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javelinpr
Joined: 04 Dec 2008
Posts: 9
Location: Puerto Rico
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 Posted: Fri Dec 05, 2008 12:30 am Post subject: |
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can anyone tell me whats a component with a letter Q and whats K??? im kinda lost on that in the schematics. I can find out how to test i just need to know what that stands for.
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i can help and try to get you any schematic you need. I just ask for some help in exchange. If you are lucky i will have it and will be able to give it to you. |
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vtech
Joined: 08 May 2006
Posts: 1264
Location: USA
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| Posted: Fri Dec 05, 2008 2:40 am Post subject: |
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| javelinpr wrote: | | can anyone tell me whats a component with a letter Q and whats K??? im kinda lost on that in the schematics. I can find out how to test i just need to know what that stands for. |
Q is designation for a transistor. Letter K is used to denote (kilo ohms) the value of resistors that are more than 1000 ohms such as 12k or 12000 ohms. |
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vtech
Joined: 08 May 2006
Posts: 1264
Location: USA
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| Posted: Fri Dec 05, 2008 4:23 am Post subject: |
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| javelinpr wrote: | i have the full schematics with the whole block diagrams, printed circuit boards and everything. If you need to take a look at those ill be more than happy to send em to you.
i replaced caps: c2901 and c2910 in the amplifier board.
by checking the fan tracings in the diagram i found its controller is at other board. so once i have this bass issue fixed(hopefully) ill work on the other board.
i will try to trace before and after the caps removed.
about the relay, everytime i turn the system it does a LOUD click. Has always done it. |
Like I mentioned, I happened to find a schematic which is identical to what you have. Did not mention anything about the sub/w level which hopefully you have already checked and should not be an issue here.
At this point, after looking at where you had a problem with cap(s), it is likely that it may be related. This unit happens to use an active subwoofer circuit and if you are not familiar with it's operation or unable to follow the path, it only make it more difficult & nearly impossible to go back and forth on the forum.
Having seen so many circuits, I can see & follow thru but it may turned out to be too much for the untrained...I;ll try to explain;
Starting at CN204 on page 29 of your pdf file, you'll see the signal to the sub/w speaker is floating(meaning that neither side is grounded ) and if you follow it back, there are various processings involved thru several stages all the way back to the connector CN201 on page 28 pins 1 & 3 labeled sig in/sig out.
Backtracking from the subwoofer speaker, you will see two mosfet transistor networks Q2212, Q2213 with drain voltage of about 43.7V needed for proper operation at that point. One of the caps,C2901 is directly tied to that supply line. Very possible that when the cap failed, it either took out the mosfet or simply killed the supply line(marked VH+)...can you see the ~42v source there?
If not you'd need to backtrack all the way back to CN201 and see where you loose the signal. Ofcourse if you had a scope it would be easier to trace the low frequency signal.
The fan circuit is easier;
Starting at CN202(fan motor) on page 28, all the way to CN303 (pin 15,16 on page26) then on page 27, it is controlled by a network of Q3716, Q3723, Q3717,Q3718 which in turn is controlled by means of a thermistor (TH101 on page 24)which senses the heat thereby pulling down pin 12 of microcntroller IC351 (through CN303 pins 12,13 on page 26).
This causes the IC 351 to send a fan-on signal (pin 31) to Q3718 thru Q3717 to turn on the fan.
Hope it is not confusing. |
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javelinpr
Joined: 04 Dec 2008
Posts: 9
Location: Puerto Rico
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| Posted: Fri Dec 05, 2008 10:44 pm Post subject: |
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i was reading that for testing mosfets here
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
what i dont understand is what is it that they call diode side of the meter. whats the diode side?
i have a cheap craftsman multimeter. i think if im going to keep doing this ill have to step up and buy a top of the line unit.
_________________
i can help and try to get you any schematic you need. I just ask for some help in exchange. If you are lucky i will have it and will be able to give it to you. |
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vtech
Joined: 08 May 2006
Posts: 1264
Location: USA
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| Posted: Fri Dec 05, 2008 11:36 pm Post subject: |
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Not sure what you mean by "diode side of the meter"? where does the article refer to that? Are you talking about how to test a diode with the meter?
Sounds like you may be getting a bit ahead of yourself. Really,not necessary worrying about Mosfets or how to test them at this point. There is a lot more to just testing devices. If you are interested to learn, Basic device & device theory is a lot more important. |
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javelinpr
Joined: 04 Dec 2008
Posts: 9
Location: Puerto Rico
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| Posted: Sat Dec 06, 2008 12:55 am Post subject: |
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ok what i want to know is a way to test the mosfets and find whats wrong on the system so i can fix it.
also want to test everything in that path so i can find the problem causing my no bass.
thanks a lot for taking the time and patience to help me understand and find a way to learn and hopefully fix the system.
_________________
i can help and try to get you any schematic you need. I just ask for some help in exchange. If you are lucky i will have it and will be able to give it to you. |
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vtech
Joined: 08 May 2006
Posts: 1264
Location: USA
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| Posted: Sat Dec 06, 2008 2:16 am Post subject: |
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No intent to discourage your apparent interest in figuring out how to test different devices--the more you know, the better off you are.
However, point being that in order to be an effective troubleshooter in any electrical/electronic circuit, there are certain rules that are always followed; you MUST start with basics such as common measurements/visuals etc BEFORE trying to learn any & all about testing devices.
Perhaps my earlier description of circuit was rather premature.
Only reason I mentioned mosfets were due to the fact that one of the replaced caps turns out to be in the same circuit that filters the drain supply. It does NOT automatically point to a defective mosfet. Proper way is to first look at the DC reading around the device before suspecting it.
So before getting too caught up in testing devices, do a series of DC readings on various points such as supply lines in the subwoofer circuit and compare it to the schematic. |
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Grinchy
Joined: 28 Jan 2009
Posts: 1
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| Posted: Mon Feb 02, 2009 4:09 pm Post subject: |
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| I know this is an old post but I have the same problem and was wondering if you found out anything or not. I'm about to delve down into this thing as well. |
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heyniceguy
Joined: 15 Jun 2010
Posts: 2
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| Posted: Tue Jun 15, 2010 3:38 am Post subject: |
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Hey,
my unit also has no signal coming out of the subwoofer. I'm an electrical engineer by trade, and ive fixed stuff like this before (mostly guitar amps and such). If you send me your schematics, i can try to fix mine, and if im successful, i'll tell you how i did it. Maybe yours can be fixed in a similar fashion.
john
(heyniceguyatgmaildotcom) |
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heyniceguy
Joined: 15 Jun 2010
Posts: 2
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| Posted: Sat Feb 19, 2011 2:19 am Post subject: SOLVED! |
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Yes... old post. But for posterity's sake, here's how i fixed mine....
Preface: see page 12 of the schematics. this circuit has a weird negative voltage biasing. for simplicity, all voltages in the circuit will be referenced to -43.7V as "ground" (so 0V will not be "ground", but "+43V"). this circuit supplies a clean "5V" to IC211 and IC221, which are the pre-buffers for the subwoofer signal.
Q2901 on the SW amp board was shorted through. The area around it was browned. It is a pass device to drop the voltage of the input (43V) down to a reasonable level (13V) for the upcoming IC291 5V regulator. this device must dissipate 30V.
there's a zener D2903 after it which clamps the voltage line to 16V in case of spikes. since the Q2901 shorted through, the zener saw 43V and tried to clamp it at 16V. No chance. It shorted through to ground. R2901 then blew up open since current through it went through the roof. , thus shutting off the 5V and the SW signal.
in the end i replaced Q2901, R2901, D2903. To be on the safe side, i replaced Q2902, Q2903, D2901, L2901. IC291, IC211, IC221 ended up being ok thanks to the 16V zener.
i have to assume Q2901 was the root cause. it sits on the board with no heatsink and must dissipate 30V in the regulator circuit. to help, i mounted the new one to one of the holes in the metal cage nearby and ran wires to the board. Also, the pads themselves were cooked and lifted. so i had to patch-wire the PWB. fired it up and its working.
now... just waiting for it to get a little warm so the fan will go on.... currently no fan yet.... |
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