I have a Mcintosh 420 amplifier in my RV. The right channel does not work. I did notice that when the speaker panel was put back up, a screw was driven thru the pos and neg wires connecting them. I don't know if this caused the problem or not since it worked for a while like that. I get a soft pop in the right side when I turn it on. Also, what is the ohm output of the left and right speakers? I ask this because there are two 4 ohm speakers on each channel wired in series. I think that tells me that the output of each channel should be 8 ohms. Do you have any idea where I could get a manual for it?

Determining the Cause of the Problem Let's assume our system has a head unit, a crossover, a two channel amplifier and two door speakers with only the right speaker working (the left speaker is not working). If the door speakers are behind the door panels then we want to make sure the speaker is the problem before removing the panel. We'll work backwards starting with the amplifier and ending at the head unit. Testing for a Speaker Problem With the vehicle and the stereo turned off disconnect the speaker wires for both the left and right speakers at the amplifier. Now connect the left speaker to the right amplifier output (which we know works). Turn on the stereo system and make sure the balance is set to the middle position.If the speaker still doesn't work then the problem is somewhere between the amplifier and the speaker Testing for an Amplifier Problem Now we'll need to see if the amplifier channel is bad. Put the left speaker back on the left amplifier channel and the right speaker on the right amplifier channel. This returns the speaker wiring to its original configuration. Again, with the vehicle and stereo off unplug the RCA cables from the amplifier's input and switch them so the left cable is in the right input and vice versa. Turn on the stereo system. Testing for an RCA Cable Problem For any intermediate components between the amplifier and the head unit follow these steps for each one. We only have a crossover so we'll just do this once. Begin by testing the RCA cables between the intermediate component and the amplifier. Unplug both RCA cables from the intermediate component's output. Now plug the working channel's RCA cable into the non-working side of the crossover. In our case the working channel is the right so plug the right RCA cable from the amplifier into the left side of the crossover. Turn on the stereo system.
If the right channel continues to work then you know the problem is in the RCA cables between the amp and the crossover. esting for a Crossover or Equalizer Problem At the input of the intermediate component (in our case the crossover) flip the RCA cables around (left to right input and vice versa). Turn on the stereo system.
If the right channel continues to work and the left channel continues to not work then you know the problem is in the intermediate component. Replace or repair this component.
If the problem is now in the right speaker and the left speaker works then the problem lies before the crossover. Turn off the stereo system and return the RCA cables to their normal places.
Testing for a Head Unit or RCA Cable Problem Pull out the head unit from the dash so you can access the RCA cables. Unplug both RCA cables from the head unit. Do not disconnect any other wiring. Plug the right RCA cable into the left channel of the head unit. Turn on the stereo system.

McIntosh parts are both expensive and difficult to find. The parts usually have to be obtained from McIntosh itself (which is overseas), and they are quite expensive.

Check at a glass fixer

it seems that the right channel is blown. the unit has no fuses inside, most likelly output transistors are gone. not easy fixable, you need to bring it to a repair shop. if you are in nj you may brong to ebcelectronics

Swap the speakers around. If the sound stays on the same channel and doesn't move with the swap, then the amp has a fault on that channel. If it does move to the other side the speaker is the problem.

If it is an amp fault you can track it down using a insulated tool and the buzz test. You simple touch points on the good channel with the tool and in places it will buzz. You compare that by touching the same places you got a buzz (on the good channel) on the bad channel instead and if it doesn't buzz or it's weaker then you have located the problem.
You can also check the voltages with a meter in the same way. As the voltages should be the same on the two channels.

is output amplifier is burned, check any burned fuse on the back. is high cmos power amplifier, need to be repaired. send to your top audio repair center.

Most likely, one channel is blown plus power supply capacitors have to be replaced, switches and controls cleaning, all lamps replaced. That would be an average repair on that model.

The new boards multiplex the connectors on the back panel to maximize use. Open the Realtek control panel and configure for sterio 2.1. Also, these new boards do not provide any power drive, so to get decent volume, you will need amplified speakers.

These units are capacitor coupled between stages. It sound to me like one or more of those caps are defective. There is an extra stage of amplification for the Phono inputs. Check the phono pre-amp section for defective caps. Dan

Yes you could be right about the power supply capacitors as they have a tendency to dry out. Another tip is to inspect the terminations of these capacitors and clean their contact points as often the screw and screw boss is a different metal and corrosion and electrolysis occurs between these and the main power supply connectors. If in doubt clean with a scotch scourer till shiny metal is exposed on connection points. Then coat contacts with electrical contact conditioner (lanolin grease is good too) before reassembly.

Some amplifiers do not have sufficient storage to sustain high bass levels into difficult speaker loads, the Mac should not be one of these however . To verify that your dedicated AC outlet is not a limiting factor - use a power board and plug an incandescent lamp into the same point as the amp and see if you see any flickering of lamp when the amp lights dim.

If no evidence of limiting of main power and connection maitenance does not solve the issue, replacing the capacitors is indicated.