Looking at the internal schematic for the LM311, it looks like it could possibly survive. Don't replace it yet.
Check Q101 and Q102 to see if either one is leaking (electrically) or shorted.
Did you check the 0,22 ohm resistors near the output transistors to see if they were OK? There are several in parallel. If they don't appear to be damaged and essentially read 0 ohms, they're likely OK.
Check Q101 and Q102 to see if either one is leaking (electrically) or shorted.
Did you check the 0,22 ohm resistors near the output transistors to see if they were OK? There are several in parallel. If they don't appear to be damaged and essentially read 0 ohms, they're likely OK.
Ok, I can’t believe it has been over three years since I started this thread, but thought I would do some more testing on my 6500D (yes it is still not working yet). Like I said, I did not give up on it, just a slow project I guess. Hopefully I will still be able to get some help with this.
I’ll start by going over stuff I checked:
(note: some of the readings may be different from when I last checked things a few years ago as I noticed when I touch my oscilloscope probes, or multi-meter probes on certain parts, example one side of R133 to get the measurements for Perry the amp starts to oscillate & produce output, but the oscillations get really blurry after a short period of time & come & go, it only does it with a metallic object, if I touch the part with plastic or wood it does nothing. This does change the readings bit from when it won’t oscillate to when it does. Also, when it oscillates & has output, when the gain control is adjusted the speaker flutters & pops / moves really badly)
At the point of these measurements the amp is oscillating right now (but the waveform is fuzzy compared to Perry’s 250D & is kind of in & out)
Checking for audio on the op-amp by the 4 conductor connector, with a sine wave fed into the amps input, gain wide open: pin-1 shows a low level signal but very blurry & you cannot really make out a sine wave, just looks terrible; pin-7 shows a higher amplitude signal / sine wave & looks like a relatively clean sine wave.
The DC voltage across R140 /R142:
R140: 1.41vDC
R142: 1.43vDC
Checking D106, R133, Q110, R112 in circuit with the amp off they test as follows with my ohm meter / diode check function. (what I am seeing for D106 looks like D108 on my board, but the board number is a little blurry, but it is right next to R133.
D106: measures 7.07v on diode check in circuit
R133: measures 907 ohm in circuit
Q110: from Base to Emitter it read close to 0.9v on diode check so I removed it from the board & out of circuit it measures 1.07v on diode check, so it appears to be faulty. Unless that’s normal for this transistor?
R112: measures 99.9 ohm in circuit
Now the DC voltage measured across them; amp at idle, no signal at input (for all voltage measurements):
D106: 5.99vDC
R133: 5.50vDC
Q110:
Base to Emitter: 0.48vDC
Collector to Emitter: 54.1vDC
R112: 0.002vDC
I’ll go ahead & post the DC voltages for the LM311. Using pin-4 as the ground reference.
LM311
Pin 1: 0.00v
Pin 2: 0.050v
Pin 3: 2.00v
Pin 4: Ground Reference
Pin 5: 15.1v
Pin 6: 15.1v
Pin 7: 0.290v
Pin 8: 15.3v
Measuring the DC voltage on all 3 terminals of Q110 using pin-4 of the LM311 for the ground reference:
Q110
B: 6.02v
C: 59.7v
E: 5.5v (when the oscillations flutter around the voltage jumps around from around 1v to 5v or so, but when it is oscillating it stayed steady at 5.5v)
On a side note, since I suspected Q110 to be faulty I soldered in a TO-92 case size 2SC2240 for testing since I had it here, but all the voltage measurements were about the same, very, very slight differences, like the last digit was plus or minus a little. The 2SC2240 may not be the greatest for that, but thought it would work for quick testing according to its specs. But the original transistor may be ok, readings looked off to me, but it may be suppose to read like that.
Alright, just trying to go back over everything again as well as the stuff I never did get around to checking. I appreciate any help on this & all the help I received in the past!
I’ll start by going over stuff I checked:
(note: some of the readings may be different from when I last checked things a few years ago as I noticed when I touch my oscilloscope probes, or multi-meter probes on certain parts, example one side of R133 to get the measurements for Perry the amp starts to oscillate & produce output, but the oscillations get really blurry after a short period of time & come & go, it only does it with a metallic object, if I touch the part with plastic or wood it does nothing. This does change the readings bit from when it won’t oscillate to when it does. Also, when it oscillates & has output, when the gain control is adjusted the speaker flutters & pops / moves really badly)
At the point of these measurements the amp is oscillating right now (but the waveform is fuzzy compared to Perry’s 250D & is kind of in & out)
Checking for audio on the op-amp by the 4 conductor connector, with a sine wave fed into the amps input, gain wide open: pin-1 shows a low level signal but very blurry & you cannot really make out a sine wave, just looks terrible; pin-7 shows a higher amplitude signal / sine wave & looks like a relatively clean sine wave.
The DC voltage across R140 /R142:
R140: 1.41vDC
R142: 1.43vDC
Checking D106, R133, Q110, R112 in circuit with the amp off they test as follows with my ohm meter / diode check function. (what I am seeing for D106 looks like D108 on my board, but the board number is a little blurry, but it is right next to R133.
D106: measures 7.07v on diode check in circuit
R133: measures 907 ohm in circuit
Q110: from Base to Emitter it read close to 0.9v on diode check so I removed it from the board & out of circuit it measures 1.07v on diode check, so it appears to be faulty. Unless that’s normal for this transistor?
R112: measures 99.9 ohm in circuit
Now the DC voltage measured across them; amp at idle, no signal at input (for all voltage measurements):
D106: 5.99vDC
R133: 5.50vDC
Q110:
Base to Emitter: 0.48vDC
Collector to Emitter: 54.1vDC
R112: 0.002vDC
I’ll go ahead & post the DC voltages for the LM311. Using pin-4 as the ground reference.
LM311
Pin 1: 0.00v
Pin 2: 0.050v
Pin 3: 2.00v
Pin 4: Ground Reference
Pin 5: 15.1v
Pin 6: 15.1v
Pin 7: 0.290v
Pin 8: 15.3v
Measuring the DC voltage on all 3 terminals of Q110 using pin-4 of the LM311 for the ground reference:
Q110
B: 6.02v
C: 59.7v
E: 5.5v (when the oscillations flutter around the voltage jumps around from around 1v to 5v or so, but when it is oscillating it stayed steady at 5.5v)
On a side note, since I suspected Q110 to be faulty I soldered in a TO-92 case size 2SC2240 for testing since I had it here, but all the voltage measurements were about the same, very, very slight differences, like the last digit was plus or minus a little. The 2SC2240 may not be the greatest for that, but thought it would work for quick testing according to its specs. But the original transistor may be ok, readings looked off to me, but it may be suppose to read like that.
Alright, just trying to go back over everything again as well as the stuff I never did get around to checking. I appreciate any help on this & all the help I received in the past!
Thank you for the help Perry!
I hate to ask, but is there any particular part number from mouser that would be the best for Q110? All the additional part numbers make it confusing on which would be best. Just want to make sure I get the right one when I order.
Any other parts I should get?
I am thinking an extra or two LM311, maybe some op-amps incase I need them, anything else that I might need or be a good idea to get for this amp?
Also, does mouser carry the thermal pads / insulators for the transistors, etc. They got ripped up over the years now. I have Kapton tape down, but one of the power supply FETS overlap the black paint they painted the amp with (they painted too far over) & does not sit flush on the heat-sink, I don’t feel like sanding the sink right there (looks like a pain) & figure the pads would be easier to use.
I hate to ask, but is there any particular part number from mouser that would be the best for Q110? All the additional part numbers make it confusing on which would be best. Just want to make sure I get the right one when I order.
Any other parts I should get?
I am thinking an extra or two LM311, maybe some op-amps incase I need them, anything else that I might need or be a good idea to get for this amp?
Also, does mouser carry the thermal pads / insulators for the transistors, etc. They got ripped up over the years now. I have Kapton tape down, but one of the power supply FETS overlap the black paint they painted the amp with (they painted too far over) & does not sit flush on the heat-sink, I don’t feel like sanding the sink right there (looks like a pain) & figure the pads would be easier to use.
I’m putting together a parts list & going over other amps I have that need parts so when I do order I can fix a few amps, but it may be a little while until I get that done & get the order placed.
For further troubleshooting until I order, I am wondering if an R1G transistor which appears to be a MMSTA06 will work in place of the 1G MMBTA06.
Looks like the same transistor pretty much. I have a couple R1G transistors & they appear to be MMSTA06. Just curious is all, could put one in for more testing to see if we could find other problems.
They both appear to be a cross for an MPSA06.
Here is the datasheet for it:
http://www.rohm.com/products/databook/tr/pdf/ssta06.pdf
For further troubleshooting until I order, I am wondering if an R1G transistor which appears to be a MMSTA06 will work in place of the 1G MMBTA06.
Looks like the same transistor pretty much. I have a couple R1G transistors & they appear to be MMSTA06. Just curious is all, could put one in for more testing to see if we could find other problems.
They both appear to be a cross for an MPSA06.
Here is the datasheet for it:
http://www.rohm.com/products/databook/tr/pdf/ssta06.pdf
Ok, I went ahead and replaced Q110 with the R1G transistor. I tested the transistor before putting it in & it tested good.
The amp appears to be doing the same with this transistor as well. All the voltages posted in post # 63 are still about the same, again, only slight changes.
I’ll post all the voltages I’m getting with this transistor in the circuit:
Measured across:
D106: 5.98vDC (again this one looks like D108 in my amp).
R133: 5.65vDC
Q110:
Base to Emitter: 0.371vDC
Collector to Emitter: 54.1vDC
Measured across:
R112: 0.002vDC
LM311. Using pin-4 as the ground reference.
Pin 1: 0.00v
Pin 2: 0.051v
Pin 3: 2.00v (the 4th digit jumps around a bit but stays about 2.00 to 2.01v
Pin 4: Ground Reference
Pin 5: 15.1v (last digit jumps around here too, 15.1 to 15.2v)
Pin 6: 15.1v (last digit jumps around here too, 15.1 to 15.2v)
Pin 7: 0.290v
Pin 8: 15.3v (last digit jumps around too, 15.2 to 15.4v)
(the readings jumped around in my other post too, I just rounded them to where they stayed close too, may not even matter)
Measuring the DC voltage on all 3 terminals of Q110 using pin-4 of the LM311 for the ground reference:
Q110
B: 6.01v
C: 59.7v
E: 5.65v
Those big surface mount resistors by the LM311 get really hot, I do realize there higher wattage resistors for a reason, the LM311 gets pretty hot too probably being heated by them. Measuring the temperature on the resistors with my cheap multi-meter temperature probe they show there at 115 degrees C, that’s 239 degrees F, I know resistors can run hot. The LM311 shows 76 degrees C which is about 168.8 degrees F. That seems a little warm for the LM311. Of course who knows how accurate the meter is, just thought I would check since I have it & noticed the resistors were really hot.
The amp appears to be doing the same with this transistor as well. All the voltages posted in post # 63 are still about the same, again, only slight changes.
I’ll post all the voltages I’m getting with this transistor in the circuit:
Measured across:
D106: 5.98vDC (again this one looks like D108 in my amp).
R133: 5.65vDC
Q110:
Base to Emitter: 0.371vDC
Collector to Emitter: 54.1vDC
Measured across:
R112: 0.002vDC
LM311. Using pin-4 as the ground reference.
Pin 1: 0.00v
Pin 2: 0.051v
Pin 3: 2.00v (the 4th digit jumps around a bit but stays about 2.00 to 2.01v
Pin 4: Ground Reference
Pin 5: 15.1v (last digit jumps around here too, 15.1 to 15.2v)
Pin 6: 15.1v (last digit jumps around here too, 15.1 to 15.2v)
Pin 7: 0.290v
Pin 8: 15.3v (last digit jumps around too, 15.2 to 15.4v)
(the readings jumped around in my other post too, I just rounded them to where they stayed close too, may not even matter)
Measuring the DC voltage on all 3 terminals of Q110 using pin-4 of the LM311 for the ground reference:
Q110
B: 6.01v
C: 59.7v
E: 5.65v
Those big surface mount resistors by the LM311 get really hot, I do realize there higher wattage resistors for a reason, the LM311 gets pretty hot too probably being heated by them. Measuring the temperature on the resistors with my cheap multi-meter temperature probe they show there at 115 degrees C, that’s 239 degrees F, I know resistors can run hot. The LM311 shows 76 degrees C which is about 168.8 degrees F. That seems a little warm for the LM311. Of course who knows how accurate the meter is, just thought I would check since I have it & noticed the resistors were really hot.
I think the heat from the resistors is definitely heating up the LM311, that whole area gets really warm.
The voltage on the collector of Q673 is pretty constant. Measured with the black probe on the amps ground terminal:
81.9vDC
Here again the last digit lightly moved from 81.8v to 82v, but it was a slow change & stayed about 81.9v.
Voltage measured across R660.
R660: 3.33vDC
The voltage on the collector of Q673 is pretty constant. Measured with the black probe on the amps ground terminal:
81.9vDC
Here again the last digit lightly moved from 81.8v to 82v, but it was a slow change & stayed about 81.9v.
Voltage measured across R660.
R660: 3.33vDC
Checking with the ohm meter, the collector of Q673 does not connect to the base of Q119, it initially showed a reading around 3 to 4M-ohm, then slowly seemed to drop a little, definitely not a direct connection anyway.
However, the collector of Q673 looks like it connects to the base of Q114, the ohm meter & continuity check show it does.
However, the collector of Q673 looks like it connects to the base of Q114, the ohm meter & continuity check show it does.
The voltage across R139:
1.56vDC
It started at about 1.3v then slowly climbed to about 1.57vDC
Then it started dropping back down very slowly. I watched to until about 1.46vDC, which took a minute or two to fall to, so it is not a super steady reading, but does take a while to change.
For reference, I’m using a Fluke 23 Series II multimeter, but I get about the same reading pretty much on my Radio Shack 22-811 meter, very close anyway.
1.56vDC
It started at about 1.3v then slowly climbed to about 1.57vDC
Then it started dropping back down very slowly. I watched to until about 1.46vDC, which took a minute or two to fall to, so it is not a super steady reading, but does take a while to change.
For reference, I’m using a Fluke 23 Series II multimeter, but I get about the same reading pretty much on my Radio Shack 22-811 meter, very close anyway.
Is R139 within tolerance?
Were any of the outputs replaced?
The small driver transistors Q118, Q122, Q121 and Q125 sometimes open. It's generally when the outputs fail but you should check them. You'll need to lift two legs to check each junction. Confirm that you have a good junction from base to emitter and base to collector for each transistor. Also make sure that there's no leakage.
Were any of the outputs replaced?
The small driver transistors Q118, Q122, Q121 and Q125 sometimes open. It's generally when the outputs fail but you should check them. You'll need to lift two legs to check each junction. Confirm that you have a good junction from base to emitter and base to collector for each transistor. Also make sure that there's no leakage.
No, none of the outputs have been replaced, they appear to be factory. I tested them in circuit when I originally started this thread & they seemed ok, or at least not shorted, but maybe I should pull them & test them out of circuit, would probably be a good idea. I know they were not shorted, but I guess they could be leaky.
R139 appears to be ok; it measures 221.8 ohms in circuit, so it seems within tolerance.
Measuring the small driver transistors with the base & emitter leads lifted, with the diode check, then ohm meter checking for leakage (they all appear ok):
Q122:
B to C = 0.665v
B to E = 0.669v
No readings reversed or on the ohm meter while checking for leakage.
Q118:
B to C = 0.657v
B to E = 0.661v
No readings reversed or on the ohm meter while checking for leakage.
Q125:
B to C = 0.658v
B to E = 0.663v
No readings reversed or on the ohm meter while checking for leakage.
Q121:
B to C = 0.657v
B to E = 0.662v
No readings reversed or on the ohm meter while checking for leakage.
Also, what symptoms would there be if the output filter capacitors were out of tolerance? I’m referring to the bank of six 470uf 63v capacitors after the output filter inductor by the speaker terminals. I noticed on one of them the jacket is split down the side, but otherwise they look ok, no bulging tops or bulges anywhere else & no signs of physical leakage or damage. Looks like the shrink tubing split is all, but was curious.
R139 appears to be ok; it measures 221.8 ohms in circuit, so it seems within tolerance.
Measuring the small driver transistors with the base & emitter leads lifted, with the diode check, then ohm meter checking for leakage (they all appear ok):
Q122:
B to C = 0.665v
B to E = 0.669v
No readings reversed or on the ohm meter while checking for leakage.
Q118:
B to C = 0.657v
B to E = 0.661v
No readings reversed or on the ohm meter while checking for leakage.
Q125:
B to C = 0.658v
B to E = 0.663v
No readings reversed or on the ohm meter while checking for leakage.
Q121:
B to C = 0.657v
B to E = 0.662v
No readings reversed or on the ohm meter while checking for leakage.
Also, what symptoms would there be if the output filter capacitors were out of tolerance? I’m referring to the bank of six 470uf 63v capacitors after the output filter inductor by the speaker terminals. I noticed on one of them the jacket is split down the side, but otherwise they look ok, no bulging tops or bulges anywhere else & no signs of physical leakage or damage. Looks like the shrink tubing split is all, but was curious.
The voltage across R140 & R142 is pretty close to each other, I notice it moves around a little like some of my other measurements, but they seem to stay fairly close.
R140: 1.42vDC
R142: 1.45vDC
Not sure if it made a difference, but since I changed Q110 it has been oscillating every time I power it on, it is not going in & out like it did, well not yet anyway. The waveform gets blurry after several seconds then changes to a slightly different looking waveform & it too is blurry most of the time.
If I let it cool down, then power it on the waveform looks pretty much like your 250D picture, though looks like there is always a little distortion or something in the waveform. I noticed if I blow around the LM311 area after the wave starts blurring & changing, it starts to go back to what it looks like when I first powered it on.
I have a hard time getting clear pictures of my scope, but I can try if you want to see what it looks like. But you may not be able to see it clear enough. I know I have tried to get pictures before & they did not look very good, could not really see the waveform clear.
So the amp has been somewhat working and does have output, if I run a sine wave into the input of the amp, it looks clean on its output, & the output sounds normal, but as soon as the gain control is adjusted the speaker pops / moves all over the place, very badly.
Sorry I type so much, just trying to cover everything.
R140: 1.42vDC
R142: 1.45vDC
Not sure if it made a difference, but since I changed Q110 it has been oscillating every time I power it on, it is not going in & out like it did, well not yet anyway. The waveform gets blurry after several seconds then changes to a slightly different looking waveform & it too is blurry most of the time.
If I let it cool down, then power it on the waveform looks pretty much like your 250D picture, though looks like there is always a little distortion or something in the waveform. I noticed if I blow around the LM311 area after the wave starts blurring & changing, it starts to go back to what it looks like when I first powered it on.
I have a hard time getting clear pictures of my scope, but I can try if you want to see what it looks like. But you may not be able to see it clear enough. I know I have tried to get pictures before & they did not look very good, could not really see the waveform clear.
So the amp has been somewhat working and does have output, if I run a sine wave into the input of the amp, it looks clean on its output, & the output sounds normal, but as soon as the gain control is adjusted the speaker pops / moves all over the place, very badly.
Sorry I type so much, just trying to cover everything.
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