovered that cutting the power 'fixes' the issue (temporarily).
My knowledge of electronics is limited but I understand the basics and I'm reasonably handy with a soldering iron.
I a guessing that this is something to do with a dodgy capacitor?
I'd be really greatfull if anyone can advise further, I love my old HiFi setup and would really like to keep it going for as long as I can!
Thanks for reading my post, thanks very much in advance for any help
You're almost right about dodgy parts. The symptoms you describe suggest the speaker relay (aka output relay) is the problem. Its contacts are likely dirty due to contamination or by a slow accumulation of arcing refuse etc. When you turn off and repower the amplifier, the contact is remade and this probably dislodges a little of the debris, making a fresh but only temporary contact. If the relay cover is removable, you may be able to clean the offending contacts with a small strip of card drawn between them - do not use an abrasive other than an ultra-fine treated paper type intended for the purpose.
Otherwise, the simplest remedy would be to replace the relay with a similar type, having the same footprint and contacts which you can search by drawing dimensions, from a major parts supplier like Farnell, RS components or CPC. There is a little more to that, as the coil voltage and contact current ratings must be met or bettered too.
Otherwise, the simplest remedy would be to replace the relay with a similar type, having the same footprint and contacts which you can search by drawing dimensions, from a major parts supplier like Farnell, RS components or CPC. There is a little more to that, as the coil voltage and contact current ratings must be met or bettered too.
OK, Ian. I will look into this as first point of call. Thanks! I may be worth noting that when the channel drops out, there is still some activity audible on it, but its extremely quiet and muffle, and intermittent. Is it worth noting that switching to mono will play audio from both channels?I suppose you would expect that but thought I might just mention it....
Thanks again, mate.
Thanks again, mate.
I remember your original thread on this.
As Ian suggests, this does sound a little like relay troubles. Typically if that is the case then turning the volume up can often 'fix' the issue for that particular listening session as the higher current punches a way through the oxidation.
Does this amp actually use a relay ? If it did then the sound should not fade out as you turn off...... so I suspect not from your description.
As Ian suggests, this does sound a little like relay troubles. Typically if that is the case then turning the volume up can often 'fix' the issue for that particular listening session as the higher current punches a way through the oxidation.
Does this amp actually use a relay ? If it did then the sound should not fade out as you turn off...... so I suspect not from your description.
Hi, Mooly. You helped me fix this amp last time, I'm still really greatfull
I tried the speaker selector switch as you described last night, in fact, I gave all the switches a good move back and forth several times, nothing seems to remedy it other than turning the power off, even after a split second it 'clears' the problem for a short while. This amp has speaker 'A/B/Off' selector, I have tried the speakers in both A and B outlets, the problem persists.
I will crack the case open this afternoon. I have a can of servisol somewhere so I will give all the switches etc a good 'drink' and operate them excessively while the amp is off. I'l also check the fuse carriers and fuses as suggested.
Will post up any findings! Thanks very much.
I tried the speaker selector switch as you described last night, in fact, I gave all the switches a good move back and forth several times, nothing seems to remedy it other than turning the power off, even after a split second it 'clears' the problem for a short while. This amp has speaker 'A/B/Off' selector, I have tried the speakers in both A and B outlets, the problem persists.
I will crack the case open this afternoon. I have a can of servisol somewhere so I will give all the switches etc a good 'drink' and operate them excessively while the amp is off. I'l also check the fuse carriers and fuses as suggested.
Will post up any findings! Thanks very much.
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It sounds a bit of an odd one from what you describe. Any drastic fault would upset the DC conditions and you would certainly know about that... so whatever is going on is something subtle.
When the fault occurs, does physical movement or impact or prodding the PCB have any effect ?
If you don't find anything obvious then you have to resort to basic checks at key points in the circuit. A good check in this case would be to confirm that the output stage is drawing current which is easily done by measuring the voltage dropped across the 0.47 ohm emitter resistors.
See what you find first and gather as much evidence as you can.
When the fault occurs, does physical movement or impact or prodding the PCB have any effect ?
If you don't find anything obvious then you have to resort to basic checks at key points in the circuit. A good check in this case would be to confirm that the output stage is drawing current which is easily done by measuring the voltage dropped across the 0.47 ohm emitter resistors.
See what you find first and gather as much evidence as you can.
Ok, Mooly. I tried sort of prodding all the switches/pots but nothing seemed to make a difference. I also wiggled all the leads, the output lead from the pre amp is soldered in and RCA plugs at the other end, I suspected that at first but it doesn't seem to be at fault, and the headphone output working ruled that out as well. During 'fault conditions' the watts power gauge needle read barely anything on the right channel. I will see how things look inside anyway and maybe get some pics.
Apologies for the wrong direction earlier, folks - I hadn't found the schematic at the time and as you say Mooly - it don't 'ave a relay - few if any Japanese power amplifiers did before the 1980s
Still, I agree with Mooly about the switch, as I have had the problem on similar old models when the rotary speaker switch contacts wear and their closing force weakens to only a light touch and grime accumulates on the wiping faces. That's S1 shown on the attached block diagram. I'd take a close look at the individual contact pressures and any wobbly assembly rivets, if your headphones are still working OK.
Still, I agree with Mooly about the switch, as I have had the problem on similar old models when the rotary speaker switch contacts wear and their closing force weakens to only a light touch and grime accumulates on the wiping faces. That's S1 shown on the attached block diagram. I'd take a close look at the individual contact pressures and any wobbly assembly rivets, if your headphones are still working OK.
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This description could suggest bad solder joins for output transistors: when using headphones, the drivers give enough power. As soon as you switch to speakers, much more current is needed, and you have the fault.
It happens that tin wears when there is high current.
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