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Need a little bit of help.

D

dave

Jan 1, 1970
0
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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M

martin griffith

Jan 1, 1970
0
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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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)
 
T

Tom MacIntyre

Jan 1, 1970
0
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.

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

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
 
J

Joerg

Jan 1, 1970
0
Hello Tom,
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.

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
 
K

Ken Taylor

Jan 1, 1970
0
dave said:
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?
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
 
J

Joerg

Jan 1, 1970
0
Hello Ken,
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?

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
 
L

Luhan Monat

Jan 1, 1970
0
Ken said:
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
Hi,

The parts that are already shorted do not tend to heat up. Instead, they
cause other parts to heat up. All of this leads to a "Night of the
Living Dead" scenerio where dead parts come back to consume the living.
 
K

Ken Taylor

Jan 1, 1970
0
Luhan Monat said:
Hi,

The parts that are already shorted do not tend to heat up. Instead, they
cause other parts to heat up. All of this leads to a "Night of the
Living Dead" scenerio where dead parts come back to consume the living.

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
 
D

dave

Jan 1, 1970
0
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.
 
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