MC2205 Main Filter Caps Shorting?
- Thread starter Thinker
- Start date
Someone here said something like $40.00 from Mac for the exact same probable problem to happen again.
I say hard wire it and be done with the problem forever...I did the last one hard wire and zip ties and it will be holding the amp together in the next life.....
No one will see the cabling so its a who cares kind of deal especially when it never fails again....and is strong enough to hold the amp in mid air. The original ribbon cables all fail IMHO, and its due to their losing their hermetic seal to outside air and moisture...The ribbon was used to speed up assembly, and they were cost efficient, until you take into account there long term failures...Upgrade, and hard wire and be done with it forever..Just my humble point of view..:yes:
Anything below 10MVDC is acceptable to me, Polarity is a non issue. Beat up amplifiers exhibit high DC offsets. Even car amp makers have offset limits on their first run products and their rebuilds. It's a very tell tale test tech number for Balanced complimentary class AB amplifiers.
I have seen numbers as high as 100 to 300 MVDC per channel and of course those amps were tripping their internal protection circuitry for no apparent reason. Solve the offset and VIOLA ! amp is normal again...
In the case of Mac and their super Auto transformers the transformers shunt any DC fundamentals to ground protecting your expensive speakers much faster and smoother then any electronic protection circuitry probably ever could.
Down side is hidden DC offset can cause excessive overheating of output devices and unstable amp operation and reduced output power levels since the DC eats up the amps audio power and can grow with higher levels of audio drive thus keeping the amp from its real world potential. I never buy an amp without checking its DC offset....and I never let one off my bench until its under proper spec and no ghosts or DC fundamentals being output to speakers or transformers in this case...
Bravo Mac and their infinite foresight about auto transformers and solid state amplifiers, and speaker protection !
Oh and the transformers also limit the amps interaction with unstable speaker loads so the amp sees a more stable load to play into, and it also keeps a 200 watt per channel amp at 200 watts per channel no matter what load you connect. So its also a power limiter of sorts, that protects the amp from crazy low or unpredictable speaker loads pulling all sorts of odd power levels beyond what the amp was meant to do.
JL and PG did similar electronic versions of this in many of their 2000 YM and on car amps. It kept low ohm bass crazy people from blowing up perfectly good amp by trying to get 2, 3, and 4 times their rated 4 ohm power out of their amps, by running supper odd ball low ohm impedance's to the amp output stages.
I was thinking the same thing, any suggestions for how to go about it, wire gauge etc.? it would be awesome if you had any pics
I'm guessing that the negative DC offset is ok?
opps sorry been resting today here are the pics you asked for..Oh and your DC offset is fine IMHO... anything below my threshold of 10MVDC is fine
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Yeah I'm with c_dk this is first i heard of your power guard lamp being on constantly??????????????So whats up my friend just the power guard lamp ?
Thinker
Super Member
Found it!
So the power guard lamp on the right channel has been on ever since the amp started working.... When I first got the amp everything came on but the output relay wouldn't engage and the meters wouldn't respond, the normal lights were lit though.
I took the whole thing apart, cleaned the connections and put it back together and voila meters came on and the relay kicked in (without delay) but the right power guard light was on and the right meter on watts showed full power, also the right heatsink got toasty fast.
That's when I found out that one of the output transistors was bad. I replaced all the output transistors for both channels and reassembled the amp. The right meter no longer showed full power and that's were this thread came in with the relay coming on with the amp instead of with a delay and the right limit light coming on but some times going off if the relay was switched on and off a couple times.
So I figured it out today. I knew that something was wrong because the right limit light would come on even with the right driver board disconnected. The transistor on the power board that controls the limit light doesn't engage unless the transistor on the driver board engages and makes a path to ground. So I thought it was the transistor on the power board that controls the limit light had gone bad and I tested it today, it tested fine, then I was really confused, I thought it has to be connecting to ground some how to engage so I took my multimeter to ground and pin 4 of the cable that goes to the driver board and there was a resistance reading of 7 kohm, I thought this can't be right and checked the left side and there was no reading "open" so I followed the cable and I didn't see anything but I thought just to be safe I took a q-tip and rubbed all around the section where the wire was soldered to the power board socket measured again and there was no reading "open" connected everything and the limit light went off, and the relay has a slight delay on and turns off after the amp much faster. There had to be something small conducting in there, a fine strand of metal or a speck of solder, something and it was causing a connection to ground.
I can't help but, laugh to think that my mind boggling problem was caused by something so small and simple. I'm reminded of the saying: you can laugh or you can cry, I prefer to laugh.
So the power guard lamp on the right channel has been on ever since the amp started working.... When I first got the amp everything came on but the output relay wouldn't engage and the meters wouldn't respond, the normal lights were lit though.
I took the whole thing apart, cleaned the connections and put it back together and voila meters came on and the relay kicked in (without delay) but the right power guard light was on and the right meter on watts showed full power, also the right heatsink got toasty fast.
That's when I found out that one of the output transistors was bad. I replaced all the output transistors for both channels and reassembled the amp. The right meter no longer showed full power and that's were this thread came in with the relay coming on with the amp instead of with a delay and the right limit light coming on but some times going off if the relay was switched on and off a couple times.
So I figured it out today. I knew that something was wrong because the right limit light would come on even with the right driver board disconnected. The transistor on the power board that controls the limit light doesn't engage unless the transistor on the driver board engages and makes a path to ground. So I thought it was the transistor on the power board that controls the limit light had gone bad and I tested it today, it tested fine, then I was really confused, I thought it has to be connecting to ground some how to engage so I took my multimeter to ground and pin 4 of the cable that goes to the driver board and there was a resistance reading of 7 kohm, I thought this can't be right and checked the left side and there was no reading "open" so I followed the cable and I didn't see anything but I thought just to be safe I took a q-tip and rubbed all around the section where the wire was soldered to the power board socket measured again and there was no reading "open" connected everything and the limit light went off, and the relay has a slight delay on and turns off after the amp much faster. There had to be something small conducting in there, a fine strand of metal or a speck of solder, something and it was causing a connection to ground.
I can't help but, laugh to think that my mind boggling problem was caused by something so small and simple. I'm reminded of the saying: you can laugh or you can cry, I prefer to laugh.
