Hi I have a Transistor Tester based on the originals circuit diagrams and code under the mikrokontroller.net site. It worked well for so many hours. I had measured many unsorted capacitors transistor and coils last weekend. While was working it started moving slowly between menu's, as an example I wanted to move from Capacitor menu to coil menu and then to transistor. Moving out and into the menus was a bit slower than before. So I decided to reboot the Tester. On Reboot it delayed popping up the first screen around 1.5 minutes. Finally I got the message on the LCD Cell 29mv 2mv VCC=4.98 Volts. Then immediately after the two minutes the messsage: on the LCD: Short Probes ! <Blinking for more than 2 minutes contnuously> After the two minutes have elapsed, the LCD showed: 1 --||-- 3 > 100nF So I Inserted a 100nF. It took the tester 3 minutes refreshing the screen coming back to the same 1 --||-- 3 > 100nF. Finaly after 2 or 3 minutes it counted the Capacitor right, and exited displaying on the LCD FW Version 1.2k Tests Ok Pressing the button will reboot or shutdown. Pressing the button will enter the same diagnostics again. Is it the code gone bad ? The Schematic features all the new revised parts by Karl-Heinz. Troubleshooted all Transistors and replaced them anyway with 2 2N3904 (NPN) and 1 2N3906 (PNP) Has anyone else faced this problem or similar ? On the board there is an smd device P6KE6V8A and TL431 for Reference 2.49v and another transient device protection smd SRV05−4 I am suspecting that one of these has gone bad ! Any ideas welcome. Thank you Enjoyed reading the manual.
yes I managed to cause the same problem on 3 of my testers, and after receiving the 4th one i figured it out and fixed all of them XO go figure. It's the 6 pin ESD protection In my case I tried to float the ground on the pwm output +6V(beginner obviously) and the supply for that chip, MC5 i believe are the SMD marks I have datasheet if you need it, has narrow max voltage between its supply rails (+/-5 iirc) Good luck!
Can you give more details about the solution? What is the ESD protection ?
Hi Yes I can provide some description. On this transistor tester, there is a spark / ESD protector chip which is basically a diode protection immediately after the probes. Its an smd chip and what it does is to protect from transients esd from electrolytic caps etc the main circuit. Its all diodes. One of the diodes has gone bad shorting out the probes hence all the boot up delayed response from the At Mega. I completely removed the chip that cured the problem. However be twice as cautious now. The chip am referring to is SRV05−4. Thanks for responding
: Edited by User
Dimitris K. wrote: > Hi > Yes I can provide some description. > On this transistor tester, there is a spark / ESD protector chip which > is basically a diode protection immediately after the probes. Its an smd > chip and what it does is to protect from transients esd from > electrolytic caps etc the main circuit. Its all diodes. One of the > diodes has gone bad shorting out the probes hence all the boot up > delayed response from the At Mega. I completely removed the chip that > cured the problem. However be twice as cautious now. The chip am > referring to is SRV05−4. > > Thanks for responding Just saw your answer. Thank for your reply. I removed completely the srv05-4 chip but this did not solve the problem in my case. I even reprogrammed the MCU. I will check all the components in case there is a bad one. John