Solid blast of clicks on lowest setting

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jimmyjames
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Joined: Sat Jul 23, 2016 7:07 am

Solid blast of clicks on lowest setting

Post by jimmyjames »

I apologize if this is already answered somewhere but I'm not sure what terms to search for.

I just finished assembling the kit and put in two brand new batteries. I turned the hv_adjust all the way counter clockwise and flipped the switch. I was immediately greeted by a squeal of clicks and a solid red LED with a pause every second or so. I tried turning the hv_adjust the other way and it makes no difference. The mute button is working. I took it outside just to be sure and it does the same thing.

I had a little trouble with soldering the larger IC base where the solder was connecting two of the pins. I did my best to clean it up. Is it possible that there's something like that or something else wrong with my assembly? How might I debug that. I also saw something in some of the posts about 'avalanching' tubes.

Here's some pics of my assembly (too much resolution to show in post):

http://oi66.tinypic.com/24wvsjm.jpg
http://oi66.tinypic.com/120ihht.jpg

How do I go about debugging this issue?

Thanks.
jimmyjames
Posts: 5
Joined: Sat Jul 23, 2016 7:07 am

Re: Solid blast of clicks on lowest setting

Post by jimmyjames »

I carefully removed the tube and it is still doing the same thing. Any ideas?
jimmyjames
Posts: 5
Joined: Sat Jul 23, 2016 7:07 am

Re: Solid blast of clicks on lowest setting

Post by jimmyjames »

Tested the variable resistor and the resistance across the top two leads ranges from around 11 to 0.7 Ohms depending on the setting.
jimmyjames
Posts: 5
Joined: Sat Jul 23, 2016 7:07 am

Re: Solid blast of clicks on lowest setting

Post by jimmyjames »

OK. I re-flowed the solder on the variable resistor in order to get good contact with it's wires to test the resistance prior to my last response. Went to eat and when I came back I turned the unit on and no beeps at all. I put my hand near the unit and again it went crazy (without the tube installed.) I turned the hv_adjust down to the lowest setting and then, I have to touch both of the tube holding tabs to get it to respond with again a solid sound. No distinct clicks.

I put the tube back in and turned it on (lowest setting) and it's a still a solid wall of clicks.

This seems like progress but I'm not sure what the next step is.
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mightyohm
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Re: Solid blast of clicks on lowest setting

Post by mightyohm »

Hello,

If the noise continues when the tube is removed, it's definitely not an avalanche problem. And once the tube is disconnected, the HV adjust has no effect. It should be set around the middle of the range.

Most likely your problem involves the main micro controller (U2) and the surrounding components, particularly the geiger counter pulse detect circuit, which includes Q2, C2, R7, R4, and R3.
I can see some suspect solder joints on those components as well as other components on the PCB.

You should go back and carefully reflow any components that don't have a nice "hershey kiss" shaped solder joint. Make sure the solder is covering both the lead and the pad. If there is excess solder you can remove it with a solder sucker or solder wick.
Also, when you trim the leads, make sure you trim them just above the solder joint. Make sure the lead isn't bent over and going sideways, because it can cause a short to the ground plane on
the bottom of the PCB.
When you reflow the pins, heat up those joints, add a very tiny amount of solder, then keep the iron on the joint long enough for the solder to flow nicely around the lead, and finally remove the iron.

Make sure Q2 is the correct 2N3904 and that you didn't mix up Q2 with Q1 (FJN3303F).

You can check the voltage on TP1 - with no tube connected it should be sitting at around 3.0-3.2V with fresh batteries.
jimmyjames
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Joined: Sat Jul 23, 2016 7:07 am

Re: Solid blast of clicks on lowest setting

Post by jimmyjames »

OK sounds like I made some errors. Is it possible to overheat the components? I was a little nervous about how hot some of them were getting. I would touch some of them after soldering and they were hot enough for my reflexes to kick in and I've worked as a cook.
Matt.n2eee
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Joined: Wed Jul 27, 2016 12:20 pm

Re: Solid blast of clicks on lowest setting

Post by Matt.n2eee »

I'm guessing it involves the 555 timer oscillator (U1). Does the number of clicks per second equal to the frequency of the 555? You might have some parasitic capacitance or a bridged solder joint somewhere
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mightyohm
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Re: Solid blast of clicks on lowest setting

Post by mightyohm »

jimmyjames wrote:OK sounds like I made some errors. Is it possible to overheat the components? I was a little nervous about how hot some of them were getting. I would touch some of them after soldering and they were hot enough for my reflexes to kick in and I've worked as a cook.
It is possible, but unlikely. It's more likely to have a bad solder joint because the solder isn't making good contact between the pad and the lead, or maybe the solder is shorting between two connections.

I wrote a comic book with Mitch Altman and Andie Nordgren here that can teach anyone how to solder: http://mightyohm.com/blog/2011/04/solde ... omic-book/
Check it out!
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mightyohm
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Re: Solid blast of clicks on lowest setting

Post by mightyohm »

Matt.n2eee wrote:I'm guessing it involves the 555 timer oscillator (U1). Does the number of clicks per second equal to the frequency of the 555? You might have some parasitic capacitance or a bridged solder joint somewhere
I have seen cases where U1 can cause interference if long wires are connected to other parts of the circuit. This shouldn't happen on an unmodified kit, however.
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