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Junebug VPP short

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3v0

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I built another batch of Junebugs and all worked but one.
I washed the backside of the PCB with flux cleaner.
You can see parts of the PCB at http://www.rocklore.com/3v0/jbp/

VPP is fine (reports 11.9V) without a processor in the target socket.
With a processor and all switches open reported VPP drops to 8.1.
With a processor and switch positions 1-3 closed a short is reported.

VUSB is 4.85 with and without the target chip.

Target pin 1 connects to the charlieplexed LEDs. On a working Junebug without a target processor this pin to gnd is an open circuit. With this unit is shows 2.6K to gnd.

I can not think of a logical reason for VPP to drop with the processor installed and the switches open.

My DVM reads a bit on the low side so 11.9 could be 12 and 4.85 could be very close to 5.

3v0
 
I would guess that the Vpp line is somehow shorted to one of the 1320s pins and the clamp diode is conducting Vpp to ground (probably via a resistor/LED). Have you tried metering from each pin to Vpp (before the switch).

Mike.
 
Please check whether any deposits are there under the IC socket od 18F1320and the dip switch. perhaps you need to remove them and resolder /replace. also It is customary to clean the surface with little warm distilled water using a sort of brush., it would help removing any film deposits.

With this, I hope the board should restore to normal.
 
On one PCB there was a trace between the 16 pin header on the top and the 18F2550 that had a little blob of copper shorting the traces. A razor took care of it.
 

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VPP is good with dip switches 1-3 closed but no target

gerty: Yes, it is a good guess and one of the first things I tried. I swapped out the 18F2550 also.

Pommie/Mike:
Pommie/Mike said:
Have you tried metering from each pin to Vpp (before the switch).
Just checked. They are infinite without the 18F1320. Same with.

mvs sarma said:
Please check whether any deposits are there under the IC socket od 18F1320and the dip switch. perhaps you need to remove them and resolder /replace. also It is customary to clean the surface with little warm distilled water using a sort of brush., it would help removing any film deposits.
Do you think this could be a problem given that VPP is good with dip switches 1-3 closed but no target (18F1320) in the socket. With the target in place it fails regardless of dip switch 1-3 setting. This is what puzzles me.

I cleaned the bottom of the PCB with a spray designed for PCB cleaning and dried with compressed air as per label. Did not do the top. I did not solder there but I suppose it would not hurt.

Bill said:
On one PCB there was a trace between the 16 pin header on the top and the 18F2550 that had a little blob of copper shorting the traces. A razor took care of it.
traces-to-check-gif.22602
I checked between pin 14 & 1-13 on the 2550. They all showed infinite resistance. To check the outer trace I tested between pin 9 & 10-14 these agreed with the resistances measured on a know good Junebug.

Thanks everyone. They were all good ideas but I am still scratching my head.

3v0
 
I dropped water on my firefly, and now the ZIP socket doesn't read my chip in there anymore. Only in the tutor position.
 
I dropped water on my firefly, and now the ZIP socket doesn't read my chip in there anymore. Only in the tutor position.
First check the manual to see if you are setting SW5 correctly. Position 4 must be off and 5 and 6 set correctly based on what chip have in the ZIF socket.

If that does not work I would check SW5 with an ohm meter to see if positions 4 through 6 are working correctlly. Clean or replace the switch. How to clean it?

For water I would flush the switch with distriled water to disolve any minerals then blow it and the rest of the board dry with compressed air.

EDIT: I am still working on my problem and am willing to share the thread with Robert's problem. In general it is better to start a new thread because some will say you are hijacking their thread. Which is true.
 
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Strange as it sound the charlieplex LEDs may be at fault. I bent pins 1, 15, and 16 up on the 18F1320 so they did not go into the chip socket. The short is gone.

Pin 1 which is RA0 has a resistance of 7.2 K to VUSB and 2.6K to GND. Both the schematic and a know good Junebug show them to be infinite.

At this point I would like to pull R2. That would tell me which side of the resistor the short is on. Or maybe the resistor is defective.

But at this point the unit can be used with a breadboard so I will stop now. Maybe after I have a few more built and working I can work on this one again.

EDIT: This was sort of interesting. It was weird that the target chip influenced VPP with the target switches open. I knew there was a problem with pin 1 but did not see how it could be the problem with VPP. It is but the current draw is not enough to change VUSB esp when the charge pump in not active. I would guess that if I had a DSO I could see VUSB drop when the charge pump went active.

3v0
 
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does somebody experienced with junebug's PIC18F2550 heating. My hand made junebug PICKit 2's 18F2550 is slightly heating while operating....after 5 minutes of operation it becomes more hot....What to check for ya?

680uH isn't simply available here. even the near values are not available. I've a lots of copper wire....Can somebody tell me how to make the inductor by winding in hand??
 
Place an amp meter between the power from the USB and the junebug.

These chokes are worth under $1 each. Maybe 35 cents in the US. Import a few and sell the rest off to get the shipping back.

does somebody experienced with junebug's PIC18F2550 heating. My hand made junebug PICKit 2's 18F2550 is slightly heating while operating....after 5 minutes of operation it becomes more hot....What to check for ya?

680uH isn't simply available here. even the near values are not available. I've a lots of copper wire....Can somebody tell me how to make the inductor by winding in hand??
 
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Place an amp meter between the power from the USB and the junebug.

That's a nice idea for temporary use. But what to do for permanent? Will I put a small resistence there? like 100Ω ?

I'm looking out for the 680uH baby...

I've cut the BS250 and shorted D & S as I was not sure about it's pinouts. Even I've cut the 2N7000 for examing.

Without the inductor; everything remains fine; except the Vpp..

Any other other idea regarding 2550 heating??
 
Place the amp meter in the circuit to see how much current the circuit is drawing. Not to fix the problem. I asked you to do this becasue often peoples idea of what hot is varies. Better to check if the current is out of wack.

But my 2550 is just warm to the touch. You may have a wiring error.
3v0

That's a nice idea for temporary use. But what to do for permanent? Will I put a small resistence there? like 100Ω ?

I'm looking out for the 680uH baby...

I've cut the BS250 and shorted D & S as I was not sure about it's pinouts. Even I've cut the 2N7000 for examing.

Without the inductor; everything remains fine; except the Vpp..

Any other other idea regarding 2550 heating??
 
That's a nice idea for temporary use. But what to do for permanent? Will I put a small resistence there? like 100Ω ?

I'm looking out for the 680uH baby...

I've cut the BS250 and shorted D & S as I was not sure about it's pinouts. Even I've cut the 2N7000 for examing.

Without the inductor; everything remains fine; except the Vpp..

Any other other idea regarding 2550 heating??
You are in India , as per the profile. Many RF chokes are sold in TV spares market at Rs 2 or max Rs5.
Any drum core type coil with less than 1mH will work well. If you can indicate your address by mail to me, perhaps I can send you few of them

Perhaps you can salvage an IFT of transistor radio and use the drum core winding as it is using the winding that shows higher coil resistance. all the metal can and tuning drum can be removed. other pins can be cut off.
 
well Mr MVS,

I'll look out for ya, if the RF chokes of TV is not available, I'll just use a very much available IFT of Silicon radios......

Thanks.....That was anice tips, I was just thinkibng 'bout that:)
 
Mvs,

I'm in trouble. The maximum inductor value available here is 100 uH. That's simply not enough.

MVS told me I can use a transistor radio IFT in place of the inductor.
In those IFT's, there are two pins in one side, and other side has three pins.
So, where to connect;in the two pinned side or the three pinned side??
I'll remove the metal exterior, the tuning mechanism.

What things to be checked for Vpp error? I think :

the PNP transistor, the inductor, the IN4148 diode....any more??

and I use BC548B transistor in all NPN transistor places, which were 2N3904.
I use BC558 transistor in all PNP transitors places,which were 2N3906.
Both have reverse layout. ie C-B-E. the 2N390x have E-B-C layout.

Any problem...any suggestions???...Hope Mr. MVS will solve the IFT problem...
 
I'm in trouble. The maximum inductor value available here is 100 uH. That's simply not enough.

Here's a thread (post #5) where there is a claim that a 100 uH inductor will work in a pinch. I suppose you should take it with a grain of salt. I've heard a number of times that less that 680 uH will work. How much less I don't know.

http://forum.microchip.com/tm.aspx?m=369639

Inductance adds in series. Are the inductors small enough to use several in series?
 
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