Failing Bus Pirate -- Strange Failure Mode

[mdszy]

So I've had this Bus Pirate V3.6 for quite some time and have recently dug it up from my bin-o-crap to try using it again. However, it isn't working properly.

The device fails selftest, here are the errors:

Code: [Select]

~
Disconnect any devices
Connect (Vpu to +5V) and (ADC to +3.3V)
Space to continue
Ctrl
AUX OK
MODE LED OK
PULLUP H FAIL
PULLUP L OK
VREG OK
ADC and supply
5V(4.80) OK
3.3V(3.32) OK
Bus high
MOSI OK
CLK OK
MISO OK
CS OK
Bus Hi-Z 0
MOSI OK
CLK OK
MISO OK
CS FAIL
Bus Hi-Z 1
MOSI FAIL
CLK FAIL
MISO FAIL
CS FAIL
MODE and VREG LEDs should be on!
Any key to exit
Found 5 errors.

I tried hooking up the device to a logic analyzer and sending some SPI data to the analyzer. It worked, except for the CS pin. I had to disable CS in the analyzer but when I did, it showed the data being transmitted just fine. However, the CS line didn't seem to be working. I measured the voltage on the CS pin with my multimeter and that showed it having a high-level voltage of 3.3V, but a low-level voltage of 2.5V or so.

I'm honestly stumped as to what's gone wrong. Like I said, the other SPI pins seemed to be working as the data was transmitted properly, but only the CS pin was failing. Could that *one* IO pin on the MCU have failed somehow?

I've attached a schematic of the Bus Pirate if it ends up helping anyone.

http://dangerousprototypes.com/docs/images/4/4d/Cct-BusPirate-v3.5.png

[CJay]

It's possible but to me it looks like the 4066 would be a more likely culprit.

As it's been in a 'bin' for a while are you sure nothing has been damaged on the board, a resistor cracked or some crud on the board?

(and an aside, I *hate* schematics like that which are not much more than a bunch of chip pinouts, the bus pirate is simple enough a device that it could be a 'proper' schematic)

[mdszy]

It's possible but to me it looks like the 4066 would be a more likely culprit.

As it's been in a 'bin' for a while are you sure nothing has been damaged on the board, a resistor cracked or some crud on the board?

(and an aside, I *hate* schematics like that which are not much more than a bunch of chip pinouts, the bus pirate is simple enough a device that it could be a 'proper' schematic)

1. I did check the 4066 and it seems almost like that could be the problem. When I enable/disable pull ups, the input/output of each switch element show an open circuit on my meter.
2. I've checked all the resistors according to the schematic and they're all showing their nominal values. The only difference is on two of the three resistor networks, all three resistors measure 8k instead of 10k, and on the third they all measure 10k. I imagine that's not really a problem though.

[macboy]

There's not much to a Bus Pirate. Replace the 4066 first. If that doesn't do it, replace the MCU. You'll need to program the BP bootloader onto it so that it can receive a firmware update, so you'll need a PIC programmer. A Bus Pirate itself can act as a PIC programmer (via PicProg software) but not with the CS line broken.