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Junebug VPP problems

Discussion in 'Microcontrollers' started by edeca, Jun 18, 2008.

  1. edeca

    edeca Active Member

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    I just bought and received a Junebug. I assembled it over a few nights and finally got it connected. I think the PICkit 2 software upgraded the OS on the 18F2550.

    However, I get an error as soon as I start PICkit 2 or attempt any action (reading the tutor PIC etc.). The error reads "PICkit 2 VPP voltage level error. Check target & retry operation". I have attached a screenshot of this.

    Between U5V and GND is just under 5V. No difference using a powered USB hub.

    I have been through the troubleshooting section of the program a few hundred times now ;) Essentially, with /MCLR ON and VPP tested, a short circuit is detected by the software and VPP is turned off. I have checked the datasheet for the BS250K. With /MCLR OFF, VPP is detected between 11.9 and 12.1V and the test passes. When VPP is on in any MCLR state, there is a high pitched hum/whine from something that can be heard from a few cm away. Does anybody else notice this with their Junebug?

    I replaced the 2N7000 with a new one in case (I thought I damaged it during construction). I also removed the BS250K and jumpered between U5V and +5V at Bill's suggestion. No difference and the problem persists without the BS250. The high pitched 'hum' when VPP is on also persists, so it wasn't the BS250.

    On the few occasions where I have convinced the Junebug to see the tutor PIC, I cannot program a .hex. I can (twice) read the PIC, but of course it is empty as I just got it! It seems that whatever internal check the software does triggers the VPP error and I have to 'Check Communication' to get the software to talk to the board again.

    I am happy to try any tests people suggest with a meter. The BS250 is currently removed and I only have a 180mA replacement, the Junebug manual suggests 250mA. The replacement I bought is: UNBRANDED | BS250-MBR | CPC

    Does anybody have any ideas? I've almost given up which is sad as the board is great and I can't wait to start programming.
     

    Attached Files:

  2. skyhawk

    skyhawk New Member

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    I believe that I've seen that message when I inserted the target chip backwards.
     
  3. edeca

    edeca Active Member

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    That's an interesting idea but I have tried all combinations of with & without target PIC and DIP switches 1/2/3 ON and OFF. Therefore the error occurs even without a target PIC.
     
  4. dave

    Dave New Member

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  5. skyhawk

    skyhawk New Member

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    In addition to my bought PICkit 2, I've also built two copies of the programmer portion of the Junebug on stripboard. When I forgot to wire the target feedback I got that message.
     
  6. edeca

    edeca Active Member

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    Are there any components that are specifically worth checking? My soldering isn't great but the board isn't covered in dull grey blobs! :)

    If anybody has other suggestions that would be great.
     
  7. skyhawk

    skyhawk New Member

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    That's pin 3 on the 18F2550. In the troubleshooting mode you might check to see that 5.0 volts is present.
     
  8. RobertD

    RobertD New Member

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    I have a problem with my junebug that the pickit2 doesn't power the firefly and doesn't read the 16F88 in the socket. When I click on the box Vdd target in pickit2 it doesn't click.

    Also, each time I start up PK2, it needs to upload newer version, seems it doesn't upgrade when it uploads the new version, it has to do it every time. So I'm thinking of bringing it back to the store to have them check it out.
     
  9. blueroomelectronics

    blueroomelectronics Well-Known Member

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    I've posted this in another thread but will repost it here.
    This simple mod will bypass both the 2N7000 & BS250. This should eliminate them from the test, if the problem persists then the answer isn't in replacing the Q2 or Q5 (could be one of the other NPN or PNP transistors or even the 1N4148 diode)
    [​IMG]
     
  10. edeca

    edeca Active Member

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    OK, I'll do that tonight. How can I test the 1N4148 or the other transistors? My meter has a diode test function.. I'll have to read up on that.
     
  11. skyhawk

    skyhawk New Member

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    Now that I've had a chance to reread the thread, a few comments:

    The talk about the BS250 and 2N7000 made me think about the 5 V side of things, but now I see that seems to be a rabbit trail, since it is VPP not VDD that's the issue.

    If the 12.0 V is being generated (Did you measure the voltage across C1?) then the pump circuit consisting of Q1, D1, L1, and C1 should be OK. If VPP can be switched then that would indicate that Q3 and Q4 are working, but the hum/whine suggests there might be a problem there. Q6 does the reset, and it along with its base and collector resistors sounds like the place to look for problems.
     
    Last edited: Jun 19, 2008
  12. blueroomelectronics

    blueroomelectronics Well-Known Member

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    A hum or whine would seem to indicate the inductor is straining as if there is a load on VPP (VPP can only supply about 20ma) check the transistors for solderbridges.
     
  13. picbits

    picbits Well-Known Member

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    Not looked at the schematics but if this has a switch mode supply then maybe the output capacitor is either duff or inserted the wrong way round.
     
  14. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Ahh if the VPP cap is backwards or the wrong one it'll be very unhappy and that would cause the inductor to whine. The 22uF cap I use on the kits bought directly from me or Creatron Online use a low profile 22uF @ 25V e-cap that is slightly shorter located under the diode than the 220uF @ 6.3V power filter cap located to the right of the vertical SIP resistor.
     
  15. edeca

    edeca Active Member

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    I'm fairly certain that the capacitors are the right way round. C1 is the smaller 22uF 25v and C5 is 220uF 6.3v. I have checked all the transistors for solder bridges and there don't appear to be any. A diode test across the legs as described here Transistors seems to show they are OK.

    You can see the capacitors in the attached picture. The stripes are the right way round.

    With "Test VPP" pushed in troubleshooting mode, I notice the following voltages between the test point and the ground loop I installed at the bottom of the board:

    Either side of inductor: 5v
    -ve side of D1 1N4148 signal diode: 12.35v
    +ve side of C5: 5.12v
    +ve side of C1: 12.35v
    Pin 2 of 18F2550 (AN0): 4.48v

    Although the error with /MCLR ON and 'Test VPP' says that VPP is 'shut off'.. the same measurements as above are noted with /MCLR either ON or OFF. RB2, labelled "VPP_EN", is 5.1v in either case.
     

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  16. blueroomelectronics

    blueroomelectronics Well-Known Member

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    It looks spot on for the VPP stuff, 4.5V is what pin 2 should read when VPP is generating 12.35V I would say everything on the collector side of Q4 (PNP) looks fine. What does VPP on the ICD header say when +C1 is 12V and VPP test is on?

    Check for cold solder joints on the 4.7K and 10K SIPs.
     
  17. picbits

    picbits Well-Known Member

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    SIPs ? Plenty of scope for getting one of those in back to front as well ;)
     
  18. edeca

    edeca Active Member

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    They don't have a common pin, it's an 8 pin case with 4 x resistors. So I don't think they can be wrong.
     
  19. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Hope it's a 10pin SIP with 5 resistors! yes you cannot get it backwards :)
     
  20. tunedwolf

    tunedwolf Well-Known Member

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    Remove Q4 and test VPP again, if all is well with Q4 out of circuit, your problem lies around Q6 or SW6 and other reset components, R16, 17, D3 & SW4. Perhaps U2 also.
    The fact that you are generating 12.35V suggests that the SMPS is likely fully functional, I suspect that something is pulling excess current, perhaps a leaky diode or transistor junction, or reversed polarity or orientation.



    rgds
     
  21. edeca

    edeca Active Member

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    VPP on the ICD header reads the same as +C1 (as far as my meter is accurate).

    Check for cold solder joints on the 4.7K and 10K SIPs.[/QUOTE]

    I'll have a look along them in a while and touch up any 'bad' ones. If that doesn't work, I've got some time to sit and look over the circuit again. If you have any suggestions based on the above reading, that would be great.
     

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