That feeling when you hurt something you love

Ymir_Lifer

Canadian
This could be a very long intro, so long story short will do. Since my back got messed up, I have used audio as my main hobby and to pass a lot of time. I really enjoy playing (with) this old stuff though, so that helps a lot . A major downside though, I shake really bad most of the time, and big twitches or spasms are not that uncommon. I have been very paranoid of that being the cause of death for a piece of my beloved gear for a long time. Not paranoid enough, I guess.

Of course, it just HAD to be my favorite item that I have acquired so far along this journey. My JVC A-X-900, I can't really put into words why I like it so much, but I really do (did:tears:) enjoy that piece, and that's what counts.

Basically, I twitched after a voltage measurement, and the bloody probe landed between the outputs' copper rails. It was a short contact, but it don't take long. There was no big smoke, just a quick zap and a bit of 'that smell.' About the only test I have done since, (now that I'm REALLY shaking,) is check the bias. Sure enough, one channel shows 0. Am I going output shopping now?

There are many things I have yet to learn about electronics in general, but I like to think I learn quick. And if that fails, my Dad has been designing electrical components (automotive stuff, from Ford to Freightliner) for longer than I've existed, he is by far the greatest 'resource' I have available. Unfortunately, the last audio project he did was also before my existence, so, as he admits, memories are hazy. He's also not going to be home for a few days. Which really sucks because I'd love his opinion right about now. With all that in mind, is there anybody here with the patience to get me headed in the right direction? I honestly don't know where to start, and doubt that I could afford to have someone do it for me. Although, I may have to at this rate...

There are manuals here: http://elektrotanya.com/jvc_a-x900b.pdf/download.html or at hifiengine, if you have an account.

Any help you can give will be extremely appreciated.
 
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Here are some pics of my idiocy. Now that my blood pressure has lowered a bit, I had a look and found this.
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Looks like I managed to blow a trace right off the board. Is there even the slightest chance this is going to be all thats wrong?

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Where it zapped...
 
That blow out is between the orange and brown wires, right under the little Japanese character, just above the 'V' in 'volt control.'
This is the only 'visible' damage I am seeing so far.

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Could I solder a small bit of wire between, or just solder 'bridge' together, those 3 points? Or is there a better way to do this?

Oh how nice it would be if this were it...
 
I would take a shot and use a small piece of wire to bridge across the blown circuit trace. I would then use a dim bulb test to power it it for the first time.
 
Hi ymir...

Saw this post and your follow ups. I can only suggest patience. The likelihood of that being the only damage is sadly, slight. I am concerned that if you bridge the foil with wire (which will work) you might then find the smoke that you really didn't find before.

There will be persons along here soon with MUCH more experience than I to help you I am sure.

Yes, I do feel your pain and I do understand how you can "love" a piece of audio gear.

best of luck...
 
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You can bridge the broken traces. But I think a short like that could take some component with it... At least some semi-condictor, diode or transistor...

If just repairing the trace doesn't work, you need to locate the short in the schematic. And from there, we can guess what components blew.

Just to make you feel better: I've burned my amp, in perfect working order, a couple of times. One of them, I've burned an obsolete IC, the led vumeter driver, and I had to replace with a newer one, modifiying the circuit. It took more than 1 year until I felt confident to do that repair. Another time, burned the original output darlingtons, and had to get newer replacements. And for sure I had some other of this "accidents". SO, everybody was there.

Now, I stopped to burn things, once I decided to not risk anything, not even a little bit. Don't risk and you'll be fine. Be 100% sure of your moves before doing any measurement or repair. That worked for me. 0% (or almost 0%...) accidents or incidents in a couple of years.
 
looking at the print, the spot you fried is the primary DC feeding the collectors of the outputs on one side. Looks like your probe ground touched one of the main rails, or shorted the 2 rails together.
You may luck out and just have a blown etch, as this type of short shouldn't affect the output stages. Although it could have damaged something else in the power supply. Easiest way is to see if you have a high DC voltage on one side and of the etch run before the break and nothing on the other side of the break. I would also check (WITH POWER OFF AND PLUG REMOVED) the 2 rails for a short condition using an ohm meter. If either of the rails show a short, then you have more problems such as bad outputs etc.
Tom
 
Thanks for the quick reply's, help and, of course, sharing your screw ups everyone.
Being the guy most people around here only ever call once in a blue moon to fix their broken junk, this was a serious confidence killer. It's especially painful to remember that not very long ago, I was damn near 'surgeon steady,' and now shake like an old man (I'm 25.) Hearing others experiences helps to not take it as hard though.

The obsolete parts are definitely a worry of mine. Along with the fact that I've been trying to find another one of these for months now, unsuccessfully. They don't really seem to come up often. That said, if anyone knows where there is one hiding, please let me know.

looking at the print, the spot you fried is the primary DC feeding the collectors of the outputs on one side. Looks like your probe ground touched one of the main rails, or shorted the 2 rails together.
You may luck out and just have a blown etch, as this type of short shouldn't affect the output stages. Although it could have damaged something else in the power supply. Easiest way is to see if you have a high DC voltage on one side and of the etch run before the break and nothing on the other side of the break. I would also check (WITH POWER OFF AND PLUG REMOVED) the 2 rails for a short condition using an ohm meter. If either of the rails show a short, then you have more problems such as bad outputs etc.
Tom

You got it, the probe did short the 2 rails for 1 channel together. That etch is completely gone, it measures open. So I haven't tested DC on each side.

I'm not sure if this is what you meant to measure, but here goes. It might be hard to explain without knowing the right terms but I'll do what I can.

The 2 'good' rails measure .825Mohm between them, while the other 2 are open.

If i measure between 1 good and 1 bad I get: .61M between the rails on the PS caps side. and under .5ohm between the rails on the outputs heatsink side.

If I go criss-cross between good and bad there is 60Kohms 1 way and .8M, depending on which 2 are measured.
 
I wonder if medical marijuana could help with those spasms. Just a thought. Not trying to get anyone hooked on pot use but it has shown great promise in treating epilepsy, especially the high CBD strains that don't get you high.

Hope you get everything figured out. I understand the love of good gear. I don't even work on my own gear but would love to have that knowledge.
 
I slipped with a probe in a machine at work and did an enormous amount of damage. It can happen to anyone. Get yourself a good set of clip leads and get used to using them. They at least minimize the chance of trouble in many situations.
 
Actually what I meant was to measure each rail to ground.
Should be very High resistance like you have above, with your 2 good rails

Cris cross isn't necessary.

But measuring from rail to rail on each side should be done, and you should get very high resistance approaching an open.

The side that has the blown etch will show open from rail to rail, because of the blown etch. Before you repair the etch, I suggest you measure the DC voltage on both sides of the blown etch. the side that has the rail connected to it will show 0 volts. The other side of the blown etch should show ~70 volts or so. The connections next to it, that go to the other rail should read ~70volts, but opposite polarity of the other rail. If this is the case.
If this is the case, and you can see both + and - DC voltage continue with below steps to repair etch. If one (+ or -) of the voltages can't be found on either side of the blown etch, then you have problems from the power supply, that could be a blown fuse, melted wire of other issue

If you have no shorts rail to ground, or rail to rail on each side, you can solder a wire across the blown etch.
I would then suggest power up using a dim bulb tester for initial power up.
 
Gee, are the stereotypes really that strong, or did everyone see the Canadian 'dope flag' in the background of my pictures:D? In all seriousness though, as far as medications I've taken go, marijuana has been just as beneficial as the hardcore painkillers, but with less side-effects.

The rails to ground all show high resistance. The 2 rails facing the heatsink are equal, both at .69M. The bad cap-side rail to ground: .3M, and .87M for the good cap-side rail.

The bad rails now measure 35kohm between them. I swear they were open last night, but I guess that was not my finest hour.

I haven't plugged it back in yet to measure DC. Ive been dealing with a hot water tank that went up in smoke about 2 hours before I made this mess.

As a side-note, after I asked my dad if we had a dim-bulb, he mentioned something interesting. Apparently the tungsten element has basically 0 resistance for about 150ms, until it warms up. I know they are commonly used, but that seems sketchy.

Thanks again everyone!
 
I just wandered in because I smelled pot.
'ere...

black-and-white-hands-joint-pass-smoke-Favim.com-172464.jpeg
 
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I would suggest at this point for you to repair the blown etch with a piece of wire. Then you should measure resistance between the left side rails, and compare them against the resistance between the right side rails. Measure in both directions. do a reading get the value, and then reverse probes and get the reading again.
Both sides should be the same reading after the etch is repaired.
Then measure each rail to ground. The reading should be the same for both rails that are on the cap side. The readings should be the same (rail to ground) for the rails on the heat sink side as well. If any of the resistance reading is off compared to the other side, then you have problems.

Dim bulb testing is using a tungsten light bulb in series with the hot leg of the input power to your receiver. Yes it is very low resistance when cold (off), but increases drastically as current flows, and the light comes on.
If your receiver is OK and has no shorts, and you fixed the blown ckt trace, upon power-up with dim bulb, the bulb should come on very bright, and then get dimmer as the unit stays on for a while. The unit may not allow the protect ckt to operate and produce sound, but it may, if you just connect to headphones. You should see some of the units lights come on, but they may be dim.
If there is slill a short in the receiver, the light bulb will come on very bright, and stay very bright. Your unit will not operate, and would not expect any of the units lights to come on at all.
 
Tom B, I genuinely appreciate the time you have taken to share your knowledge with me. Thanks to your efforts, (and everyone's confidence inspiring stories of course,) I think we may have gotten somewhere, and pretty damn quick too.

The only soldering iron I have here is an emergency only butane unit. The Old Man has a nice HAKO that I can use when he's back tomorrow though, so I think I will (try to) leave it until then.

Just to tame my curiosity, I figured I'd try to use a jumper wire for the measurements. If these results are truly correct, I'm glad I did. Both sides' rail-rail measurements were identical, both ways. Rail-ground also nearly identical but a bit harder to monitor. It seemed like the meter had to charge the caps up before the readings leveled off. But the readings started and ended in very close to each other.

The unit may not allow the protect ckt to operate and produce sound, but it may, if you just connect to headphones.
The weird thing is, before I realized how bad I messed up, I turned the volume up a bit and swear I heard sound from both sides, but very quiet on one channel.
Who knows though, I was so pissed off, that sound could have been the steam pouring from my ears....
 
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It's hard not to worry sometimes when you don't fully understand what has happened, or don't know how to begin diagnosing/fixing. The numerous stories of unobtainable parts is always a worry too. I can't imagine the ic's or maybe even some of the transistors in this thing are easy to find now.

Most of my tinkering in the past has been centered around things with engines, be it Powerstroke's or my little John Deere tractor and nearly everything in between. I usually know where to start when it comes to them, because I understand how they work, down to a component level in some instances. That is where most of the nervousness and uncertainty come from. Along with the now even more present fear of an unintentional twitch causing another problem. That's tough to get used to.

Not having any 'audio buddies,' to talk to, AK becomes a real asset.
 
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solder a low amp fuse where you are going to bridge the connection and then power the unit up. if the fuse blows you know theres a short some where. simple enough. steve
 
Exactly! And don't forget those clip leads. Also, temporary tape on potential hazards nearby, ie: the case itself if you're near a side or an edge etc.
 
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