chips occasionally blowing?

[kenpo]

so here and there, ever so often, my 16f628 chips blow, and I have no idea why, tho I'm quite sure it's my own fault.

in the problamatic setup, I have 19 of them on small circuits, powering some ultrabright leds (x4) and sending a pulse to a counter chip to flash some other leds. some also send a pulse to a small motoer, but they are NOT driving the motor. it simply gets an ON pulse, and rotates once. (mac floppy eject... great little motors)
I'm feeding them a 5v power supply from a 200watt PC AT power supply, so it SHOULD be clean and perfect,...

what gives? one chip acctually fried and had burn marks all over (it was a micrchip sample, woudl that matter?)

it's artwork, so we're tlaking... maybe 2-4 blown chips everytime I do a week showing... it's a huge deal for selling the work, as I can't sell soemthing that pops and blows in 3 weeks....

I'm lost, any help from the more experienced is greatly desired..

thanks,
adam

[Jerson]

Post your schematic here. It will help with the guessing.

Jerson

[Ron Marcus]

Are you driving the LEDs directly?

[kenpo]

the LED's aren't drive directly (I thought the pic could drive an ultrabight anyways though...)
though the other ultrabright leds ARE driven directly by the counter chip, on the second baord (the second board is just the counter chip + leds, pos/neg, and signal line from pic)

here's the scematic (edit: schmeatic of the main board, that is, it has mounts for servos and tip 120's, but I'm only using ONE servo mount to control the mac floppy motor thus far)

[Melanie]

OK and the other holes wire into a Tesla Coil?

Let's not make life difficult... post a proper schematic not a PCB layout which is bad enough with proper component idents, but without is just impossible.

[kenpo]

unfortunetly I don't have a proper schematic, I use windows paint to make my layouts.... :(

[mister_e]

Let's do a guess from what i can understand of it. Are you really sending your PIC i/o directly to the base of your TIP122 without any resistor in serie with the base? if so... your problem is there.

Also, as those transistor have already resistor between base and emitter.. you don't really need those you place.

If you don't want to do PCB modification, you change your TIP122 to a mosfet, some, see all, Logic type can be driven without resistor in serie with the Gate.

[kenpo]

here's the thing, the circuit has alot of ports, like for the tip122s, but they're not being used as of yet, only ONE of the 19 boards I used a tip122, and that one hasn't blown, it's perfectly fine... which is odd,( I'll obvisoly add the resister as you suggested though for the next revision, I have no qulams about redesigning and reprinting the board. I need to make more anyways).

what's being driven from the pic is the mac floppy motor, and the counter chip.
so the circuit isn't really as complicated as it has space for, there's really only like 4 things on it usually.

I'm wondering if I need to some how buffer the incoming voltage??? is the 5v clean enough? should there be a resitor somewhere for the pic voltage incoming or outgoing... I mean, really, all I cna think of (other than the tip problem, which hasn't been the source yet) is that the mac floppy needs a diode on the signal pin, perhaps theres feedback being thrown back to the pic? I send a HIGH pulse for 800 (pause) then the motoer does a rotation once around.

and running the 16f628a on internal clock, is this bad? I'm wondering if I've hooked in one of the traces to the pic wrong or something....

also, a few osc crystals blew, but I've heard that can happen alot...? so i started using the 628 to avoid external clocks

[kenpo]

here's the tiny circuit for the counter chip. 2 leads from the pic, one to make it count forwards, one to reset (though I never got the chip to reset for some reason)
and 5 led spots, one resitor as only one led is on at once. easy to understand, bare bones.


could the motor someho introduce noise (or soemthing, I'm not an engineer) into the power supply?

[NavMicroSystems]

OK,

based on your "Artworks" I can tell:

The problem is with the black track.

For best results you should always design PCBs without having a proper schematic first.
That way there is only little risk for a real surprise.
(The rare occasion that it works)

You should have a look at EAGLE (www.cadsoftusa.com)

[Ron Marcus]

<OK,

based on your "Artworks" I can tell:

The problem is with the black track.>

It could also be the rectangular pads...Surface accoustical wave heating?
Don't be dissin' Eagle ;)
Can we add PTFS to RTFM?

[Acetronics2]

[QUOTE=kenpo]so here and there, ever so often, my 16f628 chips blow, and I have no idea why, tho I'm quite sure it's my own fault.

Hi, something hurts me ...

Tip 122 base connected directly to pic port ... I know there's a current limitation !!! but this is quite an unfair practice ...

Alain

[mister_e]

Alain... look post #7 :D

@Ron
PTFS => Post The Fantastic Schematic?

[Acetronics2]

Alain... look post #7 :D

@Ron
PTFS => Post The Fantastic Schematic?

Hi, Steve

My Maple Joe stock is at zero level, it's the only decent explanation i see ...my daughter (2 1/2 ) finished it !!!

2 votes in the same way ... that's to remember here.

amitiés

Alain