...check 2SA942 "GR" might be a Hfe rating?
<http://www.datasheetcatalog.com/datasheets_pdf/2/S/A/9/2SA942.shtml>
<http://www.datasheetcatalog.com/datasheets_pdf/2/S/A/9/2SA942.shtml>
Most Japanese standard numbering follows 2SAnnn and 2SBnnn are PNP, and 2SC and 2SD are NPN's. It's not usual to just see the "A942", instead of having the whole "2SA942". I must say, I appreciated the Japanese approach to numbering. .....It made it very easy to look for gross problems without looking up a data sheet. Since these transistors are just noisey, you could still make some diode measurements and locate E, C, B. ....see if it jives with the datasheet.
.....with the datasheet: if these aren't the ones, they definitely look pretty good for differential amp parts.
.....with the datasheet: if these aren't the ones, they definitely look pretty good for differential amp parts.
anatech said:
Hi Chris,
Many years ago, I actually had no idea a semiconductor could go 'bad' in this way. So it was essentially a trial and error process, starting with the constant-current source bias (LED), followed by the VAS. Got lucky that what we tried replacing next was the input diff-amp.
Didn't look like it was a thermal, the amp would start to hiss and crackle pretty much at power up - so even up to now I am not clear if there is any temp correlation - in your experience have there been cases as such?
Cheers
Clem
i have a similar problem
Hi, first off I would like to say that this is my first post and that I'm a complete noob to audio and electronics in general.
That being said, my 2.1 system has similar symptoms. Crackles, pops and cutting in and out of the bass channel. It pops with any input and at the lowest volume. The satelites shows none of the symptoms. swapped the sub out and still pops, so I think I isolated the problem to the bass channel alone.
At first the thing only pops while warming up and disappears after while. Then the cutting in and out of the bass became more prominent. Now the channel has no sound at all.
It's a KLH AT-2100I, the one with the Ipod dock.
I would post some pics but it's kinda of a pain. It's 3 boards wired together (the ethernet input board, the amp board and some other one), and the wires aren't long enough to lay them flat, they would be laying on each other.
I have spare parts like caps and resistors from old computer PSUs and other broken crap laying around the house (I throw nothing out, and my parents rag on me all the time about my crap)
Please, any input would be appreciated and I thank you guys in advance.
Hi, first off I would like to say that this is my first post and that I'm a complete noob to audio and electronics in general.
That being said, my 2.1 system has similar symptoms. Crackles, pops and cutting in and out of the bass channel. It pops with any input and at the lowest volume. The satelites shows none of the symptoms. swapped the sub out and still pops, so I think I isolated the problem to the bass channel alone.
At first the thing only pops while warming up and disappears after while. Then the cutting in and out of the bass became more prominent. Now the channel has no sound at all.
It's a KLH AT-2100I, the one with the Ipod dock.
I would post some pics but it's kinda of a pain. It's 3 boards wired together (the ethernet input board, the amp board and some other one), and the wires aren't long enough to lay them flat, they would be laying on each other.
I have spare parts like caps and resistors from old computer PSUs and other broken crap laying around the house (I throw nothing out, and my parents rag on me all the time about my crap)
Please, any input would be appreciated and I thank you guys in advance.
The pinout is printed on the silkscreen.
The image in that datasheet is ambigues BTW. The image that shows the pinout can be seen as top-down view or bottom-up view. If it means the pins are pointing toward you, the pinout is correct: when facing the front of the transistor, it should be E C B.
I confirmed with my scope, the spikes are not visible on the input side of the LTP (and thefore the output of the preamp).
And it's not the volume control. That would be immediatly noticable, as turning the volume control would influence/cause the crackling. Also, volumepot crackling sounds quite different. This sounds like firecrackers and/or lightning strikes...
And stonedfenix, he couldn't have been referring to you, since he posted before you did
Perhaps you're confused with the ordering of posts: it's old-first in normal view, new-first in reply-view. As for your problem, it could very well be similair. The advice given should also help you. The bass module probably has a normal class-B (chip or discrete) amp. If it's a chip, fixing it should be simple. If it's discrete, do what's suggested above to isolate it. But, it could of course be something else...
halfgaar said:
Those sorts of diagrams really annoy me as well. The better datasheets show a 3d kind of angled view which makes it so much clearer. That said, somewhere the datasheet usually says if it's top or bottom view.
I find Fairchild datasheets generally better. The newer OnSemi ones also usually show the 3d view.
That's another good thing about the Japanese numbering system (JEDEC??). For a given package style, the pinout is always the same. For TO-92, it's alway ECB (leads pointed down, looking at the flat side). If the board is screened this way, I think it's a safe bet that your transistor is a "2SA942". If you want to make doubly sure of the pinout and the polarity of the device, perform diode checks from B-E, B-C, C-E. It's always good to check, but this really seems to point to the devices being 2SA942's. Noisy diff amps aren't really too uncommon.
Stonedfenix; You may have similar syptoms (popping noises, etc) with your sub. It might be for the same reasons. My guess is there's a crossover/preamp section that low-pass filters and sums left and right audio, then sends that to a power amp stage, then to your subwoofer. Is the sub's power amp contained on the subwoofer box itself? Do you feed the audio to the sub with Left and Right RCA cables? You said you changed the sub. That would indicate that the subwoofer amp might not be on the subwoofer box itself. I think we need a few more details about the noises. Are the noises very "bassy" sounding, or is there a lot of high frequency components in the pops? More information could help narrow it down
Hi Clem,
Most of the noisy components I've managed to trace were sensitive to thermal changes that would aggravate the behavior, or temporarily cure it. A few I had to find with substitution, but not channel to channel! The act of heating the part while desoldering can temporarily fix it too. Nice eh?
In old tube radios, tapping the resistor or capacitor at fault may show the fault, or temperature changes. A few of those were solder joints.
-Chris
Most of the noisy components I've managed to trace were sensitive to thermal changes that would aggravate the behavior, or temporarily cure it. A few I had to find with substitution, but not channel to channel! The act of heating the part while desoldering can temporarily fix it too. Nice eh?
In old tube radios, tapping the resistor or capacitor at fault may show the fault, or temperature changes. A few of those were solder joints.
-Chris
I once repaired an amp that would make a loud THUD sound from the speakers, and then play no sound... occasionally it would start working again.
It was only while probing around the circuit board with a multimeter, trying to get some voltage readings, that i slipped with the probe and nudged a resistor. The amp suddenly started to work. Replacing the resistor I had nudged cured the fault (it was part of a zener-transistor regulator feeding the amplifiers frontend stage). It seemed that the resistor had cracked inside, but not outside, so it would intermittently go open circuit and cut off the -ve rail.
Two other "professional" service guys couldn't find any fault, so I was quite pleased
It was only while probing around the circuit board with a multimeter, trying to get some voltage readings, that i slipped with the probe and nudged a resistor. The amp suddenly started to work. Replacing the resistor I had nudged cured the fault (it was part of a zener-transistor regulator feeding the amplifiers frontend stage). It seemed that the resistor had cracked inside, but not outside, so it would intermittently go open circuit and cut off the -ve rail.
Two other "professional" service guys couldn't find any fault, so I was quite pleased
Hi jaycee,
Your's was luck, and that's great. We all need it on the bench. I've repaired a ton of faults that other guys couldn't find, but I probably spend more time than they did. So I try to cut other guys some slack unless they do poor work. Then the gloves are off.
-Chris
The other two guys may have been under a time constraint (time = money), so you can't hold that against them. Still, they should have been able to troubleshoot the fault as long as they could make it happen on the bench.
Your's was luck, and that's great. We all need it on the bench. I've repaired a ton of faults that other guys couldn't find, but I probably spend more time than they did. So I try to cut other guys some slack unless they do poor work. Then the gloves are off.
-Chris
It turns out my posts are invisble to others until my new member status wears off.
yes it's built into the box
it's the the stripped cable with spring load clip things for the satellites but the sub has the slide in clips (excuse my awesome nomenclature
)
I had to pull the amp out, disconnect the sub leads and temporarily connect them to another sub I had laying around.
I think some bassy sounds but a lot of highs. It pops like someone flicked the cone, then loud scratching and crackling noises which slowy fades.
Please understand I am a complete noob and can't understand alot of the things you guys say. It would help if you break it down because I am willing to learn. Thanks everybody.
yes it's built into the box
it's the the stripped cable with spring load clip things for the satellites but the sub has the slide in clips (excuse my awesome nomenclature
)I had to pull the amp out, disconnect the sub leads and temporarily connect them to another sub I had laying around.
I think some bassy sounds but a lot of highs. It pops like someone flicked the cone, then loud scratching and crackling noises which slowy fades.
Please understand I am a complete noob and can't understand alot of the things you guys say. It would help if you break it down because I am willing to learn. Thanks everybody.
Hi stonedfenix,
Your symptom sounds a lot like a cracked solder joint. Same thing happens to car amps bolted to bass bins.
Take an insulated (plastic works) object and very lightly tap around the board. Tap lighter as you get closer to the area where it is most sensitive.
If you look at the joints, even with a magnafying glass, you may not see anything wrong. Resolder the larger components and try again.
-Chris
Your symptom sounds a lot like a cracked solder joint. Same thing happens to car amps bolted to bass bins.
Take an insulated (plastic works) object and very lightly tap around the board. Tap lighter as you get closer to the area where it is most sensitive.
If you look at the joints, even with a magnafying glass, you may not see anything wrong. Resolder the larger components and try again.
-Chris
Hi stonedphenix, It's definitely looking like the sub's "plate" amplifier is the problem. If you get nowhere with troubleshooting it, see if you can obtain a service manual. Who knows, maybe someone on the forum might have. If not, the manufacturer should be able to help. You'll get a lot of help here.
anatech said:
Hi Chris,
May have been a fault in the wire-bond then, internal of course - incorrectly setup wire-bonding machine - if that's the case it would have caused batches of problems... ouch...
I once had a Z80 microcprocessor that would work fine at 70degC, but would quit at room temp. Turns out that the heat would expand the bond enough to contact the pad - this never got out of Zilog of course...
Cheers!
Clem
Sure solution for a fix
This problem persists for years, I missed that
Disconnect the power of the bad channel and replace component one by one from bad to the good channel. Everytime resolder the good amp's part back. Start from power transistors and backwrds. Do not relocate multiple parts.
Gajanan Phadte
This problem persists for years, I missed that
Disconnect the power of the bad channel and replace component one by one from bad to the good channel. Everytime resolder the good amp's part back. Start from power transistors and backwrds. Do not relocate multiple parts.
Gajanan Phadte