The reed relays in this unit are very very quiet. You almost have to have your ear on top of it to hear a very faint " tink" sound.
Another Yamaha C4 needs help (and so do i!)
- Thread starter Duskstalker
- Start date
Duskstalker
New Member
like promised some pictures before / after the cap switch on the headphone board.
i proceeded to unsolder the ribbon bridges to take out the power section board next. the power cables are really short - i guess it would be best to unsolder the pins on the board where those cables are connected, so i can take the board out?
the big caps are glued on the board and the glue is still pretty strong (didnt loosen up on itself) - how to get those off without damaging the board? just more force? alcohol? acetone? nitro? heat?
i think it would be best to finish reflowing and recapping before trying to fix any other issues. i couldnt locate the relays to do some "clicking scouting" and thus just assume they work but are very silent.
i proceeded to unsolder the ribbon bridges to take out the power section board next. the power cables are really short - i guess it would be best to unsolder the pins on the board where those cables are connected, so i can take the board out?
the big caps are glued on the board and the glue is still pretty strong (didnt loosen up on itself) - how to get those off without damaging the board? just more force? alcohol? acetone? nitro? heat?
i think it would be best to finish reflowing and recapping before trying to fix any other issues. i couldnt locate the relays to do some "clicking scouting" and thus just assume they work but are very silent.
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Good thing they were not Rattlesnakes or you would be a dead man.
They look like the three in this photo.
(RL-6442-H132)
There are two located in the rear and the third one is located beside the volume control.
They look like the three in this photo.(RL-6442-H132)
There are two located in the rear and the third one is located beside the volume control.
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More force.
Duskstalker
New Member
i finally had some time to put into the amp again. its 4am here, so ill make it short - pictures later.
i've finished recapping the power and the amp board - so only the biggest board in the back is left (did some obvious bad solder points on that, otherwise untouched).
since i don't think it'll be easy for me to take the last board out (big switches), and i can reach most stuff inside the frame, i decided i could put the smaller boards back in for a quick test.
i've had some dead and leaked caps on the amp board, a corroded trace, which i cleaned and sealed again - it measured functional, but i dont have the knownledge and equipment to do in depth testing. i also reapplied new thermal paste to the regulators/transistors.
tested with headphones.
good things first:
- the c4 didnt blow up
- the c4 didnt trip fuses
- we restored full volume potential (YAY)
- we dont have weird dropouts
- (found the "ting" sound of the relays
)
the bad things:
- huuuuge distortion, the song is barely recognizable (over headphone output) ("diodes"? transistors?).
- we still have that weird balance issue going on, where left (? i believe) channel doesnt really have output.
- disabling tone control kills the signal - im not sure whats up with that, i might recheck that board tomorrow.
i've pulled out quite alot bad caps, i wouldnt be surprised if there were another few dead caps on the last board, so i'll proceed with that. aside from, do you have some ideas what to (re)check?
thanks alot in advance!
i've finished recapping the power and the amp board - so only the biggest board in the back is left (did some obvious bad solder points on that, otherwise untouched).
since i don't think it'll be easy for me to take the last board out (big switches), and i can reach most stuff inside the frame, i decided i could put the smaller boards back in for a quick test.
i've had some dead and leaked caps on the amp board, a corroded trace, which i cleaned and sealed again - it measured functional, but i dont have the knownledge and equipment to do in depth testing. i also reapplied new thermal paste to the regulators/transistors.
tested with headphones.
good things first:
- the c4 didnt blow up
- the c4 didnt trip fuses
- we restored full volume potential (YAY)
- we dont have weird dropouts
- (found the "ting" sound of the relays
)the bad things:
- huuuuge distortion, the song is barely recognizable (over headphone output) ("diodes"? transistors?).
- we still have that weird balance issue going on, where left (? i believe) channel doesnt really have output.
- disabling tone control kills the signal - im not sure whats up with that, i might recheck that board tomorrow.
i've pulled out quite alot bad caps, i wouldnt be surprised if there were another few dead caps on the last board, so i'll proceed with that. aside from, do you have some ideas what to (re)check?
thanks alot in advance!
How about the pre-out to and amplifier & speakers? The C-4 has a separate headphone amplifier as stated earlier.
Duskstalker
New Member
i tried the pre-out and it shows the exact same behavior with high distortion, only one channel. volume seems ok.
maybe we got a few dead caps / bad solder joints in the signal path, before it even reaches the amp sections. i'll recheck my soldering, too. i'll report back, when i finished recapping the last board.
EDIT:
resoldered and recapped the last board and i got that to report:
somehow i lost the pre-out - gonna recheck the connectors - maybe redo the pre out switching board.
with the tone bypass enabled (no tone control) the output is clean now - whereas it was dead silent before.
upon further investigation i found the overall volume to be rather low - you can get into listening levels, but i cant reach literally "too loud" levels - but that amp should be able to reach those, i believe.
i had one occasion where the cold amp (was running for 1-2 minutes) switched off on me when i got close to max volume.
i could further narrow down the distortion problem:
with tone bypass disabled (tone control active) the left channel gets distorted (or high volume distortion overlay), the right channel is okay. when i turn the balance to the right, the distortion is gone, and its a clean "right only" signal. high frequencies seem less prone to distortion than low frequencies.
so the distortion problem is somewhere in the tone control path for the left channel.
record out is working flawlessly.
maybe we got a few dead caps / bad solder joints in the signal path, before it even reaches the amp sections. i'll recheck my soldering, too. i'll report back, when i finished recapping the last board.
EDIT:
resoldered and recapped the last board and i got that to report:
somehow i lost the pre-out - gonna recheck the connectors - maybe redo the pre out switching board.
with the tone bypass enabled (no tone control) the output is clean now - whereas it was dead silent before.
upon further investigation i found the overall volume to be rather low - you can get into listening levels, but i cant reach literally "too loud" levels - but that amp should be able to reach those, i believe.
i had one occasion where the cold amp (was running for 1-2 minutes) switched off on me when i got close to max volume.
i could further narrow down the distortion problem:
with tone bypass disabled (tone control active) the left channel gets distorted (or high volume distortion overlay), the right channel is okay. when i turn the balance to the right, the distortion is gone, and its a clean "right only" signal. high frequencies seem less prone to distortion than low frequencies.
so the distortion problem is somewhere in the tone control path for the left channel.
record out is working flawlessly.
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Duskstalker
New Member
this is the amp board, after i removed the heatsinks. heatsinked components seemed to get scorching hot. most of it was burnt glue that wiped off - but the literal hotspot left some stains i couldnt get off. some caps really werent too fond of that hot neighbourhood.
i guess resistors should be able to cope with that heat, but what about that diode and the smaller transistor touching the big one? are those components in that area prone to heat damage? should i replace them? do all c4 units look like that?
i guess resistors should be able to cope with that heat, but what about that diode and the smaller transistor touching the big one? are those components in that area prone to heat damage? should i replace them? do all c4 units look like that?
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Disassemble and clean the switch..
Did you lose either the + or - 30v regulated DC when it shut down?
Check the solder connections of the 3 heatsinked transistors for annular cracks.
Yes..
Duskstalker
New Member
i dont know if i lost +- 30v dc - how can i check for that? its literally like someone pulled the plug. after switching it "off" and on again it fired up normally.
when resoldering the boards i resoldered those with extra care - but i'll recheck.
i've never disassembled and cleaned switches before, and i rather not risk breaking a contact slider of the C4 now - i really want that amp to run again. i'll have to have a specialist do that part for me - at least for that one, until i successfully cleaned some less "expensive" switches.
i used teslanol oszillin (i dont think you can get this in the states, german product) on the switches - its a contact cleaner / spray, which is not aggressive and doesnt need to be washed out, unlike other contact cleaners (its highly regarded among the german hifi repair shops for light "repairs"). it also is easy to clean off, if necessary - if it doesnt help, at least i dont grease up or damage the contacts for proper cleaning. i've used it with great success on crackling potentiometers - it might not be enough to clean a really dirty one, but i'd expect it to at least get a "non functional" switch to react to operation with crackling or something - some sign of life. i'll try again on that mode switch, tho.
i'm not saying its not the switch, in fact the feet look pretty tinged, i just wanted to note that i have taken (only slightly efficient) measures on those switches already and those switches dont seem to react to operation at all - be it good or bad - i cant get any potentiometer or switch on that unit to crackle or drop out on me, or at least i cant make it out. which makes it hard for me to determine whether it has a problem or just runs perfectly fine.
can a switch cause such bad, high volume permanent distortion? i mean its like the signal runs through a guitar distortion / overdrive pedal with extra gain, in case i failed to discribe it properly. i'm an absolute bloody beginner here, but isnt that a thing transistors do?
As always, thanks alot for your effort - i really appreciate it!
when resoldering the boards i resoldered those with extra care - but i'll recheck.
i've never disassembled and cleaned switches before, and i rather not risk breaking a contact slider of the C4 now - i really want that amp to run again. i'll have to have a specialist do that part for me - at least for that one, until i successfully cleaned some less "expensive" switches.
i used teslanol oszillin (i dont think you can get this in the states, german product) on the switches - its a contact cleaner / spray, which is not aggressive and doesnt need to be washed out, unlike other contact cleaners (its highly regarded among the german hifi repair shops for light "repairs"). it also is easy to clean off, if necessary - if it doesnt help, at least i dont grease up or damage the contacts for proper cleaning. i've used it with great success on crackling potentiometers - it might not be enough to clean a really dirty one, but i'd expect it to at least get a "non functional" switch to react to operation with crackling or something - some sign of life. i'll try again on that mode switch, tho.
i'm not saying its not the switch, in fact the feet look pretty tinged, i just wanted to note that i have taken (only slightly efficient) measures on those switches already and those switches dont seem to react to operation at all - be it good or bad - i cant get any potentiometer or switch on that unit to crackle or drop out on me, or at least i cant make it out. which makes it hard for me to determine whether it has a problem or just runs perfectly fine.
can a switch cause such bad, high volume permanent distortion? i mean its like the signal runs through a guitar distortion / overdrive pedal with extra gain, in case i failed to discribe it properly. i'm an absolute bloody beginner here, but isnt that a thing transistors do?
As always, thanks alot for your effort - i really appreciate it!
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Yep..Rapidly exercise the switch a couple dozen times while listening for sound quality.
Possibly solder connections on the two pass transistors with the largest heatsinks. Or one of them is breaking down under load.
Duskstalker
New Member
i wish i could put more time in this.
somehow i managed to "solve" the distortion issue - i have no idea what i've done. at this point im not sure whether it was a dying transistor, which is dead now, or a bad solder joint, i retouched a 2nd time now.
the good thing is: the distortion is gone now. tone control, tone potentiometers, input and mode switches - everything works without crackling or dropouts, no strange acting up.
this leaves us with these issues:
- the pre-out that I somehow managed to take out - i suspect a jumper cable came loose when i resoldered the boards. i checked for resistance from the pre out switches (jumper cable input) to the pre out jacks, and it measured probe resistance when "on", and infinite resistance when "off" - so i guess since the switch does measurably enable and disable throughput, the defect should be somewhere before the switch, somewhere in the boards, right? can i check for throughput that way, or did i just trick myself? if that works, ill grab the schematics and trace the pre-out path.
- slight misbalance of left and right channel
- i suspect overall too low volume, it seems like its missing an amplifier stage or something. since the pre out currently doesnt work, i can only measure by headphones, but i got the headphone volume all the way up, and 70% of the master volume results in lower than normal listening levels. all other amps and even cd players max out these phones with considerably less than half volume. before i reach "too loud" levels i would have to put both volume controls to the maximum level - which is really hard to believe. these are not hard to drive cans. also, back in the day, when the pre-out still worked (2 weeks ago) the pre-out output was extremely low, too. what could that be?
i ordered the diodes and transistors and will replace them when they arrive.
thanks alot for your support!
somehow i managed to "solve" the distortion issue - i have no idea what i've done. at this point im not sure whether it was a dying transistor, which is dead now, or a bad solder joint, i retouched a 2nd time now.
the good thing is: the distortion is gone now. tone control, tone potentiometers, input and mode switches - everything works without crackling or dropouts, no strange acting up.
this leaves us with these issues:
- the pre-out that I somehow managed to take out - i suspect a jumper cable came loose when i resoldered the boards. i checked for resistance from the pre out switches (jumper cable input) to the pre out jacks, and it measured probe resistance when "on", and infinite resistance when "off" - so i guess since the switch does measurably enable and disable throughput, the defect should be somewhere before the switch, somewhere in the boards, right? can i check for throughput that way, or did i just trick myself? if that works, ill grab the schematics and trace the pre-out path.
- slight misbalance of left and right channel
- i suspect overall too low volume, it seems like its missing an amplifier stage or something. since the pre out currently doesnt work, i can only measure by headphones, but i got the headphone volume all the way up, and 70% of the master volume results in lower than normal listening levels. all other amps and even cd players max out these phones with considerably less than half volume. before i reach "too loud" levels i would have to put both volume controls to the maximum level - which is really hard to believe. these are not hard to drive cans. also, back in the day, when the pre-out still worked (2 weeks ago) the pre-out output was extremely low, too. what could that be?
i ordered the diodes and transistors and will replace them when they arrive.
thanks alot for your support!
Mute button engaged?
Duskstalker
New Member
no, mute button lowers it even further - barely audible when engaged. i mean, thats what its supposed to do, right?
correct.