Measure the DC voltage on the LM311 near R140/142. Place your black meter probe on pin 4. Measure the voltage to each of the other pins.
Don't let the probes slip and don't touch them. All pins have ~negative rail voltage on them.
'Across' means one probe on each of the terminals of the resistor.
Don't let the probes slip and don't touch them. All pins have ~negative rail voltage on them.
'Across' means one probe on each of the terminals of the resistor.
MatthewS,
Hello! No, I have not worked on my 6500D in sometime now, a month or two ago I actually reassembled the amp so the board does not get damaged as I have been moving the amp around to make room for other things & I was afraid the board was going to get damaged from something possibly falling inside it (which already almost happened). I thought I lost some of the screws, the logo, the heat sink transistor clamps etc. however, I was able to locate it all, so it is complete.
The last time I tried to check what Perry asked me to check the amp was acting kind of funny; it seemed like when I tried to check, R133, Q110, R112 (I cannot remember which one it was but) every time (or most of the time) I put my multi-meter probes on one (maybe more) of those parts trying to check the DC voltages the amp would start oscillating on its outputs, the oscillations were clean at first, but then they would start to get really distorted on my scope & after a while they would stop again, while oscillating though the amp did have audio output, although I noticed while adjusting one of the controls on the amp (I do not remember which one) the speaker would pop or thump really bad. It seemed like every time I tried to check the voltages on those parts it would start oscillating, I checked the solder connections on & around those parts, I even tried pressing down on them with a plastic tool to try to make them make contact, but nothing, it only did it with my multi meter or scope probe.
I never did get around to posting what was going on & what I did find; I figured sooner or later I would get to it. Here I am a year later & the amp is still sitting. I really want to repair this amp & I have not given up, just need to sit back down with it & go over what Perry asked to check again. I will follow along with yours, as it seems like a similar problem. Good luck with your repair! Take care!
Hello! No, I have not worked on my 6500D in sometime now, a month or two ago I actually reassembled the amp so the board does not get damaged as I have been moving the amp around to make room for other things & I was afraid the board was going to get damaged from something possibly falling inside it (which already almost happened). I thought I lost some of the screws, the logo, the heat sink transistor clamps etc. however, I was able to locate it all, so it is complete.
The last time I tried to check what Perry asked me to check the amp was acting kind of funny; it seemed like when I tried to check, R133, Q110, R112 (I cannot remember which one it was but) every time (or most of the time) I put my multi-meter probes on one (maybe more) of those parts trying to check the DC voltages the amp would start oscillating on its outputs, the oscillations were clean at first, but then they would start to get really distorted on my scope & after a while they would stop again, while oscillating though the amp did have audio output, although I noticed while adjusting one of the controls on the amp (I do not remember which one) the speaker would pop or thump really bad. It seemed like every time I tried to check the voltages on those parts it would start oscillating, I checked the solder connections on & around those parts, I even tried pressing down on them with a plastic tool to try to make them make contact, but nothing, it only did it with my multi meter or scope probe.
I never did get around to posting what was going on & what I did find; I figured sooner or later I would get to it. Here I am a year later & the amp is still sitting. I really want to repair this amp & I have not given up, just need to sit back down with it & go over what Perry asked to check again. I will follow along with yours, as it seems like a similar problem. Good luck with your repair! Take care!
Ok, update time.
Perry,
Using pin 4 of LM311 for GND REF, I measured the following on q110:
Pin 1 (base) - 5.85v
Pin 2 (emitter) - .003v
Pin 3 (collector) - 59.3v
Which tells me this transistor is off in the weeds somewhere. I threw the board back under the magnifier, and sure enough the top was tinted. It looks like it thermaled it's life away. I'll have to pay closer attention to this in the future.
For posterity this transistor is labled G1 and I have that as;
BC847
BFS20
BF199
MMBT5551
Can I use the MMBT5551 here? it's got higher ratings..
I'm going to put these on my next order and check back in next week when this thing starts making noise again. Thanks a heap for all your help Perry!
- Matt
Perry,
Using pin 4 of LM311 for GND REF, I measured the following on q110:
Pin 1 (base) - 5.85v
Pin 2 (emitter) - .003v
Pin 3 (collector) - 59.3v
Which tells me this transistor is off in the weeds somewhere. I threw the board back under the magnifier, and sure enough the top was tinted. It looks like it thermaled it's life away. I'll have to pay closer attention to this in the future.
For posterity this transistor is labled G1 and I have that as;
BC847
BFS20
BF199
MMBT5551
Can I use the MMBT5551 here? it's got higher ratings..
I'm going to put these on my next order and check back in next week when this thing starts making noise again. Thanks a heap for all your help Perry!
- Matt
Yep. It's toast.
In the future, use a colon instead of a dash for the separator. My feeble mind thinks 'negative' when I see the dash.
G1 = MMBT5551LT
http://www.onsemi.com/pub_link/Collateral/MMBT5550LT1-D.PDF
In the future, use a colon instead of a dash for the separator. My feeble mind thinks 'negative' when I see the dash.
G1 = MMBT5551LT
http://www.onsemi.com/pub_link/Collateral/MMBT5550LT1-D.PDF
I forgot I had 9 of these left from a fosgate 200DSM I've been slowly bringing back to life. I popped the replacement 5551 into the amp today and it roared back to life!
I ran it for about an hour @ around 50 watts of output while I cleaned up the rest of the chassis, etc. Clean sine wave, no thermal issues, no other problems detected. It's ready for a home.
It's a very nice feeling to know it will be making music again somewhere. I hate to see an amp go to the dump and thats where this one was headed when I got it for free.
Note to anyone who finds this to be an issue; Remove the two through hole caps that box this part in before removal and replacement. It's not necessary but if your not careful you'll burn them.
Thanks a heap Perry! Your contributions here are invaluable!
- Matt
I ran it for about an hour @ around 50 watts of output while I cleaned up the rest of the chassis, etc. Clean sine wave, no thermal issues, no other problems detected. It's ready for a home.
It's a very nice feeling to know it will be making music again somewhere. I hate to see an amp go to the dump and thats where this one was headed when I got it for free.
Note to anyone who finds this to be an issue; Remove the two through hole caps that box this part in before removal and replacement. It's not necessary but if your not careful you'll burn them.
Thanks a heap Perry! Your contributions here are invaluable!
- Matt
Hi, I have been looking over this post for a little bit now. Im a college student taking classes for electronics Tech. I bought a MTX 6500D amp off of ebay, and the guy said that it powers up but dosent get any audio going to the subs. I plan on working on this amp next week, I just got one little question. Im going to hook the amp up to a DC power supply in our lab at school. What should I do with the remote lead from the amp?? Do I even need to worry about that??
You have to apply 12v to the remote lead for the amp to power up.
Before you do any work on the amp, read through the basic repair page (link below).
When you connect the amp to the power supply, you'll need to insert a 10 amp fuse in the B+ line (unless the power supplies have a current limiting function).
Before you do any work on the amp, read through the basic repair page (link below).
When you connect the amp to the power supply, you'll need to insert a 10 amp fuse in the B+ line (unless the power supplies have a current limiting function).
Hey thanks alot for getting back to me so soon. I have went through and spent alot of time reading up on that web page, I even gave the link to a bunch of my classmates because their is so much great info on that site. I was just a little confused about how to hook the amp up to the power supply. So should I just run the power from the PS to the ground, and the remote of the amp?? Or should it go to the ground, power, and the remote of the amp??
http://www.bcae1.com/pwrsupdc.htm
If you're not using a head unit for a signal source, the remote turn-on for the amp will go to the positive terminal of the power supply.
If you're not using a head unit for a signal source, the remote turn-on for the amp will go to the positive terminal of the power supply.
I looked at that page before I started asking questions and it kind of made sense. Why do they have a switch in between the remote lead, and the D/C source? And what size of fuse should I use, 25A? And do you think I should be use the 4-6 gauge wire for the power, or just normal test leads since I’m only doing trouble shooting?
And do you know what size of diode goes in for D3?
I'm just asking because I have looked over the board and I noticed that was missing, and their is one other peice missing, which I have no idea what it is. In the rectangle box shape on the board where it is suppose to go, it says C630. It is down by where you put in the ATc fuses, and right next to FET603 and FET604. Do you think that might be a surface mount fuses of some sort?
And do you know what size of diode goes in for D3?
I'm just asking because I have looked over the board and I noticed that was missing, and their is one other peice missing, which I have no idea what it is. In the rectangle box shape on the board where it is suppose to go, it says C630. It is down by where you put in the ATc fuses, and right next to FET603 and FET604. Do you think that might be a surface mount fuses of some sort?
I looked at that page before I started asking questions and it kind of made sense. Why do they have a switch in between the remote lead, and the D/C source?
**** That's for when you are using a signal source that can't switch the remote voltage. It allows you to turn the amp off easily.
And what size of fuse should I use, 25A?
**** Much smaller for testing (10-15 amp - 10 amp preferred).
And do you think I should be use the 4-6 gauge wire for the power, or just normal test leads since I’m only doing trouble shooting?
**** Short lengths of 14-16g are sufficient for testing.
And do you know what size of diode goes in for D3?
**** It was omitted in the later revisions.
I'm just asking because I have looked over the board and I noticed that was missing, and their is one other peice missing, which I have no idea what it is. In the rectangle box shape on the board where it is suppose to go, it says C630. It is down by where you put in the ATc fuses, and right next to FET603 and FET604. Do you think that might be a surface mount fuses of some sort?
**** It was omitted also. It would have been a capacitor.
**** That's for when you are using a signal source that can't switch the remote voltage. It allows you to turn the amp off easily.
And what size of fuse should I use, 25A?
**** Much smaller for testing (10-15 amp - 10 amp preferred).
And do you think I should be use the 4-6 gauge wire for the power, or just normal test leads since I’m only doing trouble shooting?
**** Short lengths of 14-16g are sufficient for testing.
And do you know what size of diode goes in for D3?
**** It was omitted in the later revisions.
I'm just asking because I have looked over the board and I noticed that was missing, and their is one other peice missing, which I have no idea what it is. In the rectangle box shape on the board where it is suppose to go, it says C630. It is down by where you put in the ATc fuses, and right next to FET603 and FET604. Do you think that might be a surface mount fuses of some sort?
**** It was omitted also. It would have been a capacitor.
Hey thanks alot for your help, Im still new to the whole trouble shooting thing. Im going to take it into school tomorrow, well maybe if I have time and do some work on it. Well I dont have a CD player to hook up to it, so would I be able to use a Function generator in place of a CD player?? Or would that even work?? Or do I even need it???
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