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    M-2 recap

    Now that I have my M-2 issues put to bed, I want to do a re-cap on mine. Does anyone have a list of caps or other components that should be replaced they would like to share? Thanks!!
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    M-2 amp with -80v +37.5v left side

    All is well. Trimpots were filthy. Cleaned and idle, bias, and voltage are all within spec on both channels. Thanks to all for your help! Ordering new multi-turn trimmers.
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    M-2 amp with -80v +37.5v left side

    Well half way there. Got +/- 80v on both left and right sides. Left side bias and idle perfect but now can't get the right side idle and bias which is way off. After assuring that the right side voltage was +/- 80v I then checked the right side idling current and it was about 53mv (good)...
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    M-2 amp with -80v +37.5v left side

    Not sure were I got the idea that 1N4048s were the sub but I've got some 1N4002's and will swap them out. Thanks for catching that for me!
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    M-2 amp with -80v +37.5v left side

    D688 (1885) on the drive board was shorted. Replaced both D687 and D688 with 1N4048s.
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    M-2 amp with -80v +37.5v left side

    Have all the correct fuses on hand and already ordered a dozen fuse holder clips to replace them all.
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    M-2 amp with -80v +37.5v left side

    Yes F256 was bent, I bent it back and it seems tight but I will get a new clip as well.
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    M-2 amp with -80v +37.5v left side

    Finished going through the rest of the transistors and diodes on the pre-board and all are good. No signs of any other component damage. Have new 1.5 amp fuses and waiting on the 2sc2240 replacement. Re; the fuses......when I removed fuse from the top contact/clamp of the blown F256 fuse it...
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    M-2 amp with -80v +37.5v left side

    right .. typo
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    M-2 amp with -80v +37.5v left side

    Couldn't sleep thinking about my dumb rookie mistake as I should have checked the fuses 1st!! I thought they would be harder to get to but really easy. Both that were supposed to be 1.5 amp fuses were blown ... for some reason 2 amps were installed in the 1.5 amp holders and blown. Need to...
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    M-2 amp with -80v +37.5v left side

    Finally got back to looking at the amp after the holidays and some minor hand surgery. Made things a little worse as I was checking the +80/-37.5v and used my meter probes without the shield and accidentally shorted the +80 to the chassis and now it is +40/-37.5. VR202 was checked and fine...
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    M-2 amp with -80v +37.5v left side

    On the pre-drive C board terminals marked -80 - E - +80 next to VR303 & VR302 same place on the right board which gave +80 -80 right on. I tried adjusting the trimers VR303 & VR302 and couldn't get better than +37.5v...initially it read +40v but once I touched the trimer the best I could do...
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    M-2 amp with -80v +37.5v left side

    The same place I take it on the right side only on the left side. Please excuse me if I don 't respond for a while as my daughter and her husband will be visiting for a long weekend. The visit will entail the use and testing various bourbons for the sake of science, so I won't be messing...
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    M-2 amp with -80v +37.5v left side

    Absolutely, it goes without saying.
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    M-2 amp with -80v +37.5v left side

    I just got an M-2 amp and while checking it out I found the right side power voltage, idiling current and DC balance all spot on but the left side power voltages were -80v +37.5v. Before I tear thing thing apart, does anyone have any suggestions on what to look for? From the yamha service...
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    AK is 19 years old, so we're having a raffle.

    Nov 13, 2003
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    After a summer of projects I got back to the B2 and it's up and running again. As reported above the sockets for the TO-3 VFETs were black and burned so I replaced all R & L with new ones. Looks to me like whoever removed and replaced the VFETs sometime in the past got some thermal paste on...
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    I checked all the VFETs using the DVM method described elsewhere in the forum. Attached are the results. They all appear to be similar so all bad or all good? Didn't do anymore with the DCA75 as I could get deferring results depending on the test voltage ranges used. Should I let the...
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    Rottalpha is right, I didn't lock the parameters. I'll recheck locking parameters though if the DCA75 isn't a good way to check VFETs I don't know what it will tell me. If not the DCA75, what is the best way to check?
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    these are the last.
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    These are more of the traces
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    Removed the VFET's and voltage across the red/white is 119v solid on both channels. The left channel was the one running hot and the VFET sockets on the left side were black and won't clean with contact spray. Wonder if thermal grease burned with the heat? Maybe the poor contact caused...
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    It's the 56/60-V that is about 10v low on the left (problem) side, the +/- 85v seems rock solid. As stated above driver board trimmers are burns 10 turn and the 1st thing I did when having the bias problem was to replace both trimmers with new ones. Next steps are to remove the VFets and...
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    Thanks for the reply. That's what I was afraid of, after comparing the boards I came to believe that they appear to be the same and I've come to the conclusion that the PS board needs a closer look and those trimmer pots on the PS are on my list to replace. I am getting the proper output...
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    Yamaha B2 Driver Boards - NA-06747 vs NA-06811? Difference

    Does anyone know the difference between Yamaha B2 driver boards NA-06747 and NA-06811? I've got an NA-06747 driver board that bias and Idling current float around on so I pulled a good driver board from another B2 with one dead side to get my amp up and running while I trouble shoot the driver...
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