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AUDIO FORUMS >> General Discussion and Support >> Zkit up in smoke
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Message started by Mannytheseacow on 10/27/21 at 02:48:51

Title: Zkit up in smoke
Post by Mannytheseacow on 10/27/21 at 02:48:51

Hi, I just built a Zkit and when I finished it and went through the power checkpoints I had my multimeter incorrectly set and at the first point “A” something shorted and I saw a puff of smoke come from the area of the board adjacent to the volume pot, by the 1k 6.5 w resistor and the 20 uf 250v caps.
I immediately saw my mistake with the meter settings and reset. I then went through the preflight check and everything tested exactly as supposed to. I connected speakers and input and only have one channel. The resistors looked ok so I replaced the 20uf250v caps since I had extras. Still only have the right channel making sound. Any ideas? I’ve checked all the solder joints and input/output joints.

Title: Re: Zkit up in smoke
Post by EdwardT on 10/27/21 at 13:23:06

I haven’t built that kit but the many times I’ve had smoke from a circuit board it’s been resistors or diodes. Resistors can fool you by looking fine and still being blown.

Title: Re: Zkit up in smoke
Post by Coyote on 10/28/21 at 15:24:53

If you let the magic smoke out of the box it is really hard to put it back in.

But seriously, good luck with trouble shooting it.

Cheers,

a.

Title: Re: Zkit up in smoke
Post by funch on 10/28/21 at 17:31:47

Check the two 10K resistors at the center of the board. Power goes through each, then through the 47K resistors to one half of the input tube.

Title: Re: Zkit up in smoke
Post by Mannytheseacow on 10/28/21 at 19:02:31

Thanks for the help everyone. I checked all the resistors and all were within range... except for the 100k potentiometer. One channel of the pot was fried. Whether it happened when I initially ran the test or maybe I overheated it when I did the install. When I bypass the pot both channels are working (at full volume). I have another pot on order.

Title: Re: Zkit up in smoke
Post by Brian on 10/29/21 at 03:24:50

I am glad you found the trouble.
Having something wrong can be so frustrating until the cause is found.

I hope all goes well from here.
Brian

Title: Re: Zkit up in smoke
Post by Mannytheseacow on 11/25/21 at 16:42:16

I’ve been living with this amp now for a few weeks and loving it. It has an addictive sound I can’t get enough of.
I’m still having as issue, though, where the left side keeps dropping out. I listen at about 60-70% volume and when the left side drops I’m able to bring it back by turning the volume up and then bringing it back to the original setting. Anyone have an idea where the fault is? I’ve gone through the components and everything is testing properly. Is this problem characteristic of anything that anyone else has experienced?

Title: Re: Zkit up in smoke
Post by Archie on 11/25/21 at 17:04:15

Sure sounds like something in the pot if I understand your problem correctly.

Title: Re: Zkit up in smoke
Post by Lin on 11/25/21 at 17:08:14

Sounds like it could be a bad connection somewhere, have you checked all the solder joints on that side?

Title: Re: Zkit up in smoke
Post by Mannytheseacow on 11/25/21 at 18:18:23

I just replaced the pot and it seems smooth when I test it. I rechecked all the solder joints to be sure that wasn’t the issue either.
I was able to trace it back to the 47k resistor, when I put a volt meter to ground on the tube pin 6 side of the resistor that channel comes back. Could it be the resistor is damaged but intermittently working? Sorry, I’m definitely an electronics newbie.
A couple of other things I’ve noticed- maybe it’s just me but the left side power tube doesn’t appear to glow as brightly as the right, and when I shut it down the left side distorts as it fades out.
I should also note that when I say I lose the left channel, it isn’t totally gone, but sounds still comes out very faintly.

Title: Re: Zkit up in smoke
Post by Lin on 11/25/21 at 18:44:49

Have you swapped the tubes?
I have tubes that work fine, but seem brighter than others because of construction.

Resistors are cheap and easy to replace, worth trying.

Title: Re: Zkit up in smoke
Post by EdwardT on 11/25/21 at 19:47:10

Can you see if it's black where the lead exits the resistor body? That could be your puff of smoke.

Title: Re: Zkit up in smoke
Post by Mannytheseacow on 11/25/21 at 21:41:24

I’ve changed tubes. The resistor doesn’t appear abnormal but I ordered some more and will try replacing it.

Title: Re: Zkit up in smoke
Post by Lin on 11/25/21 at 22:53:23

To follow up on my earlier question since I'm not sure I understand the answer.

You mentioned the right tube being brighter than the left, is it always that way?
If you swap left and right tubes, does the right tube still seem brighter or does it follow the tube?

Title: Re: Zkit up in smoke
Post by Mannytheseacow on 11/26/21 at 05:48:50

Thanks, Lin. Sorry I didn’t answer your question more clearly. I tried swapping left/right and replacing with new tubes and in all instances the tube inserted into the left channel socket appears dim compared to the right.

Title: Re: Zkit up in smoke
Post by Lin on 11/26/21 at 15:14:48

Can you follow the signal path and check voltages at each part to see if you find a drop on the left side?

Title: Re: Zkit up in smoke
Post by CAJames on 11/26/21 at 18:14:40

It is possible the tube socket itself has gone bad. Doesn't happen often, but it does happen.