Matrix user forums

general · Post by **general** » Tue Nov 27, 2007 1:36 pm

U3 on the development 3 board is getting very hot when changing jumpers j29 to power any ideas i checked to see whether the chip is ok it is,
theres something strange going on here

Post by **Benj** » Tue Nov 27, 2007 2:32 pm

Hello

By chip U3 do you mean the 2nd 16 pin surface mount chip just below the PPP firmware chip?

What are the specifications for your power supply. Eg Voltage, Current, Ripple?

Has this problem just started or are you using a new board?

general · Post by **general** » Tue Nov 27, 2007 3:32 pm

the external power supply is a 12V 1.6A the strange problem I am having is that im using a 16F877A programmed via the usb I made sure that i am not using rb3 since this is the only one in the left position of jumper J5
when setting up either the option registers adcon1,or t2con the pic behaves very strange, j14 is in the digital position,
the overheating of the multiplexer when i set the jumper,o power it drops the suppy to 2.5v

Post by **Benj** » Tue Nov 27, 2007 3:51 pm

Hello

The 1.6A for the Power supply is far too high but the board should not be pulling that much current (<100mA) so it should be alright. It sounds like the chip U3 has become damaged somehow. The only thing that should get slightly warm is the Voltage regulator U2. Is there anything you can think of that you did to potentially damage the board.

general · Post by **general** » Tue Nov 27, 2007 4:25 pm

analog mux/demux chip when disconnected and tested on a ic tester tests fine however when p[aced back into the board it latches up, i think i may have inadvertently blew it,( may have moved all three jumpers on the j5 connector to the lhs) reading the manual only one of the jumpers needed to be in the left justified position, so I think the chip may be internally latching up,
when the the vpp pin 12 X0 was lifted up the from board with firmware chip removed it was ok i think this may be a preprogrammed pic device to support the usb and lvp modes, then reconnected the problem disappeared however when the firmware was plugged back it it latched up
So 80 percent certain thats the chip is at fault, cmos compatible so 18 volts is maximum supply so for testing i used a 12v power supply, ive ordered a replacement from rs so i let you know if it has cured the problem,initially i wasnt using the lvp mode does the usb use anymore resources ie pins that could affect my 16f877 operation

Post by **Benj** » Tue Nov 27, 2007 4:58 pm

Hello

As long as you have the LVP disabled in the software config and all of the LVP selection jumpers set to I/O then there should be no other interference with the 16F877As operation.

Let me know how the chip replacement goes.

general · Post by **general** » Tue Nov 27, 2007 5:27 pm

when the jumper is in the i/o mode with faulty chip in the the board is unable to identify the pic hoever when rb3 is in the lvp mode then the board successfully indentifies the the pic, so do you think that it is a side effect of the u3 being faulty that this anomalie is happening

Post by **Benj** » Tue Nov 27, 2007 5:36 pm

Hello

It may be that the software config still has the LVP enabled, Use the expert mode of PPP to disable the LVP pin.

general · Post by **general** » Thu Nov 29, 2007 11:41 am

appreciate your prompt replies and help, The LVP mode has been disabled in the expert mode, I think i read somewhere to fully disable this mode, you need to apply the 13V supply for it to come into effect, Is it becuase that the lvp mode even though it is selected within the PPPv3 software is conflicting, and causing this overheating of the u3

general · Post by **general** » Fri Nov 30, 2007 5:13 pm

thanks for help replacement of U3 cured the problem,