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FSBUS Com Board Voltages.

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Here is my setup:12V power supply6 inch flat serial cableCOM, key, display Controller.I have been trying to find out why I can't get 13.5 volts to pin 4 of the pic to flash it. On the Com board I am getting 19 volts into the 78L12 and 13.7 out of it. Then it passes through the prgm jumper and through a 680ohm resistor and drops to 7 Volts! How can I get 13.5 volts after a 680 ohm resistor if it is coming in at 13.7? I have been struggling with this for a week and don't see how it is phisically possible to only drop .2 Volts through a 680 ohm resistor.I have already tried the following: Looked for any shorts, crossovers, false resistors, power supply...I just can't think of anything else. Ive spent alot of money making these boards and Im disapointed I can't get them to work. PLEASE HELP!Jason

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Hi jason,If you are sure you have no s/c on the line(mclr) then the 7v you are measuring maybe the average your meter is reading due to the tx line.Try this,forget about this voltage and try and carry out the troubleshooting option in Fsbus.that is are you able to toggle the pins on the pic when you tick the boxes.This will tell you if you have the correct signals to the pic.Please note that to make sure the cable you use does pass the correct signals to the fsbus comm bd.I think if you use the 10pin connector and a 9 pin serial connector via ribbon cable to an idc type then these pins dont line up.This of course can be confirmed by metering out the cable from the pc end of the cable to a point on the fscomm bd.ie tx on pcb should go tx(pin 3) on serial cable plug(pc end) and like so for the other pins.Hope this helps.post again if you need any further help.Les

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Hi Jason,basically there is a 10mA current drain after your 680 Ohm resistor in order to drop 7V. This could be caused by the transistor which is in "normal mode" cut off. In flashing mode however it is pulsed by the serial input signal coming from the com port pin 3. These programming pulses will swing between nearly 0V to approx. 14V. If by any reason the input line from the com port to the Bias of the transistor is getting slightly higher than about .6V to .7V the transistor will start conducting and a current flows to ground, resulting in a drop of voltage after the 680Ohm resistor occurs.Disconnect the com port and check your voltage again. It should not drop at all.If there is no s/c or wrong cabling involved (is the 680 Ohm really 680 or is it prob. 6.8K or higher?)it could either be the transistor itself (very unlikely though) or it must be a cabling /and or s/c on your com board.One thing I can say for sure is that FSBUS is "fool proof" as long as there is everything correctly wired and no s/c, wrong components, etc.In most cases the cause for malfunction is a s/c or cabling error.In your case I strongly assume you have a mismatch in your cabling (10pol to 9pol sockets)Hope this helps.Best rgds and good luckPeter

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Thank you for your replies. I checked the cabling and made a few wire changes. I have communication between the PC and the MCLR pin when I use the diagnostic tool. I am getting a volatge swing from 6.8 to 7.8 volts to pin 4 of the pic. This confirms my wiring is now correct. However, in program mode the bias of the Transistor is still at .6 volts from the MAX232. With the COM board disconnected from the PC I still am only getting ~7 Volts at MCLR. The 680 resistor is correct as is 2.2k ohm next to it. I have tried supplying the board with 19 volts but the 78L12 still puts out 13.7 volts and this is dropped to 7 volts after the 680 resistor. I have double and triple checked the components. How many volts are you getting before the 680 and 2.2k resistors at the prgm pin? I would think this should be well over 13 volts since it still needs to go through these resistors.Thanks for you help once again. I couldnt do this without you all!Jason

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Hi jason,Hang in there,we will get to the bottom of this.i am still puzzled a little with one of your comments regarding the diagnostics.To answer your question the voltage on the mclr pin is 13.6v.The 78L12 is a 12volt regulator.when you place the LED in series with the centre leg you will raise the output voltage by 1 to 2 volts depending on the led colour.so in our case it will be 12v plus approx 2v which will be 14v.So in your case raising the input voltage will not increase output because this a regulator and regulates to apprx 14v.So your test has told me your regulator works fine.I donot know what your level of electronics is so will start pretty basic,i appologise if i am to basic.Would you please follow the following instructions.1.Remove all leads from the Fscomm board except the power supply. ie fscomm is standalone.Measure the voltage at collector TR1 with S1 jumper in and short cicuit jumper across d7. If the voltage rises to the 13.7 then you have a problem with Tr1 being driven from something.Well cover that later if neccessary. If not then remove TR1 and see what the volatge does,if it rises Then possibly the TR1 is leaky. If it still does not rise then the only possibility is that you have a s/c to something else,probably a hair line solder bridge.My guess would be the base of the 10 pin socket.look with a magnifying glass.To me what appears is that the 680 ohm resistor has an additional resistor to ground somewhere and these resistors for a voltage divider the junction providing 7v which is to low.With my fscomm bd the voltage changes from 13.7 to 13v with the FSkey bd plugged in.So you can see a very light loading.So try as above and let me know the results.Good luckles

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Les,I followed your procedure and this is what happened. When I jumped D7, the voltage didnt rise. When I removed Tr1 the voltage went up to 13.6. I have changed the transistor and still get the same results. With the serial cable on the COM board, I get 7 volts at Tr1 collector, and .60 volts at the bias. Shouldnt that be 0 at the bias?Jason

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Hello again,To clarify the post above:)Here is more info:With 13.5 volts going to MCLR in FSBUS troubleshooter: TR1(collector: 7.42V, base: .53V, emitter 0V)R1 ( IN: 13.7V, Out: 5.0V)R2 ( IN: 13.7V, Out: 7.42V)With 0 volts going to MCLR in troubleshooter:TR1 (collector: 6.85V, base .63V, emmiter 0V)R1 ( IN: 13.7V, Out: 5.0V)R2 ( IN: 13.7V, Out: 6.85V)Now Im wondering if there is a problem with my serial port( or MAX 232) not dropping the voltage enough on TR1 base???Thanks,Jason

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Hi jason,Jumpering d7 should have done the same as removing tr1.At least the voltage went to 13.6 with tr1 removed.This leads me to believe that the problem is with the switching voltage.Please try the following;Remove all leads except the p/s to the FScomm board.Measure the voltage at pin 13 of max232,it should be o volts.This is where the voltage maybe comming from for you to measure a base volts of 0.6. on tr1.Make sure the pc is not connected to the Fscomm bs.If you measure a voltage here then you must have either a short cicuit to something or the max232 has a problem.just to help on troubleshooting a small explanation might help.Because what i understand from your second post it appears that tr1 is not being switched in test mode.When you go into test mode and click the mclr box you are switchingpin 3 on serial port between 0 and 5 volts.This in turn will switch tr1 on and off and produce the 13.6v or o v.or in your case it should have been 7v and ov.The same sort of thing happrns to the clock and data lines but in these cases rts and dtr are switched to change the pic data and clock lines. With no pc connected to my Fscomm bd i have 0 volts at pin 13 of max232.Hope this helps,post again if you still have probsGood LuckLes

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Hi Jason,your problem lies in the fact that pin 3 of the Com port is not switching between 0 and 5V using the FSBus trouble shooting function.Measure directly on the COM Port of your PC (without FSCmm connected!) whether you are getting the toggle between 0 and 5V.Make sure the pin connection FSCom and Com Port is correctly wired.It looks like PIN 3 is not Pin3 or that the MAX is pulling Pin 3 to .6 V.(rather unlikely though).Let

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Hi Jason,just forgot to mention that you could try one other thing. Jumper the FSCom board into Flash mode and then shorten D7 (or the Bias of TR1) to ground (you may use that jumper at D7). In this case the Voltage on the collector of TR1 MUST rise to about 14V.This would proof the correct function of Tr1.Still there is to be found the reason why Pin3 isn

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Hi,Ill try testing the com port when I get home. So pin 13 of the max232 should produce 0-5 volts only!? This is directly from the com port?Thanks,Jason

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Hi Jason,to clarify the function of the MAX it is a receiver / transmitter and code converter (converting V24 signals to TTL level and vice versa).So the PIN 13 of the Max is an input as it receives data from the tx out of the Com port (pin3).Therefor it should not have any effect on pin 3

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Hello,Been on vacation for a while. Here is what I did to test the board. Disconnected the jumper wire from pin 13 of the MAX232 to R11.Supply the board with powerMeasured 13.5 volts at S17.0 volts at TR1 collector.60 volts at TR1 base0 volts at TR1 emmitter.When I bought TR1 they cross referenced it to a NTE123AP and said it is electrically identicall. But I should not be getting .6 volts flowing from the base of TR1. I know the current is going this way because there is a voltage drop accross R11 to ~.5 volts. I have done a continuity test on the transistor but it checks fine. Does anyone out there know if the transistor I have IS a substitute for the BC548B?

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Hi jason,The transistor you are using should be alright,just checked data sheet.You lifted off the link to tr1,you should not have any voltage on the base of the transistor.If you used the pcb layout of DIRKS Docs then the only possibility is a short.Lifting the link still leaves a few tracks close to other connections.You lifted the transistor earlier and the voltage rose.So this says to me that you are getting another connection from somewhere ie a short.Try this,remove just the base lead of tr1 from the pcb ,ie just lift this leg clear of the board.See if collector rises now.If so you need to CLOSELY look at the pcb for track shorts.Good LuckLes

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