I bought an M-2 off the bay a while back. Cosmetically it was very sharp, not a mark anywhere, but I could not get an idle reading on the L/H channel. DC offset and 80+/- were right on. R/H channel adjusted fine. The heat sinks on the L/H would not get warm, certainly not as warm as the R/H side.
First thing I noticed was the 1.5 amp 10V fuses were both blown. I replaced them, crossed my fingers and plugged it in. Switch on, poof...
I looked for the obvious, chased a few circuits using the schematic, but I knew I was in way over my head.
In comes Avionic to the rescue! With Dave's technical help I first removed all the sony bond from the power supply and replaced the caps (Sir byrd helped me order the caps).
I never knew the M-2 had the dreaded goo. This one does but only on the power supply caps.
All cleaned up, not hard but time consuming.
New caps (not bad for a rookie?)
Poof, fuses still blow and still no L/H idle signal. Goo needed gone and caps should be replaced anyway so certainly value added work.
Dave and I decided to switch around the 3 bridge diodes as two of them were not original and we thought this may be causing trouble. Negative, but I replaced all three anyway as the schematic showed them to be the same.
Dave and I started thinking about this 10V circuit. It seems to supplement the 83V rail voltage to get it up to 93V. Kinda of strange, but we were thinking maybe the 83V was trying to back track into the 10V circuit. Bingo, replaced two diodes and fuses stopped blowing, but still no idle signal on the L/H.
We decided to replace the trim pots with some nice Bourns units. Very nice modification but still no idle.
I had checked every thing on the board but Dave recommened I remove some of the resistors to check them out of ciruit. This I did and they all measured per speck so I reinstalled them. Bingo! I got an idle signal and it adjusted just fine. There must have been some bad solder joints although they sure looked fine.
Listening to the amp now it is mighty fine! Heat sinks are nice and warm on both sides.
I want to personally thank fellow AK'er Avionic as I could never have done this without his excellent guidance. May much Karma come your way Dave!
Life is good!
First thing I noticed was the 1.5 amp 10V fuses were both blown. I replaced them, crossed my fingers and plugged it in. Switch on, poof...
I looked for the obvious, chased a few circuits using the schematic, but I knew I was in way over my head.
In comes Avionic to the rescue! With Dave's technical help I first removed all the sony bond from the power supply and replaced the caps (Sir byrd helped me order the caps).
I never knew the M-2 had the dreaded goo. This one does but only on the power supply caps.
All cleaned up, not hard but time consuming.
New caps (not bad for a rookie?)
Poof, fuses still blow and still no L/H idle signal. Goo needed gone and caps should be replaced anyway so certainly value added work.
Dave and I decided to switch around the 3 bridge diodes as two of them were not original and we thought this may be causing trouble. Negative, but I replaced all three anyway as the schematic showed them to be the same.
Dave and I started thinking about this 10V circuit. It seems to supplement the 83V rail voltage to get it up to 93V. Kinda of strange, but we were thinking maybe the 83V was trying to back track into the 10V circuit. Bingo, replaced two diodes and fuses stopped blowing, but still no idle signal on the L/H.
We decided to replace the trim pots with some nice Bourns units. Very nice modification but still no idle.
I had checked every thing on the board but Dave recommened I remove some of the resistors to check them out of ciruit. This I did and they all measured per speck so I reinstalled them. Bingo! I got an idle signal and it adjusted just fine. There must have been some bad solder joints although they sure looked fine.
Listening to the amp now it is mighty fine! Heat sinks are nice and warm on both sides.
I want to personally thank fellow AK'er Avionic as I could never have done this without his excellent guidance. May much Karma come your way Dave!
Life is good!
Last edited: