Hi allI'm at my wits end here. I have built myself a COM board and a KEY board. When trying to flash for the first time I get the famous "read after write check failed" error message.I have searched the forum and checked, double checked and tripple checked my PCB to no avail. I don't "seem" to have any shorts. I have 12.5V on pin 4, 0V on pin 5, 4.0V on pin 12 and 13, 4.5V on pin 14 on the PIC. Also I don't seem to get connected to the COM board. The FSBus2 Router is showing not connected, as opposed to FSBus Router 1.30 which seems to connect even if I don't have the COM board connected! How can I check this?What I would like to ask you guys is really how to logically trouble shoot a PCB with a simple multimeter? Is a oscilloscope needed to accurately find faults? What values, voltage, resitances, currents or whatever could be appropriate is a correctly working board showing in different points?Attached are four pictures of my COM board. Take a look and tell me if something seems way out of order please!http://forums.avsim.net/user_files/36529.jpghttp://forums.avsim.net/user_files/36530.jpghttp://forums.avsim.net/user_files/36531.jpghttp://forums.avsim.net/user_files/36532.jpgThanks,

Hi!Certainly you have some chance to check your pcbs with a single multimeter as I've done it.It's gonna be a little bit tricky because the problem can be on the other panel than the comIII.First of all you have to check those pins on the pic. Don't forget to switch the flash jumpers on the com panel and on the other panel(for example the key) panel) and to go to the troubleshooter and check all the pins otherwise you cannot measure the correct voltages. pin 14 must have around 13 volt(555 gives this voltage). That cause the error (unfortunately this explanation cannot say where is the error). If you don't have the voltage try to find out where it can be lost. Check all the pic's pins to have contact where it should have. Check the cable between the comIII and the other panel. All pins must connect correctly. Also check it for shortcuts. Check the cable coming from the pc to comIII. You can follow the lines and pins form the schematic's. It can help you a lot to find the error (which pin's shoul connect where). Check the diodes and the diodes to way for the correct way. Check the pictures here:http://mikkila.wabbits.org/fsbus/doc/photos_e.phpWell that's it for first runGood luck to find an error.Ps: on my first panels i draw it from myself. It was pain in the a**...There were a lot of errors on them. I tried out the way of photoprinting. That is much easier if you do it correctly.Take a transparency(i dont know the correct name, sorry) you can buy it for inkjets or laser printer. (The results much better with laserprinter). Buy a "positive 20" spray, this is a light sensitive spray for making pcb's. Dry it for 10 minutes with a hairdryer.Put the printed transparency on it and but them between 2 glasses.Put it in front of the qartz lamp and leave it there for 15 minutes.Put the pcb in the tn120 liquid(this makes the p20 spray to dissolve where it has got the light and what is remaining on the panel that is egzactly what you need. Put it in FeChlorid liquid and wait...(30 min's for me)Some forums asked how to etching pcbs..... This is how ;)

Those condensators around MAX. I prefer more use of electrolyitc capacitors.But, sounds like you have someking of voltage problem. Voltage on pins 12 and 13 should be close to 5 volts. Not 4. Also 12.5 volt is enough for flashing but normally it is around 13.5 volts.Looks like you are missing volt on everywhere.Check what are voltages on COM board. After 7805, after 78L12 and on tarnsistors. Also check bus-connectors. Try to figure out where is leak.- J

Hi,sometimes, using another PC solves the problem. Give it a try.regards Dirk

Hi Mats ,I am myself currently building the COM board and I have a hard time to find the place of the components ( I am not an electronic wizzard ). I was just wondering if the resistor R3 wich is just below the grey wire on picture N

Thanks guys for your input!I will try your different solutions and I will try to make a schematic with my voltages put in. I will also try flashing using another computer as I've seen some issues with this.Dirk, I also read that it sometimes could be hard to flash the PIC for the first time? Is this something you can confirm?Regards,

>Hi Mats ,>>I am myself currently building the COM board and I have a hard>time to find the place of the components Follow link.http://mikkila.wabbits.org/fsbus/doc/photos_e.phpAnd com board, full size.http://mikkila.wabbits.org/image.php?disps...g&a=fsbus%2FdocAddition, for me. Board looks just fine.- J

Actually I think I got it correct ;-)Check out this schematic:home.hccnet.nl/r.vries/images/fscom-comp.gifHope it helps,

Hi !I thing it's a good way for building your pcb to soldering non heat sensitive parts to the boards like ic holders, resistors and wires.(for the resistor it doesn't matter which way you put it in)Later on you can solder the condensators diodes or electrolit capacitors. (the last two must face in the right way). Try to put those component first which are obvios (there's no other component around). If you follow these lines probably you cannot put any parts in the wrong place.Try to measure the voltage at 555. Pin1 is where you can find the small dot on the ic and going upwards anticlockwise. Pin1 groundPin2 5vPin3 5vPin4 10vPin5 6vPin6 5vPin7 groundPin8 10v

Hi,>Try to measure the voltage at 555. Pin1 is where you can find>the small dot on the ic and going upwards anticlockwise. I did measure everything up tonight and these are the results,My values on the 555:>Pin1 0.0V>Pin2 4.3V>Pin3 4.0V>Pin4 8.5V>Pin5>Pin6 4.3V>Pin7 0.0V>Pin8 8.5VSeems like I have an under voltage. I have a 9Vdc power supply at 9VA. After the 1N4002 diod I get the 8.5V and that is what I have at pin 8 and 4. To me it looks like 9V power supply is not enough to drive these circuits. How sensitive are these circuits to the voltage level? As I understand it the 7805 voltage regiulator has to provide 5V (I have 4.5V) and the 78L12 should provide 13V (I have 12.5V). I can't really understand how the 78L12 should provide more than 12 V though as this is what it is designed for. Or did I put this one backwards...because I have 14.3V on the other side of the regulator?So many questions and so little time :-)Thanks for any help,

Hi!I've just compared you photos with my comIII.Are those electrolit capacitors around the max232? I've got the same big black type there as you have around the flash jumper.Try also measure the the resistances arount the 555. If this cannot helps i give up....:(Ps: my idea is somewhere should drop too much voltages (between ground and..... anywhere :( ).good luck.

Those capacitors around the MAX232 are tantalum electrolytic ones. Shouldn't be any difference I hope... But then again I'm not an expert on electronics.How do I accurately measure the resistances around the 555 without breaking up the circuit? I mean when measuring, the current could go which ever way right?I seem to loose 0.5V over the rectifier diod D4. Voltage dropping to 8.5V and that's it.Lets recall here:The first problem I have to solve is with the FSBus router not indicating connection with the FSBus COM board. I have checked and double checked the wiring between the PC and the PCB and it is correct. This is the first thing I have to check. what, apart from wiring could cause this? Could the MAX232 driver be dead? How can I check the line driver?From what I understand the 555 is a timing device and the 78L12 a voltage regulator that will give the flash voltage. The MAX232 is a RS232 line driver/reciever, converting RS232 signals from the COM port to TTL levels for the boards. Hoping to solve this any year now ;-)

Diode drops always 0.5-0.6 volts. So that 8.5v after D4 is correct.Also, 9 volts input is just fine, it should work with it.But. When 7805 get 8.5 volts it cuts it directly to 5 volts. Nothing else. It wont care if incoming voltage is 8 volts or 12 volts or anything between. If you measure 4.5 volts after 7805 you have problem somewhere else.Speculation. Part one. Ground is 0.5 volt too high or one reason is short somewhere what causes 7805 run at maximum power when it starts to produce heat and drops voltage. 555 is actally somekind of capacitor pump what generates 15-16 volts from 9 volt input. And 78L12 with led requlates that voltage to 13.6 volts (led rises 78L12 ground level approx 1.6 volts from 12 to 13.6). This is for programming mode.MAX232 is serial driver. As you quessed right. Three transistors on board are for programming mode. Those tantal condensators should be fine for MAX, but there Might be troubles with them. It is cheap to change them to electrolytic one if intrested.TR1 drives MCLR line (13.5 volt) what enables and starts programming mode.TR2 is for programming data.TR3 is for clock signal. So when in programming mode, all data going To PIC is thru TR2 and TR3. Read after write. Data From PIC is thru MAX.As i see your problem. You have some voltage troubles. You should get that 4.5 volt up to 5 volts. And if you have 4 volts on PIC pins 12 and 13 (data and clock), it is not enough. It should be close to 5 volts.What is voltage on 7805 pins. Input is 8.5v. What is on ground (does it float?) and output Should be 5v. You have 4.5?In test mode. Does all MCLR, Data and Clock lines go down? (pins 4, 12 and 13 on PIC)- J

Thanks for the tips Jari,Did some more troubleshooting and it seems it's the 7805 that doesn't manage to give me 5V. I de-soldered it and connected it clean to a 9V source and still Vo was 4.5V so off to the electronics store tomorrow and get some new ones...lolAre these regulators sensitive to mishandling?Also checked the Test Mode and all three of MCLR, DATA and CLOCK did go down when unchecked so it seems the transistors are working.Tried to figure out how the 555 circuit works to no avail though, and I still claim it's a general timer circuit. Voltage on pin 3 is 4 V and it seeems it's the connected cap and diods that generates the high voltage for the 78L12. Haven't figured out how yet, but I'll get there.Again thanks,

>Tried to figure out how the 555 circuit works to no avail>though, and I still claim it's a general timer circuit.>Voltage on pin 3 is 4 V and it seeems it's the connected cap>and diods that generates the high voltage for the 78L12.>Haven't figured out how yet, but I'll get there.Goot that you find reason for that 4.5 volt problem.About 555 and other things aroud it. It is generic timer. But. Circuit is capacitor pump. Pump itself is capacitor C10 and diodes D1 and D2. Resistor R8 and capacitor C9 is just for timer circuit. For understanding how it works. Follow link. It is for generating negative voltage from positive. But basics are similar.http://margo.student.utwente.nl/el/misc/te...#ASCIISCHEM_020- J