Hi,
i've got an intermittent problem with a Yamaha a100 amp.
Here are some clues :
From time to time, the right channel stops working.
From time to time, the right channel comes back to life.
From time to time, before it stops working or before it comes back to life, a noise can clearly be heard (attached is a sample of it).
This noise comes and goes in a fade in/fade out way.
Volume doesn't affect anything (well except volume when the channel works of course).
Both speakers and phones are affected.
Any advice ?
I suppose a recap would solve it but i'd like your opinion.
Thanks ! Fred.
i've got an intermittent problem with a Yamaha a100 amp.
Here are some clues :
From time to time, the right channel stops working.
From time to time, the right channel comes back to life.
From time to time, before it stops working or before it comes back to life, a noise can clearly be heard (attached is a sample of it).
This noise comes and goes in a fade in/fade out way.
Volume doesn't affect anything (well except volume when the channel works of course).
Both speakers and phones are affected.
Any advice ?
I suppose a recap would solve it but i'd like your opinion.
Thanks ! Fred.
hm, you wouldn't go for a recap then ?
does a defect transistor could work for like an hour or two and then make this noise for 30 sec before being mute ?
does a defect transistor could work for like an hour or two and then make this noise for 30 sec before being mute ?
Relay?
Did not check the diagram.
But if there are no parts blown, it is an intermittent loose contact, and the worst thing to track down.
Do a clean and spray of all pots and switches, also in and out connectors /jacks.
Fresh heat sink compound and re-flow of outputs (both sides).
Close look at power supply and input electrolytics, also at the voltage regulation circuit.
Then think thermal shut down if it happens only after say 20 minutes of operation.
Did not check the diagram.
But if there are no parts blown, it is an intermittent loose contact, and the worst thing to track down.
Do a clean and spray of all pots and switches, also in and out connectors /jacks.
Fresh heat sink compound and re-flow of outputs (both sides).
Close look at power supply and input electrolytics, also at the voltage regulation circuit.
Then think thermal shut down if it happens only after say 20 minutes of operation.
I had that exact problem with a Samson S700 amplifier, after the channel fade away when I slightly hit the unit on the front/top the channel came back.
So after cleaning contacts, revising/reflowing the soldering on the volume pots and the input signal paths with no success, I started poking the pcb with a tin plastic rod on different locations with a 125Hz tone playing, it turned out to be the output relay with cold solders, so reflowed both relays on the unit and problem solved.
Regards
So after cleaning contacts, revising/reflowing the soldering on the volume pots and the input signal paths with no success, I started poking the pcb with a tin plastic rod on different locations with a 125Hz tone playing, it turned out to be the output relay with cold solders, so reflowed both relays on the unit and problem solved.
Regards
Hitting the unit won't change anything, i already cleaned pots and such, relay works ok.
but after looking here and there with multimeter and a small cheap oscilloscope, looks like nothing comes out of IC102.
Voltages are ok and similar on both channels, i can read the output on the 11 & 12 pins of IC101 but can't see anything on IC102.
Still seams weird for it to be intermittent ...
i'll order one and change it, cleaning and freshing up solder joints will help i guess.
but after looking here and there with multimeter and a small cheap oscilloscope, looks like nothing comes out of IC102.
Voltages are ok and similar on both channels, i can read the output on the 11 & 12 pins of IC101 but can't see anything on IC102.
Still seams weird for it to be intermittent ...
i'll order one and change it, cleaning and freshing up solder joints will help i guess.
You should have posted the schematic on post #1 🙂
1) refresh all soldering points around IC 102, from potentiometer to PCB points 35 and 40, with a fine tip sodering iron and the tiniest amount of good quality solder.
Any change?
2) short across R102 with a short piece of wire, does noise go away?
3) replace IC102 .... if you can get one that is.
One of my beefs against using dedicated ICs, except very common ones such as LM3886, etc.
And even so .... 😱
Yes, they save time to manufacturer, who has an adequate supply and probably some spare ones for warranty work .... but years later you are in the oven.
PS: I wouldn´t go for wholesale recapping , not until AFTER we solve the original problem that is.
Adding NEW variables to a still unsolved the problem is masochistic.
1) refresh all soldering points around IC 102, from potentiometer to PCB points 35 and 40, with a fine tip sodering iron and the tiniest amount of good quality solder.
Any change?
2) short across R102 with a short piece of wire, does noise go away?
3) replace IC102 .... if you can get one that is.
One of my beefs against using dedicated ICs, except very common ones such as LM3886, etc.
And even so .... 😱
Yes, they save time to manufacturer, who has an adequate supply and probably some spare ones for warranty work .... but years later you are in the oven.
PS: I wouldn´t go for wholesale recapping , not until AFTER we solve the original problem that is.
Adding NEW variables to a still unsolved the problem is masochistic.
Thank you all,
I did refresh all the soldering points from the input to the points 35/40 as @JMFahey said,
and just after that i found two dried and crackled solders (points 75 76, where a heavy moving cable is soldered).
resoldered those two and spent the afternoon working with the amp with no problem anymore !
looks like i bought two ICs for no reasons !
Thanks a lot you all, you saved me from a useless recap 🙂
I did refresh all the soldering points from the input to the points 35/40 as @JMFahey said,
and just after that i found two dried and crackled solders (points 75 76, where a heavy moving cable is soldered).
resoldered those two and spent the afternoon working with the amp with no problem anymore !
looks like i bought two ICs for no reasons !
Thanks a lot you all, you saved me from a useless recap 🙂
Okay i've claimed victory to fast ...
Turned the studio on this morning and immediately eared the noise coming out of the right speaker for 30 seconds or so before it faded away.
Then nothing for the whole day ...
It worked perfectly yesterday, and not at all today !
I'm waiting for the IC in the mail,
but i don't see why it could be it. ICs are ok or dead, but not ok one day and dead the day after, am i right ?
Turned the studio on this morning and immediately eared the noise coming out of the right speaker for 30 seconds or so before it faded away.
Then nothing for the whole day ...
It worked perfectly yesterday, and not at all today !
I'm waiting for the IC in the mail,
but i don't see why it could be it. ICs are ok or dead, but not ok one day and dead the day after, am i right ?
Put flux, and reflow the joint mentioned above.with 60-40 solder.
It might have cooled off, and cracked.
And use a bright light to check the solder joints for dries, could be another dry joint in the same area of the board.
It might have cooled off, and cracked.
And use a bright light to check the solder joints for dries, could be another dry joint in the same area of the board.
Not yet as i thought it was working with the resoldering i did.
I'll do that, but can i ask the idea behind this ? i don't undestand the logic of shorting R102.
Checking whether noise generation comes before it or after it.
Also checking whether IC102 input transistor junction is fried or not.
Test takes all of 30 seconds, way shorter than "thinking" about it, posting a question in a Forum,waiting for replies, etc.
Lamented Enzo always said: "do not search for excuses for NOT making a test".
Also checking whether IC102 input transistor junction is fried or not.
Test takes all of 30 seconds, way shorter than "thinking" about it, posting a question in a Forum,waiting for replies, etc.
Lamented Enzo always said: "do not search for excuses for NOT making a test".
Don't get me wrong, i will test, i just asked to understand what i'm about to test,
If i can get my amp to work again it's cool, but if i can actually learn something in the process it's great.
I just don't get why shorting R102, who's in the left channel, could change anything, but i'll try ...