KB3 humming

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yarek
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Re: KB3 humming

Post by yarek » Sat Jul 30, 2016 11:17 pm

earlier today it was measuring 0V in either direction and my meter was just producing a continuous beep. Now when I measure it again in the evening, I get unstable readings. It randomly jumps from one value to another between 0V and ~2.2V. But whenever it finally settles, it's at 0V.

With this diode unsoldered, everything else gives reasonable readings btw.

I'm not sure I have the right diagram btw. I couldn't find D21 on it...

Anyway, just ordered 10 of those diodes for $4.90. Let's see how that goes.

How can I get you a beer for all your help? Not too many people that are as helpful and knowledgeable as you around these days...

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Enzo
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Re: KB3 humming

Post by Enzo » Sun Jul 31, 2016 12:55 am

Look at the power amp schematic, towards the right are the two output power transistors. D21 is immediately to the right of the upper one.

yarek
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Re: KB3 humming

Post by yarek » Sun Jul 31, 2016 12:34 pm

the diagram I have lists the rectifier at CR103, and the transitors as Q101 and Q102. So I definitely have a diagram for something slightly different.

But the voltages are right, and the CR103 rectifier listed as 1N5393 is apparently a 1.5A/200V rectifier, so kinda close to the one you recommended. And I believe your recommendation is correct.

The new rectifiers have shipped already, probably will be here by next weekend and I'll be able to try it out. I hope this is the only thing that is blown out and that after I'm done, I'll be able to sell it and reclaim the space in my living room.
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Enzo
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Re: KB3 humming

Post by Enzo » Mon Aug 01, 2016 3:27 am

So contact customer service at Peavey and get the correct schematic. My KB3 power amp schematic is named KB3. 300SC is a power amp they use in various models, but I don't have a record of it in a KB3, though anything is possible.

yarek
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Re: KB3 humming

Post by yarek » Mon Aug 01, 2016 10:23 am

gotcha. I was looking for it on the Internet for a while. Didn't know Peavey gives those to people. That's nice!




edit: I thought I'd mention that after I sent my e-mail to their customer service, I got the schematic really quickly. They are really nice. Still waiting for the new rectifiers though.

yarek
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Re: KB3 humming

Post by yarek » Sat Aug 13, 2016 1:35 pm

I got new rectifiers (a pack of 10 for $4.99) last night and immediately got on the job. Soldered the new one in, fixed a couple of loose pins (for these 3-pin connectors coming from the transformer) and put it all together. And it WORKED!!!! everything worked 100%, right away. No humming, no problems, even the headphone output worked fine (which used to not be the case in the past). But this is not the end of the story.

I have misplaced the original little screws that hold the main board to the metal case so I pulled out some hex screws to replace them. They aren't as low profile so it introduced a tiny bit of stress as I tightened up the mounting bolts. But nothing to worry about, I was careful not to overtighten anything. And it still worked fine.

Then as I was packing everything up, I found the little screws that I put on the other table. And this is where it starts. You heard the saying: 'Better is the worst enemy of good'? Yeah. I took the amp out and replaced hex screws with the original ones. As I was putting the amp back into the cabinet, it slid out of my hands onto the carpet and pulled a little on the two cables that take the signal to the speaker. (#$%& I thought...). So I connected it to power and tested it again. The speaker works fine and all is good there, but for some reason there is almost no signal coming to the headset, from any of the channels (1-3, and monitor). I say 'almost' because if I turn everything up all the way, there is a little bit of signal in the headset. So this sounds like a bad connection somewhere. I checked the obvious things visually (the ribbon cable going to the small plate with speaker-out, and headphone-out, and other things that stick out and could've been pulled by the speaker cable) and found nothing wrong. I even shook the whole amp to hope it would help, but no luck.

Any ideas?

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Enzo
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Re: KB3 humming

Post by Enzo » Sat Aug 13, 2016 10:02 pm

Grasp the phones jack with your fingers and wiggle it side to side, Do the phones come and go? Is there a ribbon cable and connector between the jack itself and the main board? If so, check the solder on the ends of the ribbon and wiggle it as well to see.

yarek
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Re: KB3 humming

Post by yarek » Sun Aug 14, 2016 2:20 am

will do it the first thing tomorrow. As a little back story: it used to act this way with channels 1 and 2 in the past, but 3 used to work fine. Then it was for the first time last night, when all worked as intended. I got so excited, that I must have dropped it... sigh...

I'll check the connections and their continuity.

yarek
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Re: KB3 humming

Post by yarek » Mon Aug 15, 2016 12:16 am

finally checked it now. Well, the jack is fine, and so is the ribbon cable. But capacitor C71 near the corner of the main board is loose (probably got pulled by the ribbon cable) and that's what causing the headphone problem. If I set it just right, it sounds fine. I'll pull out my soldering iron one last time tomorrow and hopefully will get it fixed once and forever.

Your help has been instrumental (pun intended).

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Enzo
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Re: KB3 humming

Post by Enzo » Mon Aug 15, 2016 1:48 am

I'll make a note that it was key information. Raising the bar somewhat. I hope we all are in a chord. Fortunately it was a minor rather than major problem.

yarek
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Re: KB3 humming

Post by yarek » Mon Aug 15, 2016 11:10 am

haha. Yes, I finished the soldering, tested it. Put it together, and tested again. It works like it never did before.

Now, I'm serious, how can I repay for all your help?

Since we're quite a distance away and you may not want any money, I'll gladly donate to a cause that you support. You have been really helpful and I'd love to help back in return.

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Enzo
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Re: KB3 humming

Post by Enzo » Tue Aug 16, 2016 12:05 am

You can pay me best by passing it along. When you see someone with less experience than you trying to do something that you might help with, then lend them your support.

If you ever find yourself in Lansing, Michigan, look me up, and we can have a beer or coffee or whatever .

yarek
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Re: KB3 humming

Post by yarek » Tue Aug 16, 2016 12:14 am

I have a friend in Chelsea, MI. It may happen before you know it :D

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