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2230 recap

There is some sound coming through the headphones but the volume isn't adjustable at all. Turning the the volume knob makes no difference in sound level though the phones. This will consume me until the prob is remedied. Checked for loose wires at the tone controls and the 400 board and all seems secure. I hope the experts can point me in the right direction as to what to do or try next.
 
Unless something shorted, you would think the problem has to be on that board, since it was working when you started it. Maybe some experts can give some guidance on how to proceed. At this point, I would triple check for solder bridges and reflow the solder everywhere you changed a component. You can get a cold solder joint even though it looks OK. Also look for tiny cracks that might have happened in a trace when removing a component - with magnification if possible.
 
Yes everything was fine up to this point so one would think that it has to be this board whatever the prob is. It DBTed ok as well. Only other thing I did was spray a very small amount of Fader lube into the tone pots while they were off the chassis but aside from that nothing different. Will follow your advise to recheck all the joints. I think I do remember having part of a pad lift just a little and I bent the lead over the top to make sure it made good contact. This is so frustrating to get this far and have a dead stop!
 
I dropped the board once again and as suggested reflowed all solder points. Checked all that I can check but still no sound. Wondering if I should repost in a new thread for new exposure. I really need the help on this one or I will have to take it to a tech to diagnose, but was hoping to avoid that if at all possible.
 
It just has to be something simple. Maybe mixed up the NPN/PNP flavors. Put your DVM on "diode check" and look at every semiconductor junction to be sure they're going the right way, and that the transistors are what you think they are. Then I'd measure the DC voltages and compare them to the schematic. If those are right, I'd look for a swapping of signal and ground wires from the coax, or some similar wiring issue. If the collectors are right, it's still possible to have flipped the base and emitter.
 
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Remember I'm really new to this so not sure exactly what you mean or how to do it. Sorry. On that 400 board there are 8 transistors 4 each of Pt# 2sc1000 being replaced by Mouser # 512-KSC1815YTA ECB and Pt # 2sa841 being replaced by Mouser # 512-KSA992FBU ECB. Maybe I should put the old ones back in to see if that corrects the problem.
 
Yep I've checked about 5 times now thinking I may have overlooked something. I have the 992's at H403/404/408/407 and the 1815's at H401/402/406/405. All correct according to MBuras parts list and also the SM 400 Schematic. I even removed the Wima's that had the leads extended thinking that maybe they had possibly separated while installing but they are all intact. I checked continuity at the wires that connect the 400 board to the tone controls and that also checks out ok. Would it be possible to have gotten a bad New transistor?? Would it make sense to put the 8 old ones back in one at a time and test or all at once and test. Remember that everything worked just fine and sounded great up to this point. I'm at wits end with this thing. Lack of Electronic knowledge certainly doesn't help in a situation like this that's for sure. I'm flying with one broken wing hoping that someone with more experience can decipher what it might be and in turn explain in laymen terms on how to correct it. Until then I guess it will have to make to trip to a tech. Dealing with failure isn't my strong point but I honestly don't know my next step. I want to thank everyone for all the help. Couldn't have come this far without the input and suggestions of all on AK.

GT.
 
It couldn't hurt to go back with the old transistors if you know which is which. I'm with you. When I run into a wall with a problem, lack of experience leaves me at the mercy of those with experience. Ultimately it might have to make a trip to a tech. But first I would put as many original parts back as possible and test after each one. I would want to rule out that the temporary insertion of a backward transistor didn'tz zap another one.
 
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Yep both channels no sound. FM Stereo light tunes in and all lights work. I just put back the 4 old transistors where the new KSA992's were and still no luck. Also while just working on it the black wire from behind the 400 board that connects up to a bar of tabs just below the 700 board broke so I re soldered it and still no sound !!!!!! I'm losing the few brain cells that I have left.
 

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IMO, it's better to measure and troubleshoot, rather than change parts, as that's rough on the boards. The electronic knowledge you need is pretty basic, so now's the time to start on that journey! I'm assuming you have a DVM with a diode check mode. It will usually be an ohm range marked with a diode symbol, or a special range of its own. With the meter set to that range, it should read about 0.6, more or less, when you put the probes across a diode (no power applied!) in the forward direction. It should read off scale or a high number when the probes aren't connected or are connected in the reverse direction. You can check many diodes and transistors in-circuit, but not all. To check a transistor you have six possible ways to connect the leads. Somewhere there's a sticky on this, but the short version is, for an NPN, you put the positive lead on the base and should see about 0.6 measured to the emitter and to the collector. For a PNP you put the negative lead on the base and should see about 0.6 measured to the emitter and collector. That will let you track down wrong flavor devices in the wrong place, and mixed up leads.

Both channels being out means that either both channels have the same component error, or there's a power/ground issue, probably lack of same! Can you measure voltages? Measure from the chassis of the unit, which should be ground, to various points on the board. Things that should be ground should give you zero. If not, there's a disconnect in the ground system. Voltages are marked on the schematic, often only for one channel, but they apply to both. If you get something similar, there's no power or ground problem, so it has to be a connection problem. Another thing to check for are solder bridges. It's not hard to short out a signal if solder accidentally bridges two traces. A hidden problem is soldering shielded coax cable- it's easy to melt the soft center conductor so the inner wire touches the shield and the signal gets shorted out.

Regardless, don't get discouraged. These things are always the most frustrating right before you figure them out. (If you get ready to throw the thing against the wall, it's only a short drive to Rochester, and it's downhill!)
 
I think Conrad is right. Sooner or later, we are both going to have problems that require checking voltages and checking diodes and transistors for failure. Here is a link to Echowars description of transistor testing that I think Conrad was referring to. It would definitely be nice to know if the board is getting power. If we only knew where to check......:biggrin: I seem to remember that yours is a Euro unit and has some internal fuses. have you checked those?

http://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/
 
The fuses are the first thing I checked ( because I know what a blown fuse looks like ... Haha ). I agree with you both. I want nothing more than to learn all this stuff. It's a little intimidating though to say the least when someone suggest that you check this or that and it seems like another language. Also I'm the type of person that learns quickly once shown how but following written instructions is a little different. I will certainly read the link and also follow Conrads advise the best I can. ( thanks so much Conrad.) I did buy the other Fluke 115 for a reason right. So much to learn. I just got really frustrated after having come this far only to run into a brick wall but it was bound to happen sooner or later. I got lucky up to this point I guess.
 
[QUOTE="Leestereo, post: 9916151, member:



For the capacitors, C401/402, in the input high pass filter, a polypropylene type (better dielectric than polyester) can be used; also its capacitance should be increased to at least 0.47µF to obtain a F3 of <5 Hz. For example, this Panasonic ECW-F2 type would be a good choice: http://ca.mouser.com/ProductDetail/Panasonic/ECW-F2474JAQ/?qs=sGAEpiMZZMv1cc3ydrPrF%2bsu0%2bUU4qEgZe1Ftr3eLbM=[/QUOTE]



Also when and if I do get this up and running I'd like to replace those Greenies for the 400 board and Parts Connexion suggest the below. Would this be a good equivalent?


ODROP-76311
0.47uF / 400V, Orange Drop Series 715P, Polypropylene Film & Foil Capacitor, 20.8mmD x 22.4mmH x 41.9mmL, Each
$2.95 pcX USD Price
 
Trying to get a lesson from the experts here. If you wanted to check with a DMM to see if the board had power, I assume you would put the black lead on chassis. The question is, where would you test? Here is a pic of the 400 schematic, and I'm looking for a voltage to test. I see 27.2V in the top right corner (circled area). It appears to be a jumper pin, but no number is on it. It looks like the first thing it comes to is R428 on one side and R429 on the other. If one were to check the end of those resistors, should you find 27.2V at one end or the other? Or would doing that blow something up? Where would you test, and where would you put leads to first determine if the board is getting power? Thanks!
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That's what I thought after looking at the board. I noticed 404 was missing on the schematic, and it's in the middle appearing to service both sides, not to mention it's a red wire. All of the clues led me to believe that was the main power for the board, but I wouldn't trust my instincts on this. So if one put the black DMM lead on chassis and touched J404 with the red, 1) he wouldn't blow it up? (unless he shorted to something else) and 2) he would be looking for something around 27.2VDC? Trying to learn how to do rudimentary testing, but with not much experience. Thanks for the response!
 
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