Need help with diagnosing problem

[shoder]

My son and I are building the tinyTesla for his AP Physics project (which unfortunately is due in 5 days) and need some help diagnosing a problem. The fuse blew immediately on power up.

We went through Step 15 Full-system Troubleshooting on page 12 of the manual. In the middle of the page it has a bullet that says:

Meter between pins 1 and 3 of X1, the large 3-pin connector. You should read open.

We measured 888 ohms. Checking the schematic, one pin connects to the fuse (AC neutral) and the other connects to pin 2 of rectifier D4 (AC hot) which is basically the two AC inputs of the rectifier so I would expect it to show open. We then went through the process of removing (destroying) the rectifier and installing the spare. It still measured 888 ohms. (Prior to installing it we confirmed that the AC inputs show open.)

Looking at the schematic more, those pins are also connecting to one end of the transformer that is used to power the electronics. Therefore, measuring between pins 1 and 3 of X1 should not be open and that's why we're measuring 888 ohms. It's the resistance of the primary. After this, I figure that the instructions are wrong and we're all set. All of the other checks passed.

We plugged it in and nothing happened after we increased the power for the interrupter. We determined that the phasing jumpers were wrong and rotated them. This time when we plugged it in, the fuse immediately blew.

We checked the board for bad solder points that could be causing a short. They are fine. None of the electronics appear to be blown. It seems that the IGBT bridge is probably blown. We will be replacing them tonight.

What I'm concerned about is why did they blow? I would like to avoid replacing them to only have them and the fuse blow again. Is there anything that we can check to help find the root cause? Is my analysis above about pins 1 and 3 of X1 not showing open correct and the manual is wrong?

Thanks for your help,
Stephen

[Heidi]

Stephen,

You're correct that there is a mistake in the manual. It should say to ensure that you're not reading a short across the inputs, rather than verify there's an open. I'll fix it in a moment.

Have you metered your bridge? This will point out a dead IGBT or one that's shorted to the heat sink. See the IGBT check in Step 15 of the latest revision of the manual for instructions: http://onetesla.com/tinyTesla_Manual.pdf.

Good luck!

[hily]

I'm having a similar problem and I've blown the IGBTs and fuse twice now. I power it on, send it a signal and then one big spark comes from the breakpoint and then the fuse blows.
Pins 1 and 3 of both IGBTs read short. Q1 middle pin (+ probe) to Q2 middle pin was open. X1 pins 1 to 3 was around 900ohms. Everything else seems fine after the first blow I went over the board in detail and found no shorts. The intterupter appears to be outputting light and varying with power fine.

Did anyone find a cause to this problem? or have suggestions for other things to test?

[shoder]

Unfortunately, we weren't able to figure out the problem. We replaced the IGBTs (a few times) and checked for shorts (none). My son even checked it out with his physics teacher who is also an electrical engineer. They couldn't find any problems with the equipment we have available, only a multimeter. My son will be a freshman in college this fall and is hoping to be able to use the school's equipment and professor to help determine the issue(s).

[kevindeannow]

Father and I are building one tesla and are testing the CD interrupter and cannot seem to find the problem.

We have display power

We have backlight

LED seems to light but there is no message at all when we power up.

Troubleshooting says we should get word FIXED if there is no sd card and we should be able to go up , down and select to get there.

We simply have no message at all.

Thoughts? Direction

[riddler_enigma]

@kevindeannow I had the same problem, i reheated the joints and it started to work. I hope that helps.

[jondaddio]

@kevindeannow My first SD Interrupter had that same problem. I pulled my hair out, but no joy. I was meticulous in my assembly. So what could the problem be?

It turned out it was a bad MCU chip. I know because after a while I bought and assembled a 2nd SD Interrupter that worked the moment I turned it on. So then I had a known good MCU chip. I tested that known good MCU chip on the older SD Interrupter that came on with a backlight but with no message like you described. The older SD Interrupter suddenly had messages. The only change was the good MCU, so I validated my assembly skills were right on. So I think there are some MCU programming issues with whomever is programming them. I don't think they are testing the MCUs before they send them out. Just burning them and assuming they are good.

I'll let the oneTesla folks respond to my assertion/challenge. Don't get me wrong, I like the SD Interrupter. I just think there might be a quality control issue that can easily be remedied to avoid this bad MCU issue.

[Baumbayliner]

Hello I built the original one tesla coil, (full build in time lapse at --> https://youtu.be/5BIJXfLbKZA )and it worked fine for a long time. I had it sitting for a while without use and when I went to use it again I had no spark at all. I went through the low power testing and all ok. I re heated all the welds and didn't see anything damaged. I can hear the light buzz from the GDT. Any ideas on what else to check or replace? Thanks.

[itsryanhogan]

@kevindeannow My first SD Interrupter had that same problem. I pulled my hair out, but no joy. I was meticulous in my assembly. So what could the problem be?

It turned out it was a bad MCU chip. I know because after a while I bought and assembled a 2nd SD Interrupter that worked the moment I turned it on. So then I had a known good MCU chip. I tested that known good MCU chip on the older SD Interrupter that came on with a backlight but with no message like you described. The older SD Interrupter suddenly had messages. The only change was the good MCU, so I validated my assembly skills were right on. So I think there are some MCU programming issues with whomever is programming them. I don't think they are testing the MCUs before they send them out. Just burning them and assuming they are good.

I'm having the same backlight with no text problem, but luckily I bought a full set of replacement parts as well. I've tried swapping the removable IC's from the replacement kit with my board somewhat randomly, but haven't had luck yet. What exactly is the MCU? Is it the ATMega328?

[Bayley]

My guess would be an assembly error or a bad LCD module.