Hi all, I finally had time to dig into the recap of my McIntosh MA-5100. I am very new to this and am looking at this project as an opportunity to learn a lot about troubleshooting classic amplifiers so I was OK with tearing it open and replacing all of the caps (even the films, which, as I understand, rarely go bad and at best wasted my time... possibly ruined my amp).
I have also replaced some input jacks on the amp because they were smashed. Unfortunately no testing was done before moving on to the recap of the pre-amp board
I first recapped the pre-amp board (043-989). I'm having two issues after recapping this board.
Other general information:
Resistors on the output boards of both the left and right channels get extremely hot to the touch after less than a minute, regardless if a program source is playing or not. These resistors are 0.33/5W (R237/R238 for anyone with the schematic).
Mode selector switch directly follows the RCA inputs
Balance control seems to work
The Point:
Having next to zero practical experience I'm not sure where to start. I'm trying to first troubleshoot the right channel issue. Should I:
--Jonathan
I have also replaced some input jacks on the amp because they were smashed. Unfortunately no testing was done before moving on to the recap of the pre-amp board
I first recapped the pre-amp board (043-989). I'm having two issues after recapping this board.
- The right channel only outputs a very faint signal.
- I think I ruled out issues from the input jack replacements here because with the program source attached to the right channel only the amplifier still outputs through the left channel with the mode selector set to the following settings:
- R TO L & R
- STEREO REV
- MONO (L + R)
- L + R TO L
- I think I ruled out issues from the input jack replacements here because with the program source attached to the right channel only the amplifier still outputs through the left channel with the mode selector set to the following settings:
- Input signals that go through the pre-amp are practically non-existent (*extremely* faint)
Other general information:
Resistors on the output boards of both the left and right channels get extremely hot to the touch after less than a minute, regardless if a program source is playing or not. These resistors are 0.33/5W (R237/R238 for anyone with the schematic).
Mode selector switch directly follows the RCA inputs
Balance control seems to work
The Point:
Having next to zero practical experience I'm not sure where to start. I'm trying to first troubleshoot the right channel issue. Should I:
- Visually inspect the pre-amp board solder joints?
- I did this without a magnifying glass a few times. Could this affect sources that don't require pre-amplification? According to the block diagram these sources bypass pre-amp completely.
- Test all transistors?
- If not all, which would be good to test?
- Reflow solder joints on pre-amp board?
- Still not sure how this would affect non pre-amp inputs, but may fix the pre-amp issues.
--Jonathan
odd that no one even replied to your post. first rule of changing capacitors, take extensive photos of each board, and do one board at a time, always mark with a sharpie marker the polarity of each capacitor that you take out, never trust the printed circuit board or the service manual as there were many revisions of the boards of this model. After redoing one board, double check the polarity of the caps against the markings you made on the board, then connect the board and test it for a few minutes and you do this with a variac and a DBT in line, this way shorts will light up the bulb if there was something wrong and it saves the components. I would even suggest you remove and replace and solder one part a time, it may be time consuming but at least you know it will done properly. If resistors run hot on a part of the board check the capacitors beside it, one might be installed wrong.
