HV out problem and a few other catastrophes

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3 months 2 weeks ago #10274 by matt
Hi, I put together a 6 digit classic. Went step by step with all tests working fine - high volt coming out everywhere it should have been. I did do something really dumb in between the board working and not working, so I'll just get that out of the way:

I decided to switch the power LED to a different color after the build. It was surprisingly difficult and I ended up hurting the contact pads on the board for the LED. I got it working with a small jumper on the back to it's resistor, but again, dumb move and I should have just left it alone.

So I hook everything up, turn on the power - 12VDC, power light comes on both the board and RTC. All VCC and HV outs are 2v less than the input power. So - 10V when 12V applied, 7V when 9V applied... Not much heat from anything, 328 chip gets a little warm. Same low voltage on pin 7 there.

Bonus: When I unplugged the RTC board the power light for that stayed on and is still on, going 24 hours now. The battery almost burnt me when I took it out.

Are there a series of tests I can perform before giving up? I have a bench supply, o-scope, just about every tool I could need here.

Thanks!

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3 months 2 weeks ago - 3 months 2 weeks ago #10275 by Ty_Eeberfest
From the picture I'm guessing you have a Rev. 4 board. Am I right?

It sounds like Vin and Vcc are somehow shorted together, making it impossible for IC1 (the 7805) to regulate Vcc. This could be some weird failure mode of IC1 but that's improbable because it's very hard to kill a 7805. So your first move is to see if you can confirm and then find a short between Vin and Vcc. I don't see anything obvious in your picture and your soldering looks good overall, but maybe there's something I can't see. The picture isn't great, I can't see a whole lot of detail and I'm not sure if those "hair looking things" are a camera artifact or something all over the board.

The absence of HV is probably a side effect of Vcc being out of whack. The 328P should never get warm, this is also likely to be Vcc related, and there's a 50/50 chance the high Vcc has killed the 328P. If I were you I'd pull it - and the other chips too - out of the sockets until we get Vcc sorted.

There have been some issues with factory-defective RTC modules cooking their batteries. Depending on when you bought your kit you could have ended up with one. This is a subject for Ian to address - hopefully he will have an answer for you shortly.

EDIT: Probably goes without saying but do NOT plug that RTC back into the board until things get resolved!

Look into it later when the dust is clearing off the crater.
Last edit: 3 months 2 weeks ago by Ty_Eeberfest.

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3 months 2 weeks ago #10276 by Ian
Hi Ty, thanks for that.

First thing is, as Ty says, pull everything that is socketed off the board until we understand what happened.

Desoldering is more of an art than soldering, which surprises a lot of people. The first rule is sacrifice the component, you're not going to use it again even if you get it off in one piece. I learnt desoldering as a kid when I had no money for parts and found bits of junk in hedges. Half the time they didn't work, but I was a kid and had plenty of time and no other options.

So, when desoldering a component: Cut all its legs off and deal with the pins one at a time. Even if it is only an LED, you're going to struggle if you have to deal with pins together. But I suppose at this point. that is closing the stable door after the horse has bolted.

Once everything is off the board, try powering it up. See if anything gets warm. It looks like you have some equipment there, so if you have a thermal camera, have a look at what is getting hot. If you don't have a thermal camera, you can do some tracing with alcohol, which will evaporate quickly where the source of heat is. Bear in mind that the 7805 will get a little warm under normal circumstances.

If you have no luck, and it starts to get you down, you could make use of the "return to base" option, and I'll repair or replace the board.

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3 months 2 weeks ago #10277 by Ian
Hi Matt

I've got some replacement parts on the way to you. They will go out tomorrow,

Regards

Ian

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3 months 2 weeks ago #10278 by Ty_Eeberfest
Did I miss something here?

Look into it later when the dust is clearing off the crater.

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3 months 2 weeks ago #10279 by Ian
You're quite right. There's a plot twist missing from forum. Sorry.

As I understand, Matt is a friend of a friend and the friend helped him out with some spare parts. I'm replacing the spare parts from Matt's friend, as I understand it. Not 100% sure, tho'...
The following user(s) said Thank You: Ty_Eeberfest

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