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Discussion Starter · #1 ·
I'm the second owner of a Mcintosh mc440 that worked in two cars for over 12 years. Now it no longer outputs sound in either channel. The amp turns on, the fans turn on, and the PG light does not come on. The problem showed up about a month ago. After the car was started the amp had sound for a minute then stopped producing sound, but after that happened several times it finally stopped producing sound at all.

I narrowed it to the amp since the headunit is now driving the speakers fine. I have the mc440 service manual from the generosity of one of the members here, but I'm not sure what needs to be replaced. I've read in some of the posts here that the problem is usually an electrolytic for mcintosh amps, but the parts list has about 80 electrolytics. Seems like a lot of caps to replace.

I contacted Mcintosh Labs and they recommended one of their authorized service centers. I'd like to fix it myself if possible, but need a bit of guidance.

Any help would be appreciated.
 

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Discussion Starter · #3 ·
Thanks for the reply. My plan is to replace some electrolytic caps, a resistor, and a diode.

When I opened up the amp, the pcb was burnt under one of the 2x .22ohm 5 watt cement resistors. I think it's an output resistor. I found a replacement on ebay. The diode on the powersupply looks like it was previously replaced, but rather sloppy so I'm replace that as well. The diode has burnt marks around the pcb and the lead holes for the diode were enlarged to fit a bigger diode. I bought the diode found on the parts list and its much smaller, so hopefully the larger holes don't pose a problem.

So far I began the work, but had to put it down for a while.
 

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Thanks for the reply. My plan is to replace some electrolytic caps, a resistor, and a diode.

When I opened up the amp, the pcb was burnt under one of the 2x .22ohm 5 watt cement resistors. I think it's an output resistor. I found a replacement on ebay. The diode on the powersupply looks like it was previously replaced, but rather sloppy so I'm replace that as well. The diode has burnt marks around the pcb and the lead holes for the diode were enlarged to fit a bigger diode. I bought the diode found on the parts list and its much smaller, so hopefully the larger holes don't pose a problem.

So far I began the work, but had to put it down for a while.
What is the part number of the diode?

Also, if possible stand the resistors and the diode off the board a little bit to allow some airflow underneath those components. They get hot.
 

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I wonder if those nearby caps shorted out and caused the current overload.

Any pics you can attach?
 

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Discussion Starter · #8 ·
here's a couple pictures of the 2x.22ohm 5 watt resistor that I need to replace. Not sure you can see the burn at the leads. It was difficult to get good lighting in there.
 

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It seems that there was a current overload on that channel with the bad resistor, maybe the power supply is ok and the input diode overloaded?

Near the output resistor, I would suspect a cap in parallel to those two leads may have shorted. Since you have the schematic, try probing caps near those two leads with the ohmmeter. Not a guaranteed method, but I've tested a pure short on some bad caps in the past. Try comparing the values to the other channels.

If you're going to order parts, maybe you should also replace the large filtering electrolytics as a precaution. If it is a bad cap on one channel, probably best to replace the other channel's parts as well.
 

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Start with a complete recap of the unit. Why some of you think that oh its ok to just replace the bad cap, how do you come to that conclusion? The unit was built at one time with all of the components approx the same age. Chances are the amp was pushed for a number of years, so to take a chance that the one bad component replacement is good enough in the long term is just not sound repair work. Do you want to depend on the unit? Do you want the unit to last another 10-20 years? Then do a complete repair and don't screw around with questionable passives that are old and will start leaking. I have a mc431 unit, and there was no question on a complete recap of the unit.
I once had a guy working on an alpine 7909 transport control module, he replaced all of the SMD caps but he decided not to replace the 470 electrolytic cap. I asked him why didn't you replace the one cap. He said it tested good. My reply was simply, so you want to chance another failure of the unit because you did not want to replace a 25 cent cap, makes since to me.......
 

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how do you come to that conclusion?.

How? I don't know what type of time/budget/skill OP is working with to replace all 80. I mentioned even doing some precautionary replacement.

Also, it's all fun and games until you destroy a pad, have fun fixing that. I would agree to replace all, that is OP's choice.

Man, no good deed goes unpunished around here.
 

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Having completed a recap of my MC431 unit, I was not real impressed with the design of McIntosh amplifiers. single sided circuit boards, and the STK high watt drivers for the finals is not a selling point for me. I realize everyone likes the glass cover and all that , but realistically, the amps are not that special.

You really need a good solder extractor to ensure you don't mess up the pads like mentioned. I DON'T recommend solder wick anywhere on the circuit board, you will lift pads. Don't try the heat and pull method, ( and I NEVER recommend that method, I use it jokingly and sarcastically) that will screw up the board as well. So good luck.
 

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Personally, I wouldn't work on an expensive amp without an actual desoldering station. Too much work without one and too much risk of overheating the board and lifting traces. And if I'm going to replace a power supply cap in an old amp, I'm probably going to replace them all. At least the largest ones in the supply and then go from there. 105 degree C caps, brand name. No cheap or no name caps. But that's just me.

At any rate, you could have replaced that 1N4004 with a 1N4007. It's just a higher voltage rated version within the same series. Max current spec is the same.
 

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Discussion Starter · #14 ·
Personally, I wouldn't work on an expensive amp without an actual desoldering station. Too much work without one and too much risk of overheating the board and lifting traces. And if I'm going to replace a power supply cap in an old amp, I'm probably going to replace them all. At least the largest ones in the supply and then go from there. 105 degree C caps, brand name. No cheap or no name caps. But that's just me.

At any rate, you could have replaced that 1N4004 with a 1N4007. It's just a higher voltage rated version within the same series. Max current spec is the same.
You are right. It's difficult to remove caps from this mcintosh pcb. It seems the previous attempt at fixing some components on the board damaged some traces and some eyelets.

I don't have a desoldering station, only an old radio shack desoldering iron that doesn't seem very effective in removing solder from the eyelets even with flux. I'll avoid the desolder wick, thanks for the tip. If anyone has any tips to more easily remove components without a desoldering station that would be appreciated.

Right now my plan is to replace all the ps caps, and all the 10uf caps as recommended in other threads. Plus the resistor. I'll also look at the caps around the burnt resistor.

Thanks for the tip on the 1n4007.
 
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