I recapped my M-65 and have a few questions.

IMG_0054.JPG I swapped out C100 today with a bi-polar muse with the same one in the kits folks buy.
Had some Nichicon "gold tune" KG's laying around to replace the secondary main filter caps just for grins. The ones where the sonybond glue was. The original ones were Muse caps so why not? The ones I yanked (in front of meter board in photo) were general purpose VY(M) I installed 3 years ago. I'm not gluing them down so if that's a bad idea please chime in.
Hoped to touch up the cold solders in an hour or two but it took many many hours as I kept finding more. Addressed so many light and cold solders it took awhile just to clean up the flux cheese created.There were so many cracked solders at the diode farm behind the sonybond glue area I'm surprised the amp worked at all. So far so good.
The new bulbs are in the photo too. Biasing both channels as we speak. The new Bourns trimmer pots turn smooth as Tennessee whiskey & dial right in.

D.C. Offset=3.7mV Right & 6.5 mV left.
 
Last edited:
IMG_0055.JPG Considering leaving the relay alone after close inspection. Look at the build quality on the old one. No sharp contact points to pit. That thing is a burnishing tool away from being good as new. And can be done while it's soldered in place. The top pops right off.
 
Last edited:
foobarz said:
The solder all over the boards has to be checked and reflowed. A lot of reflow was done on mine, but I still think I have some bad/cracked solder in my left-channel Class A circuit because the left channel sometimes does not get warm in Class A -- it is like it does not activate. But, after I pushed the Class A cable, from the switch to the main board, something connected and it got hot like it is supposed to. The sound is fine the whole time, no noise or anything, but no heat on the left. Well, it was hot the last time I turned it on. I have not yet gotten around to checking the solder to find the problem. Again, I suspect some cracked/cold joint in the left-side class A circuit causing it not to engage sometimes.
Click to expand...

Just to follow up: I got my M-65 into the repair shop the other day. The tech reflowed a lot more of the solder joints all across the bottom of the main board (probably reflowed most of them). One solder joint was badly cracked in the right channel, but it is fixed now. Many other joints looked dull or nearly cracked, but all good now. Reflows were done on the meter board and on the buttons/lights switch boards in the front panel. I think the sound is improved now, especially since this fixed a badly cracked joint in the right-channel. I had been noticing that the right-channel seemed weaker than the left, but the difference was very subtle. The sound is strong now with better stereo image. If there is just one bad solder joint or connection, then the amp is likely to have some subtle degraded sound. You might think it is a bad recording or something else for a while, but if you play many songs you might notice a sound problem eventually.

But, another problem remained very persistent: With Auto Class A on, when measuring the bias voltage in the left-channel, the mV value (about 50mV in Class A; about 10mV otherwise) would move around erratically (to lower values) if you tapped your finger on the front panel near the AUTO CLASS A button or tapped on the left side of the meter board. If the bias mV reading goes low, then the left-channel does not warm up as it should in Class A. I had been noticing recently that the left-channel does not always heat up in Class A. Well, we tried reflowing solder joints all over the boards to try to fix this erratic bias mV reading in the left channel (right channel was fine, though it had a badly cracked solder joint). Nothing seemed to completely fix the left-channel bias problem. If I tap around on the front panel near the Auto Class A button or on the left side of the meter, it is still possible to see the left-side bias mV reading move around erratically. It usually goes back to normal, around 50mV, when I stop tapping (or sometimes it does not move around at all). Some of the reflows may have helped, but something must still be wrong with a connection somewhere. Strangely, it seems that the problem is not with the main board - it happens by tapping on the front panel or the meter board. It could be the Auto Class A switch itself. We sprayed contact cleaner on it and worked in on/off many times, but did not open it up (not sure how). My M-65 is now working normally for the most part (the problem happens less than before), but we cannot say that we really found and fixed the problem for sure. Has anyone else seen this problem before or have any suggestions on how to fix it?
 
foobarz said:
But, another problem remained very persistent: With Auto Class A on, when measuring the bias voltage in the left-channel, the mV value (about 50mV in Class A; about 10mV otherwise) would move around erratically (to lower values) if you tapped your finger on the front panel near the AUTO CLASS A button or tapped on the left side of the meter board. If the bias mV reading goes low, then the left-channel does not warm up as it should in Class A. I had been noticing recently that the left-channel does not always heat up in Class A
Click to expand...
Thank you for chiming in on this. While biasing this piece over the holiday weekend I neglected to mention class A mode results. Left channel in class A was 69mV, right side 85mV after one minute stare time. Biasing this thing is really quirky, breathing on it while tweaking the trim pot sends the values erratic as my teenager. Maybe look into the input level attenuator board. I found weak solders on that mini board as well.
 
Last edited:
foobarz said:
Has anyone else seen this problem before or have any suggestions on how to fix i
Click to expand...
I would check TR121, TR115, TR111. My left channel was happier after replacing TR115. Even though it tested "ok". TR139 takes a lot of abuse in the Class A circuit. I'd replace that and it's TR141 buddy for grins.I'd also replace the diodes nearby TR139 since it's a sonybond glue affected area.
I'm saying all this assuming the class A switch has been proven good. That's the best place to start. Testing the switch from the main board plug proves the wiring, switch and plugs.
Does the 10mV bias check display zero with trimmer fully turned CCW or is there some voltage displayed?
 
Last edited:
Blah, I spoke too soon. My for real audiophile gear came, not my capacitors...

Those should be here today. Fortunately they "only" took 3 days in customs... from Canada... with whom we have less free trade than straight up China... I swear...
 
IMG_0064.JPG I noticed there's a vacant part location by the M-60's C157 &158 area. Spare 8mm lead spacing holes right in front of the old ones in parallel. Saying this to the folks buying the re-cap kits as the new ones are smaller. Might be a perfect fit. Fyi.
I bridged the 8mm spare slots to the original 11mm cap location to anchor the caps instead of gluing them. I went with KG caps with exact lead spacing as the old muses. I'm sure the ones in kits will work fine, just sharing.
 
Last edited:
FriedChicken said:
... from Canada
Click to expand...
How's da re-cap goin eh?

Did you have to buy a higher powered solder iron for the main filter caps?

I wish we could just add electrolyte to the old main filter caps through a valve or something. I'm still clinging to the old until I find an exact fit. Has anyone reading this ever had a main filter cap go hard short? My only concern.
Thanks
 
Last edited:
Soundscape said:
How's da re-cap goin eh?

Did you have to buy a higher powered solder iron for the main filter caps?

I wish we could just add electrolyte to the old main filter caps through a valve or something. I'm still clinging to the old until I find an exact fit. Has anyone reading this ever had a main filter cap go hard short? My only concern.
Thanks
Click to expand...

Likely busy until the end of the week. I'm renovating the attic by adding insulation, before then I need to finish all attic work. I just installed four in-ceiling speakers for atmos, I still have to run wires to hook them up, run an ethernet cable to the garage, another to a wall, then add foamboard insulation before eventually adding blow-in insulation everywhere.
 
FriedChicken said:
Likely busy until the end of the week. I'm renovating the attic by adding insulation, before then I need to finish all attic work. I just installed four in-ceiling speakers for atmos, I still have to run wires to hook them up, run an ethernet cable to the garage, another to a wall, then add foamboard insulation before eventually adding blow-in insulation everywhere.
Click to expand...

Sounds manly.

Atmos... Lemme know if ya find a receiver that doesn't have the processors close to the power supply burning them up. I gave up on new **** after 2003.
Thanks
:lurk:
 
Soundscape said:
Sounds manly.
Click to expand...
If by manly you mean miserable...

Atmos... Lemme know if ya find a receiver that doesn't have the processors close to the power supply burning them up. I gave up on new **** after 2003.
Thanks
:lurk:
Click to expand...

You chose a good time to quit. I have a little fan on my receiver. It's a yamaha rx-a3040, the flagship of the last generation of yamaha's aventage line that included preamp inputs so I can use it as a separate amplifier down the line should I need it. I'm surprised more people aren't jumping on these for that reason, and I think it's a crime to exclude them from receivers.

I have a little spinny fan on it so it gets blowy air.

I am looking forward to all this being done.
 
FriedChicken said:
If by manly you mean miserable...
Click to expand...
Yes sir attic jobs are better done in the winter but we do what we do as needed...Just stay hydrated man.

FriedChicken said:
It's a yamaha rx-a3040, the flagship of the last generation
Click to expand...
I will research that one thanks. I've learned that running fans downward toward the board forces them in class B ops alot. Little fans turned upward sucking outward from the board seems to sound better in my soundscape.
 
You must log in or register to reply here.
Back
Top Bottom