Help with inchworm

Hey, I messed up pretty bad yesterday. I accidentally plugged my 15v power supply into the breadboard I was working on. It probably ruined the PIC attached and also damaged my inchworm which was attached to the circuit.

There is no visible damage to the Inchworm. The computer is unable to establish communication with the inchworm and all the reference voltages read "0.00" in the device settings in MPLAB.

I was hoping Bill or someone else could make a suggestion as to what parts of the circuit might be damaged. I've been looking at the PCB and . But I don't know enough to guess what might be wrong.


I know I messed up, but I really can't afford another programmer right now.

Any ideas?

Seek a new 16F877A

You probably fried the PIC on the Inchworm. You will need a new one and load the code into it. So you will need some other programmer to do that.

Remove the ST232 & 16F877, then power just the Inchworm and nothing on the ICD2 connector test for 5V.
If that's Ok (the regulator should be fine as it's clamped)
Insert the ST232 and with a meter is there >12V on the VPP test point?
If yes then your ST232 is probably ok
The transistors are all 30V rated so I doubt they had a problem with 15V
The PIC16F877(A) probably hated it, lucky both the ST232 and 16F877 are socketed and the repair might be one or both of those ICs.

Thanks for the help. I am glad to hear the IC's are all that needs replacing.

The ST232 is broken (3v on the Vpp TP) and I am just going to assume the PIC is shot. But everything else seems fine.

Thanks again.

Start with the ST232 but it's always handy to have a spare 16F877.

I am an engineering student, so I ordered some 16f877's from Microchip as samples. I wanted some 232 chips for my projects anyway.


Now that I am bored waiting for the parts to arrive. Can I add a 5v zener diode between power and ground to prevent this from happening in the future? I only do logic-level work on this breadboard anyway..

Any reason why I shouldn't?

ravix said:

I am an engineering student, so I ordered some 16f877's from Microchip as samples. I wanted some 232 chips for my projects anyway.


Now that I am bored waiting for the parts to arrive. Can I add a 5v zener diode between power and ground to prevent this from happening in the future? I only do logic-level work on this breadboard anyway..

Any reason why I shouldn't?

Click to expand...

You'll also need a fuse, another simple solution would be a 1N5819 diode but the Inchworm would no longer be able to be target powered.

ravix said:

Now that I am bored waiting for the parts to arrive. Can I add a 5v zener diode between power and ground to prevent this from happening in the future? I only do logic-level work on this breadboard anyway..

Any reason why I shouldn't?

Click to expand...

Because a 5V zener will conduct on a 5V supply, use a 5.6V zener instead, plus a fuse or current limiter, for when the zener goes S/C.

But in reality, far better to be more careful!, or disable the ability to power from the Inchworm.

I guess I'll just be more careful from now on.

As an update: both of the pics were okay. The ST232 just needed to be replaced.

Thanks again, Bill.

Great

That's great. The simple dumb chip took the brunt of the hit.

I whacked an 16F877A that I had plugged into my Unicorn doing testing when I did what you did. Hit it with 12 volts rather than the correct 5 volts. It went "snap, crackle, pop!!!!" after about 10 seconds. Dumb, brain dead, not thinking error. Luckily I had another 877A and I have been much more "careful" since then.

ravix said:

I guess I'll just be more careful from now on.

As an update: both of the pics were okay. The ST232 just needed to be replaced.

Thanks again, Bill.

Click to expand...

Great!

I've burned out a ST232 before, I've yet to kill an 16F887A (got one pretty warm though)