Fairlightiii Posted October 19, 2010 Report Share Posted October 19, 2010 Hello everyone. Sorry for my bad English (I'm french). I've assembled a SmashTV Core R4d kit. I've used the tutorial "Assembling_a_MIDIbox_Core.pdf" by Jim Henry. In this tutorial before inserting PIC and opto-isolator he advices to measure the voltage between four pairs of pins. He says it should be very close to 5 volts but when I do it I measure -5V instead +5V. I'm sure some of you have an idea what is the problem. Thank you for your help. Jérôme. Quote Link to comment Share on other sites More sharing options...
JRock Posted October 19, 2010 Report Share Posted October 19, 2010 Maybe you have the leads on the PSU switched around backwards. If that isn't it just switchthe leads on your multimeter around! :laugh: Quote Link to comment Share on other sites More sharing options...
Flemming Posted October 19, 2010 Report Share Posted October 19, 2010 Hi Jerome.. This is just a guess, but maybe you are using the + and - of the multimeter in the wrong way? Are you sure you did not accidentally use the red probe(+) on the 'ground' pin of PIC, and the black probe(-) on the +5V of PIC? I don't know the guide-pdf file you are using, but on the ucapps.de site, there is also a description how to measure core, it says: Apply power to the module after all parts except the PIC and the optocoupler are mounted. Check the voltage levels between the most important pins with a multimeter (analog or digital doesn't matter) before plugging the PIC and the 6N138 into the socket: IC1:MCLR(1) - IC1:Vss(12) = 5V IC1:Vdd(11) - IC1:Vss(12) = 5V IC1:Vdd(32) - IC1:Vss(31) = 5V IC2(8) - IC2:(5) = 5V Please try to check voltage again according to the stuff i quoted from ucapp.de, and let us know if you still get the same result Crossing my fingers :) Flemming Quote Link to comment Share on other sites More sharing options...
Fairlightiii Posted October 19, 2010 Author Report Share Posted October 19, 2010 (edited) Thank you for your answers. JRock: Maybe you have the leads on the PSU switched around backwards. I tested with inverted PSU leads and the problem is still there. Also I've read that PSU polarity doesn't matter... If that isn't it just switchthe leads on your multimeter around! :laugh: I checked the polarity of the leads of the multimeter and it seems OK (com="+" and v_ohm="GND"). Flemming: Please try to check voltage again according to the stuff i quoted from ucapp.de, and let us know if you still get the same result I checked the voltage but always -5V, assuming the pin 1 of the IC1 (PIC) is the one at the bottom-left and the pin 1 of the IC2 (6N138) is the one at the top-left when you can read "IC1" and "IC2" in the "right way" (= not upside down) - see the picture – I can't read the first pin of the ICs on SmashTV Core (perhaps under the sockets). If you have another idea, let me know... Edited October 19, 2010 by Fairlightiii Quote Link to comment Share on other sites More sharing options...
philetaylor Posted October 19, 2010 Report Share Posted October 19, 2010 My guess is that you have connected the Bridge rectifier (X1) the wrong way round! Cheers Phil Quote Link to comment Share on other sites More sharing options...
Flemming Posted October 19, 2010 Report Share Posted October 19, 2010 (edited) This picture shows the pin numbers of the PIC pin http://circuits.datasheetdir.com/19/PIC16F874A-pinout.jpg Notice the notch in one end of the chip - you can see the same notch in one end of your PIC socket so you can easily identify the right pins to measure. Here is the optocoupler 6N138 http://msxlink.chat.ru/img/elements/6n138.jpg Same thing; there is a round 'mark' at pin1, and that mark resembles the notch in the 6N138 socket. It's hard for me to visualise 'bottom-left' and 'top-left' since i don't know which way your core is turning :D but with the links above you should be able to easily identify the right pins.. For the pins marked 'Vss' you should use the black probe of the multimeter. Red probe on 'MCLR' and 'Vdd' pins (according to this link http://encyclobeamia.solarbotics.net/articles/vxx.html) Edit: Nice, you posted a picture now :) looks correct, so just forget this! Edited October 19, 2010 by Flemming Quote Link to comment Share on other sites More sharing options...
Flemming Posted October 19, 2010 Report Share Posted October 19, 2010 My guess is that you have connected the Bridge rectifier (X1) the wrong way round! Cheers Phil Wow, that would produce such results? and the 7805 VREG would cope?? Hehe, i really need to learn this stuff soon, very very soon! Quote Link to comment Share on other sites More sharing options...
philetaylor Posted October 19, 2010 Report Share Posted October 19, 2010 The 7805 would probably cope BUT C4 and C5 might go pop ;) To be honest i'm not too sure what the 7805 would do but assuming the OP has his probes the correct way round, I really can't see what else it could be! Cheers Phil Quote Link to comment Share on other sites More sharing options...
smashtv Posted October 19, 2010 Report Share Posted October 19, 2010 I checked the polarity of the leads of the multimeter and it seems OK (com="+" and v_ohm="GND").This as written is backwards.....Plug the red lead into "V Ω" and the black lead into "COM" and you will be good to go. :) Best regards SmashTV Quote Link to comment Share on other sites More sharing options...
philetaylor Posted October 19, 2010 Report Share Posted October 19, 2010 Oops I missed that! Well spotted Smash! COM=GND(Black) V_OHM=+(Red) Cheers Phil Quote Link to comment Share on other sites More sharing options...
Flemming Posted October 19, 2010 Report Share Posted October 19, 2010 Yeah :) congratulations on your new core! Quote Link to comment Share on other sites More sharing options...
Fairlightiii Posted October 19, 2010 Author Report Share Posted October 19, 2010 (edited) Hi Tim. Thank you for your help. The multimeter came with only the chinese owner's manual and the video I see to know how plugging the leads doesn't show the right way. Best regards. Jérôme. Edited November 12, 2010 by Fairlightiii Quote Link to comment Share on other sites More sharing options...
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