Why am I toasting Protoboards?
matb
Posts: 39
Aghhh. I just toasted my 4th protoboard, and I am at a loss why. Open to ideas!
#1 Could have been anything as had prototype connections then pulled down to fit into a housing. Board now works with RCFAST and using the 5MHz xtal with no PLL, dies as soon as try to use the PLL.
Wrote it off as static or wiring stuff up.
#2 Sitting running on desk, only video out connected and a few other nuffy components. Touched the Video out signal (at resistors) and video dropped out. notice was getting warm so cut the power. As per first one only works when PLL is off (1).
Decided had to be static, even though I was sure I only touched the active video out line, on the side of the resistors away from the prop.
Bought anti-static stuff (pad, wrist strap, earthed to mains earth)
#3 Board operating with ONLY circuitry for video out on P12,13,14. Sitting on anti-static pad. Board got shoved by my keyboard (i.e. no touchy) again video stopped. Found a single loose piece of wire with one small exposed end had got under the board, presumably shorted together a pair of sensitive pins. Again now only works when PLL is off (1).
Thought it had to be power supply to give the same fault, so jumpered in 3.3V from a breadboard. Leaving the existing regs on place, but found that did not fix the symptoms.
Became very careful to keep bench clear, always power off before touching anything.
#4 Board had some unconnected headers, and the 3 resistors for video out shoved into p12,13,14 plugged in power heard a bit of a noise. Touch prop and is getting hot. Kill power. This one is dead, connect power and it gets hot quickly. No video output was connected this time.
The fault for the first 3 seem It seems really strange to get the same symptom.
I keep coming back to suspect its the power supply somehow, maybe damaged so as to not be stable enough for higher clocks, I am using a switch mode 12V DC supply shared with other loads. Looking with a oscilloscope I can't see anything wrong, a 12.8V with 200mV of ripple that seems to have the fundamental at 6MHz. (I'm very rusty with CROs and only just learning how to drive the bitscope)
This is getting really annoying, I really don't want to keep destroying boards at this rate!
#1 Could have been anything as had prototype connections then pulled down to fit into a housing. Board now works with RCFAST and using the 5MHz xtal with no PLL, dies as soon as try to use the PLL.
Wrote it off as static or wiring stuff up.
#2 Sitting running on desk, only video out connected and a few other nuffy components. Touched the Video out signal (at resistors) and video dropped out. notice was getting warm so cut the power. As per first one only works when PLL is off (1).
Decided had to be static, even though I was sure I only touched the active video out line, on the side of the resistors away from the prop.
Bought anti-static stuff (pad, wrist strap, earthed to mains earth)
#3 Board operating with ONLY circuitry for video out on P12,13,14. Sitting on anti-static pad. Board got shoved by my keyboard (i.e. no touchy) again video stopped. Found a single loose piece of wire with one small exposed end had got under the board, presumably shorted together a pair of sensitive pins. Again now only works when PLL is off (1).
Thought it had to be power supply to give the same fault, so jumpered in 3.3V from a breadboard. Leaving the existing regs on place, but found that did not fix the symptoms.
Became very careful to keep bench clear, always power off before touching anything.
#4 Board had some unconnected headers, and the 3 resistors for video out shoved into p12,13,14 plugged in power heard a bit of a noise. Touch prop and is getting hot. Kill power. This one is dead, connect power and it gets hot quickly. No video output was connected this time.
The fault for the first 3 seem It seems really strange to get the same symptom.
I keep coming back to suspect its the power supply somehow, maybe damaged so as to not be stable enough for higher clocks, I am using a switch mode 12V DC supply shared with other loads. Looking with a oscilloscope I can't see anything wrong, a 12.8V with 200mV of ripple that seems to have the fundamental at 6MHz. (I'm very rusty with CROs and only just learning how to drive the bitscope)
This is getting really annoying, I really don't want to keep destroying boards at this rate!
Comments
As for static, possible, but unlikely. The Propeller is very friendly to handling.
I assume you are connecting it to a composite monitor or TV video input?
Also, any chance that you might have another power supply?
I've found 7.5v DC is ideal for powering the Protoboard.
edit
That antistatic pad isn't a conductive surface is it?
If it is, sitting the Protoboard on it without the feet wouldn't be a good idea.
OBC
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You might have a talk with Parallax support about what they've seen in terms of causes for this type of chip damage.
Post Edited (Mike Green) : 3/17/2008 3:27:22 PM GMT
Go and get one of those big 6V lantern style ones. That way you've got stable power for a while and few hassles while you sort other variables out.
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-Phil
I am not driving any IO apart from the video output, so I figure the 12V is safe, certainly from the regulator specs. Only on other components, the cap left on the unregulated side.
A separate (low power) supply it is... I like the lantern battery idea, anything to stop me killing them off while testing.
Ah if its definitely the PLL, a external clock should recycle 3 dead ones at least as bench test ones.
Ideal power is +9v from memory.
I'd start with just the propeller programming tool connected and nothing else, use a +9v supply and make sure you check the polarity. Parallax stuff is USUALLY center pin +
J
The little surface mount caps have no markings I can see,
The 10v capacitor is on the servo supply only and that would tend to be from a 4.8v battery or maybe the 5v reg for small servos.
I use 12v OK
Graham
I would recommend checking your power supply. If there is no information on the power supply then using a 9v battery like suggested above would also help to eliminate power supply related problems.
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According to the schematic here www.parallax.com/Portals/0/Downloads/docs/prod/prop/Propeller-ProtoBoard-v1.1.pdf there are is a 10uF cap that is connected to Vin. Not sure what its voltage rating is though.
I'd try with a 9v battery first too. Maybe your AC wallwart is unregulated and is producing 19v...?
>The regulators themselves seem to be pretty robust
The linear regs are great for that!
James
Phil is on the money with ground loops. My monitor, bought especially to get a composite input, had about 2V ground offset. When I shorted the grounds there was about 200mA current. Monitor is a Samsung, values are from my hazy memory.
I now am either careful to either run from a 9v battery or use a 12V monitor running off the same supply.
Anyone got a suitable way to decouple the video output? Is decoupling the signal with a cap (say 220uF) going to be enough, or a isolation transformer maybe?
Mat Boorman