Hi,
Q11 collector voltage can not read 3 volts because the collector of Q11 thru Q18 are connected to ground. All should read zero volt. Check all the collectors voltages to see is they read the same as Q11.You may have a ground problem. Check why the collector of Q11 is reading 3.5 volts. Q11 base should be the same as Q2 collector voltage -3.5 volts.Your reading is 3.5 Do a check try to adjust the base voltage of Q2 to be as close as possible to zero by adjusting the TR1 pot. I think both Q1 and Q2 base should be reading close to zero or 0 volts with no input signal. Do you have the instruction on how to adjust the offset of the amplifier. If you have it follow it. Also read the voltage for the neg and pos rail. It should read about 35 volts when you do the test.
Q11 collector voltage can not read 3 volts because the collector of Q11 thru Q18 are connected to ground. All should read zero volt. Check all the collectors voltages to see is they read the same as Q11.You may have a ground problem. Check why the collector of Q11 is reading 3.5 volts. Q11 base should be the same as Q2 collector voltage -3.5 volts.Your reading is 3.5 Do a check try to adjust the base voltage of Q2 to be as close as possible to zero by adjusting the TR1 pot. I think both Q1 and Q2 base should be reading close to zero or 0 volts with no input signal. Do you have the instruction on how to adjust the offset of the amplifier. If you have it follow it. Also read the voltage for the neg and pos rail. It should read about 35 volts when you do the test.
Put 1 pair new mj15022 to start and it smoked R47 and R48. tested all power transistors and the all test good. Likewise started with new e10 and 14 and no luck. the same problem. Replaced Q1 and Q2. Im here trying to learn. I don't even know how to use a scope if I had one. I was hoping DYI forum would be a good place to learn from others. Sometimes others expierence with same gear has already found solutions etc.
Frank - ur not quite "getting it"...
Did you use "old" transistors for one rail, and "new" for the other?
In order to troubleshoot, you need to be careful and work systematically. For example stating a transistor number of the schematic says not one thing about what you did, or what you put in those holes... so without good information, no one is going to be able to help you, ok?
_-_-bear
Did you use "old" transistors for one rail, and "new" for the other?
In order to troubleshoot, you need to be careful and work systematically. For example stating a transistor number of the schematic says not one thing about what you did, or what you put in those holes... so without good information, no one is going to be able to help you, ok?
_-_-bear
Im confused now about what is meant by a rail. Is the Plus side one rail and the minus side another rail? Im not getting the high voltages on the plus side so ive been focusing on the minus side. Thats the set of PT that I removed and replaced 2 at a time. What happen is I took minus side out and started with 2 new mj15022 on Q17 and Q18, but the resistors started smoking. That lead me to believe it could be somthething else. Ill go back and do it again but, If you could clarify for me please. still learning the language.
Yep Power Supply "rail" you have one plus and one minus.
You have to FIRST get the voltages on the rails to be there and working.
Again:
- REMOVE all the power transistors
- test the power supply voltages.
- IF no good, remove the power supply CAPACITORS - the bank of filter caps.
- put in just ONE OR TWO caps, equal for the PLUS and the MINUS side (you have to trace the circuit to see which is plus and which is minus. They MUST be known good caps.
- retest the PS now.
- IF it is NG, remove the caps, see if you have DC voltage without the caps COMING FROM THE RECTIFIER BRICK - that will appear on the solder points of the filter caps as well as on the rectifier itself.
You CAN NOT work with just one rail of power transistors at a time.
You MUST replace the power transistors in parallel - the minus and the plus side, and you must put the proper type (NPN vs. PNP) transistor in those places.
You CAN run the amp with as little as TWO power transistors, one on the + rail and one on the - rail.
Those new transistors may or may not be silicon wire now...
I think fixing this amp is likely beyond your skill level at this point in time... as I said it is a *difficult* amp to troubleshoot and repair for a variety of reasons.
This amp typically has mostly bad filter caps and also fried output transistors - as well as small lower level components that go bad. Not easy to find and fix since the protection circuit wants to shut it down too....
This is not a good amp to do learning on...
I'd suggest that you send the amp to a pro to repair, but the problem with them is that the COST of repair is more than the COST of buying a working one used!!
Which, btw is another fix - buy a working one with one blown channel (or not) and swap boards, keep the other board for spares... regardless of which chassis gets run.
No matter what as a final repair (after it is functional) one should replace ALL of the filter caps on the board with these things - the original filter caps were marginally rated and at this point in their life cycle they blow out, short, and fail. That is expensive.
Bottom line is that unless you got lucky and found the single fault quickly, you're not going to be able to repair this amp. Sorry to bring such a negative report to you. Since you did not get lucky, it's not likely that you'll get it fixed. Otoh, there is nothing wrong with experimenting and trying, but you'd better tell ur friend something, otherwise he may be upset. If he doesn't care, keep on plugging along, as you will learn something about the innards of power amps...
Regards,
_-_-bear
PS. this amp is difficult for ME to repair, and I have been doing this stuff for decades. (of course my experience with them is limited to one interaction (I bought 4-5 basket cases from a local pro sound company), but based on that these are a bit tricky to work with even for me. If one had repaired a bunch of them, it gets easier once you know what to look for and how to deal with the beast...
You have to FIRST get the voltages on the rails to be there and working.
Again:
- REMOVE all the power transistors
- test the power supply voltages.
- IF no good, remove the power supply CAPACITORS - the bank of filter caps.
- put in just ONE OR TWO caps, equal for the PLUS and the MINUS side (you have to trace the circuit to see which is plus and which is minus. They MUST be known good caps.
- retest the PS now.
- IF it is NG, remove the caps, see if you have DC voltage without the caps COMING FROM THE RECTIFIER BRICK - that will appear on the solder points of the filter caps as well as on the rectifier itself.
You CAN NOT work with just one rail of power transistors at a time.
You MUST replace the power transistors in parallel - the minus and the plus side, and you must put the proper type (NPN vs. PNP) transistor in those places.
You CAN run the amp with as little as TWO power transistors, one on the + rail and one on the - rail.
Those new transistors may or may not be silicon wire now...
I think fixing this amp is likely beyond your skill level at this point in time... as I said it is a *difficult* amp to troubleshoot and repair for a variety of reasons.
This amp typically has mostly bad filter caps and also fried output transistors - as well as small lower level components that go bad. Not easy to find and fix since the protection circuit wants to shut it down too....
This is not a good amp to do learning on...
I'd suggest that you send the amp to a pro to repair, but the problem with them is that the COST of repair is more than the COST of buying a working one used!!
Which, btw is another fix - buy a working one with one blown channel (or not) and swap boards, keep the other board for spares... regardless of which chassis gets run.
No matter what as a final repair (after it is functional) one should replace ALL of the filter caps on the board with these things - the original filter caps were marginally rated and at this point in their life cycle they blow out, short, and fail. That is expensive.
Bottom line is that unless you got lucky and found the single fault quickly, you're not going to be able to repair this amp. Sorry to bring such a negative report to you. Since you did not get lucky, it's not likely that you'll get it fixed. Otoh, there is nothing wrong with experimenting and trying, but you'd better tell ur friend something, otherwise he may be upset. If he doesn't care, keep on plugging along, as you will learn something about the innards of power amps...
Regards,
_-_-bear
PS. this amp is difficult for ME to repair, and I have been doing this stuff for decades. (of course my experience with them is limited to one interaction (I bought 4-5 basket cases from a local pro sound company), but based on that these are a bit tricky to work with even for me. If one had repaired a bunch of them, it gets easier once you know what to look for and how to deal with the beast...
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Hi all,
I have another USA1300 with issue also, here's the story:
- When I received the amp from my friend, CH2 wasnt working, looked like some power/driver transitors are dead already.
- I removed all these transitors, and tried reinstalled only the drivers by new MJE15030/31 (the power transitors were still out) for checking first.
- I also noticed their collector resistors R16, R17 (22R/1W) were burnt so I replaced them with 27R/1W. Bias trimmer TR1 is also replaced.
- When I fired up this CH2 at 1/2 mains voltage (plugged the amp in 100VAC line in 220VAC mode) things didnt go well:
+ front PWR led kept staying red
+ relay didnt turn on
+ B+/B- lines were not similar (measured to chassis GND): +25/-46VDC respectively. When measured to speaker bus, the rails are even: +36V/-36V
- I removed the driver transistors and fired up the amp again, now the front led can turn green, relay turned on and supply rails have similar value to chassis GND.
Now I'm stuck here.
Any idea what is wrong here?
Regards,
Duong
I have another USA1300 with issue also, here's the story:
- When I received the amp from my friend, CH2 wasnt working, looked like some power/driver transitors are dead already.
- I removed all these transitors, and tried reinstalled only the drivers by new MJE15030/31 (the power transitors were still out) for checking first.
- I also noticed their collector resistors R16, R17 (22R/1W) were burnt so I replaced them with 27R/1W. Bias trimmer TR1 is also replaced.
- When I fired up this CH2 at 1/2 mains voltage (plugged the amp in 100VAC line in 220VAC mode) things didnt go well:
+ front PWR led kept staying red
+ relay didnt turn on
+ B+/B- lines were not similar (measured to chassis GND): +25/-46VDC respectively. When measured to speaker bus, the rails are even: +36V/-36V
- I removed the driver transistors and fired up the amp again, now the front led can turn green, relay turned on and supply rails have similar value to chassis GND.
Now I'm stuck here.
Any idea what is wrong here?
Regards,
Duong
Updates:
I realized I havent checked the NE5532, so I tried replacing this IC.
Fortunately things started to look good so I installed back 5 pairs of MJ21193/94 (the remained working ones) and the amp is considered working now.
However, the amp gets hot very fast. I'm not sure if it's because there're only 5 pairs of power BJTs or the bias is wrong after I replaced the drivers/trimmer.
With my very little knowledge in SS amps and followed a topic in QSC forum, I adjusted the trimmer to zero but the amp is still considerable hot.
Any idea?
Thanks,
Duong
I realized I havent checked the NE5532, so I tried replacing this IC.
Fortunately things started to look good so I installed back 5 pairs of MJ21193/94 (the remained working ones) and the amp is considered working now.
However, the amp gets hot very fast. I'm not sure if it's because there're only 5 pairs of power BJTs or the bias is wrong after I replaced the drivers/trimmer.
With my very little knowledge in SS amps and followed a topic in QSC forum, I adjusted the trimmer to zero but the amp is still considerable hot.
Any idea?
Thanks,
Duong
If the amp is hot, you might want to see what the bias components are doing, that includes the drivers... it should be cool sitting around.
I haven't looked at the units or schematics in years, so this is general advice.
And, the amp will try to work with *leaky* PS caps.
they are more than PS caps in this design, they are in the output circuit.
the number one failure in this amp design is/was the output caps, they are under-rated for voltage given the application, and die by getting leaky and/or shorted. so double check them.
I haven't looked at the units or schematics in years, so this is general advice.
And, the amp will try to work with *leaky* PS caps.
they are more than PS caps in this design, they are in the output circuit.
the number one failure in this amp design is/was the output caps, they are under-rated for voltage given the application, and die by getting leaky and/or shorted. so double check them.
Oh, i forgot to mention the case is closed.
Apparently both channels have to be assembled during test and bias adjustment, so the fan can run and maintain stable heatsink temperature.
I replaced trimmer pots, reinstalled both channels in their places and adjusted bias level, now the amp is working fine.
Many thanks,
Duong
Apparently both channels have to be assembled during test and bias adjustment, so the fan can run and maintain stable heatsink temperature.
I replaced trimmer pots, reinstalled both channels in their places and adjusted bias level, now the amp is working fine.
Many thanks,
Duong
Hello. All. I have a 1300 with channel one in protect. No fuses popping just no voltages Starting at the rectifiers I have 65vac and 33vac. At the positive and negative dc voltage is at around 1.8v dc. I have replaced b3 and still same result. Tried removing the fuses f1 and f2 still no change in behavior. Could I have a bad transformer???
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