Yamaha M80 - In over my head….

[SickOfItAll]

Hello. I have a Yamaha M-80 that has been with me for ever and can’t imagine life without it . It was serviced (including polychloroprene adhesive removal) by a place called Paradyme in California just before I purchased it.

The M80 has provided years of flawless service showing no signs of weakness until just a couple weeks ago. After sitting idle for a couple months while moving my small studio to more secluded location. The following power up, I was met with a noticeable hum. I moved it to a different location hoping for a ground issue but the hum was still there and coming from the rear of the unit by the main power supply board. Also, when attempting to apply a signal I noticed one channel was weak. I Immediately turned off to check the filter caps. The 47,000uf’s looked ok but the 33,000uF’s were both beginning to bulge, with one further along than the other.

I had planned for that day and had already decided to replace the 4 filter caps using banks of 12,000uF/63v CDE SPLX capacitors when the time came. They are wired in series with + drawn from the first in line & - from the last cap in line. I had built a dim bulb box prior to applying power just incase but….. couldn’t find an incandescent bullb. Against my better judgment, I powered it up anyway immediately regretting it.

First, the hum was still there as beforeI. I should have known better. I saw the two bad capacitors and immediately blamed them even though the hum wasn’t at the outputs through the speakers, it was more like transformer plates vibrating only coming from the rear of the amplifier. Not ruling out the transformer but what horrified me most was both meters maxing out as soon as it clicked out of protection (nothing connected). I was hesitant to to turn it back on to check for DC voltages at the outputs. While checking, rechecking and triple checking my connections, I found the #8 connector on the Supply board side was loose. I also realized the speaker C was pushed ‍. I couldn’t resist and fired it up one more time… unfortunately, I believe the damage was already done.

Here’s what I noticed just giving it power for a few seconds. The hum was there but the meter remained dark. Probably because I didn’t hear the click out of protection this time. HOWEVER, there was no lights at all on Main (5). Protect & Power were both dark from the moment it pushed the power button. Again, #8 on the power supply board is loose and hasn’t been reflowed yet and I am afraid to turn it back on to do any testing. I vaguely remember something about adding resistors to a couple transistors to protect the output stage but couldn’t find the information again when it was apart‍.

Oh, last but far from least (and probably most important) is there is now a direct short across the speaker jacks on both channels at the C binding posts.

Here’s where I’m at… I’m not afraid to use a soldering iron and can identify most parts on a schematic but easily get lost trying to follow a circuit where they meet, cross, go different directions etc. I have followed most of the connectors to and from the primary supply board, secondary supply board and the main board except for the loose #8 that connect from the primary supply board to the main board.

I guess what I’m trying to say is… I am way over my head and hoping someone here might have the time and/or patience to help me through this. The amplifier is like an old friend where failure is not an option. Sorry for the long winded post and thanks for your time. Paul

 

[Sparkplug]

Again, #8 on the power supply board is loose and hasn’t been reflowed yet …

This should be reflowed. Does it change anything once reflowed?

last but far from least (and probably most important) is there is now a direct short across the speaker jacks on both channels at the C binding posts.

Can you see the short, do you know where it is? If so, please fix it or just don’t use Speaker C for now.

Before going any further, please put back the caps you took out and return the unit back to its last working state. You can replace caps once the problem is resolved.

Then check all fuses (F301 ~ F307, ignore F303) to make sure they’re not blown.

Also check for good physical connection of cables, wires, mounting screws, etc.. If you haven’t had anything blown or haven’t seen smoke or smell of it anywhere, chances are your problem is more physical than electrical.

If everything checks out (this should take a while), please test voltages out of the power supply (±HB, ±LP, ±RB, ±LB) to make sure each subsystem is getting the juice it needs to operate. Using IC clip or mini grabbers, the black lead to the ground (speaker post is a good point to use) and the red on the voltage to be measured. Once this is done, it’ll be easier to to decide where to go.

 

[rottalpha]

Hello. I have a Yamaha M-80 that has been with me for ever and can’t imagine life without it . It was serviced (including polychloroprene adhesive removal) by a place called Paradyme in California just before I purchased it.

The M80 has provided years of flawless service showing no signs of weakness until just a couple weeks ago. After sitting idle for a couple months while moving my small studio to more secluded location. The following power up, I was met with a noticeable hum. I moved it to a different location hoping for a ground issue but the hum was still there and coming from the rear of the unit by the main power supply board. Also, when attempting to apply a signal I noticed one channel was weak. I Immediately turned off to check the filter caps. The 47,000uf’s looked ok but the 33,000uF’s were both beginning to bulge, with one further along than the other.

I had planned for that day and had already decided to replace the 4 filter caps using banks of 12,000uF/63v CDE SPLX capacitors when the time came. They are wired in series with + drawn from the first in line & - from the last cap in line. I had built a dim bulb box prior to applying power just incase but….. couldn’t find an incandescent bullb. Against my better judgment, I powered it up anyway immediately regretting it.

First, the hum was still there as beforeI. I should have known better. I saw the two bad capacitors and immediately blamed them even though the hum wasn’t at the outputs through the speakers, it was more like transformer plates vibrating only coming from the rear of the amplifier. Not ruling out the transformer but what horrified me most was both meters maxing out as soon as it clicked out of protection (nothing connected). I was hesitant to to turn it back on to check for DC voltages at the outputs. While checking, rechecking and triple checking my connections, I found the #8 connector on the Supply board side was loose. I also realized the speaker C was pushed ‍. I couldn’t resist and fired it up one more time… unfortunately, I believe the damage was already done.

Here’s what I noticed just giving it power for a few seconds. The hum was there but the meter remained dark. Probably because I didn’t hear the click out of protection this time. HOWEVER, there was no lights at all on Main (5). Protect & Power were both dark from the moment it pushed the power button. Again, #8 on the power supply board is loose and hasn’t been reflowed yet and I am afraid to turn it back on to do any testing. I vaguely remember something about adding resistors to a couple transistors to protect the output stage but couldn’t find the information again when it was apart‍.

Oh, last but far from least (and probably most important) is there is now a direct short across the speaker jacks on both channels at the C binding posts.

Here’s where I’m at… I’m not afraid to use a soldering iron and can identify most parts on a schematic but easily get lost trying to follow a circuit where they meet, cross, go different directions etc. I have followed most of the connectors to and from the primary supply board, secondary supply board and the main board except for the loose #8 that connect from the primary supply board to the main board.

I guess what I’m trying to say is… I am way over my head and hoping someone here might have the time and/or patience to help me through this. The amplifier is like an old friend where failure is not an option. Sorry for the long winded post and thanks for your time. Paul

can you post a photo of the "bulged" caps? Did you actually test them?

 

[avionic]

I am willing to bet that there is nothing wrong with the caps. Just slightly warped plastic dust covers.

When these caps go. They vent out of the bottom side.