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Forum Index : Microcontroller and PC projects : help with power up on colour Maximite
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| jeffj Regular Member  Joined: 04/02/2012 Location: AustraliaPosts: 80 |
Hi folks I hope someone can help I installed a new chip and all worked fine except the SD card would not work. After exploring the forum on this problem I found that there was no clock pulse . The computer worked ok for several weeks then suddenly stopped. I obtained another chip from Silicon Chip and carefully installed it . I just cannot get it fire up, I have double checked everything and resoldered the pins . I am getting 1.8 v on pin 80 Power up led is ok 3.3v on all of the power supply pins and 0v on the 0v pins I am getting 0.8 Mhz on pins 63 and 64 Not 8 Mhz as I was expecting I have swapped the 8 Mhz crystal and 22 pf caps -still the same There is no clock pulses on pins 80 or 39 Power into the card is only 2.5 mA Any help would be appreciated |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 5914 |
The usual suspect is the 10uF capacitor on Vcap. (Pin 85) Jim VK7JH MMedit MMBasic Help |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
Hi Jeff, From reading your description, it sounds like you've replaced your chip twice now. This can put a lot of 'strain' on the pcb tracks (heat damage can lift them) and hence the first thing I would do is get a multimeter and check continuity between the PIC pins, and the track's destination. To do this I would build a test probe comprising of a pin (or needle) to give you the ability to accurately probe each PIC pin. Attach a piece of wire to a pin/needle and then connect to your MultiMeter. If you don't have a meter handy, then make a quick circuit with an LED or Buzzer. Begin with the obvious pins supplying power; and also the reset pin and the Vcap pins. It is concerning you say only 2.5mA into 'card' (I assume you mean the whole PCB as opposed to the SD card socket). Do check correct orientation of the PIC chip (I have seen this error twice before). Also, do you have a PicKit to reprogram the firmware? Awaiting your response for more clues . . . . . For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| jeffj Regular Member Joined: 04/02/2012 Location: AustraliaPosts: 80 |
Thanks for that. 2.5 mA is for the board not just the chip. I wasn't aware of a reset pin .I will check that out . I removed the chip with a heat gun and a screen, all traces look good but I will do as you suggest. The orientation is ok. When I checked the power supplies I took care to measure the volts on the chip itself so am reasonably confidant that the tracks are ok Thanks again for your help |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3165 |
2.5mA is a sure sign that the CPU is not running. I bet that it is the capacitor on Vcap (should be Tantalum or ceramic) or possibly the crystal and its padding caps. Geoff Graham - http://geoffg.net |
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| jeffj Regular Member Joined: 04/02/2012 Location: AustraliaPosts: 80 |
Thanks for yr comments I have tested all tracks all ok I have swapped the 10 microF for another tantalum I have already swapped the crystal and caps I should have mentioned that when I was checking the oscillator,the run light came on for a few mins and then went off . I couldn't reproduce it again Which pin is the reset pin I could not find it regards jeff |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Here is a circuit diagram of the Colour Maximite. Click the diagram for a larger image. Reset is MCLR pin 13 towards the lower right hand side in this diagram. It is pulled high with a 10K resistor. A low on this line will force a reset. |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
Hi jeffj, Sounds like you are narrowing things down there. You have confirmed everything from my first post apart from two things. 1> Checking the reset pin (this must be high to run properly so check it as if it were a +v input! 2> Do you have a PicKit2 or 3 (or other programmer) to re-program the firmware? Another thing worth checking are the solder joints to all components. Sometimes what appears to be a good connection is actually a dry joint (hence open circuit). I have even had this with surface mount components recently (one of the 22pF smd crystal caps on an Explore64 module). So when checking continuity, test from/to the component lead rather then the solder 'blob'. Good luck . . . WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
Something else that springs to mind is that AVdd (pin 30 in the above diagram) needs to be connected (i.e. high). I seem to remember that if not connected (as on some TFQP breakout boards) then the thing would not fire up. That said, I am sure it pulled more than 2.5mA. Two more things worth checking: 1> Your 3v3 regulator is ok. It may reproducing the correct voltage, but if faulty, it won't be able to supply the necessary current. 2> Your PSU. If a bench power supply, have you accidentally turned down the 'available current'? Always worth checking, then re-checking the power supply in these types of situations where the circuit performs strangely! 
WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| jeffj Regular Member Joined: 04/02/2012 Location: AustraliaPosts: 80 |
Thank you all for the suggestions The reset sounds promising. Re a programmer no I do not have one I will give it a go and report back jeff |
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| jeffj Regular Member Joined: 04/02/2012 Location: AustraliaPosts: 80 |
I think I have done all suggested The reset pin is high I shorted it to earth but no effect I have already resoldered all pins and caps and checked continuity power supplies ok 5v at reg1 and 3.3 at reg2 and volts getting to chip ok pin 30 3.3v By the way whoever suggested to use cellotape to position a new chip deserves a medal works really well especially for geriatrics like me Jeff |
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| jeffj Regular Member Joined: 04/02/2012 Location: AustraliaPosts: 80 |
I have installed a new chip The current is exactly the same I Accidently shorted out one of the oscillator capacitors and 2 or 3 secs later it powered up ok. I repeated this several times. As long as power stays on it runs happily Anyone have some ideas? Jeff . |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
It sounds like you may have a 'broken' cap. I have had these break before (not on a MaxiMite or MicroMite - but on a PIC circuit requiring crystal and caps). Both SMD and ceramic through holes can break easily if too much stress is put on them. Are you able to replace the cap too see if this sorts things out. Finally, if this fails (and worth replacing both caps) then I would look at replacing the crystal. Sounds like there isn't enough initial power in the oscillator circuit to get things going - but then once started, it is fine. You're almost there by the sound of it! . . . . WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Check the datasheet of the crystal. 22pf is just a generic size and could be the wrong one. I suspect you need something smaller like 10pf. Microblocks. Build with logic. |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
Also check for dry joints on two caps & crystal - any will cause issues in this part of the circuit! For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5914 |
If it's a through-hole crystal, the case could be shorting out to a track. Jim VK7JH MMedit MMBasic Help |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Hi Jeff, I have been working 80-90hrs per week (I work in the HORSE racing game and we are building up to the Melbourne cup in a bit over a week) so I have been very quiet on TBS recently, Whilst I am not in a position to help much until the week after the Melbourne Cup (about 9th or 10th of November) I am happy to assist you in getting it going if you are still stuck then. I am in Melbourne, where are you based? These may have already been mentioned but firstly check the following. Voltage is 3.3v and seems stable on your meter (ie not varying a bit) There is 3.3v on the MCLR pin (pin 13) probably easiest to measure at pin 1 of con 7. Check that (with power off) you have 10k between Pin1 and pin2 of con 7 Check C10 (the most critical component on board) that it is connected to Pin 85 of the Pic32 and GND Make sure that polarity (if it is a polarised chip is correct) --- NOTE -- if it is a tantalum the BAR indicates the +ve leg (goes to pin 85) You could try soldering a 22uf to 47uf tantalum (care with polarity) in parallel with C10 If that all checks out OK I would guess your Pic is not flashed.. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| jeffj Regular Member Joined: 04/02/2012 Location: AustraliaPosts: 80 |
Bingo Adding a 47 microfarad across c10 did the trick .Prior to this I tried 12 pF at the oscillators with no effect In my ignorance I didn't know that tantalums are polarised It was by chance I had installed the c10 correctly regarding where I am- Sydney Thanks everyone for yr efforts I have been tearing my hair out over this I didn't have much before. |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5914 |
Good to see it working. Thanks for reporting back with the solution - it will help others who have similar problems. Jim VK7JH MMedit MMBasic Help |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
I 2nd what Jim said. Sometimes, the OP never posts back again, and we are all left wondering if the problem ever got fixed, or did the OP just give up on that totally and drop it. It's always nice to know - even if the latter is actually the decision. As you have discovered, that Vcap is CRITICAL. It absolutely must be installed correctly and working, or the PIC32 core won't run, or it will run sporadically. I have been following this thread with interest to see the final cause, so, not to paraphrase Jim, but yes, thanks for letting everyone know you have it going.  Smoke makes things work. When the smoke gets out, it stops! |
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