Ok I was tapping around and I think I found the problem. The sound comes in and out when I tilt the board up or down so I'm guessing it's one of the components thats screwed to the heatsink ( thats where it's anchored)
So I'm in the process of checking the solder. But before I start, is it dangerous to be poking around in there. I heard the caps hold a voltage for a while. It's a 4700uf, can I safely discharge it if it does have a charge.
So I'm in the process of checking the solder. But before I start, is it dangerous to be poking around in there. I heard the caps hold a voltage for a while. It's a 4700uf, can I safely discharge it if it does have a charge.
3D is good!
In the case of that Japanese data sheet - you wouldn't be able to see the pins if you were looking at the top of the transistor, would you? So logically, it shows the bottom of the transistor, with flat part of the body pointing up.
Cheers
There are also diagrams such as crosssections and wireframes and such
I mean, it could very well have bene one of those.But by your reasoning, the pinout is OK. The parts are already ordered anyway, we'll see what the result is next week.
More annoying datasheets are those of TO-126, viewed straight from front to back or vice versa...
Earlier in this thread, it was suggested it was most likely voltage amplification, so I would start at the diff amp and work forwards.
Also, the powertransistors are the only ones I didn't order
Besides, the poweramp PCB which contains everything but the powertransistors can be plugged out. When I do, the crackling stops. If the powertransistors are still powered, which I think they are, they would seem to be OK.Perhaps the manufacturer made the stupid mistake of soldering the transistors first, and then bolting them down. It's easy to break the PCB pads that way. When that has happened, resoldering the pad won't work, because it has broken of the track. Use a wire to connect it to the closest pad.
Depends on the voltage if it's dangerous to you, but it can also be dangerous to the equipment, in case of accidental short. Just wait 20 seconds or so and they should be empty. You can check it with your voltmeter. If they aren't empty, use a 1k resistor to discharge them.
Thanks much. Can I replace it with spare transistors. I have lots of old parts lying around. How can I tell which ones are compatible, like the right voltage and stuff. Or is this thing proprietary and needs a oem replacement?
Also, is it possible to mod this thing to make it sound better since I already have the thing open.
Also, is it possible to mod this thing to make it sound better since I already have the thing open.
Where would be a good place to order one of these or the replacements? Radioshack doesn't carry them nor does Ebay. Google if information overload and many has a minimum order.
Also is there any mods I can do to tweak my amp to sound better?
Can I run a car amp with a 12v adapter at home? (tried but failed)
Also is there any mods I can do to tweak my amp to sound better?
Can I run a car amp with a 12v adapter at home? (tried but failed)
I have no idea for suppliers: my local electronics store has almost everything, so I hardly use anything else.
But, heed pinkmouse's warning. Cracked solder joints can be very hard to see. I once had one under a 10x maginifier, and it was barely visible. It did look cool though, a circular crack around the pin, all the way down to the board.
It's beginning to look a bit like thread hijacking...
But anway, not likely. That would be kind of complicated. Best keep it as it is. Also, the amplifier doesn't have that much of an impact on sound quality, very little even. Speaker (and it's associated parts) are far more important.
Also a thread hijack, but a normal adapater probably has too little current capability. But, I know nothing of car audio, so can't really help.
stonedfenix said:
If you bend the pins and it 'stops' the problem, it is very very very likely it's a bad solder or a cracked trace on the pcb. Resolder it first, don't bother ordering.
IF the problem still persists: your transistor is a 2SC4467, a japanese NPN transistor.
These are its relevant specs:
Vceo 120
Ic 8A
Pc 80W
Hfe 50(min) at Vce=4V, 3A
ft 20MHz
Complement: 2SA1694
This is NOT a small-signal transistor, and based on the data it's likely that it's used with its counterpart PNP unit - check the amp board and see if there is a similarly-sized and shaped transistor with "A1694" marked. If so, it's best to try to find an exact replacement for the 2SC4467.
Cheers!
edit: the transistor is a TO3P package, data sheet here:
http://www.allegromicro.com/skncatlg/pwrxtr/2sc4467.pdf#search="2sc4467"
from post #35
Having said that. You said earlier that you had swapped the speaker in the subwoofer to check for your noise. It sounds like you swapped the woofer itself. That definitely would not have caused the pop sounds by itself. So now we're left with the left and right speaker wires connecting the Reciever to the subwoofer. Since only the left and right speaker wires connect the audio to the subwoofer, the problem must be in the amp feeding the subwoofer amplifier (Receiver), or the subwoofer amp itself. The satellite speakers are quiet, yes?
Now the problem. The sub is noisey. Most amplifiers have an input stage to take a small signal and give it gain "make it stronger" to feed the next stage. The input stage usually includes a pair of transistors that form a differential amplifier. The two transistors are exactly the same. This difference amplifier, amplifies the difference of your input signal (in transistor 1), and a portion of the output signal (in transistor 2). The differential amp has a lot of gain (output) if there's a minor difference in input voltage between transistor 1 and transistor 2. It's also what's called a tranconductance stage. It transforms the input voltage into a signal with greater current capability. Your subwoofer might be using an operational amplifier, usually called an "op-amp". These op-amps, usually have this differential amplifier built-in ....along with a lot of other stuff. Op-amps are black plastic, rectangle shaped component, that usually have 8, or 14 leads coming out of them. These kinds of pop noises "usually" are from the differential amp. I say "Usually" because it's just my opinion. So, a good first guess on this subwoofer popping issue, is to replace the two differential transistors, or the op-amp. ....whichever the subwoofer designer chose to implement.
Het Stonedfenix, If there's any explanation that you need about anything, plaese do not hesitate to ask. Questions are not bad things around here. Questions are good. I beleive mostly everybody on the forum wan't to see a successful conclusion to any project. Everybody is "in to" helping. If you get a little attitude in a reply, do not take it seriously. They are few and far between.
Having said that. You said earlier that you had swapped the speaker in the subwoofer to check for your noise. It sounds like you swapped the woofer itself. That definitely would not have caused the pop sounds by itself. So now we're left with the left and right speaker wires connecting the Reciever to the subwoofer. Since only the left and right speaker wires connect the audio to the subwoofer, the problem must be in the amp feeding the subwoofer amplifier (Receiver), or the subwoofer amp itself. The satellite speakers are quiet, yes?
Now the problem. The sub is noisey. Most amplifiers have an input stage to take a small signal and give it gain "make it stronger" to feed the next stage. The input stage usually includes a pair of transistors that form a differential amplifier. The two transistors are exactly the same. This difference amplifier, amplifies the difference of your input signal (in transistor 1), and a portion of the output signal (in transistor 2). The differential amp has a lot of gain (output) if there's a minor difference in input voltage between transistor 1 and transistor 2. It's also what's called a tranconductance stage. It transforms the input voltage into a signal with greater current capability. Your subwoofer might be using an operational amplifier, usually called an "op-amp". These op-amps, usually have this differential amplifier built-in ....along with a lot of other stuff. Op-amps are black plastic, rectangle shaped component, that usually have 8, or 14 leads coming out of them. These kinds of pop noises "usually" are from the differential amp. I say "Usually" because it's just my opinion. So, a good first guess on this subwoofer popping issue, is to replace the two differential transistors, or the op-amp. ....whichever the subwoofer designer chose to implement.
Hi stonedfenix,
What clem-o said was correct. Resolder the connections first. If you need to replace the transistor, get the exact part, if you can't then use a proper substitute (NOT NTE or ECG !!) and also the proper complimentary transistor for the replacement. You will also need to adjust the bias current.
Given my understanding of your experience, you really should take this amplifier to a proper repair shop and have them do all replacements and bias set ups. There are a lot of small things involved. Do not use a friend who is not an experienced tech, TV repair shops are not an especially good bet either. Nix a shop if they use NTE or ECG, that only proves they do not kow what they are doing.
-Chris
What clem-o said was correct. Resolder the connections first. If you need to replace the transistor, get the exact part, if you can't then use a proper substitute (NOT NTE or ECG !!) and also the proper complimentary transistor for the replacement. You will also need to adjust the bias current.
Given my understanding of your experience, you really should take this amplifier to a proper repair shop and have them do all replacements and bias set ups. There are a lot of small things involved. Do not use a friend who is not an experienced tech, TV repair shops are not an especially good bet either. Nix a shop if they use NTE or ECG, that only proves they do not kow what they are doing.
-Chris
Thanks mrshow2 for the clearer explaination. I am pretty certain it is one of the differential transistors that's faulty.
I much rather try to do this myself in my attempt to learn the inner workings of electronics. I learn faster in a hands on approach so this would be a good opportunity.
Well I resoldered it a couple of times but still no avail.
I see the complement transistor right next to the broken one.
So if I am understanding you guys correctly, I can replace this transistor with another 2sc4467 with no problems or would need to adjust the bias current.
And if there is none available and decide to use a replacement I would need to switch out the complementary A1694. If so what complement should I get and what equipment can I use to adjust the bias current.
Sorry for the attempted thread jacking, I'm not that familiar with the ettiquette. I shall scour the old theads to see I can find something.
I much rather try to do this myself in my attempt to learn the inner workings of electronics. I learn faster in a hands on approach so this would be a good opportunity.
Well I resoldered it a couple of times but still no avail.
I see the complement transistor right next to the broken one.
So if I am understanding you guys correctly, I can replace this transistor with another 2sc4467 with no problems or would need to adjust the bias current.
And if there is none available and decide to use a replacement I would need to switch out the complementary A1694. If so what complement should I get and what equipment can I use to adjust the bias current.
Sorry for the attempted thread jacking, I'm not that familiar with the ettiquette. I shall scour the old theads to see I can find something.
Hi stonedfenix,
Now the "other stuff". It's not the basic idea of the job, but rather the details that can bring you grief. You will need mica insulators and fresh heatsink grease. No, you can not shop at Radio Shack. Mouser, Digikey or Newark are better bets for this. When you work, keep the transistor mounting area absolutely clean. No, you can not use the old grease. When mounting the new parts, do not overtighten them. Check how snug the originals are before taking them out. Do your best to tighten the new parts to the same torque. After the parts are mechanically mounted you can resolder them. Clean off the old flux and make sure there are no shorts. I would recommend a Fluke multimeter for measurements, or a good bench meter.
-Chris
The bias current must be at least checked and possibly corrected. A digital meter showing at least two decimal places in mV is required. It would be nice if the meter's specifications supported the indication.
Yes.
Now the "other stuff". It's not the basic idea of the job, but rather the details that can bring you grief. You will need mica insulators and fresh heatsink grease. No, you can not shop at Radio Shack. Mouser, Digikey or Newark are better bets for this. When you work, keep the transistor mounting area absolutely clean. No, you can not use the old grease. When mounting the new parts, do not overtighten them. Check how snug the originals are before taking them out. Do your best to tighten the new parts to the same torque. After the parts are mechanically mounted you can resolder them. Clean off the old flux and make sure there are no shorts. I would recommend a Fluke multimeter for measurements, or a good bench meter.
-Chris
It's also possible that the pad itself has come of off the PCB, as I described earlier. Resoldering has no use, because the pad connects to nothing. You need to connect the pad to the nearest pad on the track with a short wire in such cases.
Indeed, when using an identical one, bias current can be left as it is.
You can determine what complement you need once you determined the replacement. The datasheet of the replacement should say what the complement is.
The bias current can be easily measured with a voltmeter. I don't know if it's possible there are amp designs in which it doesn't work like this, but usually you can measure the voltage over collector/emittor resistors. The value of those resistors then determine the current. Measure what the voltage is with the old transistors, and when inserting the new ones, adjust until it's back to normal (there should be a pot for that). Try to do this as precise as possible, and at the same temperature for both measurements. So, either when the amp has warmed up, or when it's still cold.
As an example, in this design, measure between the two collectors of the power output transistors. By doing so, you measure the voltage drop over the two collector resistors.
As for the isolation, using silicone isolaters is also an option (as opposed to mica). They cool less efficiently, but are easier because you don't need grease. My advice, is to stick to what's in use now. If it's mica, clean it up and use it again. Be careful, because it breaks easily. If it's a silicon pad, no need to worry. Just mount it back as it was before.
The reason to stick to the the current method of isolation, is because it's possible the designer kept the thermal resistance into account when designing the thermal compenstation circuit. In class-B, this can be very sensitive. This is also the reason to calibrate the bias current as precise as possible. But, without a distortion meter, you most likely will never get it optimal...
That said, I don't think that particular amp is constructed and designed with such precision, so it doesn't matter that much. But in any event, use identical isolation for both transistors (not one mice and the other silpad). They need to be as equal as possible.
Also, I think you'd be better off with an identical transistor. It's a relatively new amplifier, I would guess, so obtaining the right transistor should be possible.
Thread hijacking simply means you should start a new thread for a new topic, instead of posting in an existing one, that has nothing or very little to do with that thread subject. Fixing you crackling problem is related to mine, so that can be done in this thread.
Searching is a different matter altogether. If you need to start a new post for something, you of course are free to do so, if you have searched first
I believe I'm once again starting a reputation for talking too much...
EDIT: BTW, the datasheet of that transistor says that it's a tripple diffused planer transistor. That's new to me, what is it?
halfgaar said:
Identical doesn't guarantee that its forward voltage and gain are exactly the same as the original - just in the same family. It's prudent to check and re-bias as needed.
Triple-diffused planar yada-yada... never paid much attention to this as well, hehehe... it refers to the process used (and layout) in making the transistor, usually to "improve" it. Unfortunately such things sometimes make the 'new' version incompatible with an older one - for example, the new process produces a faster transistor... or one with less Cob...
Hi Clem,
I agree ..... yada yada. Not that important for repairing this amp.
Hi halfgaar,
Beta and VBE will change the bias current. VBE changes with geometry (transistor wafer, they are not identical) temperature and design. You must at least confirm the bias is correct. It may e wrong from the factory or other fingers.
As far as insulators go, silicone isolaters also tend to cut through easily. Old mica is often damaged. A short through the insulator is not a happy thing. They must be completely clean if you wish to attempt to reuse them. I just bought more, guess what I don't do?
-Chris
I agree ..... yada yada. Not that important for repairing this amp.
Hi halfgaar,
The beta will not vary enough to be important. The gain will be in the 0.99 range plus or minus a very little bit. Feedback determines the circuit gain.
Beta and VBE will change the bias current. VBE changes with geometry (transistor wafer, they are not identical) temperature and design. You must at least confirm the bias is correct. It may e wrong from the factory or other fingers.
As far as insulators go, silicone isolaters also tend to cut through easily. Old mica is often damaged. A short through the insulator is not a happy thing. They must be completely clean if you wish to attempt to reuse them. I just bought more, guess what I don't do?
You have far too much faith in modern product design. They normally use as little as they can get by with to last the warranty period. Have you seen some of the new radiators? The extra fins tacked on a next to useless, but they make you feel good I guess. Some of the plastic insulators are one use only. Use mica and grease if you can.
-Chris
Hi everybody,
Since there is some difference of opinion on whether the bias current will need to be adjusted, I'll try to make it easier. What if I replaced it with an identical transistor made by the same company. I did some research and found ok the SK symbol stands for Sanken. Would they make a batch of indentical transistor with different forward voltages and gain.
What is the pad? I was wiggling the transistor while it was running and playing music, and the sound cut in and out. So I'm pretty sure it's the transistor. But just in case I'll check the pad.
Since there is some difference of opinion on whether the bias current will need to be adjusted, I'll try to make it easier. What if I replaced it with an identical transistor made by the same company. I did some research and found ok the SK symbol stands for Sanken. Would they make a batch of indentical transistor with different forward voltages and gain.
What is the pad? I was wiggling the transistor while it was running and playing music, and the sound cut in and out. So I'm pretty sure it's the transistor. But just in case I'll check the pad.
......So you're going to replace output devices?? Those really wouldn't cause the noise problems. If you do replace the output devices, You will need to at least check the bias. Same manufacturer, same part number, even same wafer, I'd check the bias. The Vbe will be different from device to device. It's a very critical adjustment. Things can go way wrong in a hurry with misadjustment. I'd hold off on replacing outputs unless there's really a problem there.