• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

MAC 4100 FM Problem

rbspop

rbspop

rbs55pop
Couple of MAC 4100 tuner problems: I can receive 6/45 FM stations with "Mono" switch out. However with the "Mono" switch depressed I get all of the (45/45) stations in my area. With an FM antenna attached the meters are "dead center and about 8-10 on the strength meter. With the FM Mute switch depressed I only get two FM stations. I get no AM stations (with or without antenna). Any and all help will be appreciated.
Thanks,
bruce
 
Register to hide this ad
Sounds like it needs a thorough alighnment.........hours of tech time labor with specialized equipment.

About the only test you can do is see how close the meter needle lines up with the broadcast stations published transmission frequency.

As the tuner fades out of alighnment it often will shift its centering receiving off of where the station is transmitting.

In any case you will need to find a pro tech.
 
c_dk said:
Sounds like it needs a thorough alighnment.........hours of tech time labor with specialized equipment.

About the only test you can do is see how close the meter needle lines up with the broadcast stations published transmission frequency.

As the tuner fades out of alighnment it often will shift its centering receiving off of where the station is transmitting.

In any case you will need to find a pro tech.
Click to expand...

The pointer is about a full stop? off (e.g. 102.5 is at 103.5). Would that also cause no AM? I have taken it to an authorized McIntosh tech ... after three months nothing. Took it to AARL tech ... after a week he called and said he didn't have time. I live in Reno and there are no techs in the vicinity. Do you know of a good one?
 
Well can not answer about the validity of a "authorised" Mac tech.....

However if to tune a station broadcast at 102.5, their FCC assigned broadcast frequency, at 103.5 something is wrong with the alighnment. When I have worked on tuners in the past the only acceptable deviation was.......zero.......none, nada.

The muting circuit is a threshold, if the signal is above the threshold you get the station if below it is silenced. This is to reject the noise when tuning through the noisy "dead" air spaces. It is therefore understandable why engaging it will eliminate stations.

The threshold is adjusted during a alighnment.

The mono switch just combines the L and R audio signals within the tape loop path so you are just listening to the combined signal.

You obviously need a FM antenna attached, the AM antenna was attached at the factory and unfortunately has sometimes been mistaken for a handle. If it got yanked off sometime over the last 40 years it would explain your AM issues.
 
c_dk said:
Well can not answer about the validity of a "authorised" Mac tech.....

However if to tune a station broadcast at 102.5, their FCC assigned broadcast frequency, at 103.5 something is wrong with the alighnment. When I have worked on tuners in the past the only acceptable deviation was.......zero.......none, nada.

The muting circuit is a threshold, if the signal is above the threshold you get the station if below it is silenced. This is to reject the noise when tuning through the noisy "dead" air spaces. It is therefore understandable why engaging it will eliminate stations.

The threshold is adjusted during a alighnment.

The mono switch just combines the L and R audio signals within the tape loop path so you are just listening to the combined signal.

You obviously need a FM antenna attached, the AM antenna was attached at the factory and unfortunately has sometimes been mistaken for a handle. If it got yanked off sometime over the last 40 years it would explain your AM issues.
Click to expand...

Hi, Thanks for answering. The AM antenna looks as though it is new (all wires are attached. Both internally and externally but no AM). With a FM antenna attached I get the same amount of stations. The signal strength meter, however, goes from a "6" to an "8 - 10" but still no right channel.....
 
It is important you separate your units issues into distinct problems.

FM issues like channel centering on broadcast frequency is different than AM issues.

While a badly aligned FM tuner could cause no right channel the question has to be asked if the right is there when listening to a record or CD.

The newest MAC4100 is 35 years old, oldest over 42, and there are numerous part in them that had a expected life span of 20 years.

They are a tremendous unit when restored and well worth the 5-6 hours of tech time needed to restore them to their proper function.
 
c_dk said:
It is important you separate your units issues into distinct problems.

FM issues like channel centering on broadcast frequency is different than AM issues.

While a badly aligned FM tuner could cause no right channel the question has to be asked if the right is there when listening to a record or CD.

The newest MAC4100 is 35 years old, oldest over 42, and there are numerous part in them that had a expected life span of 20 years.

They are a tremendous unit when restored and well worth the 5-6 hours of tech time needed to restore them to their proper function.
Click to expand...

I have both channels on all of the inputs except FM. I was just hoping that there was a cap, resistor, or ic to check before I start to do a full circuit trace.
I have replaced all (except the FM and AM) the caps and some transistors, resistors, etc. as the unit didn't work at all when I first got it (turns out it was a shorted cap on the equalizer board).
I would think (I am not a tech) that the problem probably lies in the right channel of the FM circuitry. I check that and post back with results.
 
Before I would start replacing parts that tune the circuits I would check with a tech who has the appropriate test gear for proper alignment.

I would think they would be inclined to not accept a unit that had been tinkered with as it typically ends up with two unhappy parties.
 
Last edited:
c_dk said:
Before I would start replacingarts that tune the circuits I would check with a tech who has the appropriate test gear for proper alignment.

I would think they would be inclined to not accept a unit that had been tinkered with as it typically ends up with two unhappy parties.
Click to expand...

I would never even start to play with anything related to the AM/FM except maybe to check voltages...
 
You must log in or register to reply here.
Back
Top Bottom