MA-6100 "pops" when changing inputs...

[boatdrinks77]

Hi guys, got a McIntosh MA-6100, bought it with the understanding that one channel cuts out once in a while. I got it home, disassemled, cleaned / de-oxed all the switches and pots, reassembled. Been running it for about 6 hours with no problems (channel NOT cutting out)

My only complaint is that I have a "click" or "pop" when changing the INPUT SELECTOR switch. Can anyone help me with this issue ? Thanks in advance.... Dan

 

[c_dk]

All the inputs pop? Typically the ph2 and tape head, a turntable was expected to be in ph1, will have shorting plugs installed so a popping across those means a very crazy issue assuming the shorting plugs are in place.

Have you done any of the known needed maintenance beyond just contact cleaning?

 

[boatdrinks77]

All the inputs pop? Typically the ph2 and tape head, a turntable was expected to be in ph1, will have shorting plugs installed so a popping across those means a very crazy issue assuming the shorting plugs are in place.

Have you done any of the known needed maintenance beyond just contact cleaning?

The shorting pins were not installed. I installed them.

I still have a fairly loud pop when switching between PHONO 2 and TAPE HD. I get a slight click from PHONO 1 to TUNER 1, but NOT from TUNER 1 to PHONO 1 .........

switching from TUNER 1 to TUNER 2 to AUX, then back to TUNER 2 to TUNER 1 is quiet.

Other than that, the amp seems to function great . Dan

 

[Jcamp]

The shorting pins were not installed. I installed them.

I still have a fairly loud pop when switching between PHONO 2 and TAPE HD. I get a slight click from PHONO 1 to TUNER 1, but NOT from TUNER 1 to PHONO 1 .........

switching from TUNER 1 to TUNER 2 to AUX, then back to TUNER 2 to TUNER 1 is quiet.

Other than that, the amp seems to function great . Dan

Did you ever figure out what was causing the pop?

 

[c_dk]

If the shorting pins were installed in the two phono and tape hd inputs and the unit still pops I would suspect a iffy ground from those high gain inputs.

A proper restoration of a MA6100 involves securing those grounds.

 

[Jcamp]

Looks like shoring plugs fixed it!. Yes did the grounds.

 

[Jcamp]

Shorting plugs fixed pop on both phono inputs but not on tape HD. With no plugs tape hd pops and with plugs major low-frequency oscillation occurs.

 

[c_dk]

Tape head uses the same basic circuit as the phono but with different EQ and gain to match the NAB EQ as well as a different selector path.
Sounds like you are not getting a good ground on that input to short the noise to ground.

 

[Jcamp]

Tape head uses the same basic circuit as the phono but with different EQ and gain to match the NAB EQ as well as a different selector path.
Sounds like you are not getting a good ground on that input to short the noise to ground.

Thanks for the reply. All grounds are good, I checked all components on the preamp boards also. The pop and oscillation seems to be triggered when the selector hits half way between phono 2 and tape hd. That shouldn't matter because it just connects phono 2 to tape hd when its between the two. This is driving me crazy.

 

[c_dk]

Are you purposely hanging the control in the "no mans land" between selections?

I have these selectors become loose, that is the stacked sections, because the nuts and long bolts loosen it allows there to be flex between the fingers and rotating contacts.

If you do not have a lifted ground in the tape head wiring path the continue to connect the shorted ground between inputs must be disrupted within the control itself.

Awkward English for sure, forgive me Patrice, how this transfers to French or what ever language, must be really something.

 

[Jcamp]

Are you purposely hanging the control in the "no mans land" between selections?

I have these selectors become loose, that is the stacked sections, because the nuts and long bolts loosen it allows there to be flex between the fingers and rotating contacts.

If you do not have a lifted ground in the tape head wiring path the continue to connect the shorted ground between inputs must be disrupted within the control itself.

Awkward English for sure, forgive me Patrice, how this transfers to French or what ever language, must be really something.

Today I found the pops and oscillation is happening in the eq circuit. It occurs when the selector is at half way between sources, two pins on the eq board get shorted and the oscillation starts.

 

[c_dk]

This is becoming circular......you need to experiment with how to insure the three inputs are shorted to ground when not in useand have nothing connected to them.

You have either a problem selector which is unobtanium and will need therefore detailed repair or your expected good ground isn't.

 

[Jcamp]

This is becoming circular......you need to experiment with how to insure the three inputs are shorted to ground when not in useand have nothing connected to them.

You have either a problem selector which is unobtanium and will need therefore detailed repair or your expected good ground isn't.

Just tested and all sources short to ground when not used

This is becoming circular......you need to experiment with how to insure the three inputs are shorted to ground when not in useand have nothing connected to them.

You have either a problem selector which is unobtanium and will need therefore detailed repair or your expected good ground isn't.

I got it. Had to remove and replace some components on the pre boards. You still need a turntable or shorting plugs in.