Dear Friends,
I'm giving an overall to my C27, but I'm facing a problem. I've recaped it since there were some channel noise issues. Since the problem was not solved by recaping I went into replacing the transistors on the circuit board.
I've replaced the 4 transistors BC560C (Mcintosh ref 132-176) by BC560CTA and the 8 transistors BC546c obsolete (Mcintosh ref 132-175) by BC546ABU.
all EU versions.
upon replacing the transistor I lost all the sound from the C27🙁. Only if I place the volume at the max I can hear something.
Does any one have any idea on what is happening?
Thank for your help
I'm giving an overall to my C27, but I'm facing a problem. I've recaped it since there were some channel noise issues. Since the problem was not solved by recaping I went into replacing the transistors on the circuit board.
I've replaced the 4 transistors BC560C (Mcintosh ref 132-176) by BC560CTA and the 8 transistors BC546c obsolete (Mcintosh ref 132-175) by BC546ABU.
all EU versions.
upon replacing the transistor I lost all the sound from the C27🙁. Only if I place the volume at the max I can hear something.
Does any one have any idea on what is happening?
Thank for your help
so you can then guess the follow-up questions are then something like "what measurements have you taken?
and "did you compare those results to what you see in a service manual or compare those results with what you expect from a review of the schematic?"
good luck ...
mlloyd1
Ok, if you don't have the schematic, sign up and get it here, or I can email it to you if you can't sign up.
https://www.hifiengine.com/manual_library/mcintosh/c27.shtml
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I think you should do some of the trouble shooting in the last post I suggested in your previous thread: http://www.diyaudio.com/forums/solid-state/299001-problem-mcintosh-mc2200-2.html
This "usual suspects" method of repair, replacement without taking data on the fault, leads to problems of the sort you have just experienced. In any event, even when shotgun replacing e-caps, I change at most 2 at a time between power up music trials, to make sure I didn't make it worse. If I do make it worse, I know just where the problem is: one of the two components I just replaced.
Either your new transistors have a different pinout than the old, or you twisted some leads, or you made a bad solder joint. Most probably the latter. I do it too. I did run into two different pinouts of J174 transistor when replacing one - the modern and the archaic. Date of revision on datasheets can be important.
A list of DC faults you can look for is in that post. After you get the preamp back to working but noisy, you can use the sound probe to search for which stage is creating the noise. Unless the noise is a lot louder than music, you can't use an AC VOM to spot it, and it is difficult to spot it with a scope. DVM are too slow to indicate pops and brief noise bursts, they average over seconds.
Best of luck with this American classic.
This "usual suspects" method of repair, replacement without taking data on the fault, leads to problems of the sort you have just experienced. In any event, even when shotgun replacing e-caps, I change at most 2 at a time between power up music trials, to make sure I didn't make it worse. If I do make it worse, I know just where the problem is: one of the two components I just replaced.
Either your new transistors have a different pinout than the old, or you twisted some leads, or you made a bad solder joint. Most probably the latter. I do it too. I did run into two different pinouts of J174 transistor when replacing one - the modern and the archaic. Date of revision on datasheets can be important.
A list of DC faults you can look for is in that post. After you get the preamp back to working but noisy, you can use the sound probe to search for which stage is creating the noise. Unless the noise is a lot louder than music, you can't use an AC VOM to spot it, and it is difficult to spot it with a scope. DVM are too slow to indicate pops and brief noise bursts, they average over seconds.
Best of luck with this American classic.
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