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Forum Index : Microcontroller and PC projects : (MM) Keep blowing up Keyboards...
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| MM_Wombat Senior Member  Joined: 12/12/2011 Location: AustraliaPosts: 139 |
Hi, My MM keeps blowing up keyboards. They work ok for a few days , then they don't work anymore. I disconnect the power before removing / inserting. What is the problem? PS2 keyborad--- not usb with ps2 adapter. 
Any help would be great... Wombat Keep plugging away, it is fun learning But can be expensive (if you keep blowing things up). Maximite, ColourMaximite, MM+ |
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bigmik Guru  Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Hi Wombat, Please check the voltage on the K/B... it should be 5V.... Maybe you have a filter cap backwards in the power supply area... Is it an ALtronics kit? If it is I would suspect C13 or C1.... maybe your power pack has not good filtering inside... I assume that you are using an external pack as there is not much that could kill your keyboard if powered by USB... Try adding 1000uF cap across C13. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| MM_Wombat Senior Member Joined: 12/12/2011 Location: AustraliaPosts: 139 |
Voltage at keyboard connector on pins 3 & 4 was 4.53 V from 9V regulated(kit #3220) Yes Is is an altronics kit EDIT :- Using the power pack I had plugged in last time, measures 6.1V at pins 3 & 4 Keep plugging away, it is fun learning But can be expensive (if you keep blowing things up). Maximite, ColourMaximite, MM+ |
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donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Ouch, that will possibly kill it. Check what Mick suggested. You should never have 6V at the keyboard. Should be 5V at the output of IC3, and of course 3.3V at the output of IC2. IC2 sounds like it is saving your PIC32 from blowing up. Try the link to power the unit up from USB, and check the voltage at 3 and 4 of the keyboard. If it is 5V instead of 6.1, then it is in the 7805 area. Cheers Don... https://www.dontronics.com |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
There is the problem..... now to find the cause... I suggest C13 or C1 is soldered in backwards... check the polarity.. If they look ok they could be either faulty or most likely the Power supply you are using has not got enough filtering built in or worse it is actually 9V AC output. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| MM_Wombat Senior Member Joined: 12/12/2011 Location: AustraliaPosts: 139 |
I checked all the polarized capacitors, at C1 , C7 and C5. All of them have the +ve leg in the hole marked +. as per the picture.. 
The 7805 looks a little tarnished, should it be replaced...? Cheers Wombat Keep plugging away, it is fun learning But can be expensive (if you keep blowing things up). Maximite, ColourMaximite, MM+ |
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djuqa Guru Joined: 23/11/2011 Location: AustraliaPosts: 447 |
Are you still using that altronics 3220 Reg. kit to power the MM? If so is the Plugpack supplying the input to the Kit DC? As others have suggested 7805 may be cooked/shorted internally . 5.0V should be output from it if it is working correctly and supplied with a GOOD DC source of Approx 7V or more. Not 6.1v or 4.53v, both of these indicates something WRONG with the 5v Rail derived from the 7805. VK4MU MicroController Units |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yes I agree, replace the 7805 I built a Piclog with a free standing 7805 that didn't have a heat sink, and it was run on 24 volts for a while. The platic case near the 7805 showed signs of heat, and the 7805 output voltage was way off. Replacing it fixed the problem. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Hmm, As I dont have an Altronics MM, I went by the schematic on Page 33 of the Silicon Chip artical which has C13 (not marked as C13) as 330uf, the same Capacitor on the schematic for MM from Geoff has it as 330nF (0.33uf)... Looking at your picture it is obvious the part supplied is the (0.33uF) nonpolarised part... Not sure which is the correct but personally I dont think there is enough filtering if C13 is 330nF... given that many DC plug packs are not well filtered.. I reckon this is your problem... your plug pack that is used is either a poor filtered version or worse is an AC plug plack and in either case it looks like your 7805 is cooked... Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Sorry I tried to do an edit to fix my spelling errors and did a quote.. Ignore this post please Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
I had a look at my MM and the components look like they are all in the right positions. I suspect your trouble comes from what you mention in your previous thread (MM - DM) Computer PSU for Power several days back. The supplies being unregulated were feeding as much as 14.8 volts to the 7805. Judging by the colour of it in your photo it may now have a problem. |
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| ajkw Senior Member Joined: 29/06/2011 Location: AustraliaPosts: 290 |
M'mmm, I didn't get heatsinks with mine so I made a couple. Mine runs off 12V and this arrangement keeps the reg's cool enough. I cut them from Aluminium sheet, note it is rather important that they do not touch each other. Cheers, Anthony. 
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| BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Anthony I am interested in that audio device sitting on your MM. Can you provide some details about it and that small driver board that seems to go with it. Bob |
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| ajkw Senior Member Joined: 29/06/2011 Location: AustraliaPosts: 290 |
Bob, The speaker is a transducer speaker not a piezo, I think I got it at Jaycar, see AB3440. It wasn't very loud connecting it straight to the Maximite audio out so I had to replace the resistors in-between with links. Works ok but has a very variable frequency response curve. It certainly does add sound however. The driver board is not related to the speaker but is my RTC based on a DS1302 chip. You can also see the CR2 battery for it's backup supply. Works very well. I can supply more details if required. Cheers, Anthony. |
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| BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Thanks for the info about the speaker. I have a ChronoDot V2.1 High Precision RTC on the way for use as my clock. I may ask you more about your program to run the clock when I get mine connected. This one uses an I2C connection. Does your one? |
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| MM_Wombat Senior Member Joined: 12/12/2011 Location: AustraliaPosts: 139 |
Ok Thanks for the input , to all those that contributed. I have replaced the 7805, and am using that pesky powerpack to power the voltage regulator (altronics kit #3220) and the maximite doesn't get hot, the voltage regulator doesn't get hot, and my keyboard has survived for another day.. Maximite was running all day, performing admirably, on the spi 7 segment led project.. Cheers Wombat Keep plugging away, it is fun learning But can be expensive (if you keep blowing things up). Maximite, ColourMaximite, MM+ |
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| centrex Guru Joined: 13/11/2011 Location: AustraliaPosts: 320 |
For BobD Go back to the very last post in the url below, you will find all the time keeping software you are ever likely to need and it all runs on a Maximite. http://www.thebackshed.com/forum/forum_posts.asp?TID=4421&PN =3 regards cliff Cliff |
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| BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Thanks for that info Cliff I'll have a look. Bob |
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