M44 overloading Help!!

vegasrich77 · Post by **vegasrich77** » Sun Feb 21, 2010 2:26 am

I have my M44 running my mids and highs and just the other day out of nowhere they started fading out completely then they would fade back in. I looked at the amp as the sound started to fade out and the overload red LED came on. This would happen right when I first turn the radio on so it's not from the amp running along time. I took the amp apart and could not find any thing wrong with it visually...no leaky caps and no burnt areas on the board.

Does anyone know what could be causing this?

PLEASE HELP!!!!

Post by **ttocs** » Sun Feb 21, 2010 7:24 am

disconnect the speakers and rca's from the amp and power it back up. If it still reads overload then you probably have a bad amp, if it goes away then check your speaker connections for shorts.

Post by **Eric D** » Sun Feb 21, 2010 7:54 am

That might be caused from a loose wire strand somewhere inside the amp. I had the exact same issue on a M44 I worked on this week. It was a solder glob across two traces though, not a wire.

vegasrich77 · Post by **vegasrich77** » Sun Feb 21, 2010 9:04 am

I disconnected everything but the power and it still goes into overload. I will take it back apart and see if any wire strands or if a glob a solder is causing it.

Thanks for the help guys!

Post by **ttocs** » Sun Feb 21, 2010 3:55 pm

check the caps on it and see if they are showing any signs of expanding. Also take a piece of paper and try to slide it under the caps to see if there is anything leaking.

vegasrich77 · Post by **vegasrich77** » Sun Feb 21, 2010 7:13 pm

I check the caps and they look fine to me. I also checked with a piece of paper and everything is dry...no leaking.

I have attached some pictures....tell me what you think. If you need any additional pictures let me know.

Post by **ttocs** » Sun Feb 21, 2010 9:24 pm

nothing jumps out at me but it is hard to tell from picture. Look for spots on the board where it might have got hot and discolered it. If there is still nothing then take some compressed air and blow everything out of it and power it back up with the cover off.

vegasrich77 · Post by **vegasrich77** » Mon Feb 22, 2010 6:19 am

I looked at the board again and there is no areas that are discolored or anything that looks like heat damaged. I blew everything off with compressed air. I hooked the power back up and the same thing happpens. The weird thing is it does it randomly....as soon as the amp turns on it will go into overload then the green power LED will come on wait a couple of seconds and it will go into overload for a few seconds then less then a second later it will go back to green. I'm not moving the amp or even have any type of signal going to it, just the power, ground and remote wire is hooked up. Have any other ideas?

I wanted to thank everyone for trying to help me fix this... THANK YOU!!

Post by **Eric D** » Mon Feb 22, 2010 8:27 am

When too much current flows through the outputs, this engages the overload circuit. There are about 4 transistors and several resistors for EACH channel of the amp which make up the overload circuit.

Do you have a DMM (digital multi meter)?

bogart · Post by **bogart** » Mon Feb 22, 2010 8:36 am

Are you thinking bad bjt Eric....could well be a power supply issue too....not too sure....

Post by **Eric D** » Mon Feb 22, 2010 9:58 am

If one of the channels has an issue, output BJT, or even in the voltage gain stages, it may offset the output enough to trigger the overload circuit.

vegasrich77 · Post by **vegasrich77** » Mon Feb 22, 2010 10:08 am

I do have a DMM and what is a BJT?

bogart · Post by **bogart** » Mon Feb 22, 2010 10:16 am

I've seen problems like this in ms amps and the voltage gain between the ic and the bjts, easy to tell...check the voltages on the ic....

should be able to close the gates in the audio-path....lift the gate resistors and measure the in-circuit resistance of the bjts and see if there is a difference between the two sides...if one sides n or p channels are grossly out of tolerance you should see it through the comparison...

Eric...if it is an issue in the gain stages and it sounds like a bjt issue doesn't it....I've had the smaller drives in this circuit fail...I do believe you are referring to the smaller bjt's that turn the audio outputs on and off....and have some connection to the bias...not as confident or familiar with these amps as I would like....but I know that if these go out of tolerance you can have a distorted output...or protection engages depending on the severity of the failure....but anyway...should all of these on the board be replaced as with the audio outputs in the event of an issue ...or the series...

this is interesting to me....

bogart · Post by **bogart** » Mon Feb 22, 2010 10:25 am

it is a fet in the audio path...transistor....I will need to look some stuff up and have a look at the m44 here...but you can test all that you should have too with a dmm....

Eric knows way more about these amps then I do and he is better at explaining how to test and I generally have to look it up....

test the ic first....more info on this tonight....from me...if eric may be able to assist before I can get all the test info outlined

your ic has several legs that act as triggers if the voltage on the leg's are to high or to low the ic won't fire the bjt....overload protect....run the chip on google and find the trigger voltage for the proper legs...don't know them off hand...shit....

I am guessing that it is a transistor...either one of the smaller ones or audio output....but check it all....more on this later....

bogart · Post by **bogart** » Mon Feb 22, 2010 10:27 am

bjt means bi-polar junction transistor...your audio output bjt's are under the heat sink....there are two types...n channel and p channel and each drives one half...or 180 degrees of the the audio signal....if you think of a sine wave one runs the top half and one runs the bottom half of the wave. the systems biasing tunes the alignment between the two on each channel....there are three of each on each side all tied together via the gates...

there are smaller green and black ones in the visible board...these generate enough current to turn the audio outputs on and off when the ic turns over....the ic doesn't generate enough current to drive the large bjt's....if askew...they can do what you have described...but you should start by checking the ic....

Eric...I can't help much now as I am not home......

vegasrich77 · Post by **vegasrich77** » Mon Feb 22, 2010 12:04 pm

WOW...

I think I kind of understand what your saying. How do I go about testing all this stuff? what is my next step?

bogart · Post by **bogart** » Mon Feb 22, 2010 12:33 pm

look at the ic....sg2525a if I am not mistaken...should be a toshiba unit....but if you run the chip online you will be able to do some digging and come up with the schematic for the ic....on this it will give you the input pins and what you will be looking for in a protection circuit or circuit are the error amp pins and look and the schematic outlines...you will see the target value for each pin....KNOW YOUR GROUND....on the ic....power it up and test the legs per the schematic for the ic....you will most likely find a value of over 3.6 volts on one of the error pins which will mean that it is triggered....

follow the trace....see what you find...be careful....when you pull the amp apart farther you will see all your fets....power supply fets are irz or such....your bjts will be bigger and you can do the same for them....one could be an sc such and such and one an sa....but what ever you will see that one is an n channel...the other a p channel.....eric may be better at describing this then me....I don't have the amp in front of me....

And what I would do to test it may well not be the best or the easiest....I am just a hobbiest....mad tinkerer I guess....

I will pull the m44 of leeds here out this evening once I am done with another project that I have to do this evening....take some pics and give this outline some thought......

I suspect Dc will tell you how to test and where to look first...I have the ic diagrams on file but I have to look all the stuff up too

bogart · Post by **bogart** » Mon Feb 22, 2010 12:35 pm

my typing blows...sorry for the typo's in abundance....

Post by **Eric D** » Mon Feb 22, 2010 1:20 pm

I will gladly help were I can. I have a M44 right next to me so I can snap photos and give you some direction. However, I am swamped at the moment. My father-in-law's business computer took a shit, and I am leaving soon to work on it (1 hour drive each way). So I am done for tonight.

I would start by looking for shorts with the DMM on all 8 of the output transistors, and on all 16 of the smaller transistors which drive the main output transistors. If you look on the board for the bias controls (4 small orange potentiometers), you will find 4 transistors near each pot sticking up off the board. On some amps 2 of the 4 will be green. On other amps 2 of the 4 will have yellow dots on them. These are drivers for that channel. 4 channels x 4 drivers, is 16 in all.

vegasrich77 · Post by **vegasrich77** » Mon Feb 22, 2010 1:48 pm

Ok, I will start checking the transistors and let you know what the results are.

Thanks again for all the help!

vegasrich77 · Post by **vegasrich77** » Mon Feb 22, 2010 9:48 pm

OK, I thought I knew how to test transistors but now that I read some stuff online....I'm confused. Can either of you point me in the direction or emplain to me what I need to look for and kind of how to?

Post by **Eric D** » Tue Feb 23, 2010 7:33 am

I put the DMM in diode check mode and then I check all 6 possible combinations of ways to put the two leads on a three pin device. If you find two leads which measure shorted in both directions, there is a chance that device has failed.

vegasrich77 · Post by **vegasrich77** » Fri Feb 26, 2010 1:54 am

OK... I checked all the transistors and they tested ok. After I finished testing them I was a little bored so I decided to check the amp again. With the amp still completely out of its case, I first hooked up power only to it and it didn't go into overload mode once. I let it sit powered up for about a half hour and nothing happened. I tried shacking it lightly and tapping on the caps trying to get it into overload and still never went into overload. Then I decided to see what would happen if played some music through it. I took two 6 1/2 Peerless speakers and started playing music through it at a low volume at first. I did each channel by themself and let it play for 3 or 4 minutes everything was working fine. Then I started trying every different configuration possible, left and right front channel, left and right rear channel, turning the gain all the way up, adjusting the crossovers, I bridged both sides and played the rear by itself and played the front by itself it was working fine. By this time the amp was getting nice and warm. I thought everything was fine until I really started turning up the volume to almost max listen level and all of a sudden it went into overload for a split second (WTF!!!). With playing around with different configurations again i found that it only does it when the front channels are being used but still not all the time.. At one point I had the gains turned all the way up the music was very load (I think i pissed off some of my neighbors) and it would play fine then it would go into overload for a split second. The amp was never very hot, just warm. Is this amp just have a mind of it's own or do you guys know what it might be? The only thing I can think of is a loose solder connection but i checked the whole board and everything looks fine.

Any suggestions??

Post by **Eric D** » Fri Feb 26, 2010 4:44 am

Sounds like the amp is fine. If you start clipping the amp heavily and output current increases significantly it will go into overload. Overload should not have anything to do with heatsink temp, that is what the thermal light is for.

vegasrich77 · Post by **vegasrich77** » Tue Mar 02, 2010 12:29 am

So I thought everything was fine but I was wrong, it's still goes into overload. I have gotten a little further with where the problem area is...the front two channels. I tried both channels by themselves and the amp would go into overload at about 1/4 of the normal volume. I then bridge the front channels and let it play at half volume and full volume and it never went into overload. Does this information help you at all?