 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : Maximite disc access
| Author | Message | ||||
| envirotronics Newbie  Joined: 18/02/2016 Location: AustraliaPosts: 23 |
Hi All, I have just built the MAXIMITE COLOUR PCB AND GOT IT WORKING WITH A VGA SCREEN AND PS2 KEYBOARD. i WROTE A FEW LINES OF CODE AND PRINTED STUFF ON THE SCREE ETC. TWO PROBLEMS: 1) REGULATORS ARE RUNNING VERY HOT - CURRENT DRAWN IS 280ma (NOTES SAY 160ma)?? 2) CANT ACCESS THE SCANDISC, MESSAGE COMES BACK "CANNOT ACCESS DISC" I FORMATTED THE DISC (8GB) ON MY PC TO FAT32 STANDARD. |
||||
TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 6270 |
Welcome to the forum What voltage are you using to supply the Maximite? Reducing the supply to 9V helps keep the 5V regulator cool. Can you try a different SDcard? Some sizes/brands have been difficult. Do you get a different error message if you try to read the card with it not present? Have you update the MMBasic to the latest version? Jim VK7JH MMedit |
||||
| envirotronics Newbie Joined: 18/02/2016 Location: AustraliaPosts: 23 |
Hi Jim. I am using a 9VDC Regulated supply. I have also connected the system directly to my Lab power supply and no change. I will try a different SD card and also see what the system says when there is no card present Thanks for the advice Regards - Graham Hobbs |
||||
| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6270 |
A 9V supply should be ideal for the supply. I don't have a genuine Colour Maximite but I do have a UBW32 configured as a colour MM It draws about 160mA when supplied via the USB and no keyboard connected. It is running MMBasic V4.4B and occasionally has trouble reading the SD card. I eject and reinsert and that will normally fix things. Jim VK7JH MMedit |
||||
| envirotronics Newbie Joined: 18/02/2016 Location: AustraliaPosts: 23 |
Hi Jim, I have just made a few more checks. I am running MM 4.4B (could that be the problem? I cant see why the unit is drawing 260ma current) I have made measurements all over the board. Looks like I will have to start cutting tracks to localise the main current drain. I had hoped to avoid that. Following up on your question about card messages: 1) With no card in place - try to save file - system message is- "cannot access the SD card" 2) With Card in place on save - "SD card not found" Cheers Graham |
||||
| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6270 |
You don't have write protect on do you? My card has a habit of switching itself to write protect as I insert it. V4.4B should be OK VK7JH MMedit |
||||
| envirotronics Newbie Joined: 18/02/2016 Location: AustraliaPosts: 23 |
Hi Jim, I did suspect that. i am going to change the card holder and see if that cures the problem. I did try another card but same results. Cheers Graham |
||||
| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2934 |
@envirotronics, Did you build the MaxiMite yourself? If so, did you substitute any comments with something you thought 'should be ok'? If it is the PCB with the J1 (Power Switch or Link) jumper, then have you 'removed' the link/jumper/switch and fed in 5v from your bench supply? If not then measure how much current if powered by 5V directly? This could isolate an issue around (damaged?) the 7805 Vreg. Also check D3 is correct way round - if incorrect you will be pumping power into the USB lead causing excess current draw 
I'm sure you've already done this, but disconnect all things that are plugged in (i.e. screen and keyboard) and see if it still draws excess current. Does the PIC get hot? Due to the circuit being so simple with minimal components, unless you have a faulty capacitor, the next thing to heck for is solder shorts on pins. You could also write a quick program to switch all GPIOs to OFF/HiZ/Input to see if this changes anything. If you have a short between a pin set as an output with another part of the circuit then you have the potential for issues - however this should not result in the excess current that you are seeing. Hope you track the issue . . . . . WW |
||||
| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2934 |
@envirotronics Forgot to comment about your disk access issue! Some SD Sockets have CD/WP switches that are 'internally' linked to GND (i.e. the case). Others have a pin in which you select the 'common' of both switches. With the MaxiMite circuit this should not be an issue in either case! However, I have come across some SD sockets that are Normally Open, and others that are Normally closed. Maybe worth checking the CD pin with a meter to check if you have the correct type (and also indeed that it is switching polarity on the PIC pin when the SD card is inserted/removed) WW |
||||
| envirotronics Newbie Joined: 18/02/2016 Location: AustraliaPosts: 23 |
Hi WW, I did build the PCB myself. I took great care and double checked everything including diode polarity etc. I will follow up other suggestions you have made and see what happens Appreciate your guidance. Cheers Graham |
||||
OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 982 |
If I recall correctly back a couple of years ago a similar discussion led to a reversed polarized capacitor. Just thought I would throw that in. GM |
||||
| austfox Newbie Joined: 05/03/2016 Location: AustraliaPosts: 18 |
It's been a while since I built the COlour Maximite, so I opened it up and remembered how little there is inside. Checked the current draw and it is indeed around 160mA. Are you heatsinking the 7805? Mine is, and even with a 9V supply it does run quite warm. Perhaps a photo of the board may help? Steven. |
||||
| envirotronics Newbie Joined: 18/02/2016 Location: AustraliaPosts: 23 |
Hi Steven, Thanks for confirming the 160ma current draw. I have isolated various components on the PCB which are fed from the 3.3 Volt supply and narrowed the major current drain the the PIC itself - The AVDD Pin 30.(200ma) Noting I can do about this i believe. I guess I got lumbered with a dud chip! I am now thinking of buying another unit fully assembled and tested as I have wasted so much time already on this kit. Unless somebody has a better suggestion? Thanks to everyone for their kind input Cheers Graham |
||||
| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2934 |
Graham, Does the PIC get hot? With the AnVddpin pulling 200mA - was this tested by isolating the pn (i.e. cutting track, or removing the 10R resistor and measuring here)? It is worth checking for shorts (solder blobs) 'under' the PIC pins (I have seen this before). I recommend running solder over all pins (shorting them all out) and then using wick+flux to clean them all up. This will/should remove any shorts. Then check the power drawn again on AnVdd. Also remove the 100nF to AnVdd - if faulty this will cause excess drain; so measure without. If all these things don't resolve it (or point to a clue), then it looks like your PIC maybe at fault. Have you considered replacing it? If no 'external' cause can be found then surely it is worth replacing the PIC chip itself? WW |
||||
| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2934 |
Silly question - but have you measured the 3v3 voltage line with the circuit powered up? If it is much below 3v3, then does it rise up to 3v3 with AnVdd disconnected? (remove the 10R to do this) |
||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
