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Old 30th December 2004, 05:07 PM   #1
mjarve is offline mjarve  United States
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Question McIntosh 5100 - worth restoration?

Not exactly DIY, unless you count DIY restoration, but I have an opportunity to get a McIntosh 5100 integrated amp in non-working condition in direct exchange for a harman/kardon 930 receiver in perfect working order. As they say, a bird in the hand is worth two in the bush, but this may be my only chance to get a piece of Mac gear, unless by some strange fortune I win the lottery.

The problem with the Mac is that it outputs 27VDC at the speaker terminal, cooking speakers. I am thinking that a driver or output transistor is bad, or if it capacitor coupled (would it be?) the output cap for that channel may have shorted. I have not seen the amp yet, and the person who owns it right now is not very technically inclined.

So my first question is this: Is a h/k 930 a fair exchange for a Mac 5100? The little research I performed indicated that it would be, as at least on paper, the amps are very comparable, and the 930 actually had a higher retail price than the 5100 (1973 and 1972 respectively). The 5100 has a higher book value now though.

My second question is: Are McIntosh components, in particular the 5100, fairly easy to service (parts still available, etc.) or is it a money pit? I even heard one rumor that I could send it to McIntosh Labs for repair, costing me only shipping one way, although the Mac site does not bare that out.
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Old 31st December 2004, 02:56 AM   #2
anatech is offline anatech  Canada
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Hi mjarve,
McIntosh, last I checked, still fully supported their products. There may be some substitutions needed, by the unit should be repairable.
Is this the MA 5100, 45 W/Ch ?

If this is both channels, check the 115VDC bias for the differential pairs. This is not a full rail output, so you don't have a classic shorted output situation. Also, it isn't blowing fuses. This suggests the output stages are okay.
I'd say, go for it. -Chris
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Old 31st December 2004, 03:00 PM   #3
mjarve is offline mjarve  United States
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Indeed, it is the 45WPC SS version. The current owner indicated, oddly enough, that it sounds fine despite the fact that it will blow the speaker.

I'm going for it. I just know that if I do not, I'll regret it forever. Besides, I have two more 930's tha could use some attention as well.
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Old 31st December 2004, 03:11 PM   #4
anatech is offline anatech  Canada
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Hi Mike,
Good choice. I've rebuilt lots of 930's. The Mac is worthwhile. It is repairable and it's not transformer output.
-Chris
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Old 22nd February 2009, 10:05 AM   #5
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Default Mac 5100 problem

The unit seems to be sputtering, almost like motorboating bit not quite. It seems to cut in and out. The power supply so far seems ok, most voltages are ok, still have more to check.
The 115 volt line for the differential as mentioned in another post here seems ok.
Any ideas guys??
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Old 23rd February 2009, 02:53 AM   #6
anatech is offline anatech  Canada
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Hi tubenut99,
Where are you located? PM me if you don't want to broadcast your location.

You may have open decoupling capacitors, or high impedance. That is a sure way to cause motor-boating. Does it at least keep time to the music?

Hi Mike,
If it has pre out / main in loops or switch, disconnect the amp from the rest of the electronics. If you have shorting RCA plugs, put them into the main in jacks. If you can make them easily, it is safer that you do so. 27 VDC at the speaker output is not very nice.

Your fault should be in the voltage amp section of the amplifier. Check the solder joints around the Vas transistor. They can run pretty warm in some designs. That would be Q211 mounted of the PCB. Also, R231 is a pull up resistor, 3K6. Check both and the solder connections. Basically, check all parts that run hot and their solder connections.

Happy hunting Mike!

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