McIntosh MC-240 trouble

Archived from groups: rec.audio.tech (More info?)

This can be the main filter capacitors, and or also a regulation problem in
the power supply. I have seen faults in the output stage also cause hum and
noise.

If you are not experienced at servicing these amplifiers, your best solution
would be to give it out to someone who is experienced at servicing this type
of amplifier. It is also a fairly high end unit, and is worth investing in a
proper repair. At home you may not have the proper test gear to verify its
operation after parts have been changed.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Tom Noll" <tom6l6@yahoo.com> wrote in message
news:12a8a681.0405060547.3e9b6940@posting.google.com...
Hello,

Last night when I turned off the stereo I noticed a new noise. As I
went over to pull the switch, I noticed an obvious hum, which sounds
like 60Hz, coming from the chassis of the MC-240. There is also seems
to be some vibration present. I believe that there is no change in the
sound as presented as signal to the speakers; no hum or excess noise.
This is the sort of sound that comes from an overloaded transformer--
but the power transformer was not overly warm, I think. My setup
involves no preamp, just a CD run straight into the amp. All
connections look unchanged and good.

Today I'll check the voltages out. I have no technical experience with
this amp, but know my way around with a DVM.

Is this hum a sign of some particular problem? Is there some
particular component or measurement I should look into?

Thanks for any help or suggestions.

Best regards,

Tom

Archived from groups: rec.audio.tech (More info?)

tom6l6@yahoo.com (Tom Noll) wrote:

>Hello,
>
>Last night when I turned off the stereo I noticed a new noise. As I
>went over to pull the switch, I noticed an obvious hum, which sounds
>like 60Hz, coming from the chassis of the MC-240. There is also seems
>to be some vibration present. I believe that there is no change in the
>sound as presented as signal to the speakers; no hum or excess noise.
>This is the sort of sound that comes from an overloaded transformer--
>but the power transformer was not overly warm, I think. My setup
>involves no preamp, just a CD run straight into the amp. All
>connections look unchanged and good.
>
>Today I'll check the voltages out. I have no technical experience with
>this amp, but know my way around with a DVM.
>
>Is this hum a sign of some particular problem? Is there some
>particular component or measurement I should look into?
>
>Thanks for any help or suggestions.
>

If the hum comes only from the chassis, and is not present on the
speaker's sound, then it may be a mechanic problem. Check for lossen
screws on the power transformer mounting.
>Best regards,
>
>Tom

---
Ing. Remberto Gomez-Meda <gomerem@hotmail.com>
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.

Archived from groups: rec.audio.tech (More info?)

Tom,

The parts list from McIntosh does list the caps as 250 Volt, and you
should replace both of them, as they are in a series voltage doubler
arrangement and the caps must be identical. The capacitor with the
black cardboard sleeve has lots of voltage on the can itself, which is
why the can is also insulated from the chassis. You can go a bit higher
in capacitance (up to around 330uf) and higher voltage ratings are OK.
It might be difficult to find these caps, you might want to try someone
like Antique Electronics Supply (www.tubesandmore.com). Remember there
are hazardous voltages inside this amp, and misconnection of these caps
is dangerous. Best of luck.

Regards,
Tim Schwartz
Bristol Electronics


Tom Noll wrote:
>
> Thanks for your help, guys. The first filter cap had leaked and all
> the high voltages are much too low, so the doubler caps are bad too.
>
> Next question: what voltage rating do I need to replace that doubler
> cap which floats and is wrapped in black cardboard? For both caps the
> schematic calls for 250 mF no voltage rating given, the bare can is a
> 250 V unit. I've noticed that schematic values are not always
> reliable.
>
> The other question is how could that amplifier have sounded so good
> when it was so out of whack? Ans: the Macintosh engineering for fault
> tolerance is well-earned.
>
> Thanks again, and with best regards,
>
> Tom