do STKs break internally from a hard landing or jolt? SOLVED

CT Jim

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When I have time I keep checking an Onkyo TX-2000 receiver which worked fine until it fell off a collapsed shelving unit, landing square on it's side. It powers up, I can trace points so I know the transformer is putting out, but the sound in both spks and headphones is faint? If I turn it up 3/4 of the volume control, I can hear music faint? The heatsink does get warm, but no sound except faintly with volume way up!
All switches and controls work, and I don't see any board damage so I'm not sure what has happened.
I now have a nice looking doorstop. At first I thought it might be a stuck tape monitor, but when my cd source is plugged into either tape monitor, there is no difference, so all sources are faint?
Does anyone have any ideas? There is a single STK463, and the spk fuses are ohm'd ok.
 
In my experience, a drop usually cracks a circuit board somewhere. Examine your boards very meticulously.

Maybe post some pics as we might be able to see something that you might have missed.
 
I agree but I have looked closely and even tried using a light behind the board. Although I have power at numerous points I think I'll try not only a bigger lite behind but check the power board again to make sure ALL of the points and where they continue on still have the appropriate voltages. I don't have a wiring schematic for the transformer but will recheck again.
Thanks
 
Grab a coffee - This might take a minute.

I've learned (and I learned it some time ago) that just when a person thinks he knows everything, the one important thing that he does not know is the fact that he does not know everything. That's not a remark toward anyone involved here, but merely a general statement.

Conventional wisdom would indicate that a mechanical shock would not damage a component like an STK module. That is, until that module is dissected, when "conventional wisdom" and "common sense" would be tossed out the window. Some STK modules use micro-fine lead wires resistance welded to plates in the module, just like in a TO-3 transistor case. Like anything mechanical or physical, there are limitations of endurance. A shock with sufficient G force could in fact break one of those wires in the module. Is it common? Heck no. Is it possible? I'd bet a nickel it is. That's why there are G-force ratings for a lot of things people don't even suspect. Many times, that's the difference between a commercial device and mil-spec device. The latter has a tendency to be subjected to repeated mechanical shock and must survive.

I'm not saying that is what happened. It is far more likely that there is a problem on a board component joint or trace, as the 0.1 milenium tek pointed out, and as you know. However, after exhausting other possibilities, do not completely discard the possibility of your initial theory.
 
Sounds like a break of connections to me as well. Internally those STK's are pretty strong, and usually don't get affected by shock.
with headphones on, try touching the connections of the vol control, to see if you get hum coming through as you touch with control at 11 oclock. If so then your STK is good. Also try tape out to see if that feeds audio out to another unit like a tape deck.
 
I think there are some issues with STK modules internally desoldering themselves. It's possible there was a marginal joint inside the module and the physical shock dislodged it entirely.

I had a Yamaha R-500 with a STK3042-II which would only work properly if the leads were bent a certain way, as though one or more was loose inside the package. (Resoldering at the PCB end did nothing, and replacing the pack fixed it)

You might try tapping the module or its leads with a nonconductive probe and see if that restores connectivity.
 
If its both channels, no shorts, and does not blow fuses, its probably not the STK itself.

Have you ever cracked open one of those things? They are built pretty sturdy. Even the connecting wires inside are pretty strong.

I had a defective STK once where it was shorted and I cracked it open to see what had happened. Mine had four block IC's and one was burnt black hence the shorted section, but those wires running from them to the circuit board will not break easily from a drop. I tried to yank a couple of those wires with needle nose plyers and they are pretty well welded. Everything else inside is soldered to the board with no wires.

I would use a magnifying glass or light to inspect things. A hairline crack is really hard to see. I have seen cracked circuit boards where it looks like a piece of hair, but when I scrapped off the green coating, yup, sure enough, a crack.

Also, look for broken solder joints around the pots and switches.

Pics?
 
No need for high-res, I found the issue. I spent about 30 minutes with a 90 watt flood from the back, and from the front, and could not find anything. Sitting in a dark room with a single lite for illuminating the board, I didn't find anything that looked problematic.
So, I once again checked the pins on the T-115 power board, where all the transformer leads are connected. At different points I had 31+/- vdc, and I also had those readings out in the main board area, but the 3 pins, at the bottom of the pic of the top of the board, all seemed very low, around .004 vdc...... So, while powered on, volume down just in case, I rechecked the pin readings. I heard a sound from one of the pins, which I never heard before. As I pushed it around a bit, i could get the noise again???? It's the pin at the bottom right corner on the board. So, one more time turning the unit over, I saw what I call a discrepancy on the backside of the board, at the same pin making the noise! It looked different, so I re-soldered it, essentially re-20181216_194559_resized.jpg 20181216_194732_resized.jpg seating the pin, and WOOHOO, we are back in business. A couple pics attached. And another AK learning experience, taking the time to look, and look again, and poke around, and lucky find, the jolt made that pin solder crack.
Thanks for the input......
Playing fine for the last hour!!
 
Good job sleuthing the cracked joint. The tough part is usually finding the problem, as you experienced.

That must have been quite a jolt, since there isn't much mass on that wire and pin. Lucky that's all that failed. No damage to the case or chassis?
 
NO, the unit suffered no case damage, it landed squarely on the right side, and in this case the transformer and board in question is one the left end? Go figure. The unit was off when it dropped, and when i tried it, nada. But, once again it lives!!
From a visual standpoint, I don't think I could of pinpointed it, but the suggestion of poking around, with the proper non-conductive tool, is how I found it.
Now to replace a few lamps from my stash, and another old piece lives on, to be enjoyed by someone!!
 
th

Whoo-hoo!
 
OK, three days of use in my mancave, and everything is as it should be. With only 27w/side it's running a set of MICCA spks I bought from a fellow AKer a couple months ago, and sounding nice!

Time to put the lid and bottom back on, and move it to the competed pile!!
 
OK, replaced 7 lamps, of which two checked out as working. Back to a nice soft blue dial, meter showing as soft white, and the stereo, locked, and tuned lamps working fine as is the pointer. Nice little receiver at 27w/side, and the FM pulls in stations nicely. As I work toward selling extra equipment for an out-of-state move in 7 months, I think I'll keep this Onkyo, and let one of my Advent 300 receivers go to a new home.
I keep saying....3 systems, 3 systems.......ok maybe the main system has two or three power amps.....dam.....
 
IMG_20181214_232136.jpg
Can you find the cracked solder joint? And this is the blown up close up picture. Real size is like a small pin head.

Easy repairs like this I like. Good job fixing your Onkyo.
 
Left to Right #3 has discoloration hinting that it's cracked just under the surface and #4 is definately cracked. Suck off and resolder all 4 just to be on the safe side.
 
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