Need a little bit of help.

Need a little bit of help.

Did a project kit, the velleman-kit K8048, a PIC Programmer and Experimentation Board.

The first thing I did wrong was to solder in the 2 voltage regulators the wrong way round and then connect a regulated power supply when it should have been an unregulated one.

I desoldered the VR's and replaced with new ones. I purchased an unregulated psu and connected it, but nothing seems to work (no LEDs coming on). When I touch the first voltage regulator it becomes hotter and hotter. I pull out the PSU before it fries.

Can anyone suggest what could be wrong?

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The regulated versus unregulated part probaby didn't have any affect on this.

Something on the side of the circuit fed by the first VR got hurt, and too much current is being drawn. This will require troubleshooting. How many active components are being fed by that supply? You may get lucky.

One way you might try to troubleshoot this is to disconnect the power supply feed to every active component, then do an ohms check on each disconnected power feed. Very low ohms could indicate a short/low-resistance shunt.

What voltages, +/-5?

Tom

Hello Tom,

In the olden days with lots of parts on the boards there was another way but I certainly will not recommend that: Don safety goggles, apply the correct regulated VCC from a really stiff power supply and see what gets hot or smokes out...

Regards, Joerg

It sounds like the "Dead parrot" sketch. You've probablly blown any micro's etc on the board.

What test equpment do you have ?

martin

After the first death, there is no other. (Dylan Thomas)

Hello Ken,

With a DVM it is also possible to measure voltage drops and pinpoint the culprit. We have even done it on boards with full power and ground planes, to within less than a square-inch of where the short actually was. Compared to the brute force method (leave power on until something gives up) this can avoid burning out vias.

Regards, Joerg

Thanks to everyone for your advice. I'm just learning about electronics, but I will use all your advice as a starting point.

I didn't have any PIC chip connected when I first switched it on, so maybe the PIC survived.

I do have a schematic here (not very clear), but I guess it works, otherwise they would sell it (or would they?).

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Does anything else get hot? Something is obviously drawing way too much current, so it should be getting hot too. If not you may have a short circuit on your supply.

Get a voltmeter and check the input and output voltages on those regulator chips. If you can disconnect the output of the regulators easily do so and check the output voltages again. Is there a copy of the circuit you can point us to?

Cheers.

Ken

I read in sci.electronics.design that dave wrote (in ) about 'Need a little bit of help.', on Fri, 22 Apr 2005:

You bet people would! And I can't get the page; it's a 404.

regulator

and

You're right, but they may heat up (they may not be a complete short), so with an OP who is clearly a novice it's worth a try. But reaching for the meter will be even better of course.

And I love the 'scenario'. :-

Cheers.

Ken

Sorry about that page link, damn useless yahoo briefcase.

Here's another link:

I invested some money in a new multimeter and tested all the diodes. A bank of

By the way, the multimeter I bought it new from Maplin. A Mastech MAS-343. A few years ago, it was 70 pounds. I got it today for 20 pounds. I guess this is a good deal. Looks like a good multimeter to me.

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By looking in the "glass" of the LED, you normally see two connectors inside: A huge one and a much smaller one. The huge one is the cathode: This is where you connect the more negative potential, normally the ground.

Looking inside the "glass" of the LED is a good way to distinguish anode from cathode even if the wires are shortend.

Well, looks like I had most of the LEDs inserted the wrong way round. Don't know my anode from my cathode. I'm learning the hard way.

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My meter has a diode test and none of the bank of 6 LEDs are working. The LD9 is a blinking LED and I thought it was strange because it conducts in both directions. In one direction the meter flashes the values 0 and 1683 on and off. In the other direction, the LED reads a constant 586. I thought LEDs only conducted one way like diodes.

I haven't soldered the new LEDs on yet, but I will check that voltage at VR1.

thanks.

bank of 6 LEDs seem

LEDs and see what happens.

MAS-343. A few years ago, it was 70 pounds. I got it today for 20 pounds. I guess this is a good deal. Looks like a good multimeter to me.

Looks good to me too. Nice buy. I don't see why LED's 1-6 would be faulty if you didn't have the PIC in circuit. If the meter has a diode test function on it (I couldn't tell from the blurry pic I saw of one) use that to test them, or failing that just use a 9V battery and a 330 Ohm resistor in series. LD9 is a bit problematic - if it really is wired as shown it'll blow as it is straight across the 5V. I think it's probably meant to be in series with the resistor shown next to it, but that's marked as a higher value than I would have expected if that was the case. Unless it is an LED meant to run off 5V - is it a different type than the others?

Let us know the voltage at point VR1 (output of first reg) and also the 5V rail. Also check for shorts (solder dags in particular around the regulators).

Cheers.

Ken

Thanks to all!

I got it working.

The problem was all the LEDs were in the wrong way round and this seemed to make the voltage regulator heat up to burning point. After fixing all the LEDs, the VR is running cool and everything is working fine.